Environmental and Public Health Research @ RDIC

Evaluation of a pilot constructed wetland system as an appropriate technology for septage treatment in Cambodia

2011-09-02T11:52:00.005+07:00

Chiew, Hannah

Masters of Applied Science- MASc

Civil Engineering

University of British Columbia

Septic tanks are one of the most commonly used forms of onsite sanitation systems in developing countries. However, lack of regulation on the design and installation and the lack of proper disposal for the septage generated may cause serious environmental degradation and pose serious public health hazards. This study presents the findings of a pilot-scale constructed wetland system in Cambodia for the treatment of septage for 8 months. After a 6-month Acclimatization Period, the system was operated at two hydraulic loading rates (HLRs) of 15.5 and 27.4 mm/day to evaluate the impact of HLR on the treatment efficacy. During the 8-month period, the system achieved mass removal efficiency of 96% - 98% for total suspended solids (TSS), 80% - 97% for turbidity, 61% - 78% for biological oxygen demand (BOD) and 61% - 90% for chemical oxygen demand (COD), but was less efficient in removing total phosphorus (TP) and total nitrogen (TN), which exhibited efficiencies of 52% - 58% and 57% - 66%, respectively. The system also achieved 1.56 – 2.25 log reduction for E. coli and 0.49 – 0.81 log reduction for total coliform (TC). Although the HLR was almost doubled during the 2-month period, the effluent quality did not degrade appreciably in most cases, and caused little or no impact on the treatment efficacy. It is possible that harvesting prior to the start of the HLR exercise had an adverse impact on the eco system and de-stabilized the system, causing the results with lower HLR (or higher HRT) to be worse than expected. Another possible reason for the lack of difference could be due to the high variability of influent quality. It is possible that there is no apparent benefit in decreasing the HLR in this case. The k-C* , or first order removal model, was used to model the longitudinal concentration profile and estimated the removal rate constant. There were no apparent relationships between HLR and the removal rate constants in the k-C* model. The effluent may be suitable for localized and restricted irrigation with careful crop selection, or re-used with dilution due to its high nitrogen content.

Surfactant modified zeolites to reduce microbial pathogen exposure and Understanding Pathogen Exposure via Fruits and Vegetables

2011-09-02T10:49:00.007+07:00

Palmy Jesudhasan¹,
Ken Widmer²,
Andrew Shantz³Suresh D. Pillai¹

¹Texas A&M University, College Station, Texas, USA
²Gwangju Institute of Science and Technology, Gwangju, S. Korea
³Resource Development International, Cambodia

Exposure to microbial pathogens is a serious problem with global significance. The problem of microbial pathogens is an especially serious in under-developed and developing countries such as in Cambodia, Vietnam, India, Thailand and many other countries in this region. Groundwater is susceptible to fecal contamination from a variety of sources including sewage dumps, leaking septic tanks, infiltration of surface water contaminated by human and animal wastes, and careless disposal of septic wastes. In addition to microbial contamination of drinking water it is essential that we identify all routes of exposure to microbial contaminants. This includes foods both raw and cooked.

The focus of the proposed project is utilize “surfactant-modified zeolites” (SMZ), a patented technology jointly developed at Texas A&M University to determine whether it could serve as an inexpensive approach to limit human exposure of microbial pathogens in drinking water in Cambodia. The outcome of this project would be deeper understanding of the utility of the SMZ technology as a low-cost drinking water filtration technology in Cambodia. The availability of low-cost filter media can make a significant impact on reducing the exposure to waterborne pathogens in the Mekong River Basin. The underlying hypothesis of the project was that SMZ-filters will function effectively to removal microorganisms in ground waters found in Cambodia. The activities focused on laboratory studies to evaluate the performance of SMZ as a filter media to remove selected bacterial contaminants such as fecal indicators such as E.coli and male-specific coliphages. The phage MS2 was used as the candidate male-specific coliphage. A 90% reduction in E.coliand MS2 phage was observed in the initial laboratory trials. Further studies are, however, still needed to optimize the removal/reduction as a function of SMZ filter media volume.

A secondary objective of the project was to screen a selected number of produce items that are normally consumed raw or with minimal processing to identify the occurrence of fecal contamination indicators. Twenty four different commodities were purchased from the local market and analyzed for the presence of coliforms, E.coli, somatic coliphages and male-specific coliphages. Standard methods were used for these analyses. Out of 24 samples, 100% of the samples were positive for coliforms. This result was not surprising since these samples are handled with bare hands and the presence of coliforms on fresh fruits and vegetables in a market is not surprising. However, 14 out of 24 samples were positive for E.coli which is indicative that they were probably exposed to fecal contamination. However, the presence of E.coli in tropical environments is not necessarily indicative of fecal contamination solely because E.coli can multiply in moist environments. Three out of the 24 samples (12.5%) were positive for male-specific coliphages, which is a strong indication of the presence of fecal contamination in these samples. The samples that tested positive for male-specific coliphages were salad, chirneangvorng, andchirrona. Six out of the 24 samples (25%) were positive for somatic coliphages. Somatic coliphages can be considered an indicator of fecal contamination. However, they are not as strongly correlated with fecal contamination as compared to male-specific coliphages. What was indeed surprising was the large concentration of male-specific coliphages in the samples that tested positive. In the three samples that tested positive (salad, chirneangvorng, andchirrona), the concentration of male-specific coliphages were 459 PFU (plaque forming units)/gram, 600 PFU/gm, and 293 PFU/gm. These results indicate that exposure to microbial pathogens is a very strong possibility through such commodities.

Overall, these results suggest that similar to other countries, a multi-pronged approach to reduce exposure to microbial pathogens is needed in Cambodia. Ground water and fresh fruits and vegetables need to be adequately treated or disinfected prior to human use. Reducing exposure to microbial pathogens will have significant improvement on the disease burden in the community.

Quantifying the Risk: Arsenic Contamination with Particular Focus on Rice

2011-07-19T15:18:00.004+07:00

Marc O'Connor
School of the Built Environment
Northumbria University

Arsenic contamination within groundwater has been reported throughout Cambodia, with elevated levels in the Kandal province, however no peer‐reviewed study has focused on arsenic contamination from rice. This study is unique in that it contains the levels of arsenic in rice and directly relates this to total exposure and health effects. Rice samples were obtained from three markets (n=50) sourcing from all over Cambodia and were analysed for total arsenic using an Inductively Coupled Plasma Mass Spectrometry (ICPMS), a range of 4µg/kg to 1,166 µg/kg with an observed mean of 137µg/kg contributing 56% of the WHO Maximum Tolerable Daily Intake (MTDI) of 2µg of arsenic per kg bodyweight. Black sticky rice was observed to contain the highest concentration of arsenic with a mean value of 664µg/kg which alone contributed 277% of the MTDI. Secondary data of arsenic concentrations from groundwater used as drinking water in numerous provinces were added to the to the equation, were the daily intake of arsenic was above the Cambodian Maximum Contaminant Level (MCL) in each province. The cumulative exposures to arsenic contaminated areas such as, Kampong Chhnang, Kampong Thom and Takeo, which are not vulnerable to elevated arsenic levels in groundwater, are exposed to an increase in arsenic from riceof 311%, 314% and 381% of the total arsenic intake. The hazard quotient (HQ) was used to calculate the risk of populations exposed to arsenic from both groundwater and rice, taking exposure time into consideration for each province. When HQ > 1 then adverse health effects are considered occurring, with just groundwater the Kandal province was the only province above the threshold, however inclusive of both groundwater and rice Kratie and Prey Veng also passed the threshold; Signifying the importance of arsenic contamination from rice.

Sustainable Application of Bayoxide E33 Iron-Based Arsenic Adsorbent for Cambodia Drinking Water

2011-06-15T09:26:00.004+07:00

Christopher O. Cope
David. A. Sabatini
University of Oklahoma WaTER Center

Millions of people in the world are exposed to dissolved concentrations of arsenic (As) exceeding 50mg/L. The World Health Organization’s guideline is 10 mg/L. Arsenic is naturally dissolved in many groundwaters of the world, including parts of Bangladesh, India, and Cambodia, which have large populations of exposed persons. Extended consumption of dissolved arsenic can result in arsenicosis. Symptoms of this chronic disease include skin lesions, black foot disease, diabetes, and nervous, hepatic, haematological, and renal damage (Hughes, 2002). The symptoms of arsenic’s carcinogenicity include tumors of the skin, lungs, urinary bladder, liver, prostate, and kidneys, as well as other organs (Obinaju, 2009).

The US Environmental Protection Agency’s (USEPA) Arsenic Treatment Technologies Demonstration Program, targeted at small and rural communities, has found Bayoxide E33 (E33) adsorptive media to be among the most efficient and cost effective technologies at removing naturally occurring arsenic from municipal groundwater treatment and distribution systems. The defining characteristic of the E33 adsorptive media is its relatively high surface area. At a specific surface area of approximately 130 m²g^-1, E33’s high internal surface area, combined with its ferric hydroxide matrix, provides numerous adsorptive sites for arsenic compounds to come out of solution and attach onto the surface of the media.

As one of the most successful and overall cost-effective treatment technologies in the USEPA’s study, questions arise as to whether or not this media would be cost-effective in community, wellhead, and a point-of-use (POU) treatment systems in the developing world. This study aims to characterize the adsorptive behavior and economic sustainability of E33 applications in developing world countries such as Cambodia and Bangladesh.

Rapid small-scale column studies (RSSCts) indicate similar breakthrough curves and media adsorptive capacities as full-scale pilot tests for a fraction of the time and money. This study will characterize the arsenic adsorptive behaviors of E33 using RSSCTs, which will synthesize full-scale pilot treatment systems, in the lab and with two Cambodian wells of differing water qualities. These same well tests will also indicate the impact of varying water quality characteristics (e.g. pH, DO, alkalinity, and competing ions) in Cambodian groundwaters. To confirm the effectiveness of the media as predicted by the RSSCTs, full-scale wellhead and POU pilot systems will be developed and tested to treat the same two Cambodian wells.

Once the arsenic adsorptive efficiency of the media has been determined, economic analysis will predict the affordability and economic sustainability of E33 for centralized, wellhead, and POU treatment systems. This will help determine the advantages and disadvantages of these approaches and enable different NGO, government, and private sector entities to assess the various implementation methods.

Continuous Monitoring Approaches for Conventional Water Quality Parameters in the Mekong River-Tonle Sap System

2011-03-17T11:35:00.000+07:00

Kim Irvine, Buffalo State, State University of New York

Jeff Richey, Gordon Holtgrieve, University of Washington

Juha Sarkkula, Finnish Environment Institute

In assessing the potential impacts of development, such as hydropower construction, urban expansion, deforestation, agricultural runoff, and climate change on the Mekong-Tonle Sap system, it is essential to collect basic water quantity and quality data. These data can be used in support of the application of decision-making tools, such as mathematical models, to help inform management of the basin. Good policy must be founded on good data. The Mekong River Commission (MRC) oversees the collection and maintains the most readily available and extensive water quantity and quality dataset for the basin. The MRC water quality database represents monthly sample results for 99 sites across the basin, which can provide reasonable benchmarking, but for modeling purposes the MRC data must be supplemented with data having better temporal and spatial resolution. We monitored turbidity, dissolved oxygen, conductivity, temperature, pH, and fluorescence at seven different locations on the Tonle Sap-Mekong-Bassac system between 2004 and 2010 at 15 to 30 minute intervals. Monitoring was done using either Hydrolab Datasonde 4’s or YSI Datasonde 6600’s and 6920’s. All site measurements represent a fixed depth of between 0.5 and 2.0 m, although we also have profile data at three of the sites.

Our most recent detailed sampling effort (17 August – 22 August, 2010) was conducted in the Tonle Sap Lake near Siem Reap. We sampled at three sites on a transect running from the edge of the flooded forest fringe to the open lake, 2-3.5 km out from the main shoreline. Samples were collected at each site throughout a 24 hour period in order to address system metabolism questions. Two YSI datasonde 6920’s were used to measure water temperature, conductivity, dissolved oxygen, pH, turbidity, and fluorescence. Because the YSI 6920’s can only house one optical sensor at a time, one of the 6920’s was fitted with a turbidity sensor and one was fitted with a fluorescence sensor. The YSI 6920 with the fluorescence sensor was programmed to record all parameters at 15 minute time intervals and was attached to the side of the boat so that measurements were done at a depth of approximately 0.5 m. The YSI 6920 with the turbidity sensor was used for water column profiling. Profiling was done at 0.25 m increments from 0.1 m below the surface to the lake bed. Water samples (0.5 m depth) were collected on an hourly basis at each site for oxygen isotope analysis (e.g. to determine ^16:18O₂ ratios) and alkalinity; four times per day for dissolved inorganic carbon analysis; and once per day for nutrients, chlorophyll a, and zooplankton analysis. Measurements of photosynthetically active radiation (PAR), wind velocity, temperature, and relatively humidity also were made each hour.

This most recent work in the Tonle Sap was part of a larger project led by the University of Washington that is seeking to examine regional-scale landscape dynamics in river basins in Southeast Asia relative to their connectivity to the South China Sea, with an emphasis on the Mekong River. The basic premise of the larger project is that the understanding of regional scale processes requires the higher resolution now possible with satellite data, process-based models, and field measurements. By focusing on how transient forcing of the atmosphere combines with land-use change at multiple space and time scales to mobilize water and carbon to the sea, we are examining the critical and poorly understood interfaces between the atmosphere, land surface and sea function. We are in the process of summarizing the data and developing a series of articles based on the results. An earlier summary of some of the data can be found in Irvine et al. (2007): http://www.buffalostate.edu/geography/documents/publication6.pdf. This field effort has benefited from the support of numerous RDI staff, Buffalo State, University of Washington, and Royal University of Phnom Penh graduate and undergraduate students since 2004.

Vulnerability of Arsenic-Free Wells to Future Contamination

2011-03-03T10:11:00.002+07:00

Matthew L. Polizzotto, North Carolina State University

Rebecca B. Neumann, University of Washington

In South and Southeast Asia, contamination of groundwater with naturally-occurring arsenic affects the health of millions. Current efforts to mitigate arsenic exposure in the region include installing new wells that access arsenic-free groundwater. However, the vulnerability of clean groundwater to future arsenic contamination is unknown. Our goal is to assess the potential for arsenic contamination in groundwater that is currently arsenic-free. To accomplish this goal, we explicitly and systematically link field, laboratory, spectroscopic, and modeling approaches that comparatively quantify a multitude of biogeochemical and physical processes controlling arsenic in the environment.

In collaboration with RDIC, we have established a study site in the Kandal Province of Cambodia, between the Mekong and Bassac Rivers. Although the province is known for high (>100 ug/L) dissolved arsenic concentrations in domestic tubewells, at our site, dissolved arsenic concentrations are below the World Health Organization recommended limit (10 ug/L). However, the area is undergoing a period of relatively rapid development, resulting in land-surface changes and growth in groundwater withdrawals. Thus, the site, with its low arsenic concentrations and changing environmental conditions, is ideal for studying the vulnerability of wells to future arsenic contamination.

In our work, we will identify the processes that may stimulate future arsenic contamination and the time scales on which these processes may occur. Our findings will advance basic understanding of groundwater arsenic contamination, and will provide concrete, useful information about the sustainability of currently ‘safe’ wells – information that policy makers, development organizations, and individuals can use both locally to aid in decisions about specific water use options, and broadly to inform larger policy initiatives.

Low-Cost Hydrogen Sulfide (H2S) Test Strips for Bacterial Water Testing

2011-02-23T15:55:00.007+07:00

Researchers: Massachusetts Institute of Technology (MIT) Development Lab (D-Lab) - Jessica Huang, Dahlia Alkekhia, Ivy Huang, Joel Veenstra

Hydrogen sulfide (H2S) strips are simple and inexpensive tests for predicting bacteriological contamination in water sources. The test strips indicate the presence or absence of hydrogen sulfide producing bacteria through a color change (clear = clean, dark = contaminated). One advantage of the H2S test strip is that it can be incubated without electricity at room temperature and does not require any special equipment or training to use. While the low-cost H2S strip is not quantitative (i.e., cannot show how much bacteria is present) and is not the most accurate test for bacterial contamination, RDI and partnering universities completed a study from 2009-2011 verifying that the results are reasonably consistent when compared to a commercial H2S test and membrane filtration, which is a standard laboratory test for bacteria.

Most commonly, the H2S strips are used for:

• Visual aids for water and hygiene education in schools and community meetings
• Community-based monitoring of water supply and treatment systems in remote areas where it may be difficult to conduct conventional laboratory testing
• Routine monitoring of water supply and treatment systems where positive results indicate which water samples need to be sent in for further laboratory testing

The low-cost H2S test strips are produced in the RDI laboratory by a trained technician using the Mosley procedure. Strips come in sterile vials for single use with 10 mL water samples. RDI can provide instructions for use and disposal of the test strips, and used vials can also be returned to RDI for cleaning and strip refills. For more information about the test strips, please contact lab@rdic.org or download the following reports.

DOWNLOAD - Effectiveness of H2S strips for predicting bacterial contamination in water
DOWNLOAD - H2S procedures
DOWNLOAD - H2S education report
DOWNLOAD - Live and Learn H2S Water Monitoring Tool Kit

Determining Seasonal Variability in the Source and Age of Carbon transported by the Mekong River

2011-02-12T15:23:00.002+07:00

Researcher: Erin Ellis
Advisors: Prof. Jeffrey Richie
Institution: University of Washington

The organic matter carried by rivers is a key component of models of the global carbon cycle that aim to predict the time-scales over which different pools of carbon are stored on land, transferred between reservoirs, and exported to the ocean. Traditionally, model parameters for organic carbon (OC) in rivers include measurements of the amount, source, and age of carbon exported from the mouths of large rivers to the ocean. These riverine carbon fluxes (including losses of C from gas evasion) remain some of the least constrained numbers in the global carbon budget due to the complexity and variability of biological, geochemical, and physical processes occurring temporally and spatially in rivers, estuaries and coastal zones (Richey et al. 2004). Erin's Ph.D. research aims to further elucidate the role of rivers in transporting and processing organic carbon. To better understand the global carbon cycle and understand carbon preservation in coastal ecosystems, it is first necessary to know the type, age, and seasonal variability of organic matter that is transported by rivers.

The Mekong Basin serves as a template to examine carbon cycling processes in a river that experiences extreme changes in water levels in response to the dry and rainy season. Due to the arrival of the Southwest Monsoon in May, the Mekong rises from discharges less than 2,500 m³/s during the low water period (December through May) to peak flows reaching almost 40,000 m³/s during October (Mekong River Commission 2005)! Therefore, we hypothesize that there should be a large amount of variability in the type of organic carbon that is transported by the Mekong through the year in response to changes in water residence time in the basin.

Erin is particularly interested in the age of organic matter size fractions (CPOC, FPOC, and DOC) transported by rivers. Consequently, the staff at Resource Development International-Cambodia (RDIC) (http://www.rdic.org) are currently collecting samples each month during the dry season and twice a month during the rainy season. In collaboration with Anitra Ingalls (http://faculty.washington.edu/aingalls/), who is one of Erin's Ph.D. advisors, we are determining the age of the organic material transported by the Mekong Basin using radiocarbon dating. Erin is also analyzing the stable isotope composition (δ¹³C) to help determine the biological sources that this material originates from. This research project comprises one of the four research chapters of her Ph.D.

While these measurements are made on the entire OM pool, using tracers such as δ¹³C are only able to provide general descriptions of the sources of OC. Source assignments may be compromised due to overlapping end members and the presence of multiple sources leading to similar isotopic signatures. Analysis of target molecules that are representative of distinct biological sources is an alternative method to assess the origin of POC. Although these "biomarkers" typically only represent trace components of OM, they can be powerful tools to assess changes in the contribution of specific sources. Thus, an additional chapter of Erin's Ph.D. focuses on analyzing the seasonal change in the biomarker composition found on POC.

Erin is studying two biomarkers in particular: 1) lignin-derived phenols and 2) glycerol dialkyl glycerol tetraethers (GDGTs). Lignin is a phenolic polymer unique to vascular plants and is the second most abundant biomarker found on earth (40% of wood is composed of lignin). Therefore, it is a tracer of carbon derived from higher-plant material. Lignin has been routinely used to quantify the input of terrestrial OM to freshwater and marine environments, but the distribution of lignin-phenols has never been examined in the Mekong River Basin. In collaboration with Rick Keil (one of Erin's committee members) (http://depts.washington.edu/aog/), Erin has been measuring seasonal changes in the contribution of vascular-plant material found in POC from the Mekong River.

Erin is also examining changes in the seasonal distribution of GDGTs. Branched glycerol dialkyl glycerol tetraethers (GDGTs) have recently been introduced as a tracer of terrestrially produced OC (Hopmans et al. 2004). Branched GDGTs are lipids thought to be derived from anaerobic bacteria living in soils (Weijers et al. 2006a; Weijers et al. 2006b), and have been suggested to be a biomarker for soil OM (Kim et al. 2007; Walsh et al. 2008). Erin is currently exploring the seasonal variability in GDGT composition associated with FPOC. She also aims to further our understanding of their environmental distribution. She has collected soil samples (in many cases from multiple depths) throughout the Mekong Basin, including pastures, forests, rice paddies, river banks, and riparian zones.

The final chapter of Erin's Ph.D. research combines the techniques mentioned above. While informative, a major problem with radiocarbon dating of bulk size fractions is that the measured Δ¹⁴C value is a mass-balance of the many carbon sources that compose each size fraction. These constituents include materials with Δ¹⁴C values that range from modern biomass debris to sedimentary rock derived OM that is radiocarbon-dead. Recent analytical developments allow specific pools of carbon to be radiocarbon dated individually. In this approach, biomarkers of known sources are dated and the age of the biomarker is assumed to equal that of the pool for which it is a biomarker. This technique (Compound Specific Radiocarbon Analysis (CSRA)) has been highly successful in apportioning sources of carbon to the ocean by specifically targeting biomarkers of vascular plants, phytoplankton, bacteria, and petrogenic OM found in marine sediment. However, none of these studies have measured the same biomarkers in sediment transported by riverine end-members. Erin is currently using CSRA as a tool to constrain the residence time of vascular plant-derived OM exported from a watershed. Thus, Erin will be radiocarbon dating lignin-derived phenols, as higher plant material likely contributes substantially to the POC signature.

Methods

To examine how biomarker composition (GDGTs and lignin-derived phenols) change throughout the year, samples were collected every month during 2006 from the Mekong River just above the confluence with the Tonle Sap River. POM was obtained by filtering water onto GF/F filters. C:N ratios and δ¹³C of acidified samples will be measured on a Finnigan Delta XL continuous flow mass spectrometer that has been interfaced with a Carlo Erba NC 2500 analyzer. Lignin retained on GF/F filters are oxidized using copper (II) oxide coupled with a microwave digestion system (Goni and Montgomery 2000). The sample will then be extracted using ethyl acetate and quantified using gas chromatography. GDGTs are extracted from filters ultrasonically using a combination of methanol and dichloromethane. Extracts are subjected to SiO₂ gel chromatography to separate bulk polarity fractions. The fraction containing the GDGTs is dissolved in hexane and isopropanol, and then analyzed using liquid chromatography-mass spectrometry.

Field work for examining the age (Δ¹⁴C) and source (δ¹³C) began during October 2008 and will be continued through January of 2010 on the Mekong River at Phnom Penh. CPOC (> 63 μm), FPOC (0.7- 63 μm), and DOC produced via oxidation will be reduced to graphite for analysis by AMS.

The compound-specific radiocarbon analysis is being performed on lignin-derived phenols collected from suspended sediment samples during the rising and high water stage in July 2009 and September 2008, respectively. Samples were collected along the Mekong River above Phnom Penh. Additional soil/sediment samples have been collected from pastures, forests, and the Mekong River Delta. Obtaining enough material to perform CSRA on suspended sediments in rivers is challenging. Water is pumped into a continuous flow centrifuge (Sharples T1) that concentrates suspended sediment. We typically collect 1,000 L to obtain enough water for radiocarbon dating lignin and GDGTs. The suspended material is then frozen for CSRA.

We are collaborating with the Ingalls and Keil lab at the University of Washington in the development and application of a method to purify underivitized CuO oxidation products of lignin using liquid chromatography coupled to diode array detection and mass spectrometry (LC-MS). The Δ¹⁴C values of CO₂ generated from combustion of LC-purified lignin phenols will be measured using microscale AMS techniques at the Keck Carbon Cycle AMS facility at UC Irvine in collaboration with Ellen Druffel and Guaciara dos Santos.

Nitrification, denitrification and ammonification in point-of-use biosand filters in rural Cambodia

2010-12-01T12:00:00.002+07:00

Authors: Murphy, Heather M, McBean, Edward A, Farahbakhsh, Khosrow

Source:Journal of water and health. 2010;8(4):803-17

Abstract:

In order to address the United Nations Millennium Development Goal (MDG) target #7 for water and sanitation, the World Health Organization (WHO) has identified point-of-use (POU) water treatment technologies as an option for providing safe water to households. The BioSand filter (BSF) is a commonly used POU system that has been implemented in Cambodia and over 20 countries worldwide. While the health benefits of using a BSF in terms of reduction of diarrheal disease have been fairly well documented, little research has focused on the ability of this technology to treat for other contaminants that could pose health concerns. To address these concerns, a study was developed to evaluate this technology in rural Cambodia in terms of microbiological and chemical quality of the treated water. The study revealed that simultaneous nitrification and denitrification is occurring inside the BioSand filters. Nitrite concentrations in treated water consistently exceeded WHO guidelines. Seventeen of 20 filters on average did not meet the 3.0 mg l(-1) NO(2)(-) guideline and the combined nitrate-nitrite guideline ratio of 1. Denitrification seemed to predominate when BSFs were fed surface water. In addition, nitrate-ammonification occurred in some filters fed surface water, causing increases in ammonia in treated water.

A critical evaluation of two point-of-use water treatment technologies: can they provide water that meets WHO drinking water guidelines?

2010-12-01T12:00:00.001+07:00

Authors: Heather M. Murphy, Edward A. McBean and Khosrow Farahbakhsh

Source: Journal of water and health. 2010;8(4):611-30

Abstract:

Point-of-use (POU) technologies have been proposed as solutions for meeting the Millennium Development Goal (MDG) for safe water. They reduce the risk of contamination between the water source and the home, by providing treatment at the household level. This study examined two POU technologies commonly used around the world: BioSand and ceramic filters. While the health benefits in terms of diarrhoeal disease reduction have been fairly well documented for both technologies, little research has focused on the ability of these technologies to treat other contaminants that pose health concerns, including the potential for formation of contaminants as a result of POU treatment. These technologies have not been rigorously tested to see if they meet World Health Organization (WHO) drinking water guidelines. A study was developed to evaluate POU BioSand and ceramic filters in terms of microbiological and chemical quality of the treated water. The following parameters were monitored on filters in rural Cambodia over a sixmonth period: iron, manganese, fluoride, nitrate, nitrite and Escherichia coli. The results revealed that these technologies are not capable of consistently meeting all of the WHO drinking water guidelines for these parameters.

Temporal and spatial distribution of water quality in different vegetation communities of the Tonle Sap Lake Floodplain

2010-11-13T14:49:00.001+07:00

Mauricio E. Arias

Dept. of Civil and Natural Resources Engineering, University of Canterbury, Christchurch, New Zealand

Supervisory committee: Tom A. Cochrane (Advisor), Brian Caruso, Tim Killeen, and Matti Kummu.

The hydrology and ecology of the Tonle Sap is driven by the flood pulse from the Mekong. As major changes are expected in the Mekong Basin in the foreseeable future, it is crucial to understand how this ecosystem is adapted and responds to flooding. Once the historical trends and distributions of water and terrestrial properties are understood, it will be possible to predict future ecological shifts in order to help establish appropriate management strategies.

In large floodplains like the Tonle Sap, there is a strong linkage between flood pulse, vegetation, water quality, and fish ecology. It is therefore crucial to study and understand how these different ecosystem components interact. As far as water quality goes, we are looking at temporal and spatial trends of field parameters (Temperature, pH, Dissolved Oxygen, Conductivity), nutrients, and suspended solids. The main questions that we are addressing are:

1) Are there different water quality responses among flooded vegetation communities?

2) Do these responses change between dry and wet seasons?

Once the water quality monitoring is finished, we hope to compile multiple water quality databases of the Tonle Sap to determine long term trends. We also hope to be able to use these data to further enhance existing ecological models of this system.

Cholinesterase ("ChE"), Pesticides and Health Study

2010-11-04T19:57:00.002+07:00

Principle Investigator: Dr. Bill Daniel (University of Washington)

Pesticide use is increasing in Cambodia and around the world. This study will examine whether farmers, farm household members, or pesticide sellers in Cambodia are being made sick by pesticides.

There are many kinds of pesticides, such as insecticides (for killing insects), herbicides (for killing weeds), and fungicides (for killing mold). Some insecticides are made from natural substances, and others are man-made chemicals. Organophosphate (OP) and carbamate chemicals are two major kinds of man-made insecticides. They are very effective for killing insects, but most are also harmful for people. Some are very poisonous and can kill people. Many OP and carbamate insecticides are banned in developing countries, because it is too hard to use them safely. However, they are used often in Cambodia.

Cholinesterase (ChE) is a normal substance in the human body. ChE is an “enzyme” needed to make the nervous system work right. Many pesticides can hurt the nervous system and reduce ChE in the body. We can measure ChE with a blood test. Doctors sometimes use this test to decide if a person is poisoned by a pesticide. This test can tell if pesticides are affecting a person’s body, even if they do not feel sick. The ChE test does not work for all pesticides, but it works well for OP and carbamate insecticides.

Participation in this study is voluntary. Each participant will have an interview and a ChE (cholinesterase) blood test. The interview asks about pesticide use and health. The ChE blood test works best if we do it at two different points in time. Therefore, we will ask most people to do an interview and ChE blood test two times. The first will be during a period of high pesticide use. The second will be later, when there is little or no pesticide use.

This study will directly benefit study participants. The ChE blood test may help us tell a person if they were over exposed to OP or carbamate insecticides. The test can also tell if a person has anemia. Anemia is a health problem caused by weak blood. Many Cambodians have this problem. The most common cause of anemia is not having enough iron in the body. Anemia can be prevented or treated by eating foods that have lots of iron – like meat and green leafy vegetables – or by taking iron pills.

This study will also be good for society. If we find that pesticide health effects are common, this information will be useful for government planning or policy making. We will use a special kit to measure ChE. The test kit is cheaper and less complicated than the usual laboratory method for measuring ChE. Unfortunately, the test can be affected by hot weather. If we find that the test is reliable in Cambodia, then this could be a first step toward making the ChE blood test available for public health or clinical use.

Data collection will begin in November 2011 and finish in August 2012. A report should be available later in 2012.

How effective is arsenic awareness raising in Cambodia?: A focus on which education methods are the most successful and why.

2010-05-07T12:00:00.000+07:00

Researcher: Carley Allison
Advisors: Prof. Dave Cook
Institution: Northumbria University

Arsenic contamination of groundwater is a major problem for many countries around the globe. Millions of people are subject to drinking water which has arsenic levels higher than that of their countries standards. A fortunate few are aware that their tubewells are contaminated and have received mitigation and education to help alleviate the problem; however there are many more who are consuming arsenic in ignorance. Education about arsenic contamination of groundwater is in its early stages in Cambodia; this study has been conducted with the intention of discovering how effective arsenic awareness raising is in two villages in Cambodia’s Kandal Province. The RDIC (Resource Development International Cambodia) are a non-governmental organisation whose work aims to improve the lives of many people in Cambodia, through efforts such as well testing and education. The main focus of this study is to look at how effective education has been in discouraging people from using arsenic contaminated wells and which methods of education have been best received and why. The study further goes on to explore, what specifically people remember about what they have heard, and if thy feel there is any gaps in their knowledge. It is evident from the results that education has been successful in persuading people to refrain from using well water and to use alternative water sources such as rainwater. It is also clear that the distribution of education is not an easy figure to contend with as it was discovered that individuals respond differently to different forms of education. There was a general consensus that TV/ Video and door to door were effective ways to distribute education, however individual ideals were conflicting. It was concluded that education plays a vital part in potentially saving the lives of many people, yet gaps in knowledge are a possible threat.

Land Use Change Consequences for Groundwater Arsenic Contamination in Southeast Cambodia

2010-02-01T12:00:00.003+07:00

Researcher: Laura Erban
Advisors: Profs. Scott Fendorf and Steven Gorelick
Institution: Stanford University

Cambodia has recently emerged from decades of conflict into a neighborhood of more developed and productive agrarian countries and into the potential for rapid economic growth. More than three quarters of Cambodians cultivate rice for a living, most of whom depend on the wet season flood or rain-fed rice crop. Much of the low-lying landscape is water-logged during the monsoon, but parched in the dry season. Groundwater is an increasingly attractive option for domestic and agricultural consumption, as deep wells are free of the pathogens commonly found in surface supplies, and private wells are easily accessible to farmers with small plots and the means to pay for capital and operational costs. However, like most lowland countries downstream of the Himalayans, Cambodian aquifers bear a large arsenic burden. In much of the most densely populated areas, groundwater contamination with arsenic matches or exceeds the well-known hazardous levels found in Bangladesh. Recent research in both countries has elucidated the connections between different land use practices and arsenic cycling at the field and multi-village scales, demonstrating the requisite conditions for local arsenic mobilization and transport. To date, however, no regional-scale efforts have been made to investigate natural patterns of labile arsenic in the larger landscape and how the baseline system state responds to land use change. The goal of my research is to understand what changes to the quality and availability of groundwater in southeast Cambodia are likely to result from future development scenarios.

Household Drinking Water Supplies in Peri-Urban Phnom Penh: Quantification and Community Perception of Risks in Two Communities

2009-12-01T12:00:00.000+07:00

Researcher: Kim Thomas
Advisors: Profs. Ed McBean
Institution: University of Guelph

This research project seeks to evaluate the household water supplies available to peri-urban communities in Phnom Penh in terms of microbial and physical water quality through a case study approach. Water quality from different household drinking water sources is quantified and the relationships of water quality with factors such as water and treatment type, study site, storage vessel, and time are examined. A Quantitative Microbial Risk Assessment Methodology has been applied to the microbial data from the two sites to assess the level of diarrheal disease risk due to microbial contamination of drinking water being faced by community members. Additionally, community perceptions of water supplies, particularly the perception of risks due to water, are examined.

Effect of Groundwater Iron and Phosphate on the Efficacy of Arsenic Removal by Iron-Amended BioSand Filters

2009-08-05T12:00:00.002+07:00

Authors: Chiew, Hannah; Sampson, M. L.; Huch, Sokhan; Ken, Sreymom; Bostick, Benjamin

Source: Environmental Science & Technology; 8/15/2009, Vol. 43 Issue 16, p6295-6300, 6p

Abstract:
Naturally occurring arsenic in groundwater in Cambodia is a serious health concern. This study tested the efficacy of a BioSand filter amended with iron nails, Kanchan filter, as a household water treatment option with three natural arsenic-bearing groundwater sources of varying compositions and spiked with lab cultured E. coli and MS2. The effectiveness of arsenic and pathogen removal was not constant over time and was highly dependent on the influent composition. The filter was relatively ineffective in treating arsenic contaminated groundwater and effluent arsenic concentrations were between 74 and 226μg L-1, which is higher than accepted drinking water standards. The overall average arsenic removal was 39.4, 74.9, and 45.4%, respectively, and the extent of arsenic removal was not related to the influent arsenic concentration. The main reasons for poor arsenic removal was due to the combination of high influent P (>0.5 mg L-1) and low Fe (<5 mg L-1) concentrations and that the added iron nails were largely ineffective due to insufficient contact time with the water. The findings suggest that such amended filters should not he widely deployed until improvements are made to address the consistency and efficacy of treatment In addition, the filter poses some potential health risk associated with the production of elevated nitrate levels in the effluent within the filter, possibly due to nitrification and high levels of ammonia in the groundwater.

Chronic arsenic exposure through Cambodian rice (Oryza Sativa) - Understanding a potential global environmental challenge

2009-07-01T12:00:00.001+07:00

Researcher: Alexander Wainwright
Advisor: Prof. David Cooke
Institution: University of Northumbria

152 samples of Cambodian rice were collected through markets across Phnom Penh. The samples collected were grouped primarily by variety of rice and these are the figures:

20 Jasmine Rice, 20 Neang Kon, 20 Neang Menh, 10 White Sticky, 34 Ginger Flower, 9 Black Sticky, 10 E Air, 11 Bilok Chon, 10 Samrot Jasmine, 8 Samali Thai

These 152 samples are about to be analysed at Manchester University to identify arsenic concentrations with relation to the Maximum Tolerable Daily Index (MTDI) levels that a human should be exposed to.

A Critical Evaluation of the Appropriateness of Ceramic and Biosand Filters In Rural Cambodia

2009-05-01T11:44:00.001+07:00

Researcher: Heather Murphy
Advisor: Prof. Ed McBean
Institution: University of Guelph

The United Nations Millennium Development Goal (MDG) #7 -Ensure Environmental Sustainability contains three key targets, one of which is: “halve, by 2015, the proportion of people without sustainable access to safe drinking water and basic sanitation”. According to the World Bank, unless significant advances are made in the water and sanitation sector, it is unlikely that Cambodia will meet the MDG target. Household or point of use (POU) water treatment technologies have been identified as successful interventions for providing safe water to rural households. Currently, there are two water treatment technologies that have been widely implemented across Cambodia: ceramic water filters and BioSand filters. Both technologies have proven to reduce diarrheal disease by up to 50%; however, to date there is very little published research that critically evaluates the performance and sustainability of these systems in the field.

The goal of the research was to evaluate these technologies in the context of rural Cambodia. The ceramic and BioSand filters are evaluated on their performance in terms of microbiological and chemical quality of the treated water. In addition, one of the objectives was to investigate the factors that contribute to the long term sustainability of these systems in the field, and to identify factors that influence their long term use. The results are used to provide an overall assessment of the appropriateness of these technologies in rural Cambodia and provide recommendations to aid Non-Governmental Organizations (NGOs) and other groups in the decision process for choosing a point of use water treatment technology for a particular source water quality, and circumstance.

It was found that these systems are not consistently capable of meeting World Health Organization guidelines for nitrite and the low risk range for E.coli. In addition, key factors that seemed to contribute to technology success were: technology delivery mechanisms, system monitoring, quality control, maintenance practices, health and hygiene impact, sustainability, affordability, and user feedback and satisfaction.

Ultimately, this research contributes to the field of household water treatment and will hopefully aid NGOs and government agencies to make more informed decisions regarding the implementation of these technologies around the world.

Arsenic Awareness Raising Programs (ARPs) and their Effectiveness in Cambodia

2009-04-30T12:00:00.000+07:00

Researcher: Punam Khaira
Advisors: Prof. Dave Cook and Prof. Samantha Jones
Institution: Northumbria University

Arsenic contamination of groundwater, used for drinking has been identified as a major health concern worldwide. The presence of arsenic in tubewell water was identified in Cambodia in 2000 and it has been estimated that up to a million people are at risk. Scientific attention in developing countries so far has tended to focus on technical solutions, but little attention has been paid to awareness raising programs (ARP) and their effectiveness. This study evaluates the impact of the ARP implemented by the Research and Development Institute Cambodia (RDIC) to raise arsenic awareness in Kandal province, Cambodia. Data for this study came primarily from questionnaires administered to people within three sample sites: a village exposed to the ARP and two comparison villages that had received very little awareness raising. Analysis of the questionnaires revealed that the mitigation village had significantly more knowledge than comparison villages, although the level of knowledge remained fairly low over all three sites. Overall the majority of respondents had switched from tubewells due to arsenic related reasons, and also had significantly higher knowledge than those who continued to drink from tubewells. No socio-economic correlates were found overall, indicating the ARP had been effective regardless of varying social and economic backgrounds. Village level data, however, identified level of education, daily expenditure, age, knowledge of a person with arsenic poisoning and group membership, as significant determinants of an individual’s knowledge; number of household members was positively associated with knowledge, but the relationship was weak. There were also gaps in the arsenic knowledge relating to the identification and treatment of associated symptoms and diseases. As no studies of this nature have been conducted in Cambodia, it is hoped these findings will not only highlight the importance of awareness raising strategies and arsenic knowledge, but will help inform any future mitigation strategies and policies.

Time-lapse geophysical imaging of soil moisture dynamics in tropical deltaic soils: An aid to interpreting hydrological and geochemical processes

2009-03-26T12:00:00.001+07:00

Authors: Robinson, D. A; I. Lebron; B. Kocar; K. Phan; M. Sampson; N. Crook; S. Fendorf;

Source:
Water Resour. Res., 45, W00D32, doi:10.1029/2008WR006984. (2009)

Abstract:
A fundamental, and often intriguing question, in hydrology is “where does the water go?” This becomes particularly difficult to observe when water arrives at the ground surface and infiltrates into soils. The development of rapid, campaign-style imaging methods that do not need to be left in situ are therefore of great interest in tracking subsurface hydrological redistribution. We present a novel geophysical imaging approach identifying spatiotemporal variation consistent with soil water redistribution in a tropical deltaic soil. The intention is to provide additional insight into spatiotemporal soil hydrological/biogeochemical processes. The bulk soil electrical conductivity response (ECa) is primarily controlled by the clay content and type, the ions retained in the soil solution (ECe), and the soil water content (θ). Clay content can be assumed to be temporally static, whereas θ and ECe are temporally dynamic. By imaging over time, we can attempt to tease apart these contributing factors. In nonsaline soils θ is the major contributor to temporal changes in ECa. By exploiting an intensive rainfall event (75 mm), with time series spatial ECa measurements, before and after the event, we were able to identify zones of water depletion and accumulation and to provide an indication of the time required for the soil to return to its prior state. In addition, locations with more clay and salts were identified through response surface-directed soil sampling. We found important spatiotemporal variation across the level 4 ha field site that from visual inspection appeared uniform.

High Resolution Isotopic Tracing of Secular Changes in Arsenic Hazard in Circum-Himalayan Groundwaters

2009-03-01T12:00:00.001+07:00

Researcher: Michael Lawson
Advisors: Profs. David Polya and Chris Ballentine
Institution: University of Manchester

Arsenic in groundwater resources, utilized by millions of people in South and Southeast Asia as a source of drinking, cooking and irrigation water, is an issue of significant concern in the areas affected, adversely affecting the health of many of those exposed to it at high concentrations. The relative importance of various plausible mechanisms of arsenic release are still poorly quantified. In particular, whether or not arsenic concentrations will increase in the future - an issue of paramount importance for policy makers and those responsible for mitigating the current arsenic hazard, is a matter for ongoing debate in the scientific community.

Our group at Manchester have conducted extensive research in West Bengal, funded by EPSRC, CCLRC/STFC, NERC and the UKIERI PRAMA network, to identify geochemical mechanisms and in particular the critical role played by metal reducing bacteria present in the sediments in arsenic release. Our work in Cambodia initially focussed on (i) determining the spatial extent of arsenic contamination in Cambodian groundwaters culminating in the production of arsenic groundwater hazard maps based on regression-kriging techniques and (ii) led by Professor Jon Lloyd, determining biogeochemical controls on arsenic mobilisation. We have also investigated proxies for human exposure to arsenic in Cambodia and, with our partners at the Indian Institute for Chemical Biology, the genetic dependence of susceptibility to arsenic-attributable diseases.

More recently, funded by NERC, GV Instruments and the EU-ASIA link CALIBRE network, we have teamed up with RDI (Cambodia) and Stanford University, to compare the geochemical and hydrological environments, and in particular the role of groundwater abstraction practices, between Bengali and Cambodian arsenic bearing groundwater systems. We use isotopic and geochemical techniques to trace organic carbon, which is critically implicated in arsenic release, and ground-surface water interaction to determine how these influence arsenic release mechanisms as well as processes controlling its mobility and its transport in groundwater. Dating of the groundwater using tritium-3He and 14C allows us to monitor arsenic evolution over flow paths to determine arsenic release rates at different depths. This information will allow us to make predictions on how the present arsenic hazard may change in the future, and at what rate. Our results will be of benefit to policy makers not just in West Bengal or Cambodia, but also to those across the world, including Europe (see outputs of the AquaTRAIN Network) affected by arsenic contamination of shallow reducing groundwaters.

Mercury Contamination along the Mekong River, Cambodia

2009-02-10T15:28:00.001+07:00

Authors: T.P. Murphy; K.N. Irvine; M. Sampson; J. Guo; T. Parr

Source: Asian Journal of Water, Environment and Pollution, Volume 6, Number 1 / 2009
Pages 1-9

Abstract:
Sampling and analysis of mercury was conducted along the Mekong River from central to northern Cambodia. One of 10 Irrawaddy Dolphin livers analyzed had a high concentration of mercury (67 μg/g). The mercury content of fish at Kratie was on average 99 ng/g (n=160) but in some species it was up to six-fold higher. People located in a sample drainage basin with gold mines, on average, had more mercury in their hair (4.4 μg/g) than those living along the northern portion of the Mekong River (3.4 μg/g). Males, on average, exhibited higher mercury in their hair than women (5.2 vs 3.1 μg/g, respectively). Individuals had as much as 23 μg/g of mercury in their hair. While mercury levels in hair and fish were elevated and gold mines were one source, there are other unknown sources and further analysis is required to determine what sources of mercury are manageable in Cambodia.

Influence of household practices on the performance of clay pot water filters in rural Cambodia

2009-01-11T12:00:00.001+07:00

Authors: Murphy, H.M.; Sampson, M.; McBean, E.; Farahbakhsh, K.

Source: Desalination; Nov2009, Vol. 248 Issue 1-3, p562-569, 8p

Abstract:
Currently, only 41% of Cambodians have access to safe drinking water. To combat this issue, Resource Development International Cambodia (RDIC) has been promoting and developing affordable clay pot water filters to be sold across the country. Although the filters have excellent bacterial removal capabilities, researchers have identified that the contamination of water storage containers through improper household practices is an important issue that needs to be addressed. Twelve Cambodian households were selected to investigate the causes of contamination in plastic water storage containers used in clay pot filtration. Some of the findings of the study include: (1) improper maintenance and cleaning practices may cause an increase in bacterial counts (HPCs, TC and Escherichia coli) in treated water storage receptacles and (2) common causes of container contamination were improper cleaning, moving of the filter, placing the filter element on the ground, putting dirty hands inside the plastic container, and drying the container using a dirty cloth.

Arsenicosis in Cambodia: Case studies and policy response

2008-11-01T12:00:00.010+07:00

Authors: Sampson, M.L.; Bostick, B.; Chiew, Hannah; Hagan, J.M.; Shantz, A.;

Source: Applied Geochemistry; Nov2008, Vol. 23 Issue 11, p2976-2985, 10p

Abstract:
Naturally occurring As found in groundwaters has been identified to be a problem in at least 10 provinces of Cambodia with Kandal being one of the most heavily impacted. Estimates, using groundwater quality and population data for Kandal Province of Cambodia, suggest that over 100,000 people are at high risk of chronic As exposure. Levels in some areas approach 3500μg/L, against the Cambodian Standard of 50μg/L. Considerable work remains to adequately characterize the extent of As hazard and its possible health effects in Cambodia and the region. It is likely that additional populations will develop health problems attributed to As, of particular concern is arsenicosis. The symptoms of arsenicosis have been generally assumed to develop after 8–10years of consumption of water with elevated As levels, however, new cases discovered in Cambodia have been identified with exposure times as short as 3years. The rapid onset of arsenicosis may be attributed to contributing risk factors related to socioeconomic status, including malnutrition. It is thus imperative to develop strategies to rapidly identify possible regions of enrichment, to minimize exposure to As-rich waters, and to educate affected populations. To date the response to the As hazard has been led by the Ministry of Rural Development in cooperation with international organizations and NGOs, to identify at risk areas, and educate communities of the risk of As-rich water. However better coordination between government bodies, NGOs and donor agencies active in the field of water supply and treatment is essential to minimize future As exposure.

Groundwater flow in an arsenic-contaminated aquifer, Mekong Delta, Cambodia

2008-11-01T12:00:00.008+07:00

Authors: Benner, Shawn G; Polizzotto, Matthew L.; Kocar, Benjamin D.; Ganguly, Somenath; Phan, Kongkea; Ouch, Kagna; Sampson, Michael; Fendorf, Scott

Source:
Applied Geochemistry; Nov2008, Vol. 23 Issue 11, p3072-3087, 16p

Abstract:
To advance understanding of hydrological influences on As concentrations within groundwaters of Southeast Asia, the flow system of an As-rich aquifer on the Mekong Delta in Cambodia where flow patterns have not been disturbed by irrigation well pumping was examined. Monitoring of water levels in a network of installed wells, extending over a 50km2 area, indicates that groundwater flow is dominated by seasonally-variable gradients developed between the river and the inland wetland basins. While the gradient inverts annually, net groundwater flow is from the wetlands to the river. Hydraulic parameters of the aquifer (K ≈10-4 ms-1) and overlying clay aquitard (K ≈10-8 ms-1) were determined using grain size, permeameter and slug test analyses; when coupled with observed gradients, they indicate a net groundwater flow velocity of 0.04–0.4ma-1 downward through the clay and 1–13ma-1 horizontally within the sand aquifer, producing aquifer residence times on the order 100–1000a. The results of numerical modeling support this conceptual model of the flow system and, when integrated with observed spatial trends in dissolved As concentrations, reveal that the shallow sediments (upper 2–10m of fine-grained material) are an important source of As to the underlying aquifer.

Integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the Mekong delta

2008-11-01T12:00:00.007+07:00

Authors: Kocar, Benjamin D.; Polizzotto, Matthew L.; Benner, Shawn G.; Ying, Samantha C.; Ung, Mengieng; Ouch, Kagna; Samreth, Sopheap; Suy, Bunseang; Phan, Kongkea; Sampson, Michael; Fendorf, Scott

Source:
Applied Geochemistry; Nov2008, Vol. 23 Issue 11, p3059-3071, 13p

Abstract:
Arsenic is contaminating the groundwater of Holocene aquifers throughout South and Southeast Asia. To examine the biogeochemical and hydrological processes influencing dissolved concentrations and transport of As within soils/sediments in the Mekong River delta, a ∼50km2 field site was established near Phnom Penh, Cambodia, where aqueous As concentrations are dangerously high and where groundwater retrieval for irrigation is minimal. Dissolved As concentrations vary spatially, ranging up to 1300μg/L in aquifer groundwater and up to 600μg/L in surficial clay pore water. Groundwaters with high As concentrations are reducing with negligible dissolved O2 and high concentrations of Fe(II), , and dissolved organic C. Within near-surface environments, these conditions are most pronounced in sediments underlying permanent wetlands, often found within oxbow channels near the Mekong River. There, labile C, co-deposited with As-bearing Fe (hydr)oxides under reducing conditions, drives the reductive mobilization (inclusive of Fe and As reduction) of As. Here, conditions are described under which As is mobilized from these sediments, and near-surface As release is linked to aquifer contamination over long time periods (100s to 1000s of years). Site biogeochemistry is coupled with extensive hydrologic measurements, and, accordingly, a comprehensive interpretation of spatial As release and transport within a calibrated hydraulic flow-field is provided of an As-contaminated aquifer that is representative of those found throughout South and Southeast Asia.

Linking organic matter deposition and iron mineral transformations to groundwater arsenic levels in the Mekong delta, Cambodia

2008-11-01T12:00:00.006+07:00

Authors: Quicksall, Andrew N.; Bostick, Benjamin C.; Sampson, M.L.

Source: Applied Geochemistry; Nov2008, Vol. 23 Issue 11, p3088-3098, 11p

Abstract:
Enriched As in drinking water wells in south and Southeast Asia has increased the risk of cancer for nearly 100 million people. This enrichment is generally attributed to the reductive dissolution of Fe oxides; however, the complex expression of As enrichment in these areas is not yet well understood. Here, the coupled sedimentological and geochemical factors that contribute to the extent and spatial distribution of groundwater As concentrations in the Mekong River delta, Cambodia in an avulsed scroll bar sequence are examined. X-Ray absorption spectroscopy (XAS) was used to determine Fe and As speciation in redox preserved sediment collected from drilled cores. Dissolved As, Fe and S solution concentrations in existing and newly drilled wells (cores) differed considerably depending on their source sedimentology. The rapid burial of organic matter in the scroll bar sequence facilitated the development of extensive Fe-reducing conditions, and As release into the aquifer. In older features organic C levels are high enough to sustain extensive Fe reduction and provide ample SO4 which is reduced to sulfide. This S reduction impacts As levels; As is sequestered in sulfide minerals outside of the scrollbar sequence, decreasing pore water concentrations. In contrast, As is depleted in sediments from the scroll sequence, and associated with elevated pore water aqueous concentrations. The concentration and form of organic C in the scrollbar sequence is related to depositional environment, and can facilitate Fe and S mineral transformations, distinct sedimentary environments explain a portion of the inherent heterogeneity of aquifer As concentrations.

Geomorphic controls on groundwater arsenic distribution in the Mekong River Delta, Cambodia

2008-11-01T12:00:00.005+07:00

Authors: Papacostas, Nicholas C.; Bostick, Benjamin C.; Quicksall, Andrew N.; Landis, Joshua D.; Sampson, Michael;

Source:
Geology; Nov 2008, Vol. 36 Issue 11, p891-894, 4p, 2 graphs, 1 map

Abstract:
Natural arsenic contamination of groundwater is a severe public health crisis affecting nearly 60 million people in South Asia and Southeast Asia alone. Contamination is spatially heterogeneous and results from the coupled microbial decomposition of organic matter and reductive dissolution of arsenic-bearing iron minerals. Here we demonstrate that elevated arsenic concentrations arise in regions of recent organic matter deposition and thus are controlled by fluvial geomorphic processes. Arsenic contamination is best expressed within recent geomorphic features such as docked islands, scroll bars, and avulsions. Within these features, the deposition of rapidly buried reactive organic matter facilitates microbial iron reduction and arsenic release. Ultimately, the organic matter supply is exhausted and the conditions necessary for soluble arsenic to persist diminish.

Integrating Mechanisms that Control the Concentration and Distribution of Groundwater Arsenic in Cambodia

2008-10-01T15:19:00.001+07:00

Authors: Bostick, B C; Rosen, E L; Nguyen, H M; Sampson, M L

Source: Biogeosciences, 2008 Fall Meeting

Abstract:
Arsenic contamination in the groundwater of the deltaic regions of southeastern Asia affects as many as one hundred million people. In these areas, the dominant mechanism for arsenic release into solution is the reductive dissolution of arsenic-bearing iron (hydr)oxides. What continues to confound researchers, however, is the heterogeneous nature of arsenic in groundwater. Recent evidence suggests that specific geomorphic environments are linked to regions of elevated groundwater arsenic. Moreover, waters from actively cycling surficial environments represent important sources of groundwater As in many environments. Here, we examine the mechanistic link between the localized expression of iron reduction and the large scale distribution of arsenic in groundwater along the Mekong River in Cambodia in a region impacted by widespread but heterogeneous arsenic contamination. In this region, arsenic levels in groundwater were correlated to sulfate levels, and both were strongly influenced by the extent of local surface water flooding (as quantified by remote sensing). Concentrations of arsenic ranged from 0 to 2100 micrograms/L, and were always found in groundwaters with significant dissolved iron and a sulfate concentration less than 1 mg/L. This indicates that the delivery of As and S was influenced by active redox processes in near-surface environments. In many, but not all, high As regions, groundwater concentrations of conservative halide anions also were similar to those of surficial environments, indicating that they were likely derived from the same locations. Low As regions, however, had widely variable halide concentrations in groundwater that may reflect additional groundwater sources. Thus, the expression of As contamination is strongly influenced by the hydrological connectivity of the aquifer with the surface. The isotopic composition of groundwater (hydrogen and oxygen) of high As areas also is similar to that of surface waters. Dissolved inorganic carbon isotopic composition of waters is more complex, with As-impacted groundwaters having distinct isotopic signatures characteristic of either extensive or relatively limited organic matter decomposition. Regional correlations of As with dissolved organic carbon are also not uniform, suggesting that sedimentary carbon is also important in generating reducing conditions. These data indicate that the distribution of organic carbon helps determine the distribution of arsenic in the environment. Moreover, these data indicate that heterogeneity in arsenic concentrations results from the interplay of variable organic matter content and reactivity within complex hydrological systems that can at least in part be explained regionally based on depositional environment.

Linking Hydrologic Drivers to Arsenic Contamination in Asia, Results From a Field Site in Cambodia

2008-10-01T12:00:00.003+07:00

Authors: Benner, S G; Polizzotto, M L; Kocar, B D; Sampson, M; Fendorf, S

Source: Hydrology, 2008 Fall Meeting

Abstract:
Attempts to resolve the specific release mechanisms associated with arsenic contamination on the deltas of Asia have been hampered, especially in Bangladesh, by the difficulty of linking geochemical mechanisms with hydrologic drivers. At an arsenic-contaminated (100-1200 ug/L) aquifer in Cambodia, where pumping for irrigation is limited and the hydrologic system is much less complex than in Bangladesh, we have developed a conceptual model of arsenic behavior that integrates the system hydrology and depositional history, providing strong evidence that arsenic release is sensitive to human activities. Specifically, the hydrogeologic regime is dominated by seasonally-variable head gradients between the river and adjacent wetland basins but the net annual flow is from the wetlands downwards into the aquifer (0.04-0.4 m/a) followed by discharge to the river (1-13 m/a). These flow rates produce aquifer residence times on the order of 100-1000 years. When coupled with elevated concentrations throughout the aquifer, this indicates that arsenic contamination predates recent human activities. Within this flow regime, it is possible to track spatial changes in arsenic concentrations along specific flow lines: The greatest increases in dissolved arsenic concentrations (150 ug/L/m) occur in shallow sediments along the first 2-10 m of the flow path, consistent with the depth at which reducing conditions are no longer seasonally disrupted by fluctuating water levels. Estimates of arsenic delivery to the wetlands by flood deposition (1,300,000 kg/a) are of a similar magnitude to the estimated flux, via groundwater, out of the aquifer (1,000,000 kg/a), indicating that arsenic delivery, release, and transport are in approximate steady-state. Given the dependency of arsenic release and transport on hydrologic drivers, human activities that alter the hydrology (inclusive of pumping for irrigation, soil excavation, and upstream river damming) will likely also alter arsenic behavior.

Coupled Biogeochemical and Hydrologic Processes Governing Arsenic Mobility Within Sediments of Southeast Asia

2008-10-01T12:00:00.002+07:00

Authors: Kocar, B. D.; Polizzotto, M. L.; Ying, S. C.; Benner, S. G.; Sampson, M.; Fendorf, S.

Source: American Geophysical Union, Fall Meeting 2008, abstract #H41E-0913

Abstract:
Weathering of As-bearing rocks in the Himalayas has resulted in the transport of sediments down major river systems such as the Brahmaputra, Ganges, Red, Irrawaddy, and Mekong. Groundwater in these river basins commonly has As concentrations exceeding the World Health Organization's recommended drinking water limit (10 μg L-1) by more than an order of magnitude. Coupling of hydrology and biogeochemical processes underlies the elevated concentrations of As in these aquifers, necessitating studies that allow their deconvolution. Furthermore, to fully elucidate the biogeochemical mechanisms of sedimentary As release, the thermodynamic favorability of controlling biogeochemical reactions must be considered. We therefore used a combination of spectroscopic and wet chemical measurements to resolve the dominant processes controlling As release and transport in surficial soils/sediments within an As-afflicted field area of the Mekong delta. Based on these measurements, we assess the thermodynamic potential for As, Fe, and S reduction to transpire--major processes influencing As release and mobility. Our results illustrate that clay (0-12m deep) underlying oxbow and wetland environments are subjected to continuously reducing conditions due to ample carbon input and saturated conditions. Ensuing reductive mobilization of As from As-bearing Fe (hydr)oxides results in its migration to the underlying sandy aquifer (>12 m deep). Reactive transport modeling using PHREEQC and MIN3P, constrained with chemical and hydrologic field measurements, provides a calibrated illustration of As release and transport occurring within the clays underlying organic-rich, permanently inundated locations. These areas provide sufficient As to the aqueous phase for widespread contamination of the aquifer, and release is predicted to occur for several thousand years prior to depletion of As from the solid phase.

Local Drinking Water Filters Reduce Diarrheal Disease in Cambodia: A Randomized, Controlled Trial of the Ceramic Water Purifier

2008-09-01T15:24:00.001+07:00

Authors: Joe Brown; Mark D. Sobsey; Dana Loomis

Source: Am. J. Trop. Med. Hyg., 79(3), 2008, pp. 394-400

Abstract:
A randomized, controlled intervention trial of two household-scale drinking water filters was conducted in a rural village in Cambodia. After collecting four weeks of baseline data on household water quality, diarrheal disease, and other data related to water use and handling practices, households were randomly assigned to one of three groups of 60 households: those receiving a ceramic water purifier (CWP), those receiving a second filter employing an iron-rich ceramic (CWP-Fe), and a control group receiving no intervention. Households were followed for 18 weeks post-baseline with biweekly follow-up. Households using either filter reported significantly less diarrheal disease during the study compared with a control group of households without filters as indicated by longitudinal prevalence ratios CWP: 0.51 (95% confidence interval [CI]: 0.41–0.63); CWP-Fe: 0.58 (95% CI: 0.47–0.71), an effect that was observed in all age groups and both sexes after controlling for clustering within households and within individuals over time.

Contamination of drinking water resources in the Mekong delta floodplains: Arsenic and other trace metals pose serious health risks to population

2008-08-01T12:00:00.001+07:00

Authors: Buschmann, Johanna; Berg, Michael; Stengel, Caroline; Winkel, Lenny; Sampson, Mickey L.; Trang, Pham Thi Kim; Viet, Pham Hung

Source: Environment International; Aug2008, Vol. 34 Issue 6, p756-764, 9p

Abstract:
This study presents a transnational groundwater survey of the 62,000 km2 Mekong delta floodplain (Southern Vietnam and bordering Cambodia) and assesses human health risks associated with elevated concentrations of dissolved toxic elements. The lower Mekong delta generally features saline groundwater. However, where groundwater salinity is <1 g L-1 Total Dissolved Solids (TDS), the rural population started exploiting shallow groundwater as drinking water in replacement of microbially contaminated surface water. In groundwater used as drinking water, arsenic concentrations ranged from 0.1–1340 µg L-1, with 37% of the studied wells exceeding the WHO guidelines of 10 µg L-1 arsenic. In addition, 50% exceeded the manganese WHO guideline of 0.4 mg L-1, with concentrations being particularly high in Vietnam (range 1.0–34 mg L-1). Other elements of (minor) concern are Ba, Cd, Ni, Se, Pb and U. Our measurements imply that groundwater contamination is of geogenic origin and caused by natural anoxic conditions in the aquifers. Chronic arsenic poisoning is the most serious health risk for the ~2 million people drinking this groundwater without treatment, followed by malfunction in children''s development through excessive manganese uptake. Government agencies, water specialists and scientists must get aware of the serious situation. Mitigation measures are urgently needed to protect the unaware people from such health problems.

Near-surface wetland sediments as a source of arsenic release to ground water in Asia

2008-07-24T16:29:00.000+07:00

Authors: Polizzotto, Matthew L.; Kocar, Benjamin D.; Benner, Shawn G.; Sampson, Michael; Fendorf, Scott;

Source: Nature; 7/24/2008, Vol. 454 Issue 7203, p505-508, 4p, 1 diagram, 2 graphs

Abstract:
Tens of millions of people in south and southeast Asia routinely consume ground water that has unsafe arsenic levels. Arsenic is naturally derived from eroded Himalayan sediments, and is believed to enter solution following reductive release from solid phases under anaerobic conditions. However, the processes governing aqueous concentrations and locations of arsenic release to pore water remain unresolved, limiting our ability to predict arsenic concentrations spatially (between wells) and temporally (future concentrations) and to assess the impact of human activities on the arsenic problem. This uncertainty is partly attributed to a poor understanding of groundwater flow paths altered by extensive irrigation pumping in the Ganges-Brahmaputra delta, where most research has focused. Here, using hydrologic and (bio)geochemical measurements, we show that on the minimally disturbed Mekong delta of Cambodia, arsenic is released from near-surface, river-derived sediments and transported, on a centennial timescale, through the underlying aquifer back to the river. Owing to similarities in geologic deposition, aquifer source rock and regional hydrologic gradients, our results represent a model for understanding pre-disturbance conditions for other major deltas in Asia. Furthermore, the observation of strong hydrologic influence on arsenic behaviour indicates that release and transport of arsenic are sensitive to continuing and impending anthropogenic disturbances. In particular, groundwater pumping for irrigation, changes in agricultural practices, sediment excavation, levee construction and upstream dam installations will alter the hydraulic regime and/or arsenic source material and, by extension, influence groundwater arsenic concentrations and the future of this health problem.

Factors Affecting the Precipitation of Authigenic Arsenic Sulfides and the Limits They Place on Groundwater Arsenic Levels

2008-07-02T16:50:00.000+07:00

Authors: Benjamin C. Bostick; Andrew N. Quicksall; Samantha L. Saalfield; M. L. Sampson

Source: Northeast Regional Meeting (NERM) (June 29 - July 2, 2008)

Abstract:
Arsenic is a widespread natural contaminant in drinking water in South and Southeast Asia. Most commonly, arsenic contamination in groundwater is thought to arise through reductive dissolution of arsenic-bearing iron minerals in aquifer-bearing sediments; however, sulfur redox cycling may also influence arsenic phase partitioning by sequestering arsenic in sulfide phases of facilitating iron reduction. Here, we examine the combined impact of iron and sulfate reduction in regulating arsenic concentrations in Kandal province, Cambodia, a region impacted by elevated groundwater arsenic. Elevated arsenic concentrations are associated with the combination of reducing conditions and low concentrations of dissolved sulfate. Low groundwater arsenic concentrations result under more oxic conditions, or higher sulfate concentrations. X-ray absorption spectroscopy of sediment cores confirms that authigenic arsenic sulfide minerals are produced in sulfate-bearing aquifers, functionally limiting arsenic levels. Thermodynamic calculations suggest that the presence of some reactive iron(III) in these reducing environments may enhance the formation of insoluble arsenic sulfides by buffering the activity of free sulfide and thus preventing the formation of soluble arsenic(III) sulfide complexes. Lower sulfate concentrations inhibit sulfate reduction, thereby limiting sulfide mineral precipitation. Thus, the kinetic and thermodynamics of iron and sulfate cycling both play critical roles in controlling the fate of arsenic in reducing environments.

Escherichia coli in household drinking water and diarrheal disease risk: evidence from Cambodia

2008-07-02T16:44:00.003+07:00

Authors: J. M. Brown; S. Proum; M. D. Sobsey

Source: Water Sci Technol. 2008;58(4):757-63.

Abstract:
Escherichia coli counts in household drinking water may or may not reliably indicate the presence of diarrheogenic pathogens originating in feces. The extent to which a bacterial indicator like E. coli predicts risks from all classes of pathogens (viruses and parasites as well as bacteria), especially in tropical waters, is uncertain. To investigate the association between E. coli in household drinking water and diarrheal diseases in Cambodia, we conducted a 22 week cohort study in a rural village in Kandal Province. Episodes of diarrhea (all) and bloody diarrhea (dysentery), water quality, water sources, and other covariates were monitored biweekly in 180 households. Households used a variety of water treatment, storage, and handling practices.

Results suggest a weak but positive association between E. coli counts in household drinking water and diarrhea and for diarrhea with blood (dysentery), after adjusting for clustering within households and within individuals over time. Compared to households with ,1 E. coli/100 ml in drinking water, there was no observed increased risk for having 1–10 E. coli/100ml (LPR ¼ 0.98, 95% CI 0.81–1.2 for diarrheal disease; LPR ¼ 0.75, 95% CI 0.36–1.6 for dysentery). Households with measured E. coli of 11–100/100 ml did report increased diarrhea (LPR ¼ 1.2, 95% CI 1.1–1.3 for diarrheal disease; LPR ¼ 1.4, 95% CI 1.0–1.8 for dysentery), as did those with 101–1,000 E. coli/100 ml (LPR ¼ 1.2, 95% CI 1.2–1.3 for diarrheal disease; LPR ¼ 1.2, 95% CI 1.0–1.4 for dysentery) and those with .1,000 E. coli per 100ml sample (LPR ¼ 1.2, 95% CI 1.1–1.2 for diarrheal disease; LPR ¼ 1.2, 95% CI 1.0–1.3 for dysentery). Unlike the results of some previous studies, diarrheal disease risks did not increase progressively in magnitude with increasing concentration of E. coli in drinking water.

Arsenic in hair and nails of individuals exposed to arsenic-rich groundwaters in Kandal province, Cambodia

2008-04-01T15:31:00.000+07:00

Authors: Gault, Andrew G.; Rowland, Helen. A.L.; Charnock, John M.; Wogelius, Roy A.; Gomez-Morilla, Inma; Vong, Sovathana; Leng, Moniphea; Samreth, Sopheap; Sampson, Mickey L.; Polya, David A.;

Source: Science of the Total Environment; Apr 2008, Vol. 393 Issue 1, p168-176, 9p

Abstract:
The health implications of the consumption of high arsenic groundwater in Bangladesh and West Bengal are well-documented, however, little is known about the level of arsenic exposure elsewhere in Southeast Asia, where widespread exploitation of groundwater resources is less well established. We measured the arsenic concentrations of nail and hair samples collected from residents of Kandal province, Cambodia, an area recently identified to host arsenic-rich groundwaters, in order to evaluate the extent of arsenic exposure. Nail and hair arsenic concentrations ranged from 0.20 to 6.50 μg g-1 (n =70) and 0.10 to 7.95 μg g-1 (n =40), respectively, in many cases exceeding typical baseline levels. The arsenic content of the groundwater used for drinking water purposes (0.21–943 μg L-1; (n =31)) was positively correlated with both nail (r =0.74, p <0.0001) and hair (r =0.86, p <0.0001) arsenic concentrations. In addition, the nail and hair samples collected from inhabitants using groundwater that exceeded the Cambodian drinking water legal limit of 50 μg L-1 arsenic contained significantly more arsenic than those of individuals using groundwater containing <50 μg L-1 arsenic. X-ray absorption near edge structure (XANES) spectroscopy suggested that sulfur-coordinated arsenic was the dominant species in the bulk of the samples analysed, with additional varying degrees of As(III)-O character. Tentative linear least squares fitting of the XANES data pointed towards differences in the pattern of arsenic speciation between the nail and hair samples analysed, however, mismatches in sample and standard absorption peak intensity prevented us from unambiguously determining the arsenic species distribution. The good correlation with the groundwater arsenic concentration, allied with the relative ease of sampling such tissues, indicate that the arsenic content of hair and nail samples may be used as an effective biomarker of arsenic intake in this relatively recently exposed population.

Coupled Biogeochemical and Hydrologic Processes Governing Arsenic Transport within Evolving Sedimentary Basins of Southeast Asia

2008-01-01T12:00:00.000+07:00

Authors: Benjamin Kocar; Samantha Ying; Matthew Polizzotto; Shawn Benner; Mengieng Ung; Bunseang Suy; Kongkea Phan; Mickey Sampson; Scott Fendorf

Source:
Geochemica Et Cosmochimica Acta 72.12 (2008): A485-485 Suppl

Abstract:
Weathering of As-bearing rocks in the Himalayas has resulted in the transport of sediments down the major river systems such as the Brahmaputra, Ganges, Red, Irrawaddy, and Mekong. Groundwater in these river basins commonly has As concentrations exceeding the World Health Organization’s recommended drinking water limit (10 μg/L) by more than two orders of magnitude. Understanding the reason(s) for these elevated concentrations of As within the sediments of Southeast Asia has remained a challenge, owing to the difficulty of separating mechanisms responsible for As release (e.g. As and Fe reduction) and local to region hydrology. We deciphered, using a combination of field and laboratory measurements of biogeochemical and hydrologic factors, dominant mechanisms of As release and transport within surficial soils/sediments within an As-afflicted field area of the Mekong delta. Our results illustrate that clay (0-12m deep) underlying oxbow and wetland environments are subjected to continuously reducing conditions due to ample carbon input and saturated conditions. Ensuing reductive dissolution of As-bearing Fe (hydr)oxides releases As, which then migrates to the underlying sandy aquifer (>12m deep). Reactive transport modeling using PHREEQC and MIN3P was constrained with chemical and hydrologic field measurements, and provides a calibrated illustration of As release and transport within our field site. Our resulting simulations indicate that As release occurs within the clays underlying organic-rich, permanently inundated locations providing sufficient As to the aqueous phase for widespread contamination of the aquifer, and that release occurs for several thousand years prior to depletion of As from the solid phase.

Arsenic and Manganese Contamination of Drinking Water Resources in Cambodia: Coincidence of Risk Areas with Low Relief Topography.

2007-04-01T16:13:00.001+07:00

Authors: Buschmann, Johanna; Berg, Michael; Stengel, Caroline; Sampson, Mickey L.

Source: Environmental Science & Technology; 4/1/2007, Vol. 41 Issue 7, p2146-2152, 7p, 5 graphs

Abstract:
Arsenic contamination of groundwater has been identified in Cambodia, where some 100,000 family-based wells are used for drinking water needs. We conducted a comprehensive groundwater survey in the Mekong River floodplain, comprising an area of 3700 km² (131 samples, 30 parameters). Seasonal fluctuations were also studied. Arsenic ranged from 1 to 1340 μg L^-1; (average 163 μg L^-1), with 48% exceeding 10 μg L^-1 Elevated manganese levels (57% >0.4 mg potentially exposed to chronic arsenic poisoning, the magnitude is similar to that of Bangladesh (200 km^-2). Elevated arsenic levels are sharply restricted to the Bassac and Mekong River banks and the alluvium braided by these rivers (Kandal Province). Arsenic in this province averaged 233 μg L^-1 (median 100 μg L^-1), while concentrations to the west and east of the rivers were <10 μg L^-1. Arsenic release from Holocene sediments between the rivers is most likely caused by reductive dissolution of metal oxides. Regions exhibiting low and elevated arsenic levels are co-incident with the present low relief topography featuring gently increasing elevation to the west and east of a shallow valley—understood as a relict of pre-Holocene topography. The full georeferenced database of groundwater analysis is provided as Supporting Information.

Magnitude of arsenic pollution in the Mekong and Red River Deltas — Cambodia and Vietnam

2007-01-01T16:09:00.002+07:00

Authors: Berg, Michael; Stengel, Caroline; Trang, Pham Thi Kim; Hung Viet, Pham; Sampson, Mickey L.; Leng, Moniphea; Samreth, Sopheap; Fredericks, David

Source: Science of the Total Environment; Jan2007, Vol. 372 Issue 2/3, p413-425, 13p

Abstract:
Large alluvial deltas of the Mekong River in southern Vietnam and Cambodia and the Red River in northern Vietnam have groundwaters that are exploited for drinking water by private tube-wells, which are of increasing demand since the mid-1990s. This paper presents an overview of groundwater arsenic pollution in the Mekong delta: arsenic concentrations ranged from 1–1610 μg/L in Cambodia (average 217 μg/L) and 1–845 μg/L in southern Vietnam (average 39 μg/L), respectively. It also evaluates the situation in Red River delta where groundwater arsenic concentrations vary from 1–3050 μg/L (average 159 μg/L). In addition to rural areas, the drinking water supply of the city of Hanoi has elevated arsenic concentrations. The sediments of 12–40 m deep cores from the Red River delta contain arsenic levels of 2–33 μg/g (average 7μg/g, dry weight) and show a remarkable correlation with sediment-bound iron. In all three areas, the groundwater arsenic pollution seem to be of natural origin and caused by reductive dissolution of arsenic-bearing iron phases buried in aquifers. The population at risk of chronic arsenic poisonGroundwater Iron and Phosphate ing is estimated to be 10 million in the Red River delta and 0. 5–1 million in the Mekong delta. A subset of hair samples collected in Vietnam and Cambodia from residents drinking groundwater with arsenic levels >50 μg/L have a significantly higher arsenic content than control groups (<50 μg/L). Few cases of arsenic related health problems are recognized in the study areas compared to Bangladesh and West Bengal. This difference probably relates to arsenic contaminated tube-well water only being used substantially over the past 7 to 10 years in Vietnam and Cambodia. Because symptoms of chronic arsenic poisoning usually take more than 10 years to develop, the number of future arsenic related ailments in Cambodia and Vietnam is likely to increase. Early mitigation measures should be a high priority.

Evaluating sources of arsenic to groundwater in the Mekong Delta based on coupled hydrologic and biogeochemical analyses

2007-01-01T16:05:00.001+07:00

Authors: Polizzotto, M; Benner, S G; Kocar, B D; Sampson, M; Ouch, K; Ouch, K; Phan, K; Fendorf, S

Source: Hydrology, 2007 Fall Meeting

Abstract::
Tens of millions of people living on the large river deltas of Southeast Asia routinely consume groundwater with unsafe arsenic levels. While there is general agreement that arsenic is naturally derived, the particular sources of arsenic, as well as the mechanisms promoting its release from the solid-phase, remain unresolved, thereby limiting our ability to predict arsenic concentrations in space (between wells) and time (future concentrations). This uncertainty is attributed, in part, to a poor understanding of groundwater flow paths due to extensive irrigation pumping in the Ganges-Brahmaputra River system, where most research has focused. In order to elucidate the most important arsenic sources and the processes controlling arsenic contamination in Southeast Asian groundwater, we have established a field area within the minimally disturbed Mekong River Delta in Cambodia. While the Mekong Delta system in Cambodia has similar depositional history, regional hydrology, and biogeochemical conditions to other arsenic-contaminated deltaic aquifers of Asia, land use alteration, inclusive of irrigation, is minimal. Thus, the hydrology of our system remains governed by natural rather than anthropogenic processes, allowing us to formulate a steady-state, coupled hydrologic and biogeochemical model of arsenic release and transport. Using robust principles of mass balance, we show that, while liberation mechanisms within the deeper aquifer sediments may contribute arsenic to the groundwater, the majority of the dissolved arsenic is derived from arsenic release at the near-surface and is transported through the aquifer, a finding that has important implications for management of the arsenic crisis.

Effectiveness of Ceramic Filtration for Drinking Water Treatment in Cambodia

2007-01-01T15:59:00.001+07:00

Authors: Joseph Mark Brown

Source: Ph.D. dissertation submitted to the faculty of the University of North Carolina at Chapel Hill

Abstract:
For the estimated 66% of Cambodians without access to improved drinking water sources and the potentially much greater percentage without consistent access to microbiologically safe water, point-of-use water treatment coupled with appropriate storage to prevent recontamination is a promising option for securing access to safe drinking water. The ceramic water purifier (CWP) is an emerging point-of-use water treatment technology that is made locally in Cambodia and in several other developing countries based on a design originally developed in Latin America in the 1980s. Despite the filter's increasingly widespread promotion and implementation as a public health intervention within Cambodia and worldwide, its effectiveness in reducing waterborne microbes and diarrheal disease in users has not been adequately characterized. This dissertation examines: (i) the microbiological effectiveness of locally produced ceramic filters in Cambodia against bacterial and viral surrogates in the laboratory and in field use; (ii) the health impacts of the CWP and a modified CWP in a randomized, controlled trial in a rural/peri-urban village; and (iii) the continued use, microbiological effectiveness, and sustained health impacts of the CWP after up to 44 months in household use in three provinces of Cambodia.

Results indicate filters as currently produced do reduce microbial indicators in drinking water and contribute to the reduction of diarrheal disease in users. Key findings were: (i) CWPs reduced E. coli up to 99.9999%, with mean reductions of approximately 99% in both laboratory and field testing; (ii) CWPs reduced MS2, a viral surrogate, by a mean 90-99% in laboratory testing; (iii) use of the CWP reduced diarrheal disease outcomes by approximately 40% in users versus non-users, after controlling for clustering within households and within individuals over time in a randomized, controlled trial; (iv) filters maintained effectiveness over long periods, up to 44 months in field use; (v) declining use of the CWPs after implementation was observed due to breakages of the ceramic filter elements coupled with limited availability of replacement parts in communities; and (vi) CWPs in field use were susceptible to recontamination through improper handling practices.

A Microbiological Investigation of a Point of Use Drinking Water Disinfection Technology: Solar Photo-Disinfection and its Challenges in Cambodia

2007-01-01T15:54:00.002+07:00

Authors: Sinclair, Ryan; Englande, A.J.; Reimers, Robert; Rice, Janet; Abdelghani, Assaf; Samreth, Sopheap

Source: Proceedings of the Water Environment Federation, Disinfection 2007 , pp. 334-359(26)

Abstract:
In rural and underdeveloped regions of the world, simple point-of-use water treatment technologies are sometimes the only option available clean drinking water. Using the sun to disinfect drinking water has become internationally known as an efficient method to treat drinking water to a quality approaching and/or surpassing commercially available bottled water. A solar disinfection microbiology study in a Cambodia based laboratory was conducted to describe this point-of-use water treatment option. Various batch experiments were conducted to scientifically assess the technology and its efficiency in handling certain typical user challenges. Utilizing a wild type strain of Escherichia coli as an indicator for pathogenic bacteria, results of the study describe “die-off” or disinfection efficiency when 500ml plastic polyethylene terphthalate (PET) bottle are filled with river water and exposed to the sun for one day. The challenges of turbidity, volume variations, absorptive or reflective surfaces, source water chemistry, and varying weather conditions are described. Regression models are developed to characterize the disinfection efficiency. Major results were that a six-log10 removal of the indicator was possible under a wide variety of conditions including: (1) moderate levels of turbidity; (2) varying reflective/adsorptive surfaces; (3) varying volumes inside the SWD bottle; (4) and under a completely cloudy and overcast day. Additionally, the turbidity disinfection trials were shown to be not attributed to a thermal effect suggesting a potential for photocatalytic action of dissolved organic matter. The study results are specific to the Phnom Penh, Cambodia location and validate other international investigations of SWD efficiency.

Iron (hydr)oxide transformation and release of arsenic from tropical soils during iron and sulfate reduction.

2006-11-16T15:35:00.001+07:00

Authors: Kocar, Benjamin; Ying, Samantha; Polizzotto, Matthew; Mengieng, Ung; Samreth, Sopheap; Moniphea, Leng; Sampson, Mickey; Fendorf, Scott

Source:ASA-CSSA-SSSA International Annual Meetings (November 12-16, 2006)

Abstract:
Soils and surface sediments are enriched with arsenic bearing iron (hydr)oxides throughout sedimentary basins of southeast Asia– arsenic concentrations typically range from 10 to 40 mg kg -1 (DW). Seasonal monsoons result in drastically fluctuating water levels, which drive wide swings in redox processes within soils and near-surface sediments. Extensive flooding results in anaerobic soil/sediment conditions, with ensuing reduction of iron (hydr)oxides and sulfate. Aqueous concentrations of arsenic vary with redox conditions and processes and when elevated, result in migration through the soil profile to the deeper subsurface. Using ceramic-cup lysimeters and passive samplers (peepers), we measured a suite of reduced aqueous constituents, including arsenic, within soil profiles in the lower Mekong delta, Cambodia. Within a zone of seasonal wetting/drying, we observed increased aqueous concentrations of arsenic in surface soils during periods of flooding. Arsenic release is coincident with the production of Fe(II) and, to a lesser degree, S(-II) in the porewater. These results indicate that arsenic mobilization occurs in near-surface soil environments upon soil wetting, and that iron reduction and sulfidogenesis are likely dominant processes responsible for arsenic release.

Ground Water Modeling Of Arsenic Contaminated Sandy Aquifer With Response To Transient River Levels, Mekong Delta, Cambodia.

2006-11-01T12:00:00.001+07:00

Authors: Ganguly, S; Polizzotto, M; Sampson, M; Fendor, S ; Benner, S

Source:Hydrology, 2006 Fall Meeting

Abstract:
The sandy aquifer of Mekong River Delta in Cambodia is a primary drinking water source and contains elevated concentrations of dissolved arsenic (15-1300μg/L), a common problem of Southeast Asia. Both hydraulic heads and dissolved arsenic concentrations vary temporally with respect to transient hydraulic head of the Mekong River, suggesting that groundwater flow plays a potentially important role in arsenic mobilization/transportation. The river fluctuates annually 5 to 8 m, with the highest levels in mid-September due to upstream monsoonal rains and Himalayan snowmelt and the lowest levels in mid-May to early June. The hydraulic gradient between the river and adjacent aquifer changes direction biannually; when the river is rising the gradient is from the river to the aquifer, when the river is falling the gradient is from the aquifer towards the river. In contrast, wetlands overlying the aquifer exhibit time varying head change of 2.5 to 3m annually due to local rain from late September to early October and an apparent limited hydraulic connection to aquifer. Numerical modeling (using MODFLOW) is able to reproduce the aquifer head distribution by transiently altering the river boundary condition, supporting the hypothesis that the temporal variations in observed hydraulic head are primarily driven by the seasonal river fluctuations. The modeling also supports the conclusion that the observed dampening of water level fluctuations in the distal part of the study area is due to increasing distance from the Mekong River.

Arsenic hazard in shallow Cambodian groundwaters

2005-10-01T12:00:00.005+07:00

Authors: D. A. Polya; A. G. Gault; N. Diebe; P. Feldman; J. W. Rosenboom ; E. Gilligan; D. Fredericks; A. H. Milton; M. Sampson; H. A. L. Rowland; P. R. Lythgoe; J. C. Jones; C. Middleton; D. A. Cooke

Source: Mineralogical Magazine; October 2005; v. 69; no. 5; p. 807-823; DOI: 10.1180/0026461056950290

Abstract:
Our recent discovery of hazardous concentrations of arsenic in shallow sedimentary aquifers in Cambodia raises the spectre of future deleterious health impacts on a population that, particularly in non-urban areas, extensively use untreated groundwater as a source of drinking water and, in some instances, as irrigation water. We present here small-scale hazard maps for arsenic in shallow Cambodian groundwaters based on >1000 groundwater samples analysed in the Manchester Analytical Geochemistry Unit and elsewhere. Key indicators for hazardous concentrations of arsenic in Cambodian groundwaters include: (1) well depths greater than 16 m; (2) Holocene host sediments; and (3) proximity to major modern channels of the Mekong (and its distributary the Bassac). However, high-arsenic well waters are also commonly found in wells not exhibiting these key characteristics, notably in some shallower Holocene wells, and in wells drilled into older Quaternary and Neogene sediments.

It is emphasized that the maps and tables presented are most useful for identifying current regional trends in groundwater arsenic hazard and that their use for predicting arsenic concentrations in individual wells, for example for the purposes of well switching, is not recommended, particularly because of the lack of sufficient data (especially at depths >80 m) and because, as in Bangladesh and West Bengal, there is considerable heterogeneity of groundwater arsenic concentrations on a scale of metres to hundreds of metres. We have insufficient data at this time to determine unequivocally whether or not arsenic concentrations are increasing in shallow Cambodian groundwaters as a result of groundwater-abstraction activities.

Arsenic Contamination in the Flood Plain Aquifer of the Mekong Delta, Cambodia

2005-10-01T12:00:00.004+07:00

Authors: Polizzotto, Matthew L.; Kocar, Benjamin D.; Sampson, Michael; Ouch, Kagna; Ung, Mengieng; Oum, Rachna; Benner, Shawn G.; Fendorf, Scott

Source: Geological Society of America Abstracts with Programs, Vol. 37, No. 7, p. 376

Abstract:
Arsenic is a contaminant in the groundwater of Holocene aquifers throughout Southeast Asia. Most studies concerning the causes of this contamination have focused on the crisis in Bangladesh and West Bengal, India where the problem is most acute, but recently arsenic poisoning has been observed in Vietnam, Laos, Nepal, China, and Cambodia. Although reductive dissolution of ferric (hydr)oxides in aquifer materials are commonly ascribed as the source of high dissolved arsenic concentrations in Bangladesh, there are many unresolved issues concerning the distribution of arsenic and the processes of its liberation from the solid phase. In particular, establishing the hydrologic flow-paths, and therefore the potential for solute transport of arsenic, into the drinking water aquifer is difficult due to extensive irrigation and surface water sources.

We are characterizing the spatial and temporal variation in dissolved arsenic within groundwater of the Mekong Delta in the Kandal Province of Cambodia, where sediments derived from the Himalayas have led to arsenic contamination of local aquifers, similar to the situation in Bangladesh. Temporal variation in surface and groundwater levels along with the geochemistry of the aquifer, and perceived inputs, are being defined in order to assess means by which arsenic is entering the aquifer. Our findings reveal that arsenic concentrations vary spatially but are high (exceeding 100 μg/L) throughout the aquifer, and groundwater levels along with recharge gradients are dominated by seasonal fluctuation of the Mekong River. The arsenic-containing groundwater is reduced, as evidenced by low Eh and dissolved oxygen and elevated ferrous iron; additionally, in some cases dissolved sulfide is detected. Our geochemical observations are similar to the conditions reported for Ganges-Brahmaputra Delta in Bangladesh, while the hydrology is unique to the local area and represents a well constrained system.

Geologic Controls on Groundwater Arsenic Distribution in the Upper Mekong Floodplain, Kien Svay Region of Cambodia

2005-10-01T12:00:00.002+07:00

Authors: Yount, James; Breit, George; Sopheap, Samreth; Moniphea, Leng; Mengieng, Ung; Kagna, Ouch; Sampson, Mickey; Roseboom, Jan Willem

Source: Geological Society of America Abstracts with Programs, Vol. 37, No. 7, p. 376

Abstract:
Geologic and geochemical investigations of shallow fluvial aquifers in the 180 km² study area of Kien Svay district, south of Phnom Penh, Cambodia indicate that composition and age of aquifer sediments control arsenic concentration of groundwater. The sedimentary facies association along the Mekong differs from the larger, sandier fluvio-deltaic environments of Bangladesh in that distinct channel-levee–flood basin sequences are closely associated across the floodplains of the subparallel Mekong and Bassac Rivers. Organic-rich marshes and shallow lakes within the flood basins lie adjacent to levees where most of the villages and arsenic-contaminated water wells are located. Of 27 water wells sampled (20 to 65 m depth), 16 exceed the WHO As drinking water standard (10 µg/L) and 5 produce water containing more than 500 µg/L. Strong correlations of dissolved arsenic with alkalinity and ammonia are consistent with degradation of organic matter as part of the arsenic release mechanism. Excavations as deep as 5m exposed sediment with as much as 11 wt.% Corg interbedded with red paleosols. Juxtaposition of contrasting redox conditions results in arsenic accumulation in peaty layers and gray muds (up to 450 ppm As) and in Fe-stained sands (230 ppm As). High dissolved arsenic likely results from interaction of organic carbon-rich sulfate-poor water from marshes with ferric oxide coated sand. Drillers logs indicate aquifers are more tabular and continuous from 40 to 60m than overlying lensoidal levee-channel complexes of present rivers. Yet the co-occurrence of high arsenic wells with modern facies distribution suggests the modern environment influences arsenic concentration. Possible explanations may be: a) juxtaposition of organic-rich facies against channelized or tabular sand bodies containing significant Fe-hydroxide secondary coatings or b) a hydrologic connection of facies produced by the common practice of lining well casings with coarse sand to the ground surface. An area of consistently low arsenic water draws from erosional remnants of Pleistocene sediment based on surface exposures. The likely irregularity of the buried Holocene-Pleistocene contact further complicates interpretation of aquifer distribution. Although wells in the Pleistocene sediment are low in arsenic, high manganese may limit these aquifers as drinking water supplies.