28 No. 3
Analysis and Remediation of Arsenic Contamination in Groundwater
Naturally occurring arsenic contaminates a significant amount of the groundwater in the Asian country of Bangladesh, where thousands of shallow (10-40 m) tube wells sunk in the 1970s were found in the 1980s to be contaminated. Arsenicosis now seriously affects the health of many people in Bangladesh, and probably more than 100 million people worldwide. Arsenic contamination has been found in regional water supplies in Argentina, Australia, Chile, France, Ghana, Hungary, Mexico, Taiwan, the United Kingdom, and the United States.
To review the issues surrounding arsenic contamination, a project sponsored by the Committee on CHEMical Research Applied to World Needs (CHEMRAWN) was initiated, and an International Workshop on Arsenic Contamination and Safe Water was held at the Atomic Energy Centre, Dhaka, Bangladesh, on December 11–13, 2005. The workshop was organized under the joint sponsorship of the Bangladesh Academy of Sciences, the Bangladesh Arsenic Mitigation Water Supply Project, the Arsenic Policy Support Unit, the Bangladesh Chemical Society, the U.S. National Science Foundation, and IUPAC.
The opening session of the workshop included a welcoming address by the local Organizing Committee Chair Mohammed Mosihuzzaman of the University of Dhaka. The working sessions of the three-day workshop covered the following topics:
1. Current Status: Technical Aspects and Mitigation
2. Sources and Mobilization of Arsenic in Groundwater
3. Release Mechanisms and Transport
4. Measurements and Standards
5. Alternative Water-Supply Options
6. Microbial Contamination of Surface Water
Sut Ahuja, workshop chair, described how chemists and chemical engineers worldwide have responded to his appeal for assistance in addressing the problem of arsenic contamination in groundwater. Positive responses from the American Chemical Society’s International Activities Committee, various divisions of IUPAC, and the CHEMRAWN committee led to the support for this workshop covering the following objectives:
- develop a better understanding of how arsenic gets into groundwater
- focus on the need to identify one or two optimum remediation techniques that can subsequently be scaled up
- communicate the need to safely dispose of the materials used to remove arsenic
Ahuja also noted a need to develop reliable and economical methods for monitoring arsenic in the laboratory and the field, as well as a need to provide consumers with the means to confirm that any decontamination device they are using is providing potable water.
Participants generally agreed that sedimentary arsenic has been carried downstream by the Ganges-Padma-Megna River system. At the workshop, Farhana Islam (Guelph University, Canada) explained how bacteria can catalyze desorption and dissolution of arsenic in the anaerobic, reducing environment of the subsoil. K.M. Campbell (CalTech, USA) elucidated the effects of reductive mineral dissolution and porewater chemistry on arsenic mobilization. Both Sinha Ray (Centre for Ground Water studies, India) and D. Chatterjee (Kalyani University, India) discussed the genesis of arsenic in the Ganges delta, with specific reference to West Bengal. A.B.M. Badruzzaman (Bangladesh University of Engineering and Technology [BUET]), discussed his work on the hydrogeological and geochemical causes of arsenic contamination in Bangladesh. K.M. Ahmed (Dhaka University) spoke on arsenic mobilization in Bangladesh groundwater. K.M. Ahmed believes that strategically locating and properly installing arsenic-removal systems into a safe aquifer can provide nonhazardous water to a large number of people.
Feroze Ahmed (BUET) noted that 80 percent of the tube wells in 8,540 villages produce water that contains more than 50 ppb of arsenic. Currently, some 50 million persons in Bangladesh are exposed to high levels of arsenic, exceeding the World Health Organization standard of 10 ppb. Ahmed noted that a National Policy and Implementation Plan for Arsenic Mitigation has been developed, along with protocols for installation of alternative water-supply options, disposal of arsenic-rich sludge, diagnosis of arsenicosis, and water management. However, provision of alternative arsenic-safe water supplies has thus far reached only 4 million citizens, or some 2.9 percent of the population of Bangladesh.
S.M. Ihtishamul Huq (Department of Public Health Engineering [DPHE], Bangladesh) described an arsenic-screening project and subsequent arsenic-mitigation program sponsored by several stakeholder agencies. During the period of July 2002 to June 2005 the program evaluated arsenic-mitigation and -avoidance technologies in 15 regions of Bangladesh. These technologies included a pond sand filter, rainwater harvesting, the use of deep tube wells, dug-well renovation, piped water systems, and in-home arsenic-removal systems.
Several speakers at the workshop compared the cost-effectiveness and efficacy of arsenic-removal technologies applied to groundwater with the risks and benefits of those for purifying surface water, which is plentiful in Bang-ladesh. The consensus was that all of these technologies are potentially useful, and that the actual choice of which technology to deploy must be based on the specific conditions in each region. Hemda Garelick (Middlesex University, UK) described her IUPAC-sponsored project to employ multi-criteria analysis to assess current options for the mitigation/remediation of arsenic in drinking water.
S.I. Khan (Dhaka University) discussed surface-water microbiology, detection techniques, and quality assessment. Sk. Abu Jafar Shamsuddin (BUET) analyzed the risks arising from bacterial contamination of surface water compared to those associated with tube wells. He concluded that with current technologies, the worst overall public safety risks from bacterial contamination arise from the use of pond sand filters, with risks decreasing in the following order: pond sand filters, dug wells, rainwater harvesting, tube wells. Of these, pond sand filter systems, rainwater harvesting, and deep tube wells were free of arsenic contamination, but not free of bacterial contamination.
While many technologies have been developed to treat arsenic-contaminated water, on scales ranging from individual kitchen filters that sell for less than $40 to industrial-sized treatment plants, none has yet emerged as an optimal solution for the conditions encountered in Bangladesh. In February 2004, the Bangladesh Council of Scientific and Industrial Research identified four home-use systems (designated Alcan, Sidko, READ-F, and SONO) for evaluation. In most cases the materials used are not fully characterized, and the systems sold commercially have not been fully validated. However, while it is relatively easy to remove arsenic by adsorption on supported iron oxides, small point-of-use filters may become clogged after an indeterminate period of time.
Norma Alcantar (University of South Florida, USA) described her research on the use of environmentally benign mucilage from a common Mexican cactus. James Navratil (Clemson University, USA) showed how the mineral magnetite can be employed as an adsorbent, isolated using a magnetic field, and cleaned using a regenerating solution.
A.H. Khan (Dhaka University) discussed model calculations on arsenic and other metal species in the groundwater system. He noted that the process of removing arsenic by adsorption on hydrated ferric hydroxide is controlled by first-order kinetics. Furthermore, he outlined standard operating procedures for laboratory analysis of trace metals, as well as quality control protocols. Speciation of arsenic requires separations based on solvent extraction, chromatography, and selective hydride generation. Most of these methods require expensive instrumentation, and the cost of training can also be high. Thus, there is a need to develop more economical and reliable methods of analysis.
Jörg Feldmann (University of Aberdeen, UK) addressed the reliability of field kits for determining the presence of arsenic in water. Much work remains to be done in developing analytical techniques for use in the field and the home. Feldmann also discussed how speciation analysis can help researchers investigate the arsenic uptake of plants, an especially important consideration in areas where phytoremediation might be an option for arsenic removal. P. Visoothiviseth (Mahidol University, Thailand) discussed remediation of arsenic contamination of soil with the help of plants.
Rick Johnson of UNICEF discussed the advantages of alternative water-supply options, including pond sand filters, river sand filters, rainwater harvesting, dug wells, sharing of green tube wells, deep tube wells, and arsenic-removal technologies. He concluded that it will be very important to integrate water hygiene and sanitation programs and that community choice will be very important in selecting the type of water supply utilized locally. He also emphasized the need for continual water-quality testing.
Guy Howard (Arsenic Policy Support Unit) described current progress in monitoring arsenic in water supplies in Bangladesh. He noted that blanket arsenic screening of 4.73 million tube wells revealed 1.29 million wells to be above 50 micrograms/liter. His assessment was that mitigation options have been made available for some 38 percent of the contaminated wells in Bangladesh, and that over the next five years most villages will receive some support. However, the population of Bangladesh is also expected to rise from 140 million to 250 million in the near future. Priority needs for the future include updated strategies, a scaled-up mitigation response, improved cross-ministry coordination, detailed groundwater mapping, studies of the impact of arsenic on agriculture, a better understanding of the epidemiology of arsenicosis, and full-scale clinical trials of antioxidants. A.K.M. Ibrahim (DPHE) described how piped water supplies can be financed through public-private partnerships.
Nicholas Priest (University of Middlesex, UK) outlined data from WHO indicating that there is no "threshold" value for incidence of cancer caused by arsenic. He concluded that there is no safe lower limit for arsenic exposure, since even low-level exposure appears likely to cause some additional incidence of cancer in the population. Moreover, Priest noted that the latency period for the appearance of skin lesions is some 23 years after exposure to arsenic. Priest concluded that authorities should apply the "precautionary principle," taking action to reduce arsenic exposure even before very strong evidence is uncovered.
In a well-attended closing session, the participants offered a large number of recommendations, as follows.
- An inventory should be conducted of the current research in arsenic pollution.
- A better communications network should be developed among the research community.
- More research should be conducted on treatment of surface waters.
- Where appropriate, piped water systems with central purification facilities should be installed.
- More research should be conducted on the relationships between arsenic and the incidence of disease.
- More local information is needed, especially research on hydrology and microbiology.
- Current knowledge of arsenic sources must be expanded to cover the entire region.
- Studies of anaerobic microbial environments must be conducted.
- The aquifer should be mapped.
- Economical and reliable analytical methods are needed.
- Additional training, especially of analytical technicians, is needed.
- The number of available service-oriented analytical laboratories is woefully inadequate, and needs to be increased.
- International assistance is needed to develop quality control guidelines.
- More funds are needed for analytical equipment. It is very important that the instrumentation acquired be reliable and accurate, but it does not need to be state-of-the-art.
- An inexpensive method for the detection of arsenic in the field and the home must be developed.
- The aqueous chemistry of arsenic, and especially the environmental effects of speciation, must be further investigated.
- The presence of arsenic in the food chain needs to be analyzed, and its effects elucidated.
- The choice of remediation devices should be narrowed down to no more than three to allow better monitoring of these devices and enable scale-up for larger communities.
- The sludge disposal option should be further investigated.
- Efforts should be made to engage the private sector.
- Better coordination is needed between governmental and NGO operations.
- The policies that have already been promulgated need to be implemented.
- The maximum acceptable level of arsenic in drinking water should be reduced to 10 ppb.
For more information, contact Workshop Chair Sut Ahuja <[email protected]>, or Task Group Co-Chair and CHEMRAWN Chair John Malin <[email protected]>.
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