arsenic contamination of groundwater arsenic contamination of groundwater arsenic contamination of groundwater is a form of groundwater pollution which is often due to naturally occurring high concentrations of arsenic in deeper levels of groundwater. it is a high-profile problem due to the use of deep tube wells for water supply in the ganges delta, causing serious arsenic poisoning to large numbers of people. a 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning of drinking water. the problem became a serious health concern after mass poisoning of water in bangladesh. arsenic contamination of ground water is found in many countries throughout the world, including the us. groundwater arsenic contamination areas the world health organization recommends limiting arsenic concentrations in water to 10 μg/l, although this is often an unattainable goal for many problem areas due to the difficult nature of removing arsenic from water sources. approximately 20 major incidents of groundwater arsenic contamination have been reported. of these, four major incidents occurred in asia—in bangladesh; west bengal, india; inner mongolia, china; and taiwan. locations of potentially hazardous wells have been mapped in china. speciation of arsenic compounds in water arsenic contaminated water typically contains arsenous acid and arsenic acid or their derivatives. their names as "acids" is a formality; these species are not aggressive acids but are merely the soluble forms of arsenic near neutral ph. these compounds are extracted from the underlying rocks that surround the aquifer. arsenic acid tends to exist as the ions 2− and − in neutral water, whereas arsenous acid is not ionized. arsenic acid (h3aso4), arsenous acid (h3aso3) and their derivatives are typically encountered in arsenic contaminated ground water. contamination in specific nations and regions south america an analysis of water and food consumption in socaire, a rural village in chile, found that between november 2008 and september 2009, the total intake of arsenic by the villagers correlated with the amount of water and local produce consumed. the central portion of argentina is affected by arsenic-contaminated groundwater. specifically, the la pampa produces water containing 4–5300 microgram per liter. bangladesh arsenic contamination of the groundwater in bangladesh is a serious problem. prior to the 1970s, bangladesh had one of the highest infant mortality rates in the world. ineffective water purification and sewage systems as well as periodic monsoons and flooding exacerbated these problems. as a solution, unicef and the world bank advocated the use of wells to tap into deeper groundwater. millions of wells were constructed as a result. because of this action, infant mortality and diarrheal illness were reduced by fifty percent. however, arsenic has been found in the wells and, in 2008, approximately 57 million residents used water contaminated with arsenic from these shallow wells. 20% of the total deaths are related to arsenic related cancer. the bangladeshi government limits arsenic concentration in water to 50 μg/l, which is 5 times more than the who recommended limit. in the ganges delta, the affected wells are typically more than 20 meters and less than 100 meters deep. groundwater closer to the surface typically has spent a shorter time in the ground, therefore likely absorbing a lower concentration of arsenic; water deeper than 100 meters is exposed to much older sediments which have already been depleted of arsenic. the issue came to international attention in 1995. one study conducted in bangladesh involved the analysis of thousands of water samples as well as hair, nail, and urine samples. it found 900 villages with arsenic above the government limit. criticism has been leveled at the aid agencies, who denied the problem during the 1990s while millions of tube wells were sunk. the aid agencies later hired foreign experts who recommended treatment plants that were inappropriate to the conditions, were regularly breaking down, or were not removing the arsenic. according to a british geological survey study in 1998 on shallow tube-wells in 61 of the 64 districts in bangladesh, 46 percent of the samples were above 0.01 mg/l and 27 percent were above 0.050 mg/l. based on the estimated 1999 population of bangladesh, the study suggested that 28–35 million people may have been exposed to arsenic levels above 0.05 mg/l, and 46–57 million may have been exposed at the lower but still concerning level of 0.01 mg/l. throughout bangladesh, as tube wells get tested for concentrations of arsenic, ones which are found to have arsenic concentrations over the amount considered safe are painted red to warn residents that the water is not safe to drink. india in bihar, groundwater in 13 districts have been found to be contaminated with arsenic with quantities exceeding 0.05 mg/l. all these districts are situated close to large rivers like ganga and gandak. in west bengal, india, water is mostly supplied from rivers, open wells, or ponds. these may be contaminated with communicable diseases such as dysentery, typhoid, cholera, and hepatitis. since the 1970s, non-governmental organisations in india have focused on sinking tube wells to provide drinking water uncontaminated by diseases, with the unforeseen side effect of exposing some people to arsenic-contaminated groundwater. nepal nepal is subject to a serious problem with arsenic contamination. the problem is most severe in the terai region, the worst being near nawalparasi district, where 26 percent of shallow wells failed to meet who standard of 10 ppb. a study by japan international cooperation agency and the environment in the kathmandu valley showed that 72% of deep wells failed to meet the who standard, and 12% failed to meet the nepali standard of 50 ppb. pakistan 66% of 1200 samples tested contained arsenic above who recommended limit, threatening over 60 million residents. 50–60 million residents consume water with arsenic levels greater than 50 micrograms of arsenic per liter, levels far passing acceptable levels worldwide. regulation a drinking water standard of 0.05 mg/l (equal to 50 parts per billion, or ppb) arsenic was originally established in the united states by the public health service in 1942. after the passage of the safe drinking water act of 1974 (sdwa), the environmental protection agency (epa) was given the power to set the maximum containment levels (mcls) of contaminants in public water supplies. in 1996 congress amended the sdwa and created a drinking water state revolving fund to provide loans for water supply improvements, which increased the epa's power to set mandates. this amendment created the "costs and benefits rule" to determine whether the cost of implementing new mcls outweighs the health benefits. to maximize the costs and benefits of setting new mlcs, the epa began allowing more affordable technology to be substituted that did not fully meet mlc standards because it was more affordable. the epa studied the pros and cons of lowering the arsenic mcl for years in the late 1980s and 1990s. no action was taken until january 2001, when the clinton administration in its final weeks promulgated a new standard of 0.01 mg/l (10 ppb) to take effect january 2006. the bush administration suspended the midnight regulation, but after some months of study, the new epa administrator christine todd whitman approved the new 10 ppb arsenic standard and its original effective date of january 2006. many locations exceed this limit. a 2017 lancet public health study found that this rule change led to fewer cancer deaths. many public water supply systems across the united states obtained their water supply from groundwater that had met the old 50 ppb arsenic standard but exceeded the new 10 ppb mcl. these utilities searched for either an alternative supply or an inexpensive treatment method to remove the arsenic from their water. in arizona, an estimated 35 percent of water-supply wells were put out of compliance by the new regulation; in california, the percentage was 38 percent. the proper arsenic mcl continues to be debated. some have argued that the 10 ppb federal standard is still too high, while others have argued that 10 ppb is needlessly strict. individual states can establish lower arsenic limits; new jersey has done so, setting a maximum of 0.005 mg/l (5 ppb) for arsenic in drinking water. a study of private water wells in the appalachian mountains found that six percent of the wells had arsenic above the u.s. mcl of 0.010 mg/l. case studies and incidents fallon, nevada has long been known to have groundwater with relatively high arsenic concentrations (in excess of 0.08 mg/l). even some surface waters, such as the verde river in arizona, sometimes exceed 0.01 mg/l arsenic, especially during low-flow periods when the river flow is dominated by groundwater discharge. a study conducted in a contiguous six-county area of southeastern michigan investigated the relationship between moderate arsenic levels and 23 disease outcomes. disease outcomes included several types of cancer, diseases of the circulatory and respiratory system, diabetes mellitus, and kidney and liver diseases. elevated mortality rates were observed for all diseases of the circulatory system. the researchers acknowledged a need to replicate their findings. water purification solutions access to clean drinking water is fraught with political, socio-economic, and cultural inequities. in practice, many water treatment strategies tend to be temporary fixes to a larger problem, often prolonging the social issues while treating the scientific ones. scientific studies have shown that interdisciplinary approaches to water purification are especially important to consider, and long-lasting improvements involve larger perspectives than strict scientific approaches. small-scale water treatment a review of methods to remove arsenic from groundwater in pakistan summarizes the most technically viable inexpensive methods. most small-scale treatments focus on water after it has left the distribution site, and are thus more focused on quick, temporary fixes. a simpler and less expensive form of arsenic removal is known as the sono arsenic filter, using three pitchers containing cast iron turnings and sand in the first pitcher and wood activated carbon and sand in the second. plastic buckets can also be used as filter containers. it is claimed that thousands of these systems are in use and can last for years while avoiding the toxic waste disposal problem inherent to conventional arsenic removal plants. although novel, this filter has not been certified by any sanitary standards such as nsf, ansi, wqa and does not avoid toxic waste disposal similar to any other iron removal process. in the united states small "under the sink" units have been used to remove arsenic from drinking water. this option is called "point of use" treatment. the most common types of domestic treatment use the technologies of adsorption (using media such as bayoxide e33, gfh, activated alumina or titanium dioxide) or reverse osmosis. ion exchange and activated alumina have been considered but not commonly used. chaff-based filters have been reported to reduce the arsenic content of water to 3 μg/l (3 ppb). this is especially important in areas where the potable water is provided by filtering the water extracted from the underground aquifer. in iron electrocoagulation (fe-ec), iron is dissolved nonstop using electricity, and the resulting ferric hydroxides, oxyhydroxides, and oxides form an absorbent readily attracted to arsenic. current density, the amount of charge delivered per liter of water, of the process is often manipulated in order to achieve maximum arsenic depletion. this treatment strategy has primarily been used in bangladesh, and has proven to be largely successful. in fact, using iron electrocoagulation to remove arsenic in water proved to be the most effective treatment option. large-scale water treatment in some places, such as the united states, all the water supplied to residences by utilities must meet primary (health-based) drinking water standards. regulations may require large-scale treatment systems to remove arsenic from the water supply. the effectiveness of any method depends on the chemical makeup of a particular water supply. the aqueous chemistry of arsenic is complex, and may affect the removal rate that can be achieved by a particular process. some large utilities with multiple water supply wells could shut down those wells with high arsenic concentrations, and produce only from wells or surface water sources that meet the arsenic standard. other utilities, however, especially small utilities with only a few wells, may have no available water supply that meets the arsenic standard. coagulation/filtration (also known as flocculation) removes arsenic by coprecipitation and adsorption using iron coagulants. coagulation/filtration using alum is already used by some utilities to remove suspended