Arsenic contamination of groundwater

Form of water pollution

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. 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.

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 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.

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.

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.

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. Various studies have also shown that arsenic exposure during pregnancy can result in infant death, cancer, heart attacks, kidney failure, lung complications, as well as reduced intelligence, memory, and cognitive development in the child. 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.

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.

Using nanomaterials, it is possible to effectively destroy microorganisms, adsorb arsenic and fluoride, remove heavy metals and degrade pesticides usually found in water. Researchers have looked at new methods to synthesize iron oxide/hydroxide/oxyhydroxide compositions in the laboratory and used them for water purification. A product called AMRIT, meaning elixir in Indian languages, developed by the Indian Institute of Technology Madras, is an affordable water purification technology based on advanced materials, which has been validated through research articles and patents and has been approved for national implementation in India. The technology can remove several anions, especially arsenate and arsenite (two common species present in arsenic contaminated water) and fluoride from water. Currently, this technology is delivering arsenic free water to about 10,00,000 people every day.

In 2008, the Swiss Aquatic Research Institute, Eawag, presented a new method by which hazard maps could be produced for geogenic toxic substances in groundwater. This provides an efficient way of determining which wells should be tested. In 2016, the research group made its knowledge freely available on the Groundwater Assessment Platform (GAP). This offers specialists worldwide the possibility of uploading their own measurement data, visually displaying them and producing risk maps for areas of their choice. GAP also serves as a knowledge sharing forum for enabling further development of methods for removing toxic substances from water.

Researchers from Bangladesh and the United Kingdom have claimed that dietary intake of arsenic adds a significant amount to total intake where contaminated water is used for irrigation.