Arsenic contamination of groundwater

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Main article: Water pollution

Arsenic contamination of groundwater is a natural occurring high concentration of arsenic in deeper levels of groundwater, which became a high-profile problem in recent years due to the use of deep tubewells 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. [1]

Approximately 20 incidents of groundwater arsenic contamination have been reported from all over the world. [2] Of these, four major incidents were in Asia, including locations in Thailand, Taiwan, and Mainland China.[3] [4] South American countries like Argentina and Chile have also been affected. There are also many locations in the United States where the groundwater contains arsenic concentrations in excess of the new Environmental Protection Agency standard of 10 parts per billion.

Arsenic is a carcinogen which causes many cancers including skin, lung, and bladder as well as cardiovascular disease.

Contents

[edit] Contamination specific nations and regions

[edit] Bangladesh and West Bengal

The story of the arsenic contamination of the groundwater in Bangladesh is a tragic one. Many people have died from this contamination. Diarrheal diseases have long plagued the developing world as a major cause of death, especially in children. 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 for a quick and inexpensive solution. Millions of wells were constructed as a result. Because of this action, infant mortality and diarrheal illness were reduced by fifty percent. However, with over 8 million wells constructed, it has been found over the last two decades that approximately one in five of these wells are now contaminated with arsenic above the government's drinking water standard.

In the Ganges Delta, the effected wells are typically more than 20 m and less than 100 m 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 m is exposed to much older sediments which have already been depleted of arsenic.[3][5]

Dipankar Chakraborti from West Bengal brought the crisis to international attention in a research paper published in The Analyst in 1995 and reported on by David Bradley (The Guardian, January 5, 1995, "Drinking the water of death"). [6] [7] Beginning his investigation in West Bengal in 1988, he eventually published, in 2000, the results of a study conducted in Bangladesh, which involved the analysis of thousands of water samples as well as hair, nail and urine samples. They found 900 villages with arsenic above the government limit.

Chakraborti has criticized aid agencies, saying that they denied the problem during the 1990s while millions of tube wells were sunk. The aid agencies later hired foreign experts, who recommended treatment plants which were not appropriate to the conditions, were regularly breaking down or were not removing the arsenic.[8]

Chakraborti says that the arsenic situation in Bangladesh and West Bengal is due to negligence. He also adds that in West Bengal water is mostly supplied from rivers. Groundwater comes from deep tubewells, which are few in number in the state. Because of the low quantity of deep tubewells, the risk of arsenic patients in West Bengal is comparatively less. [9]

According to the World Health Organisation, “In Bangladesh, West Bengal (India) and some other areas, most drinking-water used to be collected from open dug wells and ponds with little or no arsenic, but with contaminated water transmitting diseases such as diarrhoea, dysentery, typhoid, cholera and hepatitis. Programmes to provide ‘safe’ drinking-water over the past 30 years have helped to control these diseases, but in some areas they have had the unexpected side-effect of exposing the population to another health problem - arsenic.” [10] WHO has defined the areas under threat: Seven of the nineteen districts of West Bengal have been reported to have ground water arsenic concentrations above 0.05 mg/L. The total population in these seven districts is over 34 million, with the number using arsenic-rich water is more than 1 million (above 0.05 mg/L). That number increases to 1.3 million when the concentration is above 0.01 mg/L. According to a British Geological Survey study in 1998 on shallow tube-wells in 61 of the 64 districts in Bangladesh, 46% of the samples were above 0.01 mg/L and 27% were above 0.050 mg/L. When combined with the estimated 1999 population, it was estimated that the number of people exposed to arsenic concentrations above 0.05 mg/L is 28-35 million and the number of those exposed to more than 0.01 mg/L is 46-57 million (BGS, 2000). [10]

The solution, according to Chakraborti, is “By using surface water and instituting effective withdrawal regulation. West Bengal and Bangladesh are flooded with surface water. We should first regulate proper watershed management. Treat and use available surface water, rain-water and others. The way we're doing at present is not advisable."[9]

[edit] United States

There are many locations across the United States where the groundwater contains naturally high concentrations of arsenic. Cases of groundwater-caused acute arsenic toxicity, such as those found in Bangladesh, are unknown in the United States where the concern has focused on the role of arsenic as a carcinogen. The problem of high arsenic concentrations has been subject to greater scrutiny in recent years because of changing government standards for arsenic in drinking water.

Some locations in the United States, such as Fallon, Nevada, have long been known to have groundwater with relatively high arsenic concentrations (in excess of 0.08 mg/L).[11] 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.[12]

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. The Environmental Protection Agency (EPA) studied the pros and cons of lowering the arsenic Maximum Contaminant Level (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.[13] The incoming Bush administration suspended the new 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.[14]

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% of water-supply wells were put out of compliance by the new regulation; in California, the percentage was 38%.[15]

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 are able to establish lower arsenic limits; New Jersey has done so, setting a maximum of 0.005 mg/L for arsenic in drinking water.[16]

[edit] Water purification solutions

[edit] Small-scale water treatment

Chakraborti claims that arsenic removal plants (ARPs) installed in Bangladesh by UNDP and WHO were a colossal waste of funds due to breakdowns, inconvenient placements and lack of quality control.[9]

A simpler and less expensive form of arsenic removal is known as the Sono arsenic filter, using 3 pitchers containing cast iron turnings and sand in the first pitcher and wood activated carbon and sand in the second.[17] Plastic buckets can also be used as filter containers.[18] It is claimed that thousands of these systems are in use 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 type of domestic treatment unit uses the technologies of adsorption i.e. granular media such as Bayoxide E33, GFH, Titanium Dioxide and reverse osmosis, To a less extent ion exchange and activated alumina have been considered but not commonly used.

[edit] Large-scale water treatment

In some places, such as the United States, all the water supplied to residences by water utilities must meet primary (health-based) drinking water standards. This may necessitate 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 removes arsenic by coprecipitation and adsorption using iron coagulants. Coagulation/filtration using alum is already used by some utilities to remove suspended solids and may be adjusted to remove arsenic.

Iron oxide adsorption filters the water through a granular medium containing ferric oxide. Ferric oxide has a high affinity for adsorbing dissolved metals such as arsenic. The iron oxide medium eventually becomes saturated, and must be replaced.

Activated alumina is another filter medium known to effectively remove dissolved arsenic. It has also been used to remove undesirably high concentrations of fluoride.

Ion Exchange has long been used as a water-softening process, although usually on a single-home basis. It can also be effective in removing arsenic with a net ionic charge. (Note that arsenic oxide, As2O3, is a common form of arsenic in groundwater that is soluble, but has no net charge.)

Both Reverse osmosis and electrodialysis (also called electrodialysis reversal) can remove arsenic with a net ionic charge. (Note that arsenic oxide, As2O3, is a common form of arsenic in groundwater that is soluble, but has no net charge.) Some utilities presently use one of these methods to reduce total dissolved solids and therefore improve taste. A problem with both methods is the production of high-salinity waste water, called brine, or concentrate, which then must be disposed of.

[edit] Dietary intake

Researchers from Bangladesh and the United Kingdom have recently claimed that dietary intake of arsenic adds a significant amount to total intake, where contaminated water is used for irrigation.[19] [20][21]

[edit] See also

[edit] Notes and references

  1. ^ Arsenic in drinking water seen as threat, Associated Press, 8/30/07.
  2. ^ Mukherjee A., Sengupta M. K., Hossain M. A. (2006). "Arsenic contamination in groundwater: A global perspective with emphasis on the Asian scenario". Journal of Health Population and Nutrition 24 (2): 142–163. 
  3. ^ a b The UNESCO Courier, Bangladesh's arsenic poisoning: who is to blame?
  4. ^ Chowdhury U. K., Biswas B. K., Chowdhury T. R. (2000). "Groundwater arsenic contamination in Bangladesh and West Bengal, India". Environmental Health Perspectives 108 (4): 393–397. doi:10.2307/3454378. 
  5. ^ Singh A. K. (2006). "Chemistry of arsenic in groundwater of Ganges-Brahmaputra river basin". Current Science 91 (5): 599–606. 
  6. ^ Amit Chatterjee, Dipankar Das, Badal K. Mandal, Tarit Roy Chowdhury, Gautam Samanta and Dipankar Chakraborti (1995). "Arsenic in ground water in six districts of West Bengal, India: the biggest arsenic calamity in the world. Part I. Arsenic species in drinking water and urine of the affected people". Analyst 120: 643–651. doi:10.1039/AN9952000643. 
  7. ^ Dipankar Das, Amit Chatterjee, Badal K. Mandal, Gautam Samanta, Dipankar Chakraborti and Bhabatosh Chanda (1995). "Arsenic in ground water in six districts of West Bengal, India: the biggest arsenic calamity in the world. Part 2. Arsenic concentration in drinking water, hair, nails, urine, skin-scale and liver tissue (biopsy) of the affected people". Analyst 120: 917–925. doi:10.1039/AN9952000917. 
  8. ^ New Scientist, Interview: Drinking at the west's toxic well31 May 2006.
  9. ^ a b c The Times of India, 'Use surface water. Stop digging', interview, 26 Sep, 2004.
  10. ^ a b World Health Organization, Arsenic in Drinking Water, accessed 5 Feb 2007.
  11. ^ Frederick Rubel Jr. and Steven W. Hathaway (1985) Pilot Study for removal of arsenic from drinking water at the Fallon, Nevada, Naval Air Station, Environmental Protection Agency, EPA/600/S2-85/094.
  12. ^ M. Taqueer A. Qureshi (1995) Sources of Arsenic in the Verde River and Salt River Watersheds, Arizona, M.S. thesis, Arizona State University, Tempe.
  13. ^ The history of arsenic regulation, Southwest Hydrology, May/June 2002, p.16.
  14. ^ EPA announces arsenic standard for drinking water of 10 parts per billion, EPA press release, 10/31/2001.
  15. ^ Alison Bohlen (2002) States move forward to meet new arsenic standard, Southwest Hydrology, May/June 2002, p.18-19.
  16. ^ Megan A. Ferguson and others, Lowering the detection limit for arsenic: implications for a future practical quantitation limit, American Water Works Association Journal, Aug. 2007, p.92-98.
  17. ^ Evaluation of Performance of Sono 3-Kolshi Filter for Arsenic Removal from Groundwater Using Zero Valent Iron Through Laboratory and Field StudiesPDF (272 KiB)
  18. ^ SONO ARSENIC FILTER FROM BANGLADESH - 1PDF (102 KiB) - pictures with descriptions.
  19. ^ Mustak Hossain. "Toxic rice harvested in southwestern Bangladesh", SciDev.Net, 13 July 2006. 
  20. ^ Williams, P.N. (2006). "Increase in Rice Grain Arsenic for Regions of Bangladesh Irrigating Paddies with Elevated Arsenic in Groundwaters". Environ. Sci. Technol 40 (16): 4903–4908. doi:10.1021/es060222i. 
  21. ^ *"Screening of Rice Cultivars for Grain Arsenic Concentration and Speciation" . American Society of Agronomy Proceding. 

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