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ARSENIC DEFINED 

Kevin A Kozuh and ESIRC take a look at Asenic Contamination

Water Education: Arsenic 

 

In Short: Arsenic is a naturally occurring semi-metal element found in rocks, soil, water, plants, and even animals . It is more prevalent in ground water sources like wells rather than lakes and rivers  What compounds the levels of arsenic in ground water are things like industrial, manufacturing, and agricultural runoff

 

Courtesy of Phys.org June 1, 2012

 

Arsenic is one of the most common elements on Earth and is present as arsenic salts in all water. The World Health Organization sets the safe level for arsenic in drinking water at 10 parts per billion. From the Himalayas to Southeast Asia, arsenic levels in drinking water can be more than 10 times that amount, yet the wells are rarely tested. The problem has been termed “the largest mass poisoning of a population in history”, with calls for a reinvigoration of moribund well-testing campaigns.

 

For instance, of the more than 400,000 shallow tube wells in Nepal, it is estimated that nearly 10% of them are contaminated with arsenic, which can cause a variety of health problems, including skin lesions, diseases of the blood vessels of the hands and feet, and cancer of the skin, bladder, kidney and lung.

 

Several arsenic testing kits are available on the market, but they require expensive machinery to read the outputs, and almost all of them use mercury bromide, which is extremely toxic.

 

Dr. Jim Ajioka from the Department of Pathology, along with Dr. Jim Haseloff from the Department of Plant Sciences and colleagues from the University of Edinburgh, has designed a whole-cell arsenic biosensor that is cheap, non-toxic and easy to use.

 

Some species of bacteria are natural arsenic biosensors: in the presence of less than 10 parts per billion of arsenic, they initiate the production of enzymes and an efflux pump for the detoxification and removal of arsenic. For the sensor, the team will take the genes that detect arsenic and combine them with bacterial genes that produce coloured pigments. The modified bacteria will turn green when arsenic levels are safe, and purple when arsenic levels are unsafe.

 

The test uses a harmless strain of the soil-dwelling bacterium Bacillus subtilis, which poses no threat to human health or the environment.

 

The extremely simple visual output combined with the low cost (estimated at around $0.50 per test) and the lack of need for any expensive monitoring equipment make the whole-cell arsenic biosensor ideal for use in rural areas where arsenic contamination of drinking water is widespread.

With the assistance of Cambridge Enterprise, the University’s commercialisation arm, the team has received a translational grant from the Wellcome Trust. It is anticipated that a functioning device can be built within the next 18–24 months, with field testing to follow.

 

Provided by University of Cambridge
Arsenic

Arsenic (pronounced /ˈɑrsnɪk/; also /ɑrˈsɛnɪk/ when attributive) is the chemical element that has the symbol As and atomic number 33. Arsenic was first documented by Albertus Magnus in 1250.

 

Its atomic mass is 74.92. Arsenic is a notoriously poisonous metalloid with many allotropic forms, including a yellow (molecular non-metallic) and several black and grey forms (metalloids).

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Three metalloidal forms of arsenic, each with a different crystal structure, are found free in nature (the minerals arsenic sensu stricto and the much rarer arsenolamprite and pararsenolamprite). However, it is more commonly found as arsenide and in arsenate compounds, several hundred of which are known. Arsenic and its compounds are used as pesticides, herbicides, insecticides and in various alloys.

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For more information about Arsenic, read the full article at Wikipedia.

 

Occurrence in Drinking Water

Main article: Arsenic contamination of groundwater

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Extensive arsenic contamination of groundwater has led to widespread arsenic poisoning in Bangladesh[97] and neighboring countries. It is estimated that approximately 57 million people in the Bengal basin are drinking groundwater with arsenic concentrations elevated above the World Health Organization's standard of 10 parts per billion (ppb).However, a study of cancer rates in Taiwan suggested that significant increases in cancer mortality appear only at levels above 150 ppb.

 

The arsenic in the groundwater is of natural origin, and is released from the sediment into the groundwater, caused by the anoxic conditions of the subsurface. This groundwater was used after local and western NGOs and the Bangladeshi government undertook a massive shallow tube well drinking-water program in the late twentieth century.

 

This program was designed to prevent drinking of bacteria-contaminated surface waters, but failed to test for arsenic in the groundwater. Many other countries and districts in Southeast Asia, such as Vietnam and Cambodia, have geological environments that produce groundwater with a high arsenic content. Arsenicosis was reported in Nakhon Si Thammarat, Thailand in 1987, and the Chao Phraya River probably contains high levels of naturally occurring dissolved arsenic without being a public health problem because much of the public uses bottled water.

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In the United States, arsenic is most commonly found in the ground waters of the southwest. Parts of New England, Michigan, Wisconsin, Minnesota and the Dakotas are also known to have significant concentrations of arsenic in ground water. Increased levels of skin cancer have been associated with arsenic exposure in Wisconsin, even at levels below the 10 part per billion drinking water standard. According to a recent film funded by the US Superfund, millions of private wells have unknown arsenic levels, and in some areas of the US, more than 20% of the wells may contain levels that exceed established limits.

Low-level exposure to arsenic at concentrations of 100 parts per billion (i.e., above the 10 parts per billion drinking water standard) compromises the initial immune response to H1N1 or swine flu infection according to NIEHS-supported scientists. The study, conducted in laboratory mice, suggests that people exposed to arsenic in their drinking water may be at increased risk for more serious illness or death from the virus.

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Some Canadians are drinking water that contains inorganic arsenic. Private-dug–well waters are most at risk for containing inorganic arsenic. Preliminary well water analysis typically does not test for arsenic. Researchers at the Geological Survey of Canada have modeled relative variation in natural arsenic hazard potential for the province of New Brunswick. This study has important implications for potable water and health concerns relating to inorganic arsenic

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Epidemiological evidence from Chile shows a dose-dependent connection between chronic arsenic exposure and various forms of cancer, in particular when other risk factors, such as cigarette smoking, are present. These effects have been demonstrated at contaminations less than 50 ppb.

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Analyzing multiple epidemiological studies on inorganic arsenic exposure suggests a small but measurable increase in risk for bladder cancer at 10 ppb.  According to Peter Ravenscroft of the Department of Geography at the University of Cambridge,[109] roughly 80 million people worldwide consume between 10 and 50 ppb arsenic in their drinking water. If they all consumed exactly 10 ppb arsenic in their drinking water, the previously cited multiple epidemiological study analysis would predict an additional 2,000 cases of bladder cancer alone.

This represents a clear underestimate of the overall impact, since it does not include lung or skin cancer, and explicitly underestimates the exposure. Those exposed to levels of arsenic above the current WHO standard should weigh the costs and benefits of arsenic remediation.

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Early (1973) evaluations of the processes for removing dissolved arsenic from drinking water demonstrated the efficacy of co-precipitation with either iron or aluminum oxides. In particular, iron as a coagulant was found to remove arsenic with an efficacy exceeding 90%.[110][111] 

 

Several adsorptive media systems have been approved for use at point-of-service in a study funded by the United States Environmental Protection Agency (US EPA) and the National Science Foundation (NSF). A team of European and Indian scientists and engineers have set up six arsenic treatment plants in West Bengal based on in-situ remediation method (SAR Technology). This technology does not use any chemicals and arsenic is left in an insoluble form (+5 state) in the subterranean zone by recharging aerated water into the aquifer and developing an oxidation zone that supports arsenic oxidizing micro-organisms. This process does not produce any waste stream or sludge and is relatively cheap.

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Another effective and inexpensive method to avoid arsenic contamination is to sink wells 500 feet or deeper to reach purer waters. A recent 2011 study funded by the US National Institute of Environmental Health Sciences' Superfund Research Program shows that deep sediments can remove arsenic and take it out of circulation. In this process, called adsorption, arsenic sticks to the surfaces of deep sediment particles and is naturally removed from the ground water.

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Magnetic separations of arsenic at very low magnetic field gradients with high-surface-area and monodisperse magnetite (Fe3O4) nanocrystals have been demonstrated in point-of-use water purification. Using the high specific surface area of Fe3O4 nanocrystals, the mass of waste associated with arsenic removal from water has been dramatically reduced.

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Epidemiological studies have suggested a correlation between chronic consumption of drinking water contaminated with arsenic and the incidence of all leading causes of mortality.  The literature indicates that arsenic exposure is causative in the pathogenesis of diabetes.

Chaff-based filters have recently been shown to reduce the arsenic content of water to 3 µg/L. This may find applications in areas where the potable water is extracted from underground aquifers.


This text uses material from Wikipedia and is available under the GNU Free Documentation License.

 

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Chemicals matching “arsenic”

 

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