Arsenic contamination of water has no universal solution

December 11th, 2007 - 6:32 pm ICT by admin  

Washington, December 11 (ANI): University of Wisconsin-Madison researchers have found that arsenic contamination of drinking water does not have a universal solution.

Madeline Gotkowitz, a hydrogeologist at the Wisconsin Geological and Natural History Survey, says that his teams recent work on arsenic-tainted wells shows that appropriate treatment varies depending on the source of the contamination.

According to the researcher, naturally occurring arsenic in rocks is usually associated with sulfur or iron-rich minerals, where it poses no threat to groundwater.

However, drinking water that has released from mineral form into groundwater through geochemical or biological processes, and has been chronically exposed to arsenic, may increase the risk of skin lesions and several cancers.

Gotkowitz says that arsenic associated with sulfide minerals in rock can be released by the weathering effects of oxygen-rich environments, while arsenic bound to iron oxides can be released by iron-reducing bacteria that thrive in low-oxygen conditions.

“There is different geochemistry in different (areas). That makes it a harder nut to crack. … People might have a similar symptom - arsenic in their water - but there are different solutions because the geologic environment is quite different,” she says.

In rural areas, routinely disinfected with chlorine bleach to control pathogenic and other bacteria. While bleach should kill off arsenic-producing bacteria, it also creates high-oxygen environment that may enhance release of additional arsenic from the rocks.

Gotkowitz and UW-Madison geologists Eric Roden and Evgenya Shelobolina evaluated the impact of chlorination on bacteria and arsenic levels in Wisconsin wells.

The researchers found that in wells with arsenic levels only moderately above the accepted standard, the presence of iron-reducing bacteria was associated with higher arsenic concentrations. They also noted that disinfection of such wells with chlorine adequately removed bacteria and reduced arsenic levels in the short term.

Besides, it was also noted that chlorination did not increase arsenic release from the surrounding rocks, indicating that oxidation of the rocks is not an important source of arsenic in that case.

Similar effects were seen in areas with a relatively high water table, where aquifers are exposed to less oxygen.

Based on their findings, the researchers came to the conclusion that disinfection was an effective way to control pathogenic bacteria, and that it might also limit arsenic release in wells.

“It’s not like there’s going to be an easy solution, but there are some basic indicators,” Gotkowitz says.

She further said that under low-oxygen conditions or where water levels were high, “you might want to try to control those types of bacteria as a way to improve well water quality.”

The researcher, however, insists that chlorine treatment may not be appropriate in all environments, as the oxidizing properties of bleach may pose more of a concern in arsenic-affected regions with lower water tables and wells drawing from aquifers highly contaminated with arsenic are unlikely to benefit from localized treatment.

The results were presented at the American Geophysical Union meeting in San Francisco. (ANI)

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