Arsenic contamination is a serious threat to human health. In the Ganges Delta of Bangladesh, for example, chronic exposure to arsenic has been linked to serious medical conditions, including hypertension, cardiovascular disease and a variety of cancers.
"The threat extends to Central Illinois, where there are very high levels of arsenic contamination in a number of wells," said Craig Bethke, a professor of geology at Illinois and corresponding author of a paper to appear in the November issue of the journal Geology. "We also discovered important links between the amount of organic material dissolved in the groundwater and the concentrations of sulfate and arsenic."
The researchers analyzed water from 21 wells at various depths in the Mahomet aquifer, a regional water supply for Central Illinois. "The Mahomet aquifer was produced by a glacier, which pulverized and homogenized the sediments," Bethke said. "As a result, arsenic sources that leach into the groundwater are pretty uniformly distributed."
Surprisingly, however, arsenic concentration varied strongly from well to well, Bethke said. "Concentrations may reach hundreds of micrograms per liter in one well which is enough to make people very sick but fall below detection limits in a nearby well."
The concentration of arsenic varied inversely with the concentration of sulfate, the researchers found. Methane concentration also varied with the sulfate content. "We believe this reflects the distribution of microbial populations in the aquifer system," said graduate student Matthew Kirk. "Our analyses suggest the aquifer is divided into zones of mixed microbial activity, some dominated by sulfate-reducing bacteria, others by me
Contact: James E. Kloeppel
University of Illinois at Urbana-Champaign