One of the most widespread contaminants of groundwater in Illinois, and the world, is arsenic. Most of the contamination is naturally occurring, but there are many potential human sources, including mining, fossil fuel combustion, pesticides, and wood preservation. A new study suggests a combination of human and natural contamination, where human activities may increase the release of naturally occurring arsenic.

Researchers at the USGS having been studying a petroleum spill near Bemidji, Minnesota, for many years. Glacial deposits in the area contain arsenic, as they do in Illinois and many parts of the glaciated Midwest. In a recent study, they found that the presence of petroleum is increasing the leaching of arsenic into the groundwater at levels as high as 230 micrograms for liter (the drinking water standard is 10 micrograms per liter).

The enhanced release of arsenic is due to changes in biogeochemical conditions, specifically redox conditions, which affect microbially mediated reactions. The biodegradation of the petroleum compounds has made conditions more reducing, which can lead to increased arsenic concentrations. This is similar to what we’ve found in Illinois’ aquifers, where the presence of arsenic appears to be strongly controlled by redox conditions.

I went to graduate school with the lead author of the study, Isabelle Cozzarelli. Way to go Isabelle!

Cozzarelli, IM; Schreiber, ME; Erickson, ML; and Ziegler, BA. “Arsenic cycling in hydrocarbon plumes: Secondary effects of natural attenuation,” Groundwater, 21 Jan 2015.

Here are some papers and reports we’ve written on arsenic in Illinois groundwater:

Kelly, W.R., T.R. Holm, S.D. Wilson, and G.S. Roadcap, 2005. Arsenic in glacial aquifers: sources and geochemical controls. Ground Water 43(4):500-510.

Holm, T.R., W.R. Kelly, S.D. Wilson, G.S. Roadcap, JL. Talbott, and J.W. Scott, 2004. Arsenic Geochemistry and Distribution in the Mahomet Aquifer, Illinois. Waste Management and Research Center RR-107, Champaign.

Kirk, MF, Holm, TH, Park, J, Jin, Q, Sanford, RA, Fouke, BW, Bethke, CM (2004) Bacterial sulfate reduction limits natural arsenic contamination in groundwater. Geology 32, 953-956.