BERKELEY, CA. -- A surprising alternative to microorganisms for immobilizing selenium contamination in soil and sediment has been identified by researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory. Green rust, a harmless natural iron oxide, was shown to chemically react with toxic selenium, converting it to a safer elemental form.

Selenium is a trace mineral that can be highly toxic or carcinogenic to humans and wildlife. The poisoning deaths of wild birds at the Kesterson Reservoir in the San Joaquin Valley in the early 1980s have been attributed to selenium in drainage from irrigation water. The incident was a graphic demonstration of how agricultural development can result in the accumulation of abnormally high and potentially lethal concentrations of selenium and other trace contaminants in soils and sediments.

Selenium's fate in contaminated soils has long been linked to the decomposition of plant material and other microbial activity, which was thought to be the primary means by which soluble, chemically active forms of selenium could be reduced to an elemental state. Elemental selenium is insoluble, which means it is less of a threat to move up through the soil into the food chain, or down through the soil into the groundwater.

Contrary to this past belief, however, a laboratory study led by Satish Myneni of Berkeley Lab's Earth Sciences Division, has revealed that green rust has the same effect as microorganisms on soluble forms of selenium.

"We have shown that the selenium transformation reaction in sediments and soils reduction can take place without the presence of the bacteria, via a different mechanism," says Myneni.

Joining him in this study were Tetsu Tokunaga, also with Berkeley Lab's Earth Sciences Division, and Gordon Brown, Jr., at the Stanford Synchrotron Radiation Laboratory. Their results wer
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Contact: Lynn Yarris
lcyarris@lbl.gov
510-486-5375
DOE/Lawrence Berkeley National Laboratory
27-Jan-1998