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Organic arsenic is fed to poultry to prevent bacterial infections and improve weight gain. A little bit of arsenic is taken up by the tissue and the majority of it is excreted in urine. Poultry litter -- the wood chips, feathers, droppings, and urine from under poultry houses -- is rich in nitrogen and phosphorous, so is a logical fertilizer. But what happens to that arsenic?

Virginia Tech geoscientists are determining what happens to such feed additives when they are part of the manure applied to agricultural fields. They will present their research at the Geological Society of America national meeting in Salt Lake City Oct. 16-19.

In research funded by the U.S. Department of Agriculture, Madeline Schreiber, associate professor of geosciences at Virginia Tech, carried out field and laboratory studies to discover the fate of arsenic fed to poultry. She and her graduate students found that bacteria in the litter and in shallow subsurface soil transform organic arsenic to inorganic arsenic. Organic arsenic is not highly toxic to humans, but inorganic arsenic, with its organic component removed, is toxic.

"We found that organic arsenic is highly soluble in water and is rapidly biotransformed to inorganic arsenic," Schreiber said. Despite laboratory findings that show a strong adsorption of inorganic arsenic to minerals in the soils and aquifer sediments, a surprising finding from water samples from streams receiving runoff is that low concentrations of arsenic are transported to streambeds instead of being retained by the aquifers, Schreiber said. "We think that the arsenic is adsorbed onto nanoscale particles that pass though our filters and through the soil column," said Schreiber. "This suggests that particle transport is an important mechanism in arsenic cycling in these watersheds."

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Source:University of California, Los Angeles