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Old Pesticides Never Die

They just lurk in the topsoil of old farms, says Dartmouth study 

A group of Dartmouth researchers has evidence that disturbing the land where farms once thrived can release the arsenic and lead that were applied as pesticides in the early 1900s. Once disturbed, these metals can then contaminate nearby surface waters.

from left: Xiahong Feng, Carl Renshaw, Rozanne Karini, Carol Folt, Celia Chen
A Dartmouth research team has demonstrated that disturbance of historic farmlands can release arsenic and lead into the environment. From left: Xiahong Feng, the Frederick Hall Professor of Mineralogy and Geology and associate professor of Earth sciences; Carl Renshaw, associate professor of Earth sciences; Roxanne Karimi, biological sciences graduate student; Carol Folt, dean of the faculty and professor of biological sciences; and Celia Chen '78, research associate professor of biological sciences. (Photo by Joseph Mehling '69)

"We continue to learn more about how past agricultural practices are affecting our current environment," says Carl Renshaw, associate professor of Earth sciences. "Unlike some of the pesticides used today, metals like arsenic and lead in old pesticides do not degrade over time. So the question becomes, where do they end up? As we learn more about what happens to these metals since they were applied, we can make better decisions about how to use our land."

Renshaw and his colleagues studied two New Hampshire apple orchards where the pesticide lead arsenate was once used and compared the data to a nearby, uncontaminated field. Their research was published in the January/February issue of the Journal of Environmental Quality.

The researchers confirmed earlier findings that, in the former orchards, most of the arsenic and lead remains in the top ten inches of soil. The new study goes further and shows that these toxic metals do not remain in their original mineral form. Instead, they become part of the fine silt and organic matter in the soil, which is most susceptible to erosion.

"We learned that disturbing this land, such as for tilling and replanting, mobilizes the arsenic and lead," says Renshaw. "The remobilized metals were found in sediments in a stream channel that drains the tilled orchard."

Renshaw explains that it's unclear whether the metals in the sediment are taken up by plants and animals in the stream. The researchers tested the macroinvertebrate residents (midge flies and dragonflies) at the outlet of the contaminated stream, and found that, as that time, there was no disparity in the levels of arsenic or lead.

"Historic farmlands in New Hampshire and elsewhere are increasingly being developed," says Renshaw. "While the arsenic and lead in the soils of old orchards are essentially immobile as long as the land is not disturbed, our work suggests that the development of these lands can inadvertently mobilize these metals toward bodies of water. Communities in these areas may want to take additional precautions to control erosion when old orchard lands are disturbed in order to reduce the potential for contamination of nearby surface waters."

Additional researchers on this study include: Benjamin C. Bostick, assistant professor of Earth sciences, Xiahong Feng, Christine K. Wong G'02, Elizabeth S. Winston '03, Roxanne Karimi, Carol Folt, and Celia Y. Chen '78. The research was partially funded by the Superfund Basic Research Program of the National Institute of Environmental Health Sciences and the National Science Foundation.

By SUSAN KNAPP

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Last Updated: 12/17/08