HANOVER, N.H. — Development of former farmland can disturb pesticides spread nearly a century ago and contaminate nearby water sources, according to a study by researchers at Dartmouth College.

The findings mean communities may need to take additional precautions when the soil at former orchards and farms is disturbed for development or new agricultural uses, Carl Renshaw, a professor of earth sciences, said in a news release.

The problem is that pesticides spread during the early 1900s contained both arsenic and lead, which researchers have found remain in the top 10 inches of soil. The study results appear in the January-February issue of the Journal of Environmental Quality.

But the study, which focused on two New Hampshire apple orchards where the pesticide lead arsenate once was used, found that over time these toxic metal change form and become part of the silt and organic matter in the soil.

In that new form, the metals become more susceptible to erosion, which can be accelerated by development.

"We continue to learn more about how past agricultural practices are affecting our current environment," Renshaw said. "Unlike some pesticides used today, metals like arsenic and lead in old pesticides do not degrade over time."

The study found that when disturbed, these metals can make their way into nearby surface water. It was unclear whether plants and animals that feed off that water are absorbing the metals, Renshaw said.

"While the arsenic and lead in the soils of old orchards is 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," he said.

"Communities in these areas may want to ensure additional precautions are taken to control erosion when old orchard lands are disturbed in order to reduce the potential for contamination of nearby surface water," Renshaw said.

Source: Associated Press