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Posted 05/29/02
Increased awareness of the dangers of arsenic exposure has led to the investigation of New England apple orchards, as they have long been suspected of releasing arsenic into the environment. New research by Dartmouth scientists shows these suspicions to be, for the most part, unfounded. Their study presented at the Spring Meeting of the American Geophysical Union (May 28-31) confirms previous evidence that arsenic, sprayed on trees as an insecticide, generally stays bound up in soil, limited to the upper inches.
Apple orchards, according to national and worldwide practice, were heavily sprayed with lead arsenate-an effective fungicide and insecticide-for nearly a century, although this practice fizzled in the 1950s with the introduction of DDT, and was banned in 1988.
The results from the Dartmouth study are encouraging, in that it is unlikely that arsenic has contaminated groundwater. This study goes one step further into the fate of this input however-if physical erosion is the main mover of arsenic, any disturbances which increase physical erosion, such as tilling, are likely to increase the arsenic flowing into the environment with which people are interacting.
Due to New Hampshire's naturally elevated arsenic levels any anthropogenic input has recently been subjected to heavy scrutiny, especially as the Environmental Protection Agency recommendations for arsenic concentrations in drinking water have dropped significantly. Whether the arsenic from these orchards has the potential to contaminate streams and groundwater is a matter of great concern.
It has been thought for some time that lead arsenate and arsenic in general is immobile in soils-that is, it is chemically bound with the soil particles and rarely transported away from them. However, this study may provide evidence that surface runoff can move arsenic contaminated soil to another spot, effectively mobilizing the arsenic deposition. An issue that may come up in the future is that many of these older contaminated orchards are being replanted, or torn down and sold for development.
As communicating author and graduate student Christine Wong says, "Yes, these sites have been fine while left alone for fifty or sixty years. But if they're disturbed by bulldozers is that going to affect future runoff potential?" By testing old orchard sites, where the trees and soils haven't been disturbed for nearly 100 years, and sites that had previously been undisturbed but in the last ten years had been tilled and replanted, and comparing arsenic levels with a control site where no arsenic had ever been deposited, the team is attempting to determine the potential of soils to lose their arsenic with disturbance.
The data shows that arsenic is in fact preferentially leached from soils, relative to its co-applied metal, lead. However, it does not move vertically, that is, past the upper twenty centimeters of soil. Tilling does not increase this depth to which arsenic reaches. Further research, then, lies in determining whether disturbance exposes fresh arsenic to weathering elements, allowing increased surface runoff and horizontal mobilization. If so, the researchers hope to discover where the applied arsenic goes, since it is evidently no longer in the sites.
By Audrey Campbell '02
Center for Environmental Health Sciences Intern
Dartmouth College
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