From February 21, 2006
Researchers
Find That Disturbing Former Farmlands Can Rouse Old Pesticides
(Beyond
Pesticides, February 21, 2006)
A group of Dartmouth researchers has evidence that disturbing the land
where farms once thrived can mobilize both arsenic and lead that were
applied as pesticides in the early 1900s. Once disturbed, these metals
can then contaminate nearby surface waters.
"We continue to learn more about how past agricultural practices
are affecting our current environment," says Carl
Renshaw, Associate Professor of Earth Sciences at Dartmouth. "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 they 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 are now part of
the fine silt and organic matter in the soil, which is most susceptible
to erosion.
"We learned that disturbing this land, for example 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 of yet, there
is 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 is disturbing old farmlands mobilizes old
pesticides 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 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 waters."