Where
are the Pesticides?
The U.S. Geological Survey (USGS), the U.S. Environmental
Protection Agency, the Iowa Department of Natural Resources,
and the University of Iowa Hygienic Laboratory have been studying
the occurrence and distribution of herbicides and their degradates
in Iowa's ground water. Iowa is in the heart of the Corn Belt,
a multi-state area that has the most productive farmland in
the world. The agricultural productivity of this area goes hand
in hand with the extensive use of herbicides to control weeds.
Past studies on herbicides in ground water have only studied
herbicide parent compounds and found minimal concentrations
of herbicides. The study has shown that
- Herbicide degradates are prevalent in ground water. Degradates were
8 of the 10 most frequently detected compounds in the study
. ![Graph showing the frequency of detection](https://webarchive.library.unt.edu/eot2008/20081108035708im_/http://toxics.usgs.gov//icons/dana2.gif)
- The frequencies of detection for a given herbicide in ground water
generally increased many fold when its degradates were included.
![Graph showing the frequency of detection](https://webarchive.library.unt.edu/eot2008/20081108035708im_/http://toxics.usgs.gov//icons/dana3.gif)
- A majority of a herbicide's measured concentration was in the form
of its degradates, ranging from 55 to over 99 percent of the total concentration.
![Graph showing total concentration](https://webarchive.library.unt.edu/eot2008/20081108035708im_/http://toxics.usgs.gov//icons/dana4.gif)
- This study demonstrates that obtaining data on herbicide degradates
is critical for understanding the fate of herbicides in the environment.
Furthermore, to accurately determine the overall effect on human health
and the environment from a specific herbicide, its degradates should
also be considered.
The results of this study and other Toxics Program studies have prompted
the USGS's National Water-Quality Assessment (NAWQA) Program to double
the number of degradates in its national assessment on the occurrence
of pesticides. In addition, the State of Iowa is now including pesticide
degradates in the State's plan for water-quality monitoring.
More Information on Pesticides
References
Kolpin, D.W., Thurman,
E.M., and Linhart, S.M., 1999, Finding
minimal herbicide concentrations in ground water? Try looking
for the degradates, in Morganwalp, D.W., and Buxton, H.T.,
eds., U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Charleston, South Carolina, March
8-12, 1999--Volume 2 of 3--Contamination of Hydrologic Systems
and Related Ecosystems: U.S. Geological Survey Water-Resources
Investigations Report 99-4018B, p. 247-254.
Kolpin, D.W., Thurman, E.M.,
and Linhart, S.M., 1998, The environmental occurrence of herbicides--The
importance of degradates in ground water: Archives of Environmental Contamination
and Toxicology, v. 35, n. 3, p. 385-390.
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