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/eot2008/20090508021206im_/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/eot2008/20090508021206im_/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/eot2008/20090508021206im_/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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