Since 1964, use of pesticides in U.S. has more than doubled from 540 million pounds of active ingredient to 1.1 billion pounds in 1993. This enormous increase has contributed to the contamination of thousands of aquifers across the country, polluting drinking water supplies and causing numerous health concerns. Much of this contamination is due to improper application by the farmer or landowner and can be prevented.
BMP's (Best Management Practices) greatly reduce risk of ground water contamination while still providing strong pest control. Different pesticides obviously behave in different ways, so there are no general guidelines for BMP's -- each pesticide must be looked at individually. Pesticides are subject to three different fates in the soil: Adsorption, Transfer, and Degradation.
Adsorption is a chemical process that results in a pesticide being "stuck" to a soil particle. This is usually the result of a positively charged ion attracted to a negatively charged soil particle, such as clay or organic matter.
Transfer is a process where a pesticide is removed from the application site by volitization, leaching, absorption, or crop removal. Leaching is of most concern in ground water systems as the contaminant flows through the soil with the ground water.
Decay is a process which pesticides are chemically broken down by natural processes into new compounds.
| Low risk | High risk | |
| Pesticide characteristics | ||
| Water solubility | low | high |
| Soil adsorption | high | low |
| Persistence | low | high |
| Soil characteristics | ||
| Texture | fine clay | coarse sand |
| Organic matter | high | low |
| Macropores | few, small | many, large |
| Depth to groundwater | deep (100 ft or more) | shallow (20 ft or less) |
| Water volume | ||
| Rain/irrigation | small volumes at infrequent intervals | large volumes at frequent intervals |
Send comments or suggestions to:
Student Authors: Dan Byers jgreen@vt.edu, jgreen@vt.edu and Rob Harris
Faculty Advisor: Daniel Gallagher, dang@vt.edu
Copyright © 1998 Daniel Gallagher
Last Modified: June 7, 1998
