Determining the environmental behavior of a pesticide is an important step in the regulatory evaluation process. Information developed during laboratory experiments, through field testing, and by use of environmental modeling characterizes the persistence (How long does it last?), transformation (What byproducts may be formed upon breakdown?), movement (Where might it move?), and environmental burden (What concentrations may occur in soil, air or water?) associated with pesticide use. In turn, this information is used to develop estimates of the magnitude and likelihood of exposures to wildlife and people and the potential for contamination of environmental resources (e.g., ground water).
Environmental Testing Approaches for Pesticides
Laboratory testing seeks to characterize the transformation and persistence of a pesticide in soil, water and air. The rate of breakdown is determined under various conditions and the breakdown products are identified. Factors examined under lab conditions include the influence of soil type, soil moisture, soil and water temperature, presence or absence of oxygen, and the impact of sunlight on degradation. The potential uptake and transformation of the pesticide from soil by crop plants and from water by fish is also examined.
Field-scale experiments under actual use conditions are conducted to confirm and expand upon laboratory findings. Sensitive methods of analysis for the pesticide and breakdown products identified in laboratory studies are used to track behavior of the pesticide in agricultural situations. Depending on persistence of the pesticide, studies may last a single growing season or several seasons. In addition to sampling of soil and crop plants, analyses may also be performed to understand pesticide residues which may evaporate into the air, leach into groundwater with percolating rainfall, or wash off from field surfaces with runoff water or eroding sediment.
Computer Modeling and Residue Monitoring
Laboratory and field studies are conducted under a variety of conditions, including worse-case situations, but it is not possible to do a new experiment for every combination of agricultural practices, soil type, rainfall, etc. that may occur. To expand upon available data and answer “What if…?” questions from a predictive standpoint, scientists use sophisticated computer modeling programs that simulate the behavior of a pesticide under varied conditions that might be encountered. For example, based on the observed behavior of a pesticide in soil under a small set of climate conditions, computer models may simulate how the persistence and movement of a pesticide would be affected by using a hundred years of recorded weather conditions.
Routine environmental monitoring data may also be used to corroborate and compare conclusions about pesticide behavior that were based on observations from laboratory or field studies. Environmental monitoring involves analysis of soil, water, or air samples for pesticides or other chemicals on an ongoing basis either as part of general government environmental monitoring programs or as part of a pesticide-specific program by government or industry. For example, for a number of years the U.S. Geological Survey has been monitoring pesticide and fertilizer residues which may reach streams and rivers within farm areas. Also, in selected cases a pesticide registrant may be required to sponsor regular monitoring of a pesticide as a condition of registration approval.
Dozens of laboratory and field studies have been conducted by Dow AgroSciences to characterize the environmental behavior of chlorpyrifos under a great diversity of conditions, and additional studies have been completed by government research centers and universities. In fact, chlorpyrifos is one of the most well-studied pesticides from an environmental standpoint.
Racke, K.D. “Environmental Fate of Chlorpyrifos.” Reviews of Environmental Contamination and Toxicology, 1993, Volume 131:1-154.
“Pesticides – Environmental Effects”, U.S. Environmental Protection Agency