Pesticide Movement in the Environment
Movement of pesticides from the place of application into surrounding ecosystems depends on the physical and chemical properties of the pesticide, transformation processes, and partitioning behavior. Where, when, and how a pesticide is applied also plays a role in pesticide fate (e.g., land use practices, slope, soil type, etc.) (See conceptual diagram below).
There are ultimately three fates for pesticides:
- All or a portion may remain unchanged where it was applied
- All or a portion might be carried elsewhere by transport processes
- All or a portion might be transformed into other chemical species by natural and biological processes.
Partition Coefficients for Contaminants
Partitioning behavior (the tendency for a compound to move from one state to another based on chemical properties and temperature) changes as it is broken down through natural (ex: exposure to sunlight) and biological (phase I and II Biotransformation) processes. Water is often used as the reference phase when calculations are down concerning partitioning. This is dependent on chemical properties and temperature. Partitioning coefficients are used to determine numerous environmental fate and transport characteristics for many potential contaminants including pesticides.
A compound can exist in:
- Air phase (chemical vapor in the air)
- Free phase (chemical liquid/free product)
- Water phase (chemical is dissolved in water)
- Solid phase (Chemical is sorbed to solid)
(see figure 1 in right sidebar)
Partitioning coefficients ultimately help determine the environmental transport and fate of a pesticide in the PRZM (Pesticide Root Zone Model) -EXAMS (Exposure Analysis Modeling System) model used by the EPA to determine if a pesticide exceeds a potential level of concern (LOC).
EPA's PRZM-EXAMS Model Parameter Set Up: