ARTF conducted all of its exposure studies using test substances that are registered pesticides. One of the most difficult tasks in preparing for field studies is the identification, development and evaluation of appropriate surrogate compounds for measuring exposure. The surrogate compounds selected had the following desirable characteristics:
Use is registered on many crops
- Current Restricted Entry Intervals (REIs) are relatively short
- Preharvest Intervals (PHIs) are short (for harvest studies)
- Stable under field conditions
- Residue on foliage is relatively persistent
- Analytical methods are validated, i.e., practical, reproducible, and sufficiently sensitive for detection of the test substance in all types of experimental samples.
The process of approving a compound as a surrogate involved several steps:
A potential surrogate was identified.
- Permission to use the compound was received from the major manufacturer.
- Analytical methods were either developed (if none existed) or modified to accommodate the sensitivity required by ARTF studies.
- The analytical methods were validated in a study conducted under EPA Good Laboratory Practice Standards.
- The stability of the surrogate under field conditions was evaluated within a small field study.
- Freezer storage stability of the potential surrogate was also evaluated.
Once a compound passed all of these tests and was accepted as a surrogate, the ARTF Analytical Subcommittee selected additional analytical laboratories to perform a try-out of the analytical method. If they were successful, then they were eligible to analyze samples from ARTF field studies.
The ARTF selected the following compounds as surrogate chemicals for generic measurement of exposure: