ARTF conducted all of its exposure studies using test substances that were registered pesticides. One of the most difficult tasks in preparing for field studies was the identification, development and evaluation of appropriate surrogate compounds for measuring exposure. The surrogate compounds selected had the following desirable characteristics:
· Registered for use on many crops
· Relatively short Restricted Entry Intervals (REIs)
· Short Preharvest Intervals (PHIs) for harvest studies
· Stable under field conditions
· Relatively persistent residues on foliage
· Validated analytical methods that were practical, reproducible, and sufficiently sensitive for detection of the test substance in all types of experimental matrices.
The process of approving a compound as a surrogate involved several steps:
1. A potential surrogate was identified.
2. Analytical methods were either developed (if none existed) or modified to accommodate the sensitivity required by ARTF studies.
3. The analytical methods were validated in a study conducted under EPA Good Laboratory Practice Standards.
4. The stability of the surrogate under field conditions was evaluated within a small field study.
5. 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 analytical laboratories to perform a try-out of the analytical methods. Laboratories that were successful, were then eligible to analyze samples from ARTF field studies.
The ARTF selected the following compounds as surrogate chemicals for generic measurement of exposure: