Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

7.2.1 Environmental exposure
Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
Following release into the environment through application, pesticides would experience several
different routes of environmental fate. Pesticides which would be sprayed can move through the air
(e.g., particle or vapor drift) and may eventually end up in other parts of the environment such as
non-target vegetation, soil, or water. Pesticides applied directly to the soil may be washed off the
soil into nearby bodies of surface water (e.g., surface runoff) or may percolate through the soil to
lower soil layers and groundwater (e.g., leaching) (Baker and Miller 1999, Pope et. al. 1999, Butler
et. al. 1998, Ramsay et. al. 1995, EXTOXNET 1993a). Pesticides which would be injected into the
soil may also be subject to the latter two fates. The aforementioned possibilities are by no means
complete, but it does indicate movement of pesticides in the environment is very complex with
transfers occurring continually among different environmental compartments. In some cases, these
exchanges occur not only between areas that are close together, but it also may involve transportation
of pesticides over long distances (Barry 2004, Woods 2004).
7.2.1.1 Terrestrial exposure
The estimated environmental concentration (ECC) for exposure to terrestrial wildlife would be
quantified using an USEPA screening-level approach (US Environmental Protection Agency 2004).
This screening-level approach is not affected by product formulation because it evaluates pesticide
active ingredient(s). This approach would vary depending upon the proposed pesticide application
method: spray or granular.
7.2.1.1.1 Terrestrial-spray application
For spray applications, exposure would be determined using the Kanaga nomogram method (US
Environmental Protection Agency 2005a, US Environmental Protection Agency 2004, Pfleeger et al.
1996) through the USEPA’s Terrestrial Residue Exposure model (T-REX) version 1.2.3 (US
Environmental Protection Agency 2005b). To estimate the maximum (initial) pesticide residue on
short grass (