Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

low maximum application rate. However, model estimates indicate methomyl can reach
concentrations of several hundred μg/L in surface waters given some uses that allow repeated
applications at short re-application intervals. Given variable use of these pesticides across the
landscape, and variable temporal and spatial distributions of listed salmonids, we expect
exposure is also highly variable among individuals and populations of listed salmon. However,
defining exposure and distributions of exposure among differing life stages of each independent
population is complicated by several factors. Paramount among these is the uncertainty
associated with the use of pesticide products containing these a.i.s. More specifically:
• Although the BEs and RED documents provide information on EPA regulatory decisions,
they lack a full characterization of label-specific information needed to assess exposure
(e.g., application restrictions including application methods, rates, and intervals are
lacking for many non-agricultural uses);
• EPA-authorized labels contain language that frequently does not provide clear boundaries
on product use (e.g., the maximum number of applications is commonly not specified and
labels often instruct applicators to repeat applications “as necessary”);
• Product labels authorize the application of chemical mixtures that are not specified or not
clearly defined (e.g., the ingredients of pesticide formulations are not fully disclosed,
labels recommend tank mixture applications with other pesticides and adjuvants and tank
mixtures with other pesticides are permitted unless specifically stated otherwise);
• Defining use of these products is highly uncertain because products are not likely to be
used to the full extent permitted on the labels and historical use information is limited and
may not reflect future use.
A major limitation of these assessments is that the majority of monitoring data used were not
designed to determine exposure to listed salmonids, with the exception of specific studies
conducted in Washington. Therefore, caution should be exercised in using these data for that
purpose. Additionally, the assessments lack uncertainty analyses of the monitoring and toxicity
data used, which limit the confidence in the given estimates (Warren-Hicks and Moore 1998).
Given the complexity and scale of this action we are unable to accurately define exposure
distributions for the chemical stressors. We assume the highest probability of exposure occurs in
freshwater, and nearshore estuarine/marine environments with close proximity to areas where
309