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

Sample sites for this study are best characterized as integration sites selected based on the
presence of the listed Yakima salmonid population (one of 17 independent populations that
comprise the Middle Columbia River steelhead DPS) and high diversity and intensity of
agriculture. The study design included sampling during the pesticide application season but did
not target specific applications of pesticides nor did it target salmonid habitats that would be
expected to produce the highest concentrations of pesticides (e.g., shallow off-channel habitat in
close proximity to pesticide application sites). Sampling was generally conducted on a weekly
basis, so it is likely peak concentrations associated with drift and runoff events were not
captured. Sampling stations included both agricultural- and urban-dominated watersheds, and
some storm events are captured in the sampling. Sampling favored the detection of multiple
pesticides, rather than peak concentrations in some habitats used by Middle Columbia River
steelhead.
Other available monitoring data are also applicable to assessing exposure in listed salmon, but to
varying degrees. Common aspects that limit the utility of the available monitoring data as
accurate depictions of exposure within listed salmonid habitats include: 1) protocols were not
designed to capture peak concentrations or durations of exposure in habitats occupied by listed
species; 2) limited utility as a surrogate for other non-sampled surface waters; 3) lack of
representativeness of current and future pesticide uses and conditions; and 4) lack of information
on actual pesticide use to correlate with observed surface water concentrations.
Protocols not designed to capture peak exposure. The NAWQA monitoring studies contain the
largest data set evaluated. However, these studies were designed to evaluate trends in water
quality and were not designed to characterize exposure of pesticides to listed salmonids (Hirsch
1988). The NAWQA design does not result in an unbiased representation of surface waters. For
example, some agricultural activities and related pesticide uses that may be very important in a
particular region may not be represented in the locations sampled. Sampling from the NAWQA
studies and other studies reviewed was typically not conducted in coordination with specific
applications of carbaryl, carbofuran, and methomyl. Similarly, sampling was not designed with
consideration to salmon distribution or to target the salmonid habitats most likely to contain the
greatest concentrations of pesticides. Given the relatively rapid dissipation of these pesticides in
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