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

The major threats to this ESU identified in the Status of Listed Resources and Environmental
Baseline sections include habitat loss due to blockages from hydroelectric dams and irrigation
diversions, and degraded water quality within the Willamette mainstem and the lower reaches of
its tributaries. Elevated water temperature also poses a significant threat to the status of UWR
Chinook salmon. Fifty pesticides were detected in streams that drain both agricultural and urban
areas. Forty-nine pesticides were detected in streams draining agricultural land, while 25 were
detected in streams draining urban areas. Ten of these pesticides, including carbaryl and
carbofuran, exceeded EPA criteria for the protection of freshwater aquatic life from chronic
toxicity (Wentz, Bonn et al. 1998). The combined impacts from these threats continue to affect
UWR Chinook salmon.
Based on the crop types, we expect that carbaryl and methomyl are commonly applied in the
Willamette Valley throughout the growing season. Existing stocks of carbofuran are also
expected to be applied throughout the growing season. Registered 24(c) uses in Oregon include
carbofuran application to potatoes, nursery stock, sugar beets, and watermelons. The Willamette
Basin is the largest agricultural area in Oregon. In 1992 the Willamette Basin accounted for 51%
of Oregon’s total gross farm sales and 58% of Oregon’s crop sales. About one-third of the
agricultural land is irrigated and most of it is adjacent to the mainstem Willamette River. Urban
developments are also located primarily in the valley along the mainstem Willamette River. We
expect carbaryl to be used throughout the year in urban and residential areas. Given that major
urban and agricultural areas are located adjacent to the mainstem Willamette, ESU exposure to
these pesticides is likely. We also expect that other AChE inhibiting pesticides will co-occur
with carbaryl, carbofuran, and methomyl in the waters of the Willamette Valley and exacerbate
adverse effects from AChE inhibition.
Chinook salmon fry typically select shallow off-channel habitats associated with their natal
rivers and streams. Juveniles generally rear in freshwater for several months to more than one
year before migrating to the ocean. Their duration in shallow freshwater habitats increases their
susceptibility to higher exposures of pesticides, contaminants, and elevated temperature. UWR
Chinook salmon exhibit an earlier time of entry into the Columbia River and estuary than other
spring Chinook salmon ESUs (Meyers, Kope et al. 1998). Although most juveniles from interior
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