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

Carbaryl’s thresholds for the four species ranged from 129-190 μg/L, carbofuran’s from 89-126
μg/L, and methomyl’s from 287-431 μg/L. These results can be compared to expected
concentrations shown in Figure 39, Figure 40, and Figure 41. All of the thresholds overlap with
expected concentrations for the three insecticides. The overlap primarily occurs with NMFS
modeled estimates for off-channel habitats.
When we compare the population threshold concentrations to expected levels in salmonid
habitats described in the exposure section, it is likely that some individuals within a population
will be exposed during their freshwater juvenile life stage, particularly those juveniles exposed
while using off-channel habitats. Additionally, four day averages from GENEEC runs, but not
from PRZM-EXAMS, exceed these threshold concentrations. It is uncertain how appropriate
EPA’s model estimates are for salmonid habitats, but taken at face value juveniles exposed to
GENEEC-derived concentrations would die. Population-level effects are expected from these
exposures if the majority of the individuals that comprise the populations are exposed during
their freshwater residency. The likelihood of population effects from death of juveniles increases
for those populations that spend longer periods in freshwaters such as steelhead, stream-type
Chinook, and coho salmon. We also expect additional acute mortalities from juveniles that are
exposed to 24(c) carbaryl applications in Washington estuaries, although we do not know how
many individuals are exposed each year. For those populations with lambdas greater than one,
reductions in lambda from death of juveniles can also lead to consequences to abundance and
productivity. Consequently, attainment of recovery goals would take longer to achieve for
populations with reduced lambdas. Many of the populations that are categorized as core
populations or are important to individual strata, have lambdas just above one and are essential to
survival and recovery goals. Slight changes in lambda, even as small as 3-4%, would result in
reduced abundances and/or increased time to meet population recovery goals.
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