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

ehaviors are affected by the three insecticides. Adverse effects to swimming-associated
behaviors are directly attributed to AChE inhibition, leading to potential reductions in an
individual’s fitness (i.e., growth, migration, survival, and reproduction). We therefore translate
impaired swimming to potential impacts on salmonid populations. Based on concentrations
generated in modeling, NMFS believes concentrations of carbaryl and carbofuran, applied in
accordance with current labels, are sufficient to impair swimming behavior of salmonids in some
environments. As we located no studies that evaluated the effects of methomyl on swimming
behaviors in fish, we do not know the exact levels sufficient to impair swimming except to say
that levels well below reported LC50s can impair swimming. Swimming-mediated behaviors are
frequently impaired at 0.3 – 5.0% of reported fish LC50s, and that 75% of reported adverse
effects to swimming occurred at concentrations lower than reported LC50s (Little and Finger
1990). Taken together this information supports methomyl affecting swimming behaviors below
reported LC50s. We expect methomyl at hundreds of μg/L (expected from currently approved
applications) to impair swimming.
E. Reduce olfactory­mediated behaviors resulting in consequences to survival, migration, and
reproduction.
In the Opinion regarding effects of chlorpyrifos, diazinon, and malathion on listed salmonids
(NMFS 2008), sufficient data were available to conclude that olfactory-mediated behaviors were
affected by those pesticides. Fewer data were available to assess the effects of carbaryl,
carbofuran, and methomyl on these endpoints. Evidence is unclear as to mode of action for
insecticide-mediated olfactory impairment. Thus, conclusions drawn based on data for OPs may
not necessarily be applicable to N-methyl carbamates. Data currently available are conflicting,
with the one study available for carbaryl showing no apparent effect on olfaction on juvenile
cutthroat trout at concentrations of up to 500 µg/L. Three studies regarding olfactory effects of
carbofuran were located and reviewed, and these indicated olfactory effects in several species of
fish (including two salmonids) at concentrations ranging from 1-10 µg/L. These concentrations
are within both the ranges estimated by modeling, and the ranges measured in all monitoring data
sets. No data were available for methomyl. While data are not conclusive, based on what is
known, and giving the benefit of the doubt to the species, NMFS believes it is reasonable to
assume that these types of effects will occur from carbofuran exposures. Therefore, we discuss
the potential implications at the population-level.
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