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

AChE levels recovered slightly. The treatment concentrations used in this study are very high
and indicate that brook trout are not sensitive to diet-induced toxicity of fenitrothion. The
experiment did show that AChE inhibition from the diet is possible, yet it is difficult to
determine the relative toxicity of carbaryl, carbofuran, and methomyl found in contaminated
insects consumed by Pacific salmonids.
Habitat assessment endpoints:
Prey survival, prey drift, nutritional quality of prey, abundance of prey, health of aquatic prey
community, and recovery of aquatic communities following N­methyl carbamate exposures
Assessment measures: 24, 48, and 96 h survival of prey items from laboratory bioassays
reported as EC/LC50s; sublethal effects to prey items; field studies on community abundance;
indices of biological integrity (IBI); community richness; and community diversity.
Death of aquatic invertebrates in laboratory toxicity tests were reported in each of the BEs.
Salmonid aquatic and terrestrial prey are highly sensitive to the three carbamate insecticides.
Death of individuals and reductions in individual taxa and prey communities have been
documented and are expected following applications of N-methyl carbamates that achieve effect
concentrations-several of which are at the low μg/L levels (Schulz 2004). Complete or partial
elimination of aquatic invertebrates from streams contaminated by insecticides has been
documented for carbaryl (Muirhead-Thomson 1987) as well as many other insecticides. A
review of field studies published from 1982-2003 on insecticide contamination concluded that
“about 15 of the 42 studies revealed a clear relationship between quantified, non-experimental
exposure and observed effects in situ, on abundance [aquatic invertebrate], drift, community
structure, or dynamics” (Schulz 2004). Although the top three insecticides most frequently
detected at levels expected to result in toxicity were chlorpyrifos (OP), azinphos-methyl (OP),
and endosulfan, the N-methyl carbamates carbaryl, carbofuran, oxymyl, and fenobucarb all
showed clear or assumed relationships between exposure and effect (Schulz 2004).
Drift, feeding behavior, swimming activity, and growth are sublethal endpoints of aquatic prey
negatively affected by exposure to AChE inhibitors (Courtemanch and Gibbs 1980; Haines 1981;
Hatakeyama, Shiraishi et al. 1990; Davies and Cook 1993; Beyers, Farmer et al. 1995; Schulz
2004). Drift of aquatic invertebrates is an evolutionary response to aquatic stressors. However,
insecticides, particularly carbamates and OPs, can trigger catastrophic drift of salmonid prey
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