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

We located studies that measured olfactory responses of fish to carbofuran and carbaryl. We
found no studies with methomyl. Several studies with other carbamates were found, but most
were with thiocarbamates which have a different mode of action than N-methyl carbamates, i.e.,
they do not inhibit acetylcholineterase. We do not discuss or use studies with OPs as surrogates
for effect to olfaction in salmonids because AChE inhibition does not appear to be the putative
mode of action affecting olfaction, although more empirical data are needed to confirm this.
Below we discuss the available literature of carbamate effects on fish olfaction.
The olfactory activity of juvenile cutthroat trout appeared unresponsive to carbaryl following 10
second pulses across the olfactory epithelia, and juveniles showed no preference/avoidance to
carbaryl (Labenia, Baldwin et al. 2007). No departures relative to unexposed fish were observed
at 5, 50, or 500 μg/L carbaryl from neurophysiological recordings i.e., electro-olfactograms.
Additionally, in a behavioral avoidance assay, cutthroat trout did not avoid seawater containing
carbaryl at 500 μg/L. These results suggest that cutthroat trout do not actively avoid carbaryl
and that short term exposures do not affect olfaction at the concentrations tested. We found no
other studies that evaluated other salmonids in estuarine conditions or in freshwaters. We ranked
these study results as highly relevant to the effects of carbaryl on salmonid olfaction and an
olfactory-mediated behavior, avoidance.
In one set of experiments, coho salmon exposed for 30 minutes to three carbamates (carbofuran,
antisapstain IPBC, mancozeb) separately, had reduced olfactory ability as well as disruption of
normal AChE activity (Jarrard, Delaney et al. 2004). Carbofuran reduced olfaction by 50%
(EC50) at 10.4 μg/L; IPBC reduced olfaction at 1.28 μg/L (EC50); and mancozeb reduced
olfaction at 2.05 mg/L (EC50). In addition, carbofuran reduced AChE activity in the olfactory
receptor at at 200 μg/L (68%), but none of the treatments (0.1, 10, or 200 μg/L) reduced brain or
olfactory bulb AChE activity. This could be a result of the limited exposure duration. The
authors concluded that too little information exists to develop a causal relationship between
AChE inhibition and olfaction (Jarrard, Delaney et al. 2004). The data do show that carbofuran
inhibited both olfaction and AChE activity at 10 and 200 μg/L, respectively. We ranked these
study results as highly relevant to carbofuran’s effect on salmonid olfaction.
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