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

survival appears to be the most sensitive endpoint as all three ranges encompass this endpoint
and the maximum concentration values far exceed the prey survival range. Swimming is likely
impaired at the higher end of the concentration range from monitoring data, at the middle and
higher range from EPA estimates, and throughout the range predicted in the off-channel habitat
estimates. Concentrations occurring in the off-channel habitats that NMFS modeled will kill
juvenile salmonids. Furthermore, given the LC50 values for salmonids following 96 h
exposures, we expect that fewer deaths of juveniles will occur in many of the freshwater habitats
exposed to carbaryl. Fish reproduction (based on a single fathead minnow study) would be
affected by concentrations in the off-channel habitat. We also note minimal data exist on effects
to fish growth: only a single study with fathead minnows. We expect that carbaryl will impair
swimming of salmonids, kill salmonid prey, and in certain circumstances kill salmonids when
exposed for sufficient durations. The effect concentrations shown in the figure do not account
for the potential enhanced toxicity of carbaryl to salmonids or their prey items in aquatic habitats
where other AChE inhibitors are present. We also note that pH is a major factor in carbaryl’s
persistence in aquatic habitats. At pHs above 8, carbaryl breaks down fairly rapidly (half-life of
24 h) while at pHs less than 8 carbaryl is much more resistant to hydrolysis (half-life of 1- 30 d
for pH of 7.9 – 5.7). The pH of natural surface waters commonly ranges from 7 to 9, thus pH is
an important consideration when evaluating toxicity of carbaryl.
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