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

Studies with other AChE inhibitors on salmonid prey items:
Robust evidence shows that salmonid prey taxa and communities can be substantially reduced
following exposures to the OP insecticides chlorpyrifos, diazinon, and malathion. NMFS
reviewed these data and presented its findings in a biological opinion (NMFS 2007d). We use
these findings to show the types of aquatic community responses following exposures to AChE
inhibiting insecticides. The toxic potency of a pesticide is a function of concentration and
duration of exposure, which in turn is a function of a pesticide’s physical properties and
interactions of the pesticide with environmental variables such as temperature, pH, sunlight, soil
micro-organisms, etc. With this in mind, if carbaryl, carbofuran, and methomyl are at
concentrations individually (or together in mixtures) expected to reduce salmonid prey
communities, we infer a similar magnitude of response (reductions in abundance from death and
catastrophic drift) and similar recovery period for those observed in affected aquatic
communities treated with OP insecticides.
We note that individual aquatic invertebrates exhibiting adverse sublethal responses from
carbamates will likely recover much more quickly than those exposed to OPs (Kallander, Fisher
et al. 1997). The midge, Chironomus tentans, showed complete recovery of AChE activity in 24
h following two 1 h pulses of carbaryl separated by 24 h. Additionally, two, 1 h pulses of
carbamates (carbaryl, carbofuran, aldicarb, propoxur) caused significantly fewer symptoms of
intoxication than 2 h of continuous exposure when chironomids were given 2 to6 h of recovery
in clean water between doses (Kallander, Fisher et al. 1997). In contrast, sublethal exposures to
OPs were equally toxic when exposures are either pulsed or continuous.
Reviews of field, mesocosm, and microcosm studies with the three OPs document reductions in
aquatic invertebrate populations and lengthy recovery times for populations of some taxa (Giesy,
Solomon et al. 1998; Van Wijngaarden, Brock et al. 2005). A recent study found significant
changes to macroinvertebrate assemblages of artificial stream systems following a 6 h exposure
to chlorpyrifos at 1.2 μg/L (Colville, Jones et al. 2008). The addition of chlorpyrifos to the
artificial streams resulted in a rapid (6 h) change in the macroinvertebrate assemblages of the
streams, which persisted for at least 124 d after dosing (Colville, Jones et al. 2008). The
chlorpyrifos dissipated from the system within 48 h (Pablo, Krassoi et al. 2008), however the
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