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

at or below “1 toxic unit”-where a toxic unit equals field concentrations normalized by dividing
them by the 48 h EC50 of Daphnia magna for a given AChE inhibitor.
We did not locate any microcosm, mesocosm, or field experiments that measured responses of
aquatic communities that contained salmonids and salmonid prey simultaneously; a recognized
data gap. Several studies evaluated aquatic invertebrate responses to N-methyl carbamates
(carbaryl, carbofuran, and bendiocarb) in static and running water systems. We found no field
studies with methomyl. We summarize open literature studies with aquatic invertebrates
organized by insecticide in Table 65. We found no studies that addressed effects of methomyl
on aquatic invertebrates in the field or from multispecies microcosms or mesocosms.
The available literature from field experiments indicates that populations of aquatic insects and
crustaceans are likely the first aquatic organisms damaged by exposures to carbaryl, carbofuran,
and methomyl contamination. Benthic community shifts from sensitive mayfly, stonefly and
caddisfly taxa, the preferred prey of salmonids, to worms and midges occur in areas with
degraded water quality including from contaminants such as pesticides (Cuffney, Meador et al.
1997; Hall, Killen et al. 2006). Reduced salmonid prey availability correlated to OP use in
salmonid bearing watersheds (Hall, Killen et al. 2006). We found no studies that evaluated the
effects on carbamates and that made correlations to salmonid bearing watersheds. Subsequent
effects to salmonid’s growth from reduced prey availability and quality remain untested and are a
current data gap.
We located a study addressing impacts on fish growth due to prey reduction. Although this
study was conducted on chlorpyrifos, an insecticide not considered in this Opinion, we deemed it
highly relevant due to the ecological context it provided. The study indicated that native fathead
minnows exposed to chlorpyrifos had reduced growth due to reductions in prey item abundance
in littoral enclosures (pond compartments) (Brazner and Kline 1990). The experiment tested the
hypothesis that, “addition of chlorpyrifos would reduce the abundance of invertebrates and cause
diet changes that would result in reduced growth rates.” Nominal, chlorpyrifos treatment
concentrations of 0.5, 5.0, and 20 μg/L (chemical analysis of water concentrations provided at 0,
12, 24, 96, 384, 768 h) all resulted in statistically significant reductions in growth at 31 days. A
348