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

habitats during aerial applications or severe runoff events death is possible, particularly from
carbaryl and carbofuran. The available monitoring data, if representative of salmonid habitats,
indicated that concentrations rarely achieve LC50 values for the three compounds in freshwaters.
However, it is unlikely that peak concentrations are reflected in the monitoring data, and given
the acutely toxic nature of carbamates, a brief exposure would be sufficient to cause effects. As
described in the Exposure Analysis, monitoring data are limited when compared to the range of
habitats used by salmonids. Few data were found that targeted applications and subsequent
concentrations in edge of field habitats which typically show much higher concentrations than
weekly, monthly, or seasonal monitoring efforts. Although we found no information on egg
survival following acute exposures, we do not expect death of eggs from these insecticides as
entry into the eggs via the water column is unlikely. Further support for acute lethality to fish is
found in field incidences of death attributed to carbaryl, carbofuran, and methomyl that EPA
ranked as “probable”. We located several incidents showing death of freshwater fish following
exposures to N-methyl carbamates. We expect juveniles of listed salmonids to be at the highest
risk of death when in small freshwater off-channel and edge habitats, and secondarily in
estuarine habitats where carbaryl is applied directly to mudflats. In conclusion, the available
information on measured and expected concentrations of the three insecticides supports this
hypothesis. We translate the fitness level consequences of reduced survival from mortality of
juvenile salmonids to potential population-level consequences using population models (see
population modeling section below).
B. Reduce salmonid survival through impacts to growth.
Fish growth is reduced following long-term exposures to carbofuran and methomyl in fathead
minnows and rainbow trout, respectively. EPA reported on a single test that measured growth
effects to fathead minnows following 30 and 60 d exposure to carbaryl at 0, 8, 17, 62, 210, and
680 µg/L (Carlson 1971). No statistically significant effects on growth were reported in this
study. It is difficult to extrapolate from this one study with a warm water species to potential
growth effects to ESA-listed salmonids especially given that salmonids appear substantially
more sensitive to carbaryl’s acute toxicity than fathead minnows (96 h LC50s for salmonids
range from 250-4,500µg/L carbaryl and for fathead minnows 7,700-14,600 µg/L). Additionally,
20% and 50% inhibition of AChE in salmonids occurs at concentrations as low as 23 and 185
µg/L, respectively (Labenia, Baldwin et al. 2007) and this inhibition was found to affect
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