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

capacity (Little and Finger 1990). Therefore, measurements of swimming activity are usually
more sensitive than measurements of swimming capacity. A likely reason is that fishes having
impaired swimming to the degree that they cannot orient to flow or maintain position in the
water column are moribund (i.e., death is imminent). The authors of the review also concluded
that swimming-mediated behaviors are frequently adversely affected at 0.3 – 5.0% of reported
fish LC50s 3 , and that 75% of reported adverse effects to swimming occurred at concentrations
lower than reported LC50s (Little and Finger 1990). Both swimming activity and swimming
capacity are adversely affected by AChE-inhibiting insecticides.
We located studies that measured impacts to salmonid swimming behaviors from exposure to
carbaryl. Several studies also measured AChE inhibition from OPs and provided correlations
between AChE activity and swimming behaviors. We did not locate any studies that tested
mixtures of AChE-inhibiting insecticides on swimming behaviors of any aquatic species.
Carbaryl
Experiments with carbaryl have shown that cutthroat trout’s (Oncorhynchus clarki clarki)
swimming abilities are compromised by 6 h exposures to 750 and 1,000 μg/L, resulting in
increased susceptibility to predation (Labenia, Baldwin et al. 2007). Cutthroat trout swimming
capacity was not significantly affected by carbaryl at 500 μg/L, although muscle AChE activity
was 29% relative to unexposed cutthroat. More sensitive swimming activity measurements were
not evaluated. At 750 and 1,000 μg/L, AChE activity was 24 and 23% relative to unexposed
fish, respectively. A known predator of juvenile cutthroat, lingcod (Ophiodon elongates),
consumed on average more cutthroat that were exposed to carbaryl compared to those that were
not exposed to carbaryl. The experimental design ensured that the predator was exposed to
minimal concentrations when carbaryl-exposed fish were transferred in a large experimental
chamber along with unexposed cuthroat. In the predation experiment with lingcod, cutthroat
were exposed for 2 h to 200, 500, and 1,000 μg/L carbaryl. Results indicated a dose-dependent
decrease in the ability of carbaryl-exposed trout to avoid being eaten by the lingcod predator. At
3 The current hazard quotient-derived threshold for effects to threatened and endangered species used by EPA is 5 % (1/20 th ) of the lowest fish
LC50 reported. If the exposure concentration is less than 5 % of the LC50 a no effect determination is made which likely underestimates risk to
listed salmonids based on swimming behaviors.
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