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

200 μg/L, an increase in predation was evident, although not statistically significant. At 500 and
1,000 μg/L carbaryl, cutthroat trout were consumed at significantly higher rates than unexposed
fish. Cutthroat trout’s AChE activity was also reduced in a dose-dependent fashion showing
greater reductions with increasing carbaryl concentrations. Six hour exposures significantly
reduced AChE activity in brain and muscle, where 50% reductions (IC50) in brain AChE
occurred at 213 μg/L carbaryl. The onset of inhibition occurred within 2 hours, at which point
AChE activity was near its lowest value. Benchmark concentrations corresponding to 20%
inhibition were 32 μg/L in brain and 23 μg/L in muscle tissues. Recovery of AChE activity (to
pre-exposure levels) took 42 hours at 500 μg/L carbaryl. We ranked these sets of experiments as
highly relevant to understanding the effects of carbaryl on inhibition of AChE and subsequent
salmonid swimming behaviors. The test also provided information on lack of predator avoidance
behaviors by salmonids.
Catfish (Mystus vittatus) showed increased swimming activity following 72 h of exposure to
12,500 μg/L and no mortalities were noted (Arunachalam, Jeyalakshmi et al. 1980). The 72 h
LC50 for catfish was 17,000 μg/L, indicating this species of catfish is much less sensitive to
acute concentrations of carbaryl than salmonids. Other sublethal endpoints were also affected by
carbaryl, including food intake, growth, metabolism, and rate of opercular beats. Catfish
increased their rates of opercular beats from 74 per minute exposed to freshwater alone to 124
per minute when exposed to 12,500 μg/L carbaryl, which the authors attributed to acute stress
from carbaryl. We ranked this study as relevant because swimming was measured, but the high
concentrations used, lack of chemical verification, and lack of compatibility to listed salmonids
introduces uncertainty.
Multiple behavioral responses related to swimming were assessed in rainbow trout fry (0.5-1 g)
following 96 h exposures to carbaryl at 10, 100, and 1,000 μg/L; nominal concentrations (Little,
Archeski et al. 1990). These included swimming capacity (cm/sec), swimming activity (sec),
prey strike frequency, daphnids consumed, percent consuming daphnids, and percent survival
from predation. All endpoints were significantly affected at 1,000 μg/L carbaryl relative to
unexposed fry. At 10, 100, and 1,000 μg/L carbaryl, significantly more rainbow trout were
338