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

swimming behavior (Labenia, Baldwin et al. 2007). Reduced growth occurred at 56 µg/L for
carbofuran and 142 µg/L for methomyl. Only one test result was reported for each pesticide.
We did not identify any studies that provided a quantitative relationship between growth and fish
survival in the field or lab. However, there is abundant literature that shows salmonids that are
smaller in size have reduced first year survival (Appendix 1). Additionally, exposure to
sublethal concentrations of other AChE inhibitors (chlorpyrifos and diazinon) for acute durations
does cause reduced feeding success, which likely results in impacts to growth (Scholz, Truelove
et al. 2000; Sandahl, Baldwin et al. 2005). We expect that juvenile fish exposed to carbaryl,
carbofuran, and methomyl during their freshwater residency will feed less successfully, resulting
in lower growth rates and reduced sizes. Exposure concentrations will likely vary temporally
and spatially for salmonids depending on life history, pesticide use, and environmental
conditions. The available information support that growth is likely reduced where salmonids are
exposed to more than 56 µg/L carbofuran and to concentrations below LC50 for carbaryl and
methomyl, although the exact concentrations that may cause growth reduction are currently
unknown. The weight of evidence supports the conclusion that fitness level consequences from
reduced size are likely to occur in individual salmonids exposed to the three N-methyl
carbamates. Therefore, we address the potential for population-level repercussions due to
reduced growth using species-specific population models.
C. Reduce salmonid growth through impacts on the availability and quantity of salmonid prey
We address several lines of evidence to determine the likelihood of reduced salmonid growth
from impacts to aquatic invertebrate prey. The first line of evidence we evaluated is whether
salmonid prey items are sensitive to acute and chronic exposures from expected concentrations
of the three carbamates. These primarily involved evaluating laboratory experimental results
that reported on incidences of death or sublethal effects. We located a total of 10, 4, and 14
survival estimates (24, 48, 72, and 96 h EC/LC50s) for carbaryl, carbofuran, and methomyl,
respectively. Based on an evaluation of the assessment endpoints, we found a robust body of
exposure and toxicity data that indicated salmonid aquatic prey are highly sensitive and affected
by expected exposures to each of the insecticides as well as from mixtures containing the three
insecticides. We expect death and a variety of sublethal effects to salmonid prey items.
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