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

F. Exposure to mixtures of carbaryl, carbofuran, and methomyl can act in combination to
increase adverse effects to salmonids and salmonid habitat.
The exposure and toxicity information we compiled, reviewed, and analyzed support the risk
hypothesis, although less mixture data were available for the carbamates addressed in this
Opinion than the OPs addressed in the previous Opinion (NMFS 2008). Evidence of additive
and synergistic effects on survival and AChE inhibition in salmonids were identified. Multiple,
independent study results supported additive toxicity from measured AChE inhibition. We
therefore conducted an analysis of potential mixtures on the levels of AChE inhibition and the
potential for a greater reduction in survival predicated on simple additivity. The analysis showed
that both survival and AChE inhibition of individuals is likely affected to a greater degree than
from exposure to a single chemical alone. We also expect that assessment endpoints influenced
by AChE inhibition are likely affected to a greater degree when in the presence of more than one
of the three insecticides. Considerable uncertainty arises as to the level of impairment caused by
mixtures for some endpoints, as dose responses have not been characterized for some pesticide
combinations. We conclude that this hypothesis is supported by the available information and
we assess the potential for population-level consequences below.
G. Exposure to other stressors of the action including degradates, adjuvants, tank mixtures,
and other active and other ingredients in pesticide products containing carbaryl, carbofuran,
and methomyl cause adverse effects to salmonids and their habitat.
Fifteen of the carbamate formulations contain other a.i.s, including malathion (OP insecticide),
bifenthrin (pyrethroid insecticide), rotenone (insecticide/piscicide), metaldehyde (mulloscicide),
captan (phthalidimide fungicide), and cupric sulfate (toxic to algae, aquatic invertebrates, and
fish). No data regarding the joint toxicity of these multi-a.i. products were presented in the BEs
or located in open literature. However, given that these pesticides are also toxic to aquatic life it
is reasonable to assume the salmonids and/or their prey items will exhibit a greater toxic
response when exposed to multiple a.i.s than to a single one. We are unable to estimate the
magnitude of such a response, and other than for malathion, are not currently able to evaluate
whether the response would fall into an additive, synergistic, or antagonistic category. Based on
mixture data discussed elsewhere in this Opinion, we assume additivity for carbaryl, carbofuran,
and methomyl.
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