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

prevent co-application or sequential applications of carbaryl, carbofuran, and methomyl. The
application rates assumed were consistent with current labels and generally representative of use
rates authorized for many crop and non-crop uses. An exception was the assumed carbaryl use
rate in citrus (12 lb a.i./acre), which is substantially higher than the maximum use rate approved
for most crops.
The NAWQA, CDPR, and EIM monitoring values represent the maximum concentrations found
in the respective databases. The values cited were all measured within the four states and the
vast majority is from waters that contain or drain to listed salmonid habitats. Most of the
detections in these, and other monitoring studies that did not target specific applications of the
three chemicals occurred at or below the µg/L level. We expect that exposure at these levels will
be common in drainages where the three products are used extensively.
Evaluation of Risk Hypotheses: Individual Salmonids
In this phase of our analysis we examine the weight of evidence from the scientific and
commercial data to determine whether it supports or refutes a given risk hypothesis. We also
highlight general uncertainties and data gaps associated with the data. In some instances there
may be no information related to a given hypothesis. If the evidence supports the hypothesis we
determine whether it warrants an assessment either at the population-level, or affects PCEs to
such a degree, to warrant an analysis on the potential to reduce the conservation value of
designated critical habitat.
1. Exposure to carbaryl, carbofuran, and methomyl is sufficient to:
A. Kill salmonids from direct, acute exposure.
A large body of laboratory toxicity data indicates that anadromous salmonids die following
short-term (< 96 h) exposure to the three insecticides at levels above 200 µg/L. We expect
concentrations of carbaryl, carbofuran, and methomyl in salmonid off-channel habitats will reach
lethal levels based on exposure concentrations derived from monitoring data, EPA’s modeling
estimates, and NMFS modeling estimates (See Exposure Analysis). The youngest swimming
salmonids appear to be the most likely to die from short-term, acutely toxic exposures in these
habitats. It is less likely that adults would be killed by acute concentrations in most freshwater
aquatic habitats compared to juveniles. However, if adults are present in smaller off-channel
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