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

Exposure estimates for crop applications
The BEs provide estimated environmental concentrations (EECs) for carbaryl,
carbofuran, and methomyl in surface water (Table 49). EECs were generated using the
PRZM-EXAMS model and used to estimate exposure of the three a.i.s to listed salmonids
and their prey (EPA 2004). PRZM-EXAMS generates pesticide concentrations for a
generic “farm pond”. The pond is assumed to represent all aquatic habitats including
rivers, streams, off-channel habitats, estuaries, and near shore ocean environments. EPA
indicated that the PRZM-EXAMS scenarios provide “worst-case” estimates of salmonid
exposure and it “believes that the EECs from the farm pond model do represent first
order streams, such as those in headwaters areas” used by listed salmon (EPA 2003; EPA
2003; EPA 2004). However, listed salmonids use aquatic habitats with physical
characteristics that would be expected to yield higher pesticide concentrations than would
be predicted with the “farm pond” based model. Juvenile salmonids rely upon a variety
of off-channel habitats that are critical to rearing. All listed salmonids use shallow, low
flow habitats at some point in their life cycle (Table 47). Below we discuss the utility of
the EECs for the current consultation. NMFS presents information that indicates the
EECs do not represent worst-case environmental concentrations that listed Pacific
salmonids may be exposed to. Finally, NMFS provides additional modeling estimates to
evaluate potential exposure in vulnerable off-channel habitats used by salmonids.
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