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

NMFS estimates of potential exposure in shallow water habitats used by salmonids
Direct over­spray
To estimate potential exposure of salmon to pesticides in off-channel and other shallow-water
habitats we first determined the initial average concentrations that will result from a direct
overspray of shallow surface water. NMFS is unaware of any circumstances where EPA has
authorized direct application of methomyl to aquatic habitats. However, both carbaryl and
carbofuran may be applied to aquatic habitats. For example, carbaryl is registered for use in rice
crops to control tadpole shrimp and other rice pests. The resulting concentrations in surface
water are a function of the amount applied and the volume of the water body when pesticides are
applied directly to aquatic habitats (Table 51). Carbaryl can be applied twice in rice at a rate of
1.5 lbs a.i./acre. A single application at that rate would result in an average initial carbaryl
concentration of 1,682 μg/L in 10 cm of water. Similarly, EPA estimated aquatic concentrations
of 2,579 μg/L associated with 2 applications of carbaryl at 1.5 lbs a.i./acre in a recent assessment
for the red legged frog (EPA 2007). Specimen labels for carbaryl do not place any restrictions
on rice paddy discharges, yet they warn “discharge from rice fields may kill aquatic and
estuarine invertebrates (EPA Reg. No. 264-333 and 264-349).” Although the section 3
registration for rice was canceled in 1997, the BE indicates carbofuran may still be applied in
rice from use of existing stock or in connection with emergency exemption requests. The BE
indicates it is applied to rice fields prior to flooding at a rate of 0.5 lbs a.i./acre. Assuming this
rate in 10 cm of water results in an average initial average concentration of 561 μg/L.
Carbaryl is registered for use at a rate of 2 lbs a.i./acre in cranberries. Five applications can be
made at 7 d intervals. The label for Sevin brand XLR Plus warns that the “use in cranberries
may kill shrimp and crabs. Do not use in areas where these are important resources (EPA Reg.
No. 264-333).” However, there are no restrictions regarding applications to standing water, or
label requirements to ensure bog water does not contaminate other surface waters. A single
application of 2 lbs a.i./acre to water 10 cm of water results in an initial average concentrations
of 2,242 μg/L.
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