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

average initial concentration from drift to a body of water that is 2 inches deep (~ 5 cm) and 10
m wide would be 771 µg/L. It seems highly unlikely that helicopter applications would be able
to successfully avoid direct overspray of some of the marine fish habitats on the exposed
mudflats. Additionally, the 24(C) labels do not contain buffer zone restrictions. A direct
overspray of 2 inches of water would result in an average initial concentration of approximately
18 mg/L, a concentration comparable to measured concentrations associated with initial tidal
inundation of treated mud flats (see surface water detections above). Acute exposure to these
concentrations are expected to kill a portion of exposed salmonids in a matter of hours i.e., 24 h
LC50s for carbaryl range from 948-8,000 μg/L, n= 60 (Mayer and Ellersieck 1986), and
significantly reduce AChE activity that will lead to myriad sublethal effects such as impaired
swimming.
Table 70. Estimated fish mortalities resulting from carbaryl applications in Willapa Bay and Grays
Harbor, Washington
Year Maximum Application Rates* Total Acres Treated** Fish Killed
1986 ≤ 7.5 lbs a.i./acre 398 14, 954
1987 ≤ 7.5 lbs a.i./acre 434 8,041
* Current 24(c) label allows for application of up to 8 lbs a.i./acre
** Current NPDES permit allows for a total of 600 hundred acres to be treated in Willapa Bay and Grays
Harbor, WA. The Label places no restrictions on acres or geographic restrictions for use of carbaryl on
Oyster beds in Washington.
Salmonids were not reported in the sampling data, which was taken over two seasons. The
authors report that the fish kills were extremely variable and unpredictable. The fish mortality
reported for transect surveys included only four species in 1986: saddleback gunnel, threespine
stickleback, staghorn sculpin, and arrow goby. In 1987, mortalities included English sole, sand
sole, kelp greenlings, shiner perch, saddleback gunnels, staghorn sculpin, and arrow goby.
Response of benthic community
Samples were collected in 1985 to assess impacts of carbaryl on the intertidal invertebrate
community (Tufts 1990). Treated area showed decreases in numbers of infaunal benthic
crustaceans at 15 and 30 d post-treatment while a concurrent increase in crustacean abundance
was observed on control plots (Table 71). Abundance of benthic crustaceans was low on both
control and treated plots 5 months after application in December. The authors suggest the data
may represent a seasonal decline in benthic crustaceans.
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