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

habitat had a downwind width of 10 m. Pesticide concentrations were predicted for habitats that
ranged in depths from 0.1 to 2 m. These dimensions were assumed based on research of
salmonid use of off-channel habitats (Beechie et al. 2005, Henning 2006, Montgomery 1999,
Morley S. A. et al. 2005, Roni 2002). Average initial concentration estimates derived from the
simulations ranged from 0.2-447 μg/L for each lb of a.i. applied. These simulations indicate that
applications of several lbs a.i. per acre adjacent to some off-channel habitats could result in
aquatic concentrations exceeding 1 mg/L, a value that would result in substantial toxicity to
aquatic life, including deaths of exposed salmonids.
Maximum rates of carbaryl permitted for most vegetable crops range from 1-2 lbs a.i./acre.
Several tree crops allow much higher application rates (3-8 lbs a.i./acre), with a maximum single
application rate of 12 lbs a.i./acre approved for use in California on citrus crops. Carbaryl may
be applied by ground boom, chemigation, spray blast, and aerial spray applications. Considering
application rates, methods, and no requirements for buffers to aquatic habitat, the estimated
initial concentrations of carbaryl in surface waters range from 3 μg/L to 7 mg/L in the modeled
habitats. Voluntary buffers recommended by CDPR for protection of federally listed fish would
considerably reduce the deposition. For example, drift from aerial applications with the 600 ft
buffer to a 10 m wide stream are predicted to be approximately equivalent to 2-6% of the applied
rate versus drift equivalent to 30-39% of the applied rate with no buffer. Additionally, drift from
ground application with the 120 ft buffer predict drift equivalent to 0.3 – 2% of the applied rate
versus 7-23% of the applied rate predicted with no buffer.
Current carbofuran labels reviewed by NMFS specify application rates of 1 lb a.i./acre or less for
most crops. Carbofuran can be applied by both ground and aerial methods. Simulations
assuming no aquatic buffers at these rates provide estimates of initial average carbofuran
concentrations from the low μg/L range to several hundred μg/L. The carbofuran BE indicates
several 24(c) uses have previously allowed application of carbofuran at rates as high as 10 lbs
a.i./acre. Simulations indicate that application rates in this range, with no buffer restrictions,
would result in initial surface water concentrations of 2 μg/L to over 4,000 μg/L.
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