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

Metabolites and degradates of carbaryl, carbofuran, and methomyl
Available monitoring data for some metabolites and degrades of the three a.i.s in surface water
are presented above. The BE indicates that degradation studies show 1-naphthol is found at up
to 67% of the applied carbaryl. It is also formed in the environment by degradation of
naphthalene and other polyaromatic hydrocarbon compounds. EPA suggests that salmonid
exposure to 1-naphthol is expected, particularly in alkaline waters, but indicates exposure to
aquatic organisms cannot be calculated due to lack of environmental fate and transport data for
this degradate.
The major transformation product of carbofuran in water is 7-phenol (EPA 2004). The BE
indicates other transformation products have the potential to reach the aquatic environment,
including 3-hydroxycarbofuran and 3-ketocarbofuran, and that these typically occur in small
amounts and are relatively short lived as compared to the parent. The major degradate in a soil
metabolism study was 3-ketocarbofuran, which peaked at 12% of the amount applied after 181
days.
Several transformation products were also identified in the methomyl BE (EPA 2003). CO2 was
identified as the major degradate in most metabolism studies. S-methyl-Nhydroxythioacetamidate
was identified as a highly mobile product of alkaline hydrolysis. In an
aquatic metabolism study, after 7 d, acetonitrile comprised a maximum of 17% and acetamide up
to 14% of the amount of methomyl applied. After 102 d, volatilized acetonitrile totaled up to
27% of the applied methomyl.
The BEs recognized that listed salmonids are likely exposed to several metabolites and
degradates of the a.i.s. However, estimates quantifying exposure to these transformation
products were not provided and remain a considerable source of uncertainty.
Other ingredients in formulated products
Registered pesticide products containing carbaryl, carbofuran, and methomyl generally include
other ingredients such as carriers and surfactants. NMFS searched NPIRS and located several
pesticide products that contain multiple a.i.s. NMFS located several labels of currently
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