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

In an aqueous photolysis study carbofuran photodegraded in neutral water (buffered [pH
7] solution) at 25ºC with a half-life of 6 d. In a soil photolysis study, carbofuran
photodegraded with a half-life of 78 d on a sandy loam soil. Carbofuran is moderately
persistent to microbial degradation, with half-lives on the order of a year. Near-surface
photolysis is significant under laboratory conditions in aqueous solution, with a half-life
on the order of days (EPA 2004).
Methomyl
Methomyl is a broad spectrum insecticide approved for a variety of terrestrial use sites.
Use in aquatic habitats is not permitted. EPA characterized methomyl as moderately
persistent and highly mobile suggesting methomyl may contaminate surface waters
through runoff, erosion, leaching, and spray drift from application at upland sites (EPA
2003).
Potential exposure routes for fish and other aquatic organisms include direct uptake of the
chemical from the water column or pore water of sediment, incidental ingestion of the
chemical in sediment, or ingestion of the chemical in food items. Methomyl
bioaccumulation has not been studied in fish, although it is expected to be relatively low
given low octanol/water partition coefficients (Kow ranges from 1.29 to 1.33, Table 46).
Methomyl degradation occurs through metabolism and photolysis. Site-specific factors
affecting the persistence of methomyl include aerobicity, organic matter and soil moisture
content, exposure to sunlight, and pH. Climate, crop management, soil type and other
site-specific factors also influence leaching and runoff.
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