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

Carbaryl dissipates in the environment by abiotic and microbially mediated degradation.
The environmental fate characteristics for carbaryl are listed below (Table 44).
Table 44. Environmental fate characteristics of carbaryl (EPA 2003).
Parameter Value
Water solubility 32 mg/L at 20 deg C
Vapor pressure 1.36 10-7 torrs
Henry's law constant 1.28 x 10-8 atm m3 /mol
Octanol/Water partition Kow = 229
Hydrolysis (t1/2) pH 5, pH 7, and pH 9 Stable, 12 days, 3.2 hours
Aqueous photolysis (t½) 21 days
Soil photolysis(t½) assumed stable
Aerobic soil metabolism (t½) 4 days - sandy loam soil
Anaerobic soil metabolism (t½) 72 days
Aerobic aquatic metabolism (t½) 4.9 days
Anaerobic aquatic metabolism (t½) 72 days
Koc
177- 249 ml/g
Fish are most likely to be exposed to carbaryl through direct uptake of the chemical from
the water column and across the gills, although other routes of exposure may also be
important. Potential exposure routes for aquatic organisms include direct uptake from the
water column or pore water of sediment, incidental ingestion of the chemical in sediment,
or ingestion of the chemical in food items. EPA asserts that “carbaryl is not expected to
bioaccumulate” and reports a bioacculation factor of 45 (EPA 2003). Other sources
suggest accumulation of carbaryl can occur in fish, invertebrates, algae and plants.
Residue levels in fish can be 140 fold greater than the concentration of carbaryl in water
(http://pmep.cce.cornell.edu/profiles/extoxnet/carbaryl-dicrotophos/carbaryl-
ext.html#14). In general, due to its rapid metabolism and rapid degradation, carbaryl
should not pose a significant bioaccumulation risk in alkaline waters. However, under
conditions below neutrality accumulation of carbaryl may be significant
(http://pmep.cce.cornell.edu/profiles/extoxnet/carbaryl-dicrotophos/carbaryl-
ext.html#14).
EPA reports the major degradation products of carbaryl are CO2 and 1-naphthol, which is
further degraded to CO2 (EPA 2003). Carbaryl is stable to hydrolysis in acidic conditions
but hydrolyzes in neutral environments. Hydrolysis rates increase with increasing
alkalinity. Carbaryl is degraded by photolysis in water with a half-life of 21 days (d).
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