Dichlorvos (DDVP) Risk Characterization Document - California ...

G. ENVIRONMENTAL FATE
Summary: DDVP is not likely to persist in the environment since it is volatile, does not bind to soil,
and is hydrolyzed. The half-life of DDVP was 5.2 days in aqueous buffered solution at pH 7. The
half-lives ranged from 9 to 20 days for DDVP in tap water with a pH 7.5 to 8.1. DDVP was also
degraded by soil microorganisms with a half-life of 10.2 hours. After foliar application, DDVP on the
leaves may be volatilized, hydrolyzed, and absorbed into the plants.
Hydrolysis
The half-lives of DDVP ( 14 C, 95% purity, 9-12 ppm) were 12,5, 5.8, and 0.9 days, respectively, in
aqueous buffered solution at pH 5, 7, and 9 after incubation in the dark at 25bC for 28 days (pH 5), 38
days (pH 7), or 3 days (pH 9) (Vithala, 1990a). The metabolites detected were 2,2-
dichloroacetaldehyde, des-methyl DDVP, glyoxylic acid, and 2,2-dichloroacetic acid. However, the
half-life of DDVP in tap water (pH 7.5-8.1) was longer at 9-20 days (Leafe and Feiler, 1988).
Microbial Degradation
DDVP ( 14 C, 97% purity, 12 ppm) was added to non-sterilized sandy loam soil and incubated in the
dark at 25bC under aerobic conditions (Vithala, 1990b). The half-life for DDVP in the soil was 10.2
hours. After 96 hours, DDVP residue was not detectable. The non-volatile metabolites were 2,2-
dichloroacetic acid (major metabolite), 2,2-dichloroacetaldehyde, and dichloroethanol. The only
volatile metabolite detected was CO 2 which at 360 hours was 60% of the initial DDVP concentration.
Mobility (Soil, Air, Plants)
In a soil mobility study, DDVP ( 14 C, 87% purity) was mixed in soil and water (1:4). After 3 hours of
incubation, DDVP residues remaining in sandy, silt, and clay soils were 8, 12, and 24% of the initial
concentrations, respectively (Vithala, 1990c). Desorption experiments showed that DDVP was
released from the soil.
DDVP was not found in well water samples from 17 California counties monitored from 1986 to 1992
(DPR, 1992). The minimum detection limit (MDL) for the studies ranged from 0.005 to 1 ppm with
more than 50% of the samples analyzed at a MDL of 0.1 ppm.
Application of DDVP (0.5 g/1000 cubic ft) by aerosol in a warehouse experiment showed that DDVP
was rapidly dissipated (Knight, 1985). The air concentration of DDVP declined from 17.1 mg/m 3 after
1 hour to 0.12 mg/m 3 after 16 hours.
The release of DDVP from resin strips to the ambient air was dependent on ventilation, air
temperature, and humidity. Under conditions of domestic use, the air concentrations of DDVP
increased rapidly with a highest mean concentration of 0.04 mg/m 3 at 1-2 weeks after placement
(Elgar and Steer, 1972). Three months after placement, the mean concentration in the air declined to
0.01 ug/L.
Plant Residues/Metabolism
Multiple (1-5) applications of DDVP (Vaponite , 4 pounds/acre) on figs showed that there was an
accumulation of residues 5 days after treatment (Rutgers University, 1981). The range of residue
levels in fresh figs was of