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

Dichloroethanol was detected in the urine of a volunteer after inhalation exposure of DDVP (purity not
specified, a nominal concentration of 38 ug/L) for 105 minutes (Hutson and Hoadley, 1972).
Other Studies
Metabolism in other species (mice, hamsters, and pigs) proceeded at different rates compared to
those for rats, but the metabolites were similar (Hutson and Hoadley, 1972; Page et al., 1971; Potter
et al., 1973a; Potter et al., 1973b; Loeffler et al., 1976).
In vitro studies using rat subcellular fractions showed that DDVP was metabolized by the liver
enzymes in the soluble and mitochondrial fractions (Hodgson and Casida, 1962). Desmethyl DDVP
was found in both rat liver microsomal and cytosolic fractions indicated that demethylation occurred in
both fractions (Hutson et al., 1971). Using rat liver supernatant fraction, Dicowsky and Morello (1971)
showed that the metabolism of DDVP to desmethyl DDVP was glutathione dependent. The hydrolysis
of DDVP to dimethyl phosphate and dichloroacetaldehyde, as well as the metabolism of desmethyl
DDVP to dichloroacetaldehyde and monomethyl phosphate, were glutathione independent.
In a recent study, Holstein cows (3/group) were given DDVP (0, 2, 6, or 20 ppm based on dry matter
in the feed) in capsules by gavage twice daily for 28 days (March et al., 1993). The estimated dosage
based on average amount of DDVP in the capsules for each group and a body weight of 650 kg were
0.062, 0.17, and 0.63 mg/kg-day. Milk samples, as a composite of evening and morning samples
when possible, were collected periodically from days 1 to 28 of the treatment period. Cows were
sacrificed at the end of the experiment and tissues (muscles, fat, liver, and kidneys) were collected.
All milk and tissue samples showed DDVP residue levels at below the limit of quantitation (0.01 ppm).
Cows and goats were treated with DDVP ( 32 P, 67-78% purity) by three routes of exposure (Casida et
al., 1962). Cows were exposed to DDVP by intravenous (1 mg/kg), subcutaneous (1 mg/kg), and oral
(1 or 20 mg/kg) administrations. Goats were exposed to DDVP by subcutaneous (1.52 mg/kg)
injections only. For both species and all routes of exposure, DDVP was hydrolyzed into mono- and
dimethyl phosphates, and to a lesser extent desmethyl DDVP and inorganic phosphate.
Unmetabolized DDVP (recovered in the organosoluble fraction) was found in the milk in the first 2
hours after administration. After 8 hours, the amount of organosoluble products in the milk was below
detection limit as the majority of the radioactivity was due to hydrolysis products. Over 80% of the
dose was excreted in the urine and feces after 96 hours.
Studies conducted on farm animals showed no detected residues in the milk, meat, or meat by
products of cows, goats, and steers sacrificed 1 or more days after single or multiple dermal
applications of DDVP (Shell Chemical Co., 1968). Cows were treated with DDVP after milking. When
hogs were given DDVP (9495 ppm) daily in the diet for 90 days, no residues were found in the tissues
except for the large intestines. Immediately after dosing, the mean residue level in the large intestines
was 0.36 ppm. After 24 hours, the level declined to 0.16 ppm (MDL= 0.02 ppm).
13