Insecticide Metabolism, Metabolism of 2,2-Dichlorovinyl Dimethyl Phosphate in Relation to Residues in Milk and Mammalian Tissues

Abstract

The metabolism and residues of 2,2-dichlorovinyl dimethyl phosphate-P32 (DDVP or Vapona) were examined with rats, cows, and a goat. Studies with rats also utilized carbon14 labeled DDVP, dichloroacetaldehyde, and dichloroethanol, and phosphorus32-labeled O-methyl 2,2-dichlorovinyl phosphate and , -dimethyl phosphate. In addition, several rats and a single cow were treated orally with 1,2-dibromo-2,2-dichloroethyl dimethyl phosphate-P32 (Dibrom). These insecticides are rapidly hydrolyzed in mammals to yield no persisting tissue residues and only trace levels in milk. The initial phosphoruscontaining metabolites of DDVP, , -dimethyl phosphate and O-methyl 2,2-dichlorovinyl phosphate, are low in toxicity and rapidly excreted or further degraded. The 1 -carbon of the 2,2-dichlorovinyl group in DDVP is excreted in urine predominantly as a conjugate of dichloroethanol, probably the glucuronide, in the feces as unknown derivatives, and in the expired air as carbon dioxide. Small amounts of dichloroacetic acid may be formed, and some of the C14 persists in liver, blood, and other tissues in an unidentified form. Limited metabolism studies of DDVP in plants and of DDVP and Dibrom in bovine rumen fluid are also reported.

Opinion of the Scientific Panel on Plant protection products and their residues (PPR) related to the evaluation of dichlorvos in the context of Council Directive 91/414/EEC

“…60-70 % of radioactivity from [ 32 P] dichlorvos was recovered in urine and 10 % in faeces of rats within 7 days (Casida et al, 1962). In other animals (mice, goats, cows) this ratio was similar.…”

“…was 1 % after one day of the peak seen in the stomach after one hour (in liver after 1 hour the dichlorvos content was 50% of stomach and declined to ca. 15 % after one day) (Casida et al, 1962, DAR, 2003.…”

Residue Reviews

“…As detailed in section IV and illustrated in Figure 1, the principle exposure to DDVP from resin strips is by inhalation, but it may also occur by oral and dermal routes. Initial studies (CASIDA et al 1962, HODG-SON andCASIDA 1962) indicated hepatic metabolic pathways (Fig. 7) that became the classical biochemical description of the fate of DDVP.…”

“…The resultant S-methyl glutathione is degraded to mercapturic acid and excreted. MDVP may be excreted (CASIDA et al 1962) in urine following injection of DDVP, but is hydrolyzed to methyl phosphate and DCA following inhalation or oral exposure to DDVP. Urinary excretion of substantial quantities of DMP, lesser amounts of methyl phosphate, and traces of inorganic phosphate account for the majority of phosphorus-containing metabolites (CASIDA et al 1962).…”

“…Substantial amounts of radioactivity from 1-14 C-vinyl-Iabeled DDVP appear as 14C-carbon dioxide (30 percent), 14C-glycine, 14C-serine, and a host of normal cellular constituents (nucleic acids, phospholipids, steroids, proteins, carbohydrates) . The rapid disappearance of intact DDVP measured by TLC of blood and tissue extracts may not have been recognized by CASIDA et al (1962), because the latter used 2,4-dinitrophenylhydrazine to trap DCA and with whim glyoxal would also react.…”