The Absorption and Metabolism of C14-Labeled Endosulfan in the House Fly12

Abstract

The absorption rates of technical endosulfan and each of its 4 components were studied by paper and gas chromatography. The toxicant was applied topically to cyclodiene-resistant and susceptible female house flies, Musca domestica L., and recovered as external, internal, and fecal extracts in hexane for chromatographic analysis. Endosulfan ether and endosulfan alcohol were absorbed almost completely in less than 2 hr, while residues of the high- and low-melting point isomers were detectable in external extracts 24 hr after treatment. No difference in the rate of absorption was noted between the 2 strains. Dosage-mortality determinations indicated the following relative toxicity to 3-day-old female flies of both strains low-melting point isomer > technical endosulfan > high-melting point isomer > endosulfan sulfate. Endosulfan ether and endosulfan alcohol were relatively nontoxic. The metabolic fate of C14-labeled endosulfan was studied by the aforementioned means and autoradiography. A previously unreported metabolite found in the internal extracts of both fly strains was identified as endosulfan sulfate, the oxidized form of endosulfan. Endosulfan oxidized in vitro and the metabolite found in internal fly extracts gave identical Rf values and retention times when analyzed by paper and gas chromatography. The identity of this metabolite was further confirmed by microcoulometric gas chromatography and by comparison with purified endosulfan sulfate. Judged from visual inspection of gas chromatograms of internal extracts, the high- and low-melting point isomers were metabolized to endosulfan sulfate, while endosulfan ether and endosulfan alcohol were degraded by a different route. The low-melting isomer was absorbed and metabolized to the sulfate more rapidly than the high-melting isomer. Fecal extracts contained traces of unchanged high- and low-melting point isomers but no endosulfan sulfate, indicating its possible role as an intermediate in the metabolic degradation of endosulfan. Paper chromatograms of fecal extracts revealed a water-soluble metabolite and an acetone-soluble metabolite in both strains of flies, but no hexane-soluble derivatives.