Comparison of whole-body versus snout-only exposure in inhalation toxicity of fenthion.

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Abstract
Toxicity of mist of fenthion (MPP), an organophosphorus insecticide, in rats by whole-body exposure was compared with that by snout-only exposure. During the snout-only exposure, each animal was confined in an animal holder. The 4-hr LC50 of MPP by the whole-body exposure was 0.22mg/l, and that by the snout-only exposure was 1.84mg/l. Results of the acute toxicities of MPP administered by p.o. and s.c. to rats with or without restraint in the holder indicated that the effect of restraint on the inhalation toxicity of MPP caused by the snout-only exposure seemed to be of little significance. Clipping the fur of animals immediately after the whole-body exposure reduced the toxicity. The whole-body exposure caused more marked inhibition of ChE activity of whole blood than the snout-only exposure at the same concentration. The fur clipping after whole-body exposure decreased the inhibition of the ChE activity. The whole-body exposure, the snout-only exposure, and the fur clipping after whole-body exposure caused similar inhibition of the ChE activity after exposure at each LC50. It is concluded that the acute toxicity of MPP mist by the whole-body exposure is 8 times as toxic as that by the snout-only exposure, and the difference may be caused by the chemical intake via non-inhalation route(s) during and after the whole-body exposurd.