Contribution to the toxic action of S-methyl fenitrothion

The toxicity of the S-methyl isomer of fenitrothion was found to be higher than that of both fenitrothion and technical fenitrothion. Repeated administration of the compound showed a rapid decrease in toxicity with decreasing doses.Excretion of p-nitro-m-cresol into the urine of rats was more rapid and the excreted amounts were larger from a single dose of the isomer than from fenitrothion.Single doses of the isomer increased the pentobarbitone sleeping time in mice at both 24 and 48 hr, but showed no change after 4 days. Administration of the isomer and purified fenitrothion to mice for 1 week had no effect on the pentobarbitone sleeping time, nor did a single dose of fenitrothion change the effectiveness of pentobarbitone.Dominant lethal tests in rats revealed a possible mutagenic effect from this compound.The anticholinesterase activity of the fenitrothion S-methyl isomer in vitro was found to be two to three times higher than that of fenitrothion.