Yoshimi Misu

Subacute toxicity of O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate (Sumithion) in the rat

Abstract To observe the subacute toxicity of Sumithion, 6 groups of male Wistar rats were fed for 90 days with control food and food containing 32, 63, 125, 250, and 500 ppm of the compound. Rats in the 500-ppm group showed significant inhibition of growth and various cholinergic signs for the first 2 or 3 weeks. Thereafter, they showed a clear recovery in growth and appearance. However, there were significant differences in mean body weight and food intake between the control and 500-ppm groups even at the end of 90 days. The testis- and brain-body weight ratios were higher in this group than in control groups at the end of 11, 30, 60, and 90 days. Rats in groups dosed with 250 ppm or less showed almost no changes by these measures. The decrease of cholinesterase activity in the kidney, liver, red blood cells, and plasma was dependent on the concentration of Sumithion in the diet, was somewhat delayed in its time course compared with the appearance of cholinergic signs or inhibition of growth, and showed a tendency to recover after the 30th to 60th day of feeding. The decrease in activity of the brain cortex enzyme was much less and was earlier in its appearance than in the case of the other tissues. Histopathologic observation revealed almost no significant differences between the control and each of the Sumithion-dosed groups. Sumithion had no effects on the excretion of urinary sugar and protein. There were no significant differences in the content of norepinephrine and 3-hydroxy-tyramine in the liver, spleen, and brain stem between the control and 500-ppm groups.