Toxicological potential of malathion residues in stored soybean seeds

Succinate-14C-malathion penetrates readily into soybean seeds. The total internal residues inside the seeds amounted to 58-65% of the applied dose after 30 weeks, of which 8-9% were in the form of bound residues. The major part of the internal methanol extractables are chloroform soluble metabolites which include malathion (about 60%), monocarboxylic acid (15%) and its decarboxylation product (8%). The water soluble metabolites contained only one radioactive substance, namely malathion dicarboxylic acid. The toxicological potential of the total internal residues was studied by feeding mice with the washed seeds for about 2.5 months. Treated mice suffered from deterioration of hepatic and renal function as indicated by the observed increased level of blood serum esterases and blood urea nitrogen. The results of blood biochemistry are supported by the histopathological changes observed in the liver, kidney, stomach and intestine. The organs showed degenerative changes including leucocytic aggregation, congestion and dilatation of blood vessels. Other adverse effects caused by malathion residues are indicated from cytogenetic studies on bone marrow of treated mice. Studies showed an initial bone marrow toxicity as indicated by increase in percentage of polychromatic erythrocytes over controls. This effect diminished upon prolongation of feeding period over one month. Feeding with malathion residues affected a gradual increase, with feeding period, in the percentage of polychromatic erythrocytes with micronuclei, a parameter recommended for detecting chemical mutagenes in animal test systems.