The distribution of malathion and some of its metabolites in tissues of the american cockroach, Periplaneta americana

Abstract

1. The American cockroach was treated by topical application of 14C-malathion. The distribution of the label within the body tissues was found to be both rapid and extensive. 2. As much as 40% of the applied label was still present superficially in the cuticle even 24 hr post-application. 3. The overall tissue ranking order for 14C label was found to be: foregut > digestive tract contents > skeletal muscle > fat body > hindgut > midgut > nerve cord > brain > malpighian tubules. 4. Malathion, malaoxon and malathion monoacids were detected in the nerve cord plus brain, the digestive tract, skeletal muscle and fat body at 1, 2 and 24 hr after topical application of the insecticide. 5. At 24 hr post-application a significant proportion of malathion remained unmetabolised in all tissues examined. The highest levels of metabolic transformation were found in the digestive tract and fat body. 6. Insects were prostrate 24 hr after topical application of 14C-malathion. In these insects the greatest concentration of malathion and monoacids (expressed in relation to unit tissue wt) was found in the digestive tract. On the other hand, the nerve cord and brain contained the greatest concentration of malaoxon. 7. About 18% of applied 14C-malathion label partitioned into the tissue aqueous phase up to 24 hr after topical application but very little applied label was expired as 14CO 2 or excreted. 8. Although a neurotoxic action may be the cause of prostration and death, the extensive dissemination of malathion and its products belies the concept of any tissue specificity. 9. The haemolymph, after an initial sharp rise in malathion content, maintained a steady malathion level over the 24 hr experimental periods suggesting that the haemolymph is the main distributor of the insecticide to the various body tissues.