Malathion (0,O-dimethyl S-[{1,2-bis-carbethoxy] ethyl phosphorodithioate) 
Accumulation of malathion or its metabolites in the tissues of 
hens fed labeled malathion was slow. Two to three per cent was 
excreted unchanged or as chloroform-soluble metabolites. Ninety- 
seven to ninety-eight percent is excreted as ionic water-soluble 
metabolites. Of the tissues examined, liver and kidney contained the 
greatest amount of radioactive compounds. The level of radioactivity 
remained constant for a week after withdrawal from the malathion- 
fortified feed and then slowly decreased. The amount of radioactive 
compounds decreased more rapidly in the white than in the yolk of 
the egg (March et al., 1956a). 
Apparently two major degradative pathways occur in mammals: 
that involving carboxy esterases and that involving phosphatases. The 
differences in the activity of these two systems, in mammals as 
against insects, helps account for the difference in toxicity. [In 
the urine of cows, the principal metabolite was Hareehion monoacid; 
the diacid became more important with time. Desmethyl malathion was 
also found. In fecal matter, malaoxon, dimethyl phosphate, and | 
0,O-dimethyl phosphorothioate were found (March et al., 1956b; Wells 
et al., 1958; Weidhaas, 1959; O'Brien et al., 1961b; Pasarela et al., 
1962). Other studies with rats and dogs have shown the presence of 
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