Dimethylphosphorus metabolites in serum and urine of persons poisoned by malathion or thiometon.

The urinary excretion rates of dimethyl-phosphate, -phosphorothioate and -phosphorodithioate were studied in six persons of whom four had ingested a concentrated solution of malathion and two of thiometon. The concentration decrease of single and total dimethylphosphorus metabolites was biphased, with a fast initial rate and a slow later rate. The excretion rate of total metabolites in the faster phase depended on the initial concentration in urine. At concentrations higher than 100 nmol/mg creatinine, the excretion half-times ranged from 7.5 to 15.4 h and at concentrations between 52 and 95 nmol/mg creatinine from 34.7 to 55.4 h. Non-metabolized malathion was detected only in one urine sample collected from one person immediately after hospitalization. Two persons poisoned with malathion were taken blood serum samples for the analysis of the parent pesticide and its metabolites on a daily basis after hospitalization. The parent pesticide was detectable in the serum only one day after the poisoning. The concentration of total malathion dimethylphosphorus metabolites in serum decreased very quickly within 1.5 days after hospitalization. The total metabolite elimination half-times were 4.1 and 4.7 h in the initial phase, and 53.3 and 69.3 days in the later slower elimination phase. There was no correlation between maximum concentrations of total metabolites measured in serum and/or urine on the day of admission to hospital and the initial depression of serum cholinesterase (BChE, EC 3.1.1.8) and erythrocyte acetylcholinesterase (AChE, EC 3.1.1.7).