Malathion deposition, metabolite clearance, and cholinesterase status of date dusters and harvesters in California

Date gardens in the Coachella Valley in California typically receive multip le treatments of malathion to control major insect pests. Variable amounts of malathion dust retention by skin and clothing and individual work behavi ors limit the usefulness of clothing as an exposure dosimeter in date duste rs and harvesters. To determine malathion absorption in workers, urine clea rance of dimethyl phosphates (alkyl phosphates; AP) and malathion mono- (MC A) and di- (DCA) acids were estimated from date dusters (loaders/applicator s) and harvesters (both on ground and high in trees). A series of self-admi nistered doses of malathion were either ingested in gelatin capsules or app lied to the volar surface of the forearm to guide biomonitoring. Each of th e dimethyl phosphates (dimethylthio- > dimethyldithio > dimethyl-) and both malathion mono- and diacids were present in urine as soon as 2-3 h of work . On a micromole basis dimethylthiophosphate and the malathion acids (MCA > DCA) were the most prominent metabolites in urine. Applicator exposures ra nged from 95-210 mg equivalents per day (1-3 mg/kg-day). Harvester exposure s ranged from 1-270 mu g/kg-day. Mid-season Monday morning urine specimens before work contained low or unmeasurable levels of malathion acids, indica ting that malathion is rapidly metabolized and cleared from the body in the urine. Saliva was not useful for biomonitoring. No inhibition of cholinest erase activity was measured in any members of two separate crews of harvest ers who had previous prolonged dust exposure (1 and 2 months).