Worker exposure and a risk assessment of Malathion and Fenthion used in the control of Mediterranean fruit fly in South Australia

Abstract

In 2001, an outbreak of Mediterranean fruit fly in Adelaide was controlled by South Australian Government workers applying organophosphorus insecticides (OPs) to domestic gardens. Residents made claims of adverse effects associated with allegations that worker application practices were poor and led to contamination of homes, residents and pets. The concerns led to a Parliamentary enquiry, the suspension of OP applications for fruit fly control, and the investigation of alternative methods of combating fruit fly in metropolitan Adelaide. The extent of exposure of workers and residents was not estimated. This paper describes a simulated application of the OPs concerned (fenthion and malathion) with measurements of potential exposure through inhalation, dermal contact and deposition of pesticides on surfaces. The data were used as part of a toxicological risk assessment to determine the likely impact of the use of these insecticides. Malathion, used as a 1% suspension in a protein bait mixture, was found to have little potential for airborne exposure, although some workers were found to have up to 0.315 microg/cm(2) malathion deposited on overalls (principally on forearms) and over 500 microg deposited on liner gloves and hats, respectively. Risks to workers and residents were low, with exposures likely to be a small fraction of the acceptable daily intake. Fenthion, used as a 0.05% foliar cover spray, was found between 0.02 and 0.23 mg/m(3) in air 10 m downwind from spray activity and was unlikely to pose a significant risk to residents, since exposures were of short durations of up to 20 min. Personal air samples of spray workers averaged 0.55 mg/m(3) (Workplace Exposure Standard 0.20mg/m(3)). Since workers were usually engaged in spraying for a large proportion of the day, this demonstrates the need for respiratory protective equipment. Maximum deposition of fenthion on workers overalls ranged from 0.06 to over 0.20 microg/cm(2), although little was found on gloves and hats, suggesting workers were skilled in avoiding the plume of overspray. Dialkyl phosphates (metabolites of OP insecticides) were not detected in urine of workers, and there were no changes observed in serum cholinesterase (SChE) enzyme activities 24h following the simulation. These data suggest absorption of OP insecticides by workers was negligible. Deposition on surfaces 5 and 10 m downwind ranged from none detected to 145 microg/cm(2), suggesting that exposure of residents and children in contact with contaminated surfaces (such as garden furniture or play equipment) is possible. Estimates of the potential dermal intake of fenthion by children from contaminated surfaces suggested that risks of acute and chronic effects are slight, since exposures may occur for short periods at intervals of approximately 10 days during fruit fly outbreaks.