MALATHION AND MALAOXON ENVIRONMENTAL LEVELS USED FOR EXPOSURE ASSESSMENT AND RISK CHARACTERIZATION OF AERIAL APPLICATIONS TO RESIDENTIAL AREAS OF SOUTHERN CALIFORNIA, 1989-1990

Between August 1989 and July 1990, California conducted a Mediterranea n fruit fly eradication project in southern California which included repeated aerial applications of malathion bait to urban areas where ap proximately 1.6 million people resided. Concern about the safety of th ese applications prompted the California Department of Health Services to prepare a risk assessment. The current work presents the estimates of environmental levels of malathion and malaoxon, derived from mass deposition rates during application and monitoring of air. We estimate d short and long-term malathion and malaoxon levels on outdoor surface s, plants, and soils (0.1 and 1.0 cm mixing depth), using a simple fir st-order exponential decay model and literature half-life values rangi ng from three to nine days. Direct monitoring data were used to charac terize short-term air levels, Average and upper-bound malathion levels immediately following an application were 0.091 mug/m3 and 0.207 mug/ m3 in air; 22 and 52 mg/m2 on outdoor surfaces; 3.8 and 9.6 mug/g in p lants; and 1.5 and 3.5 mug/g in soil (1 cm mixing depth). Malaoxon lev els were 0.039 mug/m3 and 0.110 mug/m3 in air; 0.15 and 0.46 mg/m2, 0. 03 and 0.09 mug/g, and 0.01 and 0.03 mug/g, respectively. Estimates of average and upper-bound levels over the duration of the eradication p rogram were roughly one-third the immediate levels in all media. No fi eld measurements were available for co-products other than malaoxon,fo r environmental persistence, or for concentrations on surfaces, soil, or plants after repeated applications. Because of limited monitoring d ata, and the likelihood that similar pest-eradication programs will be conducted, additional studies are warranted to more accurately charac terize the environmental fate of malathion and human exposures after a erial application to residential communities.