Measurements of year-long exposure to tree nursery workers using multiple pesticides

Abstract

A year-long nurseryworker pesticide exposure study was designed to measure and evaluate the exposure occurring to workers who had the potential for simultaneous exposure to multiple pesticides. This four-State study was conducted in five nurseries (four USDA Forest Service and one State) involved in conifer seedling production. Primary comparisons were made among nursery workers in the Pacific northwest and south central United States. Worker exposure was assessed by using patches attached to clothing, handrinse samples and urine excreted from potentially exposed workers. In addition, dislodgeable residue in rinsate from a water wash of pesticide-treated seedlings was also evaluated. Four different groups of field workers, designated as applicators, weeders, scouts and packers, were included. The pesticide absorbed dose, assessed by urine analysis of pesticide metabolites and the deposition of pesticide on patches attached to the clothing of field workers, was monitored as they performed their duties under normal conditions (e.g., typical clothing, pesticide application). Monitoring was performed for the 14 different pesticides which were used in these nurseries. Seven pesticides were studied in more detail using biological monitoring. For these compounds, metabolites known to be excreted in the urine of exposed humans or other mammals were used to estimate the dose of pesticide absorbed by the exposed workers. The highest percentage of positive samples came from dislodgeable residue samples (8.3%) followed by patch samples (3.2%), handrinse (2.9%), and urine samples (1.3%). To summarize the conclusions from the urinary excretion data, 12 of the 73 nursery workers in the study received a low absorbed dose of pesticide. Biological monitoring revealed that three pesticides (benomyl, bifenox and carbaryl) were found in the urine of some of the workers. Of the 3,134 urine samples analyzed there were 42 positive; 11 urine samples were positive for benomyl, while bifenox was responsible for 13 positives and carbaryl accounted for the remaining 18. The 12-week continuous monitoring of urine showed that metabolites of these materials were rapidly excreted; thus, no build-up in the body is anticipated. Margins of Safety (MOS) calculations were made to provide an assessment of the significance of the exposure. Based on the low frequency of positive urine samples in the study, the low levels of metabolites when they were found, their apparent rapid excretion rate and the No Observed Effect Level (NOEL) data, furnished from other sources, nursery worker exposure to pesticides in these conifer nurseries is below health threatening levels.