Department of Public Health Sciences

Identification of agricultural tasks important to cumulative annual exposure to dust, endotoxin and crystalline silica

Wu, J. D., M. J. Nieuwenhuijsen, S. J. Samuels and M. B. Schenker

American Industrial Hygiene Association Journal. 1999. IN PRESS.

Little data exist on the determinants of agricultural dust exposure, particularly, in dry climates. We collected field data in California over several years on the exposure of farmers and farm workers to dust occurring during the conduct of specific tasks. The field data were supplemented in some cases with task-based exposure data from the literature. In all, estimates of short-term exposure concentration were obtained for 42 tasks which were then merged with task duration and frequency data obtained by questionnaire from 546 farm operators to estimate integrated annual exposures to total dust, endotoxin and crystalline silica. Estimates of both inhalable and respirable fractions were calculated for each of the three agents. These annual exposure data were then analyzed to determine which tasks were the major contributors to the annual exposure for each agent. The procedure used to identify the important tasks involved comparisons of the cumulative distributions of exposures for all tasks with the cumulative distributions with one task exposure removed. Field supervision and mechanical mowing of weeds were common tasks important to the exposure to all three agents. There were some tasks which were important only for the exposure to a particular agent or to the inhalable or respirable component of the same agent exposure. The variability of exposure duration observed in this study was much higher than that of exposure intensity. The tasks identified to be important to agricultural exposure may be ascribed to exposure duration more than to exposure intensity. Information on task specific exposure is important for developing control strategies in the agricultural workplace.

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