Contribution of aerosols generated during mixing and loading of pesticides to operator inhalation exposure

The occupational exposure resulting from the application of crop protection agents continues to be of great interest for the purposes of identifying hazards or determining safer chemical handling methods. The purpose of the present study was to identify the potential respirator exposure of a mixer/loader to chlorothalonil, with the mixing and loading operation as the only source of aerosols (particles <13 microm diameter). Three worst-case mixing/loading scenarios were simulated in the lab: (1) a spill of undiluted chlorothalonil formulation onto a dry, horizontal metal surface; (2) a spill of undiluted chlorothalonil formulation onto a rapidly rotating shaft; and (3) pouring undiluted chlorothalonil formulation into a container of water. Aerosol generation from these scenarios was compared to that resulting from atomizing dilute chlorothalonil through hydraulic nozzles. Aerosols were captured with a cascade impactor, and quantified by gas chromatography. Results indicated that simulated spill scenarios generated aerosol concentrations between 2.1 and 5.3 ng/l, which were in the same order of magnitude as, and only marginally higher than, the detection threshold (1.7 ng/l) and background levels (2.2 ng/l). In comparison, atomization of dilute chlorothalonil through a hollow cone and flat fan nozzles resulted in airborne concentrations of 354 and 96 ng/l, respectively, related to the atomization characteristics of these nozzles. Measurement of the dimensions of the aerosol cloud indicated that aerosols resulting from a spill amounted to approximately 10(-5)% of the spilled chlorothalonil. It was estimated that a male worker respiring 29 l/min would inhale approximately 0.32-0.78 ng of chlorothalonil during a typical 30 s spill, assuming a 1% transfer efficiency between the spill site and the mixer/loader. These estimates were between 10000 and 480000 times less than literature data for respiratory exposure of chlorothalonil by applicators and harvesters, suggesting that inhalation of aerosols from mixing and loading represents a minor component of overall exposure.