Occupational exposure and drift hazard during aerial application of paraquat to cotton

Abstract

Two worker-exposure and drift trials were conducted during the aerial application of paraquat to cotton in California, USA. The dermal and respiratory exposure of pilots, flaggers, and a mixer-loader was shown to be low. Dermal exposure ranged from 0.05 (pilot) to 2.39 (flagger) mg/ hr. The dermal exposure of the mixer-loader was similar to that of the pilots. No respirable paraquat was detected in the breathing zone of any worker. The highest total paraquat concentration was 26.3 μg/m³ for a flagger, which is a factor of 19 less than the TLV for total paraquat. The combined dermal and respiratory exposure of this flagger was equivalent to 19.4 mg/8hr working day. Paraquat drift concentrations decreased with increasing distance downwind of the spray application. The highest concentrations of total and respirable paraquat were 16.7 and 0.15 μg/m³ at 50 m from the application site perimeter. The respective concentrations at 1600 m downwind were 0.5 and 0.01 μg/m³. Measurement of the particle size distribution of paraquat drift showed that 0.95 to 1.96% of spray droplets was within the respirable range at all distances downwind. The highest percentage of respirable droplets was equivalent to 1.2 (μg paraquat, which was measured at 400 m downwind. Respirable fractions of 1 and 0.95% were measured at 50 and 100 m downwind, which represented 1.8 μg paraquat. There was no evidence, therefore, of a toxic hazard to pilots, ground crew, and downwind bystanders, as a consequence of the aerial application of paraquat.