Proceedings of the Vertebrate Pest Conference

An industrial hygiene study was conducted to monitor levels of phosphine gas exposure of applicators and bystander environment during use of aluminum phosphide tablets where used to treat rodent burrows, or when entering treated fields and adjacent buildings. State-of-the-art Draeger Pac III monitoring units and Draeger Phosphine Badges were placed on 33 applicators using Fumitoxin® tablets to treat ground squirrels (Spermophilus spp.) and pocket gophers (Thomomys spp.). Applicators represented both frequent and infrequent users. Agricultural and urban area applicators and bystander conditions in 9 California counties were monitored. Bystander sites were monitored with the Pac III data logging equipment. Thirty concrete slab or raised foundation buildings and 9 outdoor park and almond or walnut production sites were monitored for phosphine gas. No applicator phosphine exposures were above either the permissible 8-hour Time Weighted Average (TWA) of 0.3 ppm (Permissible Exposure Limit - PEL), or the 15-minute Short Term Exposure Limit (STEL) of 1.0 ppm. Higher exposures were observed for non-certified infrequent users than for certified or non-certified frequent applicators. The average TWA for applicators was 0.035 ppm, about 10% of the PEL. Label directions are satisfactory to avoid excessive worker exposure and environmental impact. Several work practices were associated with higher exposure potential, and recommendations were made for their mitigation to further reduce exposure. All exposures to PH3 were related to poor handling procedures that could be avoided by following the label and proper training. Average PH3 levels at potential bystander sites inside and outside residences were well below the 0.3 ppm TWA. No building registered over 10% of the PEL. In the outside trials, there were only 2 Pac III readings of over 100 that indicated detectable 8-hour TWAs at ground squirrel sites. The sites were very heavily infested, and PH3 only slightly exceeded 10% of the PEL. No PH3 was detected above pocket gopher burrows in any field site. When used according to the current label, the potential PH3 exposures of applicators and bystanders are low relative to the Low Observed Adverse Effect Level and are within existing occupational standards. Training was associated with lower worker exposures of certified applicators and non-certified frequent users compared to non-certified infrequent users.