Predicted 1,3-dichloropropene air concentrations resulting from tree and vine applications in California

The preplant soil fumigant 1,3-dichloropropene (1,3-D) is effective for nematode control and is expected to further replace methyl bromide (MeBr) as MeBr use is phased out. Acute human exposure to soil fumigants is managed in part by using buffer zones between treated fields and occupied structures. The required buffer zone for 1,3-D in California is 91.4 m (300 ft) for all uses. However, a 30.5-m (100-ft) buffer setback is desired for 1,3-D to be an important replacement for MeBr in the orchard and vineyard markets. The Industrial Source Complex Short-Term model, Version 3 (ISCST3) was used to simulate township-wide long-term average and short-term air concentration distributions of 1,3-D. The Gaussian plume model ISCST3 can be used to assess dispersion of air pollutants and pollutant concentrations on receptors from a variety of sources and in diverse airsheds. Long-term and daily-average air concentrations can be compared with the California permitted chronic or acute toxicity endpoints, respectively, to assess the potential risk for individuals living within the township at the proposed buffer setback. Modifications to ISCST3 were made for specific nonpoint-source agricultural constraints and management practices. Chronic and acute air concentration distributions of 1,3-D with a 30.5-m buffer constraint around treated fields are similar to currently permitted air concentration distributions in California. Refinement of exposure as a function of buffer distance, application rate, and field size is possible due to the resolution of the simulation and external post-processing capabilities. Simulated examples of 1,3-D acute and chronic exposure cumulative distributions are presented.