Screening air dispersion modeling approach: Prop 65 community exposure assessments for industrial emitters

摘要

California's Safe Drinking Water and Toxic Enforcement Act (Prop 65) mandates that residents and community members be notified of instances when one or more chemicals listed by the State as either carcinogens or a cause of reproductive toxicity are released to ambient air during operations. Companies do not have to provide a notification if exposure to a listed chemical is below the safe harbor level (SHL) determined by the State. A conservative approach may be used to quantify potential exposure associated with chemical releases to ambient air as part of Prop 65 assessments. This approach includes 1) identification of nearby community receptors, 2) screening-level air dispersion modeling of facility emissions using site-specific industrial hygiene and chemical usage data, 3) estimation of the inhaled daily dose at receptor locations using the modeled airborne concentration, and 4) comparison of the daily doses to the established SHLs. The screening-level approach was applied to a hypothetical manufacturer of industrial goods. It was assumed that the manufacturer was located in a populated area and used an adhesive product containing toluene during the manufacture of their product. Receptors of interest included nearby commercial business employees, construction workers, and residents. Screening air dispersion modeling of toluene was performed using AERSCREEN based on hypothetical facility-specific industrial hygiene ventilation and emission stack data. The toluene emission rate for the hypothetical manufacturer was approximated using USEPA Toxic Release Inventory (TRI) data from the plastics and rubber industry in California. Receptors were modeled at distances between 25 and 500 m from the source. Modeled maximum one-hour airborne concentrations (μg/m~3) were converted to daily doses ((μg/day) by taking into account the receptors' inhalation rates and daily exposure durations. The daily inhalation dose of toluene for each receptor was compared to the SHL of 13,000 μg/day established by the State. All estimated daily doses were at least 15-fold below the SHL at 25 m and well below the SHL at further distances. While the emission parameters were based on a hypothetical facility, the approach in which daily doses were estimated used conservative methods based on Prop 65 and USEPA resources. Exposure assessments of more complex operations (i.e., several chemicals and release points) may be performed using this approach to assess notification requirements under Prop 65 when adequate chemical/product use and industrial hygiene control data are available.