Evaluation of recommended REACH exposure modeling tools and near-field, far-field model in assessing occupational exposure to toluene from spray paint.

Predictive modeling is an available tool to assess worker exposures to a variety of chemicals in different industries and product-use scenarios. The European Chemical Agency (ECHA)'s guidelines for manufacturers to fulfill the European Union's legal requirements pursuant to the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) initiative include recommendations for the use of modeling to predict worker exposures. ECHA recommends different models for different target populations (i.e. workers, consumers, environment) and routes of exposure (i.e. skin absorption, ingestion, inhalation), and presents them hierarchically, with Tier 1 models presented as the most simplistic, conservative models and Tier 2 models recommended for further intensive evaluation of substances or preparations. In order to assess these models for one exposure (product-use) scenario, a simulation of the scenario was completed in a controlled environment and the measured results were compared with the modeling outputs. The authors predicted, based on the design of the modeling tools, that all models would overestimate worker exposures under the simulated product-use scenario, with the lower-tiered model producing the most conservative estimate of exposure. In this study, a Tier 1 model and a Tier 2 model were evaluated for comparison with the near-field, far-field (NF-FF) deterministic model and measured experimental results in a real-time worker inhalation exposure assessment. Modeling was conducted prior to actual air monitoring. The exposure scenario that was evaluated involved the application of a toluene-containing spray paint to a work surface. Air samples were collected to evaluate short-term (15-min) and long-term (240-min) exposures. Eight-hour time-weighted averages (8-h TWAs) were calculated and compared with the modeling outputs from the recommended REACH modeling tools and the NF-FF model. A comparison of each of the modeling tools with measured experimental results was generated. The Tier 1 Targeted Risk Assessment tool overestimated the 8-h TWA airborne concentration of toluene in the spray scenario by a factor of 3.61. The higher tiered Advanced REACH Tool and NF-FF models showed greater concordance with experimental results, overestimating the TWA exposure by a factor of 2.92 and 1.96, respectively. In conclusion, the Tier 1 and 2 exposure modeling tools performed as expected for the simulated exposure scenario, providing relatively accurate, though conservative, estimates according to the level of detail and precision accounted for in each model.