Abstract
Model tools for estimating hazardous substance exposure are an accepted part of regulatory risk assessments in Europe, and models underpin control banding tools used to help manage chemicals in workplaces. Of necessity the models are simplified abstractions of real-life working situations that aim to capture the essence of the scenario to give estimates of actual exposures with an appropriate margin of safety. The basis for existing inhalation exposure assessment tools has recently been discussed by some scientists who have argued for the use of more complex models. In our opinion, the currently accepted tools are documented to be the most robust way for workplace health and safety practitioners and others to estimate inhalation exposure. However, we recognise that it is important to continue the scientific development of exposure modelling to further elaborate and improve the existing methodologies.
Highlights
Models are widely used in regulatory risk assessments for industrial chemicals as well as in the management of these and other process that generate hazardous substances in workplaces
The Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulations allow registrants to rely on exposure estimates made using a variety of mathematical models, including the Targeted Risk Assessment (TRA) tool developed by the European Centre for Ecotoxicology and Toxicology of Chemicals [1], Stoffenmanager® at www.stoffenmanager.com [2] and the Advanced
Even if there were any minor errors made in the numerical weights for the dispersion multiplier, this will have been compensated for in the calibration with quantitative estimates of exposure, with more than 3000 exposure measurement data for AdvancedREACH Tool (ART) and almost 1000 measurements for Stoffenmanager® [27,28]. This calibration process accounts for the uncertainties associated with the multipliers and the model uncertainty in the average model output, and transparently indicates the level of confidence in the model output, and enables the model user to select the level of conservatism and confidence they wish
Summary
Models are widely used in regulatory risk assessments for industrial chemicals as well as in the management of these and other process that generate hazardous substances in workplaces. A number of scientists have discussed the basis of mechanistic exposure models and questioned the acceptance of these tools for use in REACH and health and safety regulations [11] They assert that the exposure modifying factors in these models are not always clearly described or correctly implemented. In such a case it is not possible to tightly specify the contextual conditions, such as the airborne release fraction from the spray process, the room size, the ventilation characteristics of the environment where the agent will be used or the specific design of exposure control measures that may be in place All these factors would be needed for a good prediction using a mass-balanced model [12]. The tools provide a balanced conservative overestimate of exposure for the class of situations covered by the given exposure scenario
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