Application-dependent assessment of the human exposure potential to microplastics

The presence of microplastic in the environment has become a matter of significant concern regarding its impact on the food chain and, moreover, human health. The potential ways in which humans may be exposed to microplastic include ingestion, inhalation, or dermal contact. To facilitate initial estimates of the potential for human exposure, a model has been developed that incorporates all of the major stages in the transfer of microplastic from its sources to direct human contact. Due to the scarcity of data available, a simplified gradation of exposure probability has been applied. Building on the results of published mass flow models for microplastics, the model is based on normalized values for the release of microplastics from different types of applications into environmental compartments, also considering the degradation of macroplastic. Published data investigating the contamination of different foods and beverages are evaluated, and the inhalation probability is assessed using air pollution data and breathing rates. In the final step, the potential for resorption through the gastrointestinal and the respiratory tract is estimated. The results obtained from this modelling indicate a high exposure potential for microplastic from tire wear via outdoor air and for various PET applications via indoor air. Furthermore, the results demonstrate a high potential for exposure via ingestion of food for plastics used in agriculture. The model's results represent an initial attempt to estimate exposure probabilities for humans across all application categories of plastics and the most common polymers, taking into account the uncertainty of current research.