Exposure scenarios for human health risk assessment of nano- and microplastic particles

Evidence of nano- and microplastic particles being present in the human body has increased in recent years, yet there is no acceptable methodology to perform a human health risk assessment for these particles because of limitations in the exposure and hazard assessments. Exposure assessment can be improved by establishing comprehensive and justifiable exposure scenarios for a defined exposure demographic, thoroughly describing the relevant exposure pathways, and performing multidimensional data alignment, thereby facilitating probabilistic estimates of nano- and microplastic particle exposure. General considerations of exposure scenarios are outlined, along with specifics details on the complexity and prioritization for nine demographic groups: adults; women; the elderly; individuals with disease; individuals employed in high-hazard occupations; and children demographics, including early infants, toddlers, school children, and teenagers. Recommendations to advance exposure assessments and scenarios are also provided which suggest: i) the use of well-defined exposure scenarios for demographics that are prioritized according to their level of complexity and concern; ii) a thorough description of relevant activity factors (physiological parameters, behavioural traits) and exposure factors (duration, frequency, media characterization) for the chosen demographic; iii) thorough descriptions of exposure via ingestion and inhalation, and in the case of early infants, including exposure via maternal transfer; iv) multidimensional data alignment and probabilistic methods to enable credible comparisons of exposure data across studies and inform physiologically based toxicokinetic models to estimate internal exposure.