Airborne particulate matter inhalation bioaccessibility: A review of methodological aspects

Research has consistently linked exposure to particulate matter (PM) with adverse health outcomes, including cardiovascular and pulmonary morbidity and mortality. Understanding the mechanisms by which PM leads to these effects on human health is crucial for developing effective mitigation strategies. One aspect of PM research that has gained increasing attention in the past few years is the bioaccessibility of inhaled PM-bound pollutants that have potential to cause adverse health effects. To assess the bioaccessibility of PM-bound pollutants, such as polycyclic aromatic hydrocarbons, phthalate esters, organophosphorus flame retardants and metal(loid)s, simulated lung fluids (SLF) are used as a tool to mimic the conditions in the human respiratory system. In addition to different SLF, various extraction methodologies and experimental conditions (e.g., incubation period, solid to liquid ratio, and pH) have been employed to extract the bioaccessible part of these pollutants, though there is not yet a standardised procedure to do so. This review aims to critically evaluate existing inhalation bioaccessibility methodologies and explore their connection with PM characteristics. More research is needed, and a standardised procedure should be implemented to allow the comparation of data between studies. Better in vitro-in vivo relationships need to be established to enhance the feasibility of in vitro bioaccessibility assays as surrogates in human health exposure assessments. Long-term effects of bioaccessible pollutants and any potential synergetic effects between multiple contaminants should also be explored to assess health repercussions more thoroughly.