Composition, co-exposure patterns, and health risk assessment of airborne microplastics and toxic metals in the urban atmosphere of Osun State

Microplastics (MPs) and toxic metals (TMs) are both emerging and recalcitrant pollutants permeating diverse environments. This study examined the inhalation exposure to these pollutants, focusing on co-exposure pattern and risk assessment. Particulate matters (PM) were sampled during the rainy and dry seasons at Osogbo, Ile-Ife and Ilesa-Southwestern Nigeria using a high-volume air sampling equipment, followed by extraction and characterization using oxidative digestion, density separation, Fourier Transform Infrared Spectroscopy (FTIR) and optical microscopy while the metal contents were estimated using an inductively coupled plasma-optical emission spectrometer (ICP-OES). Ecological and health risk assessment were measured via contamination factors and inhalation models. The result showed higher MPs abundance particularly during the dry season ranging from (173, 900–555, 533 MPs/m3) compared to the rainy season (121,730 to 388, 873 MPs/m3) with fiber being the most dominant shape followed by fragment, whereas white and black colored MPs were most abundant. Metal analysis showed elevated levels of Fe, Al, Zn and Cu, and particularly toxic metals- Pb, Cd, Cr and Ni with Cd posing the highest ecological risk. Seasonal variations, locations and MPs abundance displayed positive correlation with TMs particularly MPs with Cu (r = 0.745, p < 0.05), Ni (r = 0.758, p < 0.051) and Mg (r = 0.588, p < 0.05). Health assessments showed that newborns and infants are more susceptible due to higher inhalation doses. This study reveals that outdoor environment could be a major contributor to MPs and TMs contamination.