Differences in allergenic and toxic risks from airborne seed hairs and atmospheric PM_2.5: Pollen, bacteria, and...

Airborne seed hairs released by poplar (Populus spp.) and willow (Salix spp.) during the fruiting period serve as unique carriers of biological particles, transporting substantial quantities of pollen-related plant materials and bacteria. However, its quantitative contribution to human allergenic and toxic risks relative to atmospheric particulate matter during the same period remains unclear. This study collected airborne seed hairs and PM_2.5 simultaneously from urban and suburban areas in Hohhot, China, during May 2-8, 2025. We conducted the first quantitative comparison of the allergenic risks induced by pollen and bacteria based on specific immunoglobulin E (sIgE), and evaluated the toxic equivalent quantity of full-volatile organic compounds (FVOCs) and non-carcinogenic risks of heavy metals in seed hairs and PM_2.5. The pollen and bacterial loads per unit mass of airborne seed hairs are 13.1 ± 12.1 and 92.9 ± 55.2 times higher than concurrent PM_2.5, resulting in corresponding sIgE levels in airborne seed hairs that are 14.9 ± 13.5 and 124.0 ± 39.0 times higher than those in PM_2.5. Pollen dominates the total allergenic risk in both carriers, accounting for 99.08% in airborne seed hairs and 99.89% in PM_2.5, while the Salicaceae and Fabaceae as key pollen, respectively. However, the toxicity of FVOCs (dominated by semi-volatile organic compounds) and heavy metals in PM_2.5 exceed 43754.2 ± 41130.6 and 41.8 ± 19.6 times greater than airborne seed hairs. We emphasize that airborne seed hairs should be incorporated as an independent seasonal high-risk factor into air quality exposure assessment and public health management.