Airborne microplastics as evolving contaminant carriers: atmospheric weathering, transformation pathways, and the...

Atmospheric microplastics represent a rapidly emerging environmental threat, yet their dynamic behavior remains poorly understood. This study synthesizes 113 publications to reveal that airborne microplastics undergo continuous transformation through atmospheric weathering, fundamentally altering their toxicological properties. The analysis introduces the atmospheric microplastic transformation and exposure framework (AMTEF), demonstrating how weathering processes such as photodegradation, oxidation, and fragmentation progressively enhance particle reactivity and contaminant-carrying capacity. Critically, only approximately 1.77% of existing studies examine this "Trojan horse" effect, despite its central role in health risks. The research proposes the evolving toxicity paradigm (ETP), which reconceptualizes microplastic hazards as dynamic rather than static, driven by surface amplification, contaminant concentration, synergistic interactions, and size-dependent transformation. Recent evidence of microplastic bioaccumulation in the human brain tissue (Nihart et al., Nat Med 31:1114-1119, 2025) further underscores the urgency of understanding transformation-driven toxicity pathways. This paradigm shift from inert particles to active vectors demands transformation-aware risk assessment protocols. The findings reveal that current toxicological models substantially underestimate exposure risks by ignoring atmospheric evolution, with implications for the 99% of humans who breathe urban air containing these evolving contaminants.