From microplastics to nanoplastics: environmental transformation pathways, detection challenges, and health implications

Abstract

The extensive buildup of plastic waste has become a significant environmental issue, especially due to the conversion of microplastics (MPs) into nanoplastics (NPs). In this review, we address the critical processes that lead to the fragmentation of MPs into NPs, including physical, chemical, and biological degradation mechanisms such as UV radiation, mechanical wear, and microbial activities in wastewater treatment systems, soils, and aquatic habitats. We place a strong focus on the analytical and methodological challenges encountered in detecting and characterizing NPs, highlighting the limitations of existing instrumentation, the absence of standardized protocols, and discrepancies in reporting metrics. Additionally, we explore the environmental behavior of NPs within the plastisphere and their interactions with co-contaminants, including heavy metals, persistent organic pollutants (POPs), and pathogenic microorganisms. Current understanding of the ecological and human health risks related to inhalation and ingestion exposure pathways is also summarized, with a focus on the uncertainties and gaps in toxicological data. Lastly, we emphasize key research gaps and future directions to facilitate the development of standardized assessment strategies and enhance the comprehension of nanoplastic risks.