Emerging Contaminants: Microplastics and their Impacts on the Environment

Abstract

Microplastics (MPs), generally defined as plastic particles smaller than 5 mm in their largest dimension. They are pervasive environmental contaminants due to their persistence, occurrence and diverse physicochemical properties. Their widespread distribution across terrestrial, aquatic and atmospheric compartments, together with their interactions with biological organisms and chemical contaminants has raised concerns regarding ecological integrity and human health. This review synthesizes the current knowledge on definition and classification of microplastics, sources, environmental transport and fate, analytical approaches for their detection and characterization, biological uptake, trophic transfer, ecological effects and human exposure. Evidence indicates that microplastics can originate from both primary and secondary sources and be redistributed through hydrological, atmospheric and biological pathways with particle size, polymer density, morphology, weathering, biofouling and aggregation influencing their environmental fate. Across diverse organisms, exposure has been associated with impaired feeding, growth and reproduction, oxidative stress, inflammation and cellular damage. MPs may also interact with chemical contaminants and plastisphere-associated microorganisms. Trophic transfer across food webs has been documented, whereas evidence for biomagnification remains limited and inconsistent. Human exposure occurs primarily through ingestion and inhalation, and particles have been reported in blood, lung, placental and other tissues; however, relationship with specific diseases remains unestablished. Major knowledge gaps include methodological heterogeneity, limited detection of nanoplastics, insufficient environmentally realistic long-term studies, uncertainty regarding trophic transfer and its implication for biomagnification. Future research should prioritize harmonized and improved analytical and quality-assurance protocols, long-term realistic exposure experiments, mechanistic toxicity studies and integrated human-health risk assessment.