Rethinking Microplastic Toxicity and Ecological Effects: From Particle Identity and Dose to Bioaccumulation, Biomagnification, and Environmental Fate

Microplastics (MPs) are ubiquitous across environmental compartments and biological systems, yet particle occurrence, ingestion, tissue detection, and trophic transfer are often interpreted as evidence of exposure, bioaccumulation, biomagnification, or ecological risk. We argue that these observations represent distinct stages of the exposure–fate–effect continuum and should not be treated as equivalent. The operational <5-mm definition is useful for monitoring but does not provide a toxicological identity for a heterogeneous particle assemblage. Biologically relevant dose should therefore consider particle-size distribution, morphology, surface properties, and associated chemicals rather than mass or particle number alone. Likewise, organism-associated particles do not necessarily represent internal accumulation, and trophic transfer does not necessarily demonstrate biomagnification. We further argue that BCF, BAF, and BMF are outcome metrics rather than mechanisms and require evidence of particle uptake, distribution, retention, and elimination before they can be meaningfully interpreted. We propose an EGP–BCF–BAF–BMF framework in which the environment-conditioned state of MPs, particularly their mobility and reactivity, provides the upstream context for biological exposure, internal fate, trophic processes, and ecological consequences.