What action breaks large plastic into microplastics?
Ultraviolet radiation photo-oxidises polymer chains, making exposed plastic brittle, while waves, sand abrasion, and repeated mechanical stress fracture it into progressively smaller pieces. This weathering generates secondary microplastics but usually does not mineralise the polymer fully. Acid rain is not the major marine fragmentation mechanism, and most organisms lack enzymes capable of rapidly digesting conventional plastics under environmental conditions. Because conventional polymers persist, fragmentation redistributes plastic into smaller pieces rather than removing its mass from the ecosystem. Trophic transfer can occur when predators consume contaminated prey, although evidence for consistent biomagnification of particle numbers remains system-dependent. Standardised sampling and contamination controls are essential because airborne fibres can enter samples during collection and laboratory processing. Particle size, shape, polymer type, weathering state, and associated chemicals all influence uptake and biological response, so microplastics are not a uniform toxicant. Laboratory effects must be interpreted alongside environmentally realistic concentrations, while field detection demonstrates exposure but does not alone prove causation.
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology