Practice question

Microplastics are conventionally defined as plastic particles smaller than 5 millimetres. Primary microplastics are manufactured at small size, such as some industrial pellets and microbeads, whereas secondary microplastics form when larger objects fragment. The category includes fibres, films, foams, and irregular fragments of varied polymers. Small size promotes ingestion by many organisms, but the particles are not necessarily invisible, organic toxins, or biodegradable materials. Prevention requires reducing unnecessary plastic use, improving collection and recycling, controlling lost fishing gear, and limiting releases of fibres and tyre-wear particles. 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.