Practice question

Persistent pollutants are resistant to chemical, photolytic, and biological degradation and are often removed slowly from organisms. If they are also bioavailable and stored in lipid or other tissues, uptake can exceed elimination and concentrations can rise through food chains. Essential nutrients are regulated physiologically, oxygen does not persist as a stored toxin, and readily biodegradable compounds are less likely to undergo strong biomagnification. 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.