Microplastics harm animals first through physical ingestion. From plankton to whales, countless species mistake these tiny fragments for prey or accidentally filter them while feeding. Once swallowed, the sharp‑edged particles can lacerate digestive tracts, block nutrient absorption, and create a false sense of fullness that leads to malnutrition or starvation. Studies on seabirds, sea turtles, and small fish show weight loss, stunted growth, and reduced survival rates directly tied to plastic loads in their stomachs.

Beyond the physical obstruction, microplastics act as chemical delivery devices. Many pellets are manufactured with endocrine‑disrupting additives like bisphenol A or phthalates, and their porous surfaces readily adsorb pollutants such as PCBs, PAHs, and heavy metals from surrounding water. When animals ingest these plastics, the contaminants can leach out in the gut, accumulating in tissues and disrupting hormone regulation, immune responses, and reproductive success. Laboratory work on oysters, crustaceans, and marine worms has documented lowered fertility, impaired larval development, and higher mortality linked to this toxic cocktail.

The effects ripple up food webs through trophic transfer. Predators that consume smaller, contaminated prey accumulate both plastic particles and the chemicals they carry, magnifying exposure at each step. Microplastics have been detected in the organs of apex species—from tuna and sharks to seabirds and marine mammals—where they contribute to oxidative stress, inflammation, and reduced overall fitness. Such bioaccumulation threatens population stability, particularly for long‑lived animals that reproduce slowly and are already under pressure from overfishing or habitat loss.

Finally, microplastic pollution degrades critical habitats and alters animal behavior. In sediments, high plastic concentrations change the texture and chemistry of the seabed, making it harder for benthic organisms to burrow and for seagrass roots to anchor. Floating fibers can smother coral reefs and entangle invertebrates, while airborne microfibers settle onto alpine meadows and forest floors, introducing foreign material into terrestrial food chains. Even sub‑lethal plastic exposure can alter feeding patterns, risk‑taking, and predator avoidance, subtly shifting ecosystem dynamics long before mass mortalities become evident.