A new study in the Proceedings of the National Academy of Sciences analyzes around 10,000 stranded or entangled marine animals to assess how lethal ingested plastics are.

Findings show seabirds are most affected by hard plastics and rubber, with six tiny rubber pieces capable of causing about 90% mortality in some seabird species; sea turtles face high risk from soft plastics, where 342 pea-sized pieces could prove lethal with 90% certainty; and marine mammals are particularly vulnerable to fishing debris, where 28 small pieces can kill a sperm whale with 90% probability.

Lethality thresholds vary by species, size, and plastic type, but overall the dangerous amounts are far smaller than public perception, underscoring the urgency of cutting plastic inputs to oceans.

The study provides data-driven insights intended to guide global conservation efforts and informs policymakers and practitioners about risk levels.

The research supports policy and cleanup initiatives, highlighting the impact of balloons, bags, fishing gear, and other plastics, and calls for reducing production, better waste management, and cleanup to protect biodiversity.

Findings could inform worldwide wildlife protection strategies and plastic pollution mitigation measures.

Experts regard the study as a rigorous contribution that frames plastic pollution as an existential threat to marine life, while noting limitations such as not addressing microplastics, larger debris ingestion, or entanglement risks.

Authors stress that reducing plastic production, improving collection and recycling, and cleaning up existing pollution are essential steps, with researchers emphasizing that even small amounts can be lethal and that the data offer a scientific basis for risk thresholds and targeted policies.

The researchers and external experts emphasize defining lethality thresholds to help policymakers craft regulations aimed at reducing production and enhancing waste management, recycling, and cleanup efforts.

Global plastic input to oceans exceeds 11 million metric tons annually, with UN projections suggesting this could triple over the next two decades.

The study focuses on plastics found in stomachs and does not account for chemical effects or entanglement, implying the true harm may be higher; nearly half of the studied animals were threatened or endangered.

The research did not assess all plastic impacts, concentrating on large plastics (>5 mm) and ingestion and excluding microplastics, sublethal effects, and entanglement.

The study is published in PNAS with international collaboration from institutions including the University of Tasmania, CSIRO, and Universidade Federal de Alagoas.