Global cigarette butt contamination: a review

Cigarette butts are toxic, persistent, and represent one of the most frequently littered waste worldwide, with trillions cigarette butts entering the environment annually, yet their global distribution is poorly known. In particular, the influence of protected areas is unclear. Here, we review cigarette butt contamination across 55 countries from 2013 to 2024, with a meta-analysis of 130 peer-reviewed studies and 2,723 records to assess protected areas influence, spatiotemporal trends, and classify levels. Results show that the global average density was 0.24 cigarette butts per square meter, with pronounced geographic variability. Hotspots occurred in 17 countries, especially in Asia and Latin America. Aquatic environments, notably beaches, exhibited higher contamination, reflecting recreational pressure and higher monitoring coverage. Cigarette butts constituted 12% of all aquatic litter on average, exceeding 50% in several countries. The 165 protected areas monitored in 37 countries displayed markedly lower contamination, reducing it by nearly fivefold compared to unprotected areas, i.e., 0.06 versus 0.29 cigarette butts per square meter. Contamination declined consistently along a protection gradient from unprotected to unclassified, multiple use, and no take protected areas, with the latter one, the most restrictive, achieving nearly tenfold reductions, averaging 0.03 cigarette butts per square meter. Over time, contamination levels remained stable in unprotected areas, and showed slight decreases in protected areas, indicating early signs of management effectiveness. We introduce a standardized index for interpreting contamination levels.