Message in a bottle: Assessing the sources and origins of beach litter to tackle marine pollution

Beaches are key attractions for tourism and recreation, and considerable effort is made to keep beaches clean, yet many beaches still have substantial litter loads. Lasting solutions to reduce the amounts of marine litter require an understanding of litter sources. We collected bottles and other single-use containers at 32 sites around the South African coast to infer their sources based on their age and country of manufacture. Bottle densities varied greatly among beaches (8–450 bottles·km⁻¹), depending on proximity to local urban centres and beach cleaning frequency. Most bottles were plastic, despite well-developed recycling initiatives for PET and HDPE bottles in South Africa. Street litter was dominated by bottles made in South Africa (99%), but foreign-manufactured bottles comprised up to 74% of bottles at some beaches, with an increase from urban (4%) through semi-urban (24%) to remote beaches (45%). Most foreign bottles were PET drink bottles from China and other Asian countries, followed by South America and Europe, with little regional variation in the contribution from these sources. This fact, coupled with their recent manufacture dates (mainly <2 years old), indicates that most foreign PET drink bottles are dumped illegally from ships. By comparison, foreign HDPE bottles were more common along the southeast coast of South Africa than along the west coast, consistent with many of these bottles arriving by long-distance drift across the Indian Ocean from southeast Asia. The most common country of origin for these bottles was Indonesia, and most newly-arrived HDPE bottles were 4–6 years old. To tackle beach litter in South Africa we need to greatly reduce plastic leakage from land-based sources, both locally and in southeast Asia, as well as improve measures to prevent the illegal dumping of plastics and other persistent wastes from ships.