Plastic bottles as marine litter tracers: evidence of illegal disposal in the Indian Ocean sector of the Southern Ocean

Abstract Marine litter is a major global concern, and identifying its origin is crucial to developing adequate and effective management strategies to curb pollution. Although the Southern Ocean is remote, with limited shipping activity and strong latitudinal frontal systems separating it from other oceans, pollution is an increasing problem in this region. Marine litter has been collected on sub-Antarctic Marion Island (part of the Prince Edward Islands in the Indian Ocean sector of the Southern Ocean) since 1993. The number of plastic bottles collected on the island has grown steadily over the last 2 decades, with the region of manufacture gradually shifting from South America to Asia. To better understand this trend, we undertook an in-depth study of plastic bottles found on Marion Island beaches from 2019 to 2024 and of those collected on nearby Prince Edward Island in November 2023, scrutinizing all marks, writing and logos to determine the country and date of manufacture, allowing us to infer their probable origins. Polyethylene terephthalate (PET) drink bottles (70% bottled waters) comprised 93% of the 1466 bottles that were collected. Overall, 87% of bottles had markings indicating the country or region of manufacture; 81% originated from Asia and 15% from South America, with most Asian bottles made in China (84%). The median age of bottled waters (1.61 years from manufacture date to collection) from the two most frequently encountered Chinese manufacturers was too short for them to have drifted from land-based sources in China. Taken together, a seasonal pattern in bottle prevalence, distant region of manufacture and young ages of plastic bottles sampled at the Prince Edward Islands indicate that vessels are discarding litter in the Southern Ocean in contravention of international maritime legislation. These findings highlight an urgent need to improve compliance with international maritime legislation governing waste management practices at sea.