A comprehensive assessment of plastic pollution inland, on riverbanks, along the coastline and at the sea surface in Southern Mindanao, Philippines.

The Philippines are projected to be a top contributor to oceanic plastic pollution by 2025, ranking first globally for riverine plastic emissions. However, comprehensive empirical data on litter leakage is lacking, impeding accurate estimates and mitigation efforts. We conducted the first thorough assessment of plastic within a 100 km radius of Davao City, Mindanao, Philippines using a stratified random sampling design. We detected 13,970 debris items across 309 transects from 33 coastal, 27 river, and 44 inland sites, and collected 1405 debris items from 27 sea surface trawls. Riverbanks showed the highest plastic pollution densities, averaging 3.6 items per m². Food wrappers and labels, both whole and fragmented, were the most abundant items across all site types, highlighting the Filipino "tingi" culture of buying and trading in small quantities. We recommend focusing on river hotspots and commonly reported items, particularly food packaging and sachets, to manage plastic pollution effectively.