Plastics in the city: spatial and temporal variation of urban litter in a coastal town of France.

Plastics are ubiquitous in the environment, causing pollution recognized as a marker of the Anthropocene era. All environments are affected, including coastal and river ecosystems, where studies have shown that plastic waste contamination is proportional to the level of urbanization. This study, to our knowledge, is the first in France to investigate the spatial and temporal distribution of litter across the Land-Sea continuum, using debris classifications based on OSPAR (Oslo-Paris Convention 1992) and EPR (Extended Producer Responsibility). Two samplings, involving the local population and various non-governmental organizations, were conducted in 2022 and 2023 in the coastal town of Banyuls-sur-Mer, France, located near the Spanish border, with the Baillaury River running through it. The entire town, as well as the port and Central Beach, were sampled. A total of 30,899 debris (1357 kg) were collected over 47.7 km of streets, riverbanks, port, and beach. Most of the debris collected in the port consisted of tires. The amount of waste collected in the town was lower than that observed on the riverbanks or at Central Beach, suggesting that coastal areas serve as the final repository for mismanaged waste. Plastics represent approximately 70% of the collected debris and exceed the precautionary threshold for ecological and socio-economic nuisances defined for European Union (EU) beaches (i.e., 20 debris per 100 m), by the Technical Group on Marine Litter of the Framework Directive "Strategy for the Marine Environment" (FD SMM). The data collection and standardization methods used in this study facilitated direct comparison across the continuum land-sea between cities, riverbanks, ports, and beaches, and with other studies, highlighting the value of participatory science in informing decision-making.