Beach litter on urban beaches and methodology for mesoplastic and pellets

Summary

This study evaluated four urban and semi-urban beaches in Oslofjord (Nakkholmen, Langøyene, Nordre Langåra, and Rolfstangen) to assess the applicability of the OSPAR beach litter protocol and the suitability of sampling for mesoplastic fragments and pellets. Sampling was conducted between June and August 2025, with successful data collection at all sites. The OSPAR survey revealed plastic including polystyrene as the dominant litter category, with Nakkholmen showing the highest litter load by both count and weight. Langøyene and Rolfstangen primarily contained visitor-related litter, though Langøyene had undergone mechanical cleaning prior to sampling. The mesoplastic protocol indicated considerably higher concentrations of pellets and fragments at Nakkholmen, suggesting site-specific accumulation influenced by current speed and other factors. Some methodological adaptations were necessary, particularly in areas with dense seaweed. In the future, protocols may benefit from morphological classification of mesoplastics to trace litter sources. While none of the beaches fully met OSPAR site criteria, two satisfied minimum requirements (Nakkholmen and Nordre Langåra). The combined use of both protocols proved effective in characterising shoreline litter, highlighting the value of integrated surveys. Continued monitoring and expansion to additional urban beaches are recommended to better understand litter dynamics and inform targeted mitigation strategies.