Plastic Detection Using a Multi-method Approach: Comparative Case Studies from Coastal Tourism Sites

This study offers a comprehensive, harmonized model for detecting and quantifying marine plastic on coastal sites and coastal waters, leveraging experiences from southern California (USA) and Zanzibar (Tanzania) (Maione, 2019, 2021; Maione et al., 2021). Selected sites present different features related to geography, presence and/or conditions of urban infrastructure and waste management systems, beach uses and users, local economies, and socio-cultural characteristics, that can contribute to plastic pollution policies and be accounted for when building marine pollution models. Data acquisition entails a combination of satellite-based earth observations with in-situ measurements using sensor data, existing water quality analyses, beach litter inventories, and water/specimen sampling among others. Observations are recorded into a database (geographic coordinates of transects and observations, photographic evidence, specimen description, count/weight/size, morphological and chemical characteristics) and processed using lab equipment. Findings show plastic as the most dominant litter type, at all surveyed sites, with beverage bottles, shopping bags, wrappings, and single-use tableware being the most common litter items. Waste characterization serves the dual purpose of supplementing the existing paucity of data on plastic waste material flows, and, depending on the degradation status of collected items, advance recommendations on their potential recovery. Subsequently, litter information was crossed-validated via interviews with local stakeholders (from the waste and tourism sectors) to evaluate sources and pathways of coastal pollution. This study provides recommendations on plastic pollution monitoring and reporting via the integration of qualitative (e.g., interviews, citizen science) and quantitative data (e.g., observations, sampling, material flow inventories) on beach and marine litter. Finally, the study provides implications for beach users and facilities located along the shoreline to mitigate and prevent plastic material lost at sea.