Advancing plastic pollution hotspotting at the subnational level: Brazil as a case study in the Global South.

Identifying sources is crucial for proposing effective actions to combat marine litter pollution. Here, we used an innovative approach to identify hotspots of mismanaged plastic waste (MPW) within Brazil and subsequent leakage to the ocean, based on population density, socio-economic conditions, municipal solid waste management and environmental parameters. We estimated plastic waste generation and MPW for each of the 5570 Brazilian municipalities, which totaled 3.44 million metric tons per year. Then, we estimated the probability of litter mobilization and transport (P) and the relative risk of leakage to the ocean (MPW × P). The Guanabara Bay and La Plata River comprised the main oceanic entry hotspots of litter produced in Brazil. The use of national databases allowed us to increase spatial and temporal granularity, offering a detailed baseline for the application of prevention and mitigation actions. However, overcoming data limitations is still a challenge in Brazil as in other Global South countries.

How far are we from robust estimates of plastic litter leakage to the environment?

Litter pollution is a global concern, and identifying sources and pathways is crucial for proposing preventative actions. Existing models of plastic litter leakage to the environment have provided worldwide estimates at a country-based level, but only a few initiatives address subnational scales. Adding relevant parameters and improving models is needed to reduce the limitations of global estimates. However, availability of information, which varies among countries and is critical in the Global South, may preclude such improvements. To understand the potentialities and limitations of subnational estimates of plastic litter leakage to the environment, we reviewed the parameters used in the literature and addressed data usability, considering Brazil as a case study. We gathered data on parameters identified for all 5570 Brazilian municipalities and evaluated their usability considering reliability and temporal and geographic granularity. We identified 51 parameters that are either currently used in models or could improve estimates, including parameters regarding territory, population density, socioeconomic condition, and solid waste generation, composition, collection, and final destination, selective waste collection, recycling, and hydrology. Only 29.4% of parameters were linked to data sources with good or very good usability, while most of them presented average usability (45.1%) and 7.8% were not linked to any data source. This panorama of low data usability reveals uncertainties and explicit difficulties of estimating plastic litter leakage to the environment, including mobilization from the terrestrial environment to the ocean. The Brazilian scenario reflects current data availability conditions and the difficulties of countries in the Global South to robustly understand plastic litter leakage and face land-based sources of marine litter.

Spatio-temporal characterization of litter at a touristic sandy beach in South Brazil.

Litter is an ecological, economic, and social problem that impacts marine environments around the world. To create prevention and mitigation measures to solve this issue, it is necessary to understand the amounts and sources of this type of pollution. Cassino Beach is an extensive sandy beach located in South Brazil (∼220 km in length) that presents multiple uses, such as touristic, portuary and fishery activities. In order to evaluate the spatial and seasonal variation of litter amounts, types and sources at Cassino Beach, litter (>2.5 cm) was collected over 27 months at two urban and two non-urban sites. At each site, the litter present in three 200 m2 areas was sampled and evaluated. A total of 19,457 items were collected, mostly composed by plastic (∼88%). Paper, metal, and cloth items were also present, but in low amounts. Fragments and cigarette butts were the major types of plastic litter, with abundances of 28.4% and 17.0%, respectively. Urban sites presented higher amounts of litter, with those related to beach use being more common, emphasizing the contribution of beachgoers to litter input at these sites. During the summer season, when beach use increases, the highest total litter concentration was found. Undefined and/or beach use-related sources were dominant in all sites and seasons. Mapping the predominant materials, types and potential sources of litter creates important baseline data that can contribute not only to beach monitoring, but also to the development of litter reduction strategies.