Microplastic pollution in Brazil's coastal marine surface waters: The first macroregional baseline from the global...

We conducted the largest microplastic (MP) survey ever conducted in the Global South, covering ≈7500 km of the Brazilian coastline and collecting 4134 surface water samples from 1024 beaches across 213 municipalities in 17 states (April 2023-April 2024). Samples were grouped into five coastal macroregions-Amazonian Equatorial, Northeastern, Eastern, Southeastern, and Southern-to align responses and predictors. MPs were quantified by epifluorescence microscopy after Nile Red staining and Calcofluor White/Evans Blue counterstaining, under rigorous quality control procedures. Concentrations showed pronounced spatial heterogeneity, with the Eastern Coastline reaching 16.87 MPs/L, followed by the Northeastern (6.95), Southeastern (5.25), Southern (3.36), and Amazonian Equatorial (1.29 MPs/L). Regional contrasts reflected hydrodynamic and anthropogenic influences: the Eastern sector, characterized by high salinity, elevated pH, and proximity to sewage outlets and highways, exhibited maximum accumulation; the Amazonian Equatorial region, with low salinity, high chlorophyll a, and enhanced surface velocity, showed dissipative conditions and vertical export; and the Southern coast displayed low loads associated with wide shelves and greater distance from point sources. Morphometric analysis revealed a gradient from larger, degraded particles in high-abundance regions to smaller, intact particles in low-abundance regions. Network analysis indicated sparse connectivity in the Eastern Coastline and denser, multi-factorial interactions in the Northeastern and Southeastern regions. These findings establish the first macroregional quantitative baseline of MP pollution in Brazilian marine surface waters, providing a standardized reference for future large-scale monitoring and interregional comparisons.