Unveiling Microplastic Pollution in the Northern Amazon: First Evidence from the Cauamé River

Although freshwater systems are potential sources of plastic debris to the oceans, knowledge about microplastics (MPs) in these systems remains limited. The Amazon Basin, the largest in the world, already shows widespread MP contamination, but data gaps persist, especially in the Northern Amazon. This study is the first to evaluate MP abundance in the Cauamé River, Roraima, in the extreme North of Brazil. Twelve sites were analyzed in two sampling campaigns, considering the dry and rainy seasons. During the rainy period, 391 MPs were detected, with abundances ranging from 50 to 365 MPs m⁻3 (mean = 206 ± 87 MPs m⁻3). In the dry period, there was an 84% reduction, with 61 MPs and abundances from 0 to 43 MPs m⁻3 (mean = 24 ± 15 MPs m⁻3). Higher abundances were associated with areas affected by sewage discharge and fishing-related waste. Particle sizes ranged from 152 to 4908 µm. Fragments accounted for 52% and fibers for 48%, with dominance of fragments between 1000 and 5000 µm. Nine colors were identified, mainly transparent (55%) and blue (22%). FTIR analysis indicated predominance of polypropylene and polyethylene terephthalate. MPs showed a heterogeneous distribution in the river surface waters.