An assessment of microplastic contamination in freshwater fish from the Upper Doce River basin (Minas Gerais, Brazil): a 2003 baseline study

Microplastics (MPs)—plastic particles smaller than 5 mm—have become a growing environmental concern due to their pervasive presence in aquatic ecosystems. This study investigates the presence of MPs in freshwater fish specimens collected in 2003 in a small urban pond (Upper Doce River basin, Brazil). From the 744 fragments detected, 258 were registered in Australoheros facetus , 260 in Geophagus brasiliensis , and 226 in Oreochromis niloticus , one of the most consumed freshwater fish species in Brazil. The results revealed MPs distributed in the gills, digestive tracts, and ovaries. The most abundant microplastic types were fibers and fragments, with polypropylene (61.4%) and polyethylene (38.6%) being the predominant polymers. MP abundance differed significantly among organs, with the highest accumulation observed in the gills, reflecting their vulnerability to MPs due to continuous ventilation, exposing gill tissues to suspended particles. This study represents the oldest record of the quantity and types of MPs in fish from the Doce River and poses a risk to the evaluated species and potentially human populations. In addition, by providing historical baseline data from biological collections, this study advances scientific understanding of the temporal persistence, organ-specific accumulation, and early dissemination of MPs in Neotropical freshwater ecosystems.