Microplastics in Cuban freshwaters: Diversity, temporal changes, and effects on extracellular enzymatic activity

Plastics, as synthetic polymers, are emerging contaminants that can harm organisms and ecosystems. This study investigates the presence of microplastics in sediments of two rivers in western Cuba, assessing their temporal variability, diversity, and characterizing the types of microplastics in these ecosystems. Additionally, the study examines the relationship between microplastic concentrations, the extracellular enzymatic activity of benthic microbial communities, and nutrient levels in sediments. Sediments from two stations, the Paila (urban river) and Baños del San Juan (rural river), were analyzed using micro-FTIR for chemical identification, and nutrients and extracellular enzyme activities were determined by colorimetric methods. The results showed higher microplastic concentrations at the Paila station compared to the Baños del San Juan station. The identified microplastics included polyethylene terephthalate (41.9%), polypropylene (25.8%), acrylic (6.5%), polyvinyl chloride (6.5%), polyethylene (3.2%), polyurethane (3.2%), and polyvinyl alcohol (3.2%), with polyethylene terephthalate being the most abundant in both sampling stations. The highest microplastic diversity was observed at the Paila station in April, with June showing the highest concentrations of microparticles. Redundancy analysis showed that nitrite, polypropylene, ammonium, and precipitation were the variables influencing extracellular enzyme activities at both sampling stations. Higher levels of polypropylene were associated with increased levels of nitrite and ammonium. Additionally, it is suggested that polypropylene inhibits proteolytic and catalase activity in the sediments of the studied stations. This investigation is the first report in Cuba of the presence of microplastics in freshwater ecosystems and one of the few studies in the Latin American and Caribbean region.