Microplastics transfer from a malfunctioning municipal wastewater oxidation pond into a marine protected area in the Colombian Caribbean

Wastewater is an important source of microplastics (MPs) in aquatic ecosystems, threatening their biodiversity and environmental services. This study examines the contribution of MPs from the effluents of a municipal wastewater treatment pond system (WTS) to a stream that flows into the Cispata marine protected area (MPA) in the Colombian Caribbean. Samples of influent and effluent wastewater and sludge in the WTS were analyzed to determine the abundance and types of MPs. Additionally, the wastewater flow rate was measured using a volumetric method, and its MP load calculated. The abundance of MPs in the influent and effluent of the WTS was 15 and 5 items L-1 of wastewater, and 11 and 4 items Kg-1 dw of sludge, respectively. Fibers (67-75%) prevailed in the wastewater, while fragments (56-67%) were predominant in the sludge. Whereas the removal of MPs entering the WTS was 67%, the wastewater effluents still contribute approximately 1.3 million items day-1 to the stream flowing into the MPA. Our study highlights that a poorly functioning WTS causes substantial MP discharges into sensitive aquatic coastal ecosystems. These WTS require ongoing maintenance and improvements to ensure their long-term optimal operation and function of reducing pollutant loads and environmental risks in recipient aquatic ecosystems.