Coastal populations and river discharges as sources of microplastic pollution of the Ciénaga Grande de Santa Marta, Colombian Caribbean

The large-scale production of plastic began in the 1950s, leading to a significant global increase and has become one of the world's major problems since its disintegration generates small particles of microplastics (MPs), considered pollutants of emerging concern, which are commonly found in most ecosystems. In Colombia, research on microplastics (MPs) in coastal ecosystems is still in its early stages. This study seeks to advance understanding of MPs contamination in surface waters of the Ciénaga Grande de Santa Marta (CGSM), the most significant coastal lagoon in the Colombian Caribbean, which has been designated both a Biosphere Reserve and a Ramsar site of international importance. The study focuses on examining the relationship between MP pollution and two primary sources: coastal populations and discharges from tributary rivers into the lagoon system. Water samples were collected at 33 stations during the dry season (March 2021) and rainy season (May 2021), and MPs were identified and quantified by microscopy. The effect of the distance from river mouths (km) and populated zones (km) on the abundance of MPs was evaluated by applying a Generalized Additive Model (GAM) in R. The study revealed that the abundance of MPs was significantly influenced by proximity to pollution sources, with higher concentrations observed closer to river mouths and coastal settlements during both dry and rainy seasons. The seasonal composition of MP in the two studied zones reveals a consistent prevalence of filaments during the seasons, indicating the persistent influence of various sources of contamination. The findings show that inadequate waste management practices and the lack of proper infrastructure for waste disposal are key factors contributing to microplastic pollution in the area. The study provides critical insights for addressing deficiencies in waste management while promoting active community engagement to preserve the ecological and socioeconomic value of this vital lagoon complex. The CGSM is not only a key coastal ecosystem in Colombia but also supports diverse livelihoods and cultural heritage, emphasizing the importance of sustainable management.