Microplastic Loads in Freshwater Lakes: Prioritized Regions and Management Strategies

Background: Microplastic contamination in freshwater lakes has grown up to a main concern in recent years. While there is no knowledge about the global distribution and loads of microplastics in the lacustrine environment. Methods: We commence to solve this matter based on trawl net method investigations in freshwater lakes. Through redundant analysis (RDA) and structural equation model (SEM), we first identify the main influencing factors that affect the microplastic concentrations in freshwater lakes. Then, we use Machine Learning and number to mass transformation tactics to fill in gaps and reach a global prediction (Fig. 1). Findings: (1) We found cropland plays a similar positive effect with population density on microplastic concentration, while vegetation has the opposite effect. The findings highlight the importance of these land use types in the lake basin for the first time. (2) Totally, we demonstrate an average microplastic concentration of 0.57 items/m³ in lakes and reservoirs around the world. The accumulated microplastic load in the upper 20 m of lakes and reservoirs is 10,167 tons, which is equal to 508 million plastic bottles. (3) The concentration hotspots of lacustrine microplastics gather in east and southeast Asia, India, north back of Black Sea and Nile Delta. North America, Africa and Asia are continents with highest microplastic loads (Fig. 2), but with different causation (concentration-dependent and/or area-dependent, shape composition affected). The giant lakes around world contribute highest microplastic loads. Significance: The findings of this study provide a feasible approach to estimate the microplastic loads of global lakes, and assist to make reasonable policies to mitigate the microplastic pollution in freshwaters.

Fig. 1 Research framework of how to make global estimation of microplastic loads in lakes/reservoirs.

Fig. 2 The predicted microplastic loads in lakes worldwide (lake area>100 km²). The red dotted lines are boundary lines of continents in the present study.