Plastic debris is one of the most significant organic pollutants in the aquatic environment. Due to properties such as buoyancy and extreme durability, synthetic polymers are present in rivers, lakes and oceans and accumulate in sediments all over the world. However, freshwater sediments have attracted less attention than the investigation of sediments in marine ecosystems. For this reason, river shore sediments of the rivers Rhine and Main in the Rhine-Main area in Germany were analyzed. The sample locations comprised shore sediment of a large European river (Rhine) and a river characterized by industrial influence (Main) in areas with varying population sizes as well as sites in proximity to nature reserves. All sediments analyzed contained microplastic particles (<5mm) with mass fractions of up to 1 g kg-1 or 4000 particles kg-1 respectively. Analysis of the plastics by infrared spectroscopy showed a high abundance of polyethylene, polypropylene and polystyrene, which covered over 75% of all polymer types identified in the sediment. Short distance transport of plastic particles from the tributary to the main stream could be confirmed by the identification of pellets, which were separated from shore sediment samples of both rivers. This systematic study shows the emerging pollution of inland river sediments with microplastics and, as a consequence thereof, underlines the importance of rivers as transport vectors of microplastics into the ocean.
Sascha Klein, Eckhard Worch, and Thomas P. Knepper, Environ. Sci. Technol., Vol. 49 (10), pages 6070-6076, May 2015