Microplastic Pollution in Benthic Midstream Sediments of the Rhine River

Area of Science:

• Environmental Science
• Analytical Chemistry
• Marine Biology

Background:

• Rivers act as primary pathways for microplastic (MP) transport to oceans.
• Understanding MP fate in fluvial systems, including sediments and biota, is crucial but limited.
• Benthic compartments are understudied regarding MP contamination and characteristics.

Purpose of the Study:

• To comprehensively analyze microplastic concentrations, compositions, and distribution in Rhine Riverbed sediments.
• To investigate the influence of sediment depth on microplastic abundance and characteristics.
• To identify dominant polymer types and their potential sources in the fluvial benthic environment.

Main Methods:

• Collection of 25 riverbed sediment samples from ten sites in the Rhine River using a diving bell and dredging.
• Application of automated micro-Fourier-transform infrared (μFTIR) spectroscopy for unbiased microplastic analysis.
• Identification and quantification of microplastics in the size range of 11-500 μm.

Main Results:

• Microplastic concentrations varied from 0.26 to 11.07 × 10^3 MP kg^-1, with particles <75 μm comprising 96% of the total.
• Microplastic abundance decreased with increasing sediment depth.
• Acrylates/polyurethane/varnish (APV) cluster (70%) was ubiquitous, suggesting antifouling paint as a source; denser polymers (>1 g cm^-3) predominated (85%).

Conclusions:

• Rhine Riverbed sediments act as a sink for a high abundance of microplastics, particularly small particles.
• The prevalence of APV suggests significant input from maritime activities, specifically antifouling paints.
• The dominance of denser microplastics in sediments contrasts with findings in surface waters, highlighting complex environmental partitioning.