Riverine microplastic contamination in southwest Germany: A large-scale survey

Abstract

Microplastic (MP) contamination of freshwater ecosystems is still in the focus of research and public attention, as aquatic environments have a high ecological, economic, and recreational value. We now know that rivers do not only function as pathways of MPs into oceans but may also act as temporary MP sinks. However, due to methodological differences, the comparability of studies on MP contamination of rivers is still limited. To compare MP contamination between different river systems, to analyze if there is a constant increase in MP contamination from the upper to the lower course of the river, and to investigate if there are distinct MP distribution patterns, we set up a large-scale survey. We chose two large river systems, the Rhine and Danube catchments with their tributaries and sampled 23 rivers of different sizes at 53 sampling locations in southwest Germany. Surface water sampling, sample processing, and analysis were performed with the same methodology to obtain comparable results on MP number, polymer type, and particle’s size and shape. Fully quantitative data were generated down to 300 µm by using a manta trawl net with a 300-µm mesh size for sampling. Nevertheless, we also included the non-quantitative sampled fraction of particles down to a size of 20 µm in our FTIR analysis after plastic-friendly sample purification by enzymatic oxidative treatment. Plastic concentrations recorded in surface water at the sampling locations ranged from 0.7 to 354.9 particles/m³. Concerning all samples, the number of particles increased toward lower size classes (61.0 ± 34.2% below 300 µm), and fragments were the prevailing shape (90.7 ± 13.6%). Polyethylene (49.2 ± 25.9%) and polypropylene (33.2 ± 22.6%) were the most frequent polymer types. Our survey did not reveal distinct MP distribution patterns or a constant increase of MP abundance within river courses in the investigated river systems. Next, to provide a large-scale dataset of microplastic contamination in surface waters of southwest Germany, our study shows that a representative sampling of MPs in rivers is challenging. MP particles are not homogeneously distributed in rivers, and this indicates that spatial and temporal changes in MP abundance should always be considered in MP monitoring approaches.

A review on microplastics in major European rivers

“…Organic and inorganic matter presents another factor that influences the measured results. It accumulated in nets or sieves used to sample the water (Schrank et al, 2022) and as a result, particles with dimensions even smaller than the mesh sizes were also trapped and retained because they could not pass through the clogged meshes (Urgert, 2015; van der Wal et al, 2015). Since the presence of particulate matter is different for each individual sample, measurements of microplastic concentration in the water column do not necessarily demonstrate the actual abundance of the particles within the size range of interest, even when the sampling is carried out with an identical setup.…”

“…Furthermore, in many studies only a subsample of all microplastic debris was analyzed with the outcome extrapolated to the total number of microplastic types. This carries a risk of erroneous estimates of the proportion of individual types of plastics that are present in the whole sample and might lead to biased results (Schrank et al, 2022). Hence, the total number of particles identified by means of laboratory methods becomes important because the more particles are examined, the more statistically significant are the polymer determinations (Fath, 2019; Koelmans et al, 2019).…”

“…We found that PS, PP, and PE were the most frequently identified microplastics. This is likely due to a high availability of plastic products containing these polymer types, as it was suggested that commonly used plastic products are at an increased risk of improper disposal through littering into the environment (Schrank et al, 2022). According to PlasticsEurope (2019), these three plastic types account for more than half (56.1%) of Europe's demand for plastic (PE: 30.3%, PP: 19.7%, and PS: 6.1%), whereas the demand for other types of plastics (PVC: 9.6%, PET: 8.4%, polyurethane: 7.8%) is much lower.…”

“…This often results in high uncertainties in regard to microplastic pollution at longer temporal scales (Munari et al, 2021). To improve the understanding of factors that impact the presence of microplastics (Devereux et al, 2022), continuous monitoring of plastic debris in rivers over longer timeframes should be encouraged (Schrank et al, 2022; van der Wal et al, 2015) as it would better reflect the effects of dynamic natural processes and anthropogenic activities (Hohenblum et al, 2015; Santillo et al, 2019).…”

Laboratory assessment for determining microplastics in freshwater systems – characterization and identification along Somesul Mic River

“…Pollution with plastic/microplastic materials has often been reported in worldwide rivers (Rhine, Danube, Elbe, Yellow River, Amazon) [13][14][15][16][17] or other freshwater systems also used as drinking water sources [18][19][20]. The abundance of MPs in freshwater systems has been reported to vary depending on sample source in ranges from 10 -3 to 10 3 particles/L [21] or to over 10 4 particles per liter with particle size distribution of 95% in the size range of 6.5 and 100 µm [22], to absolute concentrations of 0.008mg/L to 0.039mg/L [23].…”