Spatial distribution of microplastic in surface water, sediment and biota along a river

The interest in studying microplastics (MPs) in freshwater is continuously increasing. Still, one of the unknowns to date is the spacious variation of MP transport. Moreover, further field studies with freshwater organisms need to be performed. Here, we investigate the spatial distribution of MP in water surface (60 μm mesh size Neuston trawl), subtidal sediment, fish (GI of catfish, Silurus glanis), and macroinvertebrates (Hydropsychidae) along the length of the Ticino river in the North of Italy (six sites of an 80 km transect). In this study we aim to provide additional insight in (1) microplastic transport along a river and (2) sampling and extraction techniques for freshwater ecosystems. Environmental samples from different matrices require specific solutions and conditions to chemically digest organic material. Preliminary tests on MP extraction were already performed; the applied digestion protocol includes 30% hydrogen peroxide with iron catalyst (H2O2 + Fe) which is more appropriate for plant material and 10% potassium hydroxide (KOH) for animal tissues. Samples were digested for 1h at 50°C before sodium chloride solution (NaCl) was added for density separation (repeated once) and the solution filtered. For the planned analysis, particles on the filter will be visually identified with a stereo microscope and transferred onto silver membrane for the chemical analysis for polymer identification by Fourier transform infrared spectroscopy. Procedural blank will be included to assess sample contamination in the laboratory. Analysis will be completed in winter and results presented at the conference. Positive control samples of grinded, amorphous PS particles of different size categories were used to evaluate efficiency of the entire MP extraction techniques. Results from preliminary tests confirmed the presence of MP in surface water, sediment and fish GI content. The chosen solutions digested animal tissue, plants, plankton and other organic material in the samples sufficiently. The mass recovery of PS particles was 98.2% ± 0.96 (SD) for extraction using H2O2+Fe and 97.1% ± 2.4 for extraction using KOH. A first quantification of MP in water sample from the North of the Ticino revealed 5.6 MPs/m3. The concentrations are expected to increase with the length of the river towards the Po estuary. This study will provide insight into the extent of microplastic pollution in the Ticino river and give indications about major input sources based on the analysis of complex matrix samples from different sites. The use of positive control, which is highly recommended for an adequate assessment in high-quality research, verified a high mass recovery of MPs (PS). The extraction of further grinded, amorphous polymer types will be tested and the results presented at the conference. Moreover, the simultaneous analysis of water, sediment and biota samples along the sites of the river, could give an indication weather MP ingested by benthic invertebrates and fish reflect the environmental contamination.