Conceptual framework for exploring riverine macroplastic fragmentation

     Field-based information on the rates of macroplastic fragmentation in rivers is currently mostly unavailable. However, obtaining such data in future research is crucial to understanding the production of secondary micro- and nanoplastics in rivers, the transfer of these harmful particles throughout the natural environment, and assessing the risks they pose to both biota and human health.
     To support future experimental works addressing this gap we developed a conceptual framework which identifies two types of riverine macroplastic fragmentation controls: intrinsic (resulting from plastic item properties) and extrinsic (resulting from river hydromorphology and climate)^[1].  First, based on the existing literature, we identify the intrinsic properties of macroplastic items that make them particularly prone to fragmentation (e.g., film shape, low polymer resistance, previous weathering). Then, we conceptualize how extrinsic controls can modulate the intensity of macroplastic fragmentation in perennial and intermittent rivers. Using our conceptual model, we hypothesize that the inundated parts of perennial river channels—as specific zones exposed to the constant transfer of water and sediments—provide particular conditions that accelerate mechanical fragmentation of macroplastic resulting from its interactions with water, sediments, and riverbeds. The unvegetated areas in the non-inundated parts of perennial river channels provide conditions for biochemical fragmentation via photo-oxidation. In the non-inundated sections of perennial river channels, unvegetated areas create conditions favoring biochemical fragmentation through photo-oxidation. In intermittent rivers, the entire channel zone is hypothesized to support both physical and biochemical fragmentation of macroplastics, with mechanical fragmentation prevailing during periods of water flow.
     Our conceptualization can support planning of future experimental and modelling work aimed at the direct quantification of plastic footprint of macroplastic waste in different types of rivers.

The study was completed within the scope of the Research Project 2020/39/D/ST10/01935 financed by the National Science Center of Poland.
References
1. Liro, M., Zielonka, A., van Emmerik, T.H.M., 2023. Macroplastic fragmentation in rivers. Environment International 180, 108186. https://doi.org/10.1016/j.envint.2023.108186