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Macroplastic fragmentation in rivers
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This paper presents a framework for understanding how larger plastic waste in rivers breaks down into microplastics and nanoplastics over time. The researchers identified key factors that control fragmentation, including the type of plastic, its shape, and river conditions like sunlight exposure and water flow. Understanding this process is important because rivers are a major pathway for microplastics to spread through the environment and eventually reach drinking water sources.
The process of macroplastic (>0.5 cm) fragmentation results in the production of smaller plastic particles, which threaten biota and human health and are difficult to remove from the environment. The global coverage and long retention times of macroplastic waste in fluvial systems (ranging from years to centuries) create long-lasting and widespread potential for its fragmentation and the production of secondary micro- and nanoplastics. However, the pathways and rates of this process are mostly unknown and existing experimental data not fully informative, which constitutes a fundamental knowledge gap in our understanding of macroplastic fate in rivers and the transfer of produced microparticles throughout the environment. Here we present a conceptual framework which identifies two types of riverine macroplastic fragmentation controls: intrinsic (resulting from plastic item properties) and extrinsic (resulting from river characteristics and climate). 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). Second, we formulate a conceptual model showing how extrinsic controls can modulate the intensity of macroplastic fragmentation in perennial and intermittent rivers. Using this 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 the physical fragmentation of macroplastics resulting from their mechanical 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 intermittent rivers, the whole channel zone is hypothesized to favor both the physical and biochemical fragmentation of macroplastics, with the dominance of the mechanical type during the periods with water flow. Our conceptualization aims to support future experimental and modelling works quantifying plastic footprint of different macroplastic waste in different types of rivers.
More Papers Like This
Macroplastic fragmentation in rivers
AI summary Read the abstract
This review examines how large plastic debris in rivers gradually breaks apart into micro- and nanoplastics through physical abrasion, UV degradation, and biological activity, with river systems acting as long-term reservoirs and transfer pathways for plastic pollution. The authors propose a conceptual framework identifying which properties of the plastic item and which river characteristics control how quickly fragmentation occurs, finding that retention times can range from years to centuries. Understanding these fragmentation rates is essential for predicting how much secondary microplastic pollution ultimately reaches the ocean and enters food chains.
Conceptual framework for exploring riverine macroplastic fragmentation
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This paper presents a conceptual framework for studying how macroplastic debris fragments into smaller particles in rivers, identifying key physical and chemical processes and calling for field-based fragmentation rate data to improve plastic pollution models.
First attempt to measure macroplastic fragmentation in rivers
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Researchers developed the first method to directly measure how large plastic debris fragments into microplastics while traveling through rivers. They found that river transport causes significant breakdown of plastic waste into smaller pieces, confirming that rivers are major producers of secondary microplastics. This is important for understanding where microplastics come from, since rivers eventually carry these particles to oceans and drinking water sources.
Insights into the in-situ degradation and fragmentation of macroplastics in a low-order riverine system
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Researchers studied the in-situ degradation and fragmentation of larger plastic debris into microplastics within a low-order stream system. The study found that these small, often overlooked waterways are active sites where plastic materials break down, serving as important conduits for microplastic generation and transport to downstream coastal environments.
Influence of sediment size on microplastic fragmentation
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Researchers examined how sediment grain size influences the physical fragmentation of microplastics in river environments, where the mechanical controls on microplastic storage, remobilization, and transfer pathways remain poorly understood. The study found that sediment size plays a meaningful role in breaking down plastic particles, contributing to the generation of smaller microplastic fragments in fluvial systems.
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