![]() By applying their model to hundreds of rivers globally, Meijer et al. Their modelling study produces transport probability maps, which indicate for each location in the river basin the probability that MPW produced at that location would be emitted into the oceans within 1 year. (2021) was the first to examine in more detail what happens in between the MPW production on land and the emission to the ocean. ![]() In other words, they look at what comes in and predict what comes out, but do not take any overland transport and accumulation processes into account. ![]() These models use estimates of the MPW generation within a river basin and, combined with waste management, population and hydrological related variables, predict the fraction of MPW that is emitted to the ocean at the river mouth. Plastic transport and emission models have been developed over the past years to make an estimate on the amount of MPW that is emitted to the oceans via river emissions ( Lebreton et al., 2017 Schmidt et al., 2017). However, several studies suggest that a fraction of the MPW is retained in terrestrial and freshwater systems ( Tramoy et al., 2020 van Emmerik et al., 2022). It is assumed that MPW generated on land is the main source of riverine and marine plastic pollution ( Biermann et al., 2020 Lau et al., 2020 Wayman and Niemann, 2021). Each year vast amounts of MPW with a land-based source enter the natural environment, where it is transported across terrestrial systems by aeolian and aquatic processes ( Lebreton et al., 2017 Schmidt et al., 2017 Barboza et al., 2019 van Emmerik et al., 2019 Materić et al., 2020). When high production rates and extensive usage of plastics exceed the capacity of the (local) waste management systems, when waste is leaking from dumps or open uncontrolled landfills, or when waste is littered, we refer to it as mismanaged plastic waste (MPW) ( Geyer et al., 2017). Furthermore, economic activities feel negative effects as well, for example when plastic debris damages vessels or when heavily polluted beaches repel tourists. But also indirectly, for example the increased flood risk in urban areas due to plastic waste clogging the drains ( Njeru, 2006 van Emmerik and Schwarz, 2019). Human health and livelihood in general is threatened as well, directly through for example the consumption of contaminated seafood ( Vethaak and Leslie, 2016 Ribeiro et al., 2020). Plastic pollution causes harm to wildlife, through ingestion or entanglement ( Sigler, 2014). The Plastic Pathfinder contributes to a better mechanistic understanding of plastic transport through terrestrial environments, and upon future calibration and validation, can serve as a practical tool to optimize plastic waste prevention, mitigation, and reduction strategies. When the wind and/or surface runoff conditions exceed their respective thresholds, the model simulates the transport and (re)distribution of plastics, resulting in plastic accumulation hotspots maps and high probability transport route maps. The terrain surface friction, a function of the slope and land use, is converted into thresholds that define the critical wind and surface runoff conditions required to mobilize and transport macroplastic waste. The plastic transport driving forces are wind and surface runoff, while plastic transport is resisted by terrain surface friction. Here, we introduce a new conceptual model to forecast plastic transport on land: the Plastic Pathfinder a numerical model that simulates the spatiotemporal distribution of macroplastic (>0.5 cm) at a river basin scale. Yet, the transport pathways over land remain highly uncertain. Land-based plastic waste is the major source for freshwater and marine plastic pollution. ![]()
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