Plastics in an urbanizing world: sustainable strategies for rivers and seas

Plastics are part of our daily life. As a result, macro- and microplastics are found in many rivers and seas worldwide. Microplastics often originate in water systems from personal care products, household dust, laundry, and car tire wear. Macroplastics such as bottles, litter, and plastic bags are not often managed properly, resulting in water systems. Macroplastics can also be the secondary source of microplastics in waters, which may even increase pollution levels. It becomes more difficult to stop the use of plastics in our activities despite some promising efforts (e.g., the increased availability of reusable products). In addition, with ongoing urbanization, more plastics are expected in the waters. Furthermore, plastics have connections to more than five Sustainable Development Goals (SDGs) such as food security (SDG2; e.g., plastic mulching as a pollution source), sustainable sanitation (SDG6; e.g., better treatment leading to less microplastics in waters from sewage), sustainable cities (SDG11; e.g., more microplastics from car tire wear and sewage), responsible consumptions (SDG12; e.g. control waste generation) and climate change (SDG13; e.g., more floods leading to more plastics in waters), etc. This opens opportunities to explore sustainable strategies to reduce plastics in rivers and seas to increase the benefits for other SDGs. In this study, we model the effects of sustainable strategies on reducing future macro- and microplastics in rivers and seas in the 21st century under the urbanization trends. For this, we use the MARINA-Plastics model, developed and evaluated in our earlier studies1-3. Here, we integrate insights on the effects of the combined sewage connections and treatment and their individual effects on microplastic reductions in rivers up to 2100 worldwide1-2. For seas, we utilize the insights of the sustainable strategies for both macro- and microplastics in the future3. For rivers, our results for microplastic reduction differ over time worldwide. By 2030, the model suggests that controlling waste generation (e.g., less use of microplastics in personal care products) may be more effective in reducing microplastics than better sanitation (more sewage connections plus better wastewater treatment). In contrast, better sanitation seems more effective in reducing microplastic pollution by 2100. For seas globally, microplastics are expected to double by 2100 in an unsustainable scenario with increased urbanization. This pollution is projected to be reduced to below the level of 2010 when assuming the implementation of sustainable strategies such as better treatment. For macroplastics, increases are somewhat projected between 2010 and 2100 in an unsustainable scenario whereas large reductions are projected in a sustainable scenario by 2100. In all our scenarios, many European, North American, and Asian rivers were pollution hotspots in 2010, mainly due to microplastics. In an urbanizing future, many African rivers may become new plastic pollution hotspots mainly as a result of both microplastics (from urbanization activities) and macroplastics (from increasing waste production). Sustainable strategies for these hotspots should be combined to reduce plastic pollution. These insights could support SDGs.           1: Ayeri et al., (2024) 10.1021/acs.est.4c077302: Guo et al., (2024) 10.1002/sd.32793: Micella et al., (2024) 10.1029/2024EF004712