River export of macro- and microplastics to seas by sources worldwide.

Seas are polluted with macro- (>5 mm) and microplastics (<5 mm). However, few studies account for both types when modeling water quality, thus limiting our understanding of the origin (e.g., basins) and sources of plastics. In this work, we model riverine macro- and microplastic exports to seas to identify their main sources in over ten thousand basins. We estimate that rivers export approximately 0.5 million tons of plastics per year worldwide. Microplastics are dominant in almost 40% of the basins in Europe, North America and Oceania, because of sewage effluents. Approximately 80% of the global population live in river basins where macroplastics are dominant because of mismanaged solid waste. These basins include many African and Asian rivers. In 10% of the basins, macro- and microplastics in seas (as mass) are equally important because of high sewage effluents and mismanaged solid waste production. Our results could be useful to prioritize reduction policies for plastics.

The Plastic Age: River Pollution in China from Crop Production and Urbanization.

Many rivers are polluted with macro (>5 mm)- and microplastics (<5 mm). We assess plastic pollution in rivers from crop production and urbanization in 395 Chinese sub-basins. We develop and evaluate an integrated model (MARINA-Plastics model, China-1.0) that considers plastics in crop production (plastic films from mulching and greenhouses, diffuse sources), sewage systems (point sources), and mismanaged solid waste (diffuse source). Model results indicated that 716 kton of plastics entered Chinese rivers in 2015. Macroplastics in rivers account for 85% of the total amount of plastics (in mass). Around 71% of this total plastic is from about one-fifth of the basin area. These sub-basins are located in central and eastern China, and they are densely populated with intensive agricultural activities. Agricultural plastic films contribute 20% to plastics in Chinese rivers. Moreover, 65% of plastics are from mismanaged waste in urban and rural areas. Sewage is responsible for the majority of microplastics in rivers. Our study could support the design of plastic pollution control policies and thus contribute to green development in China and elsewhere.

Future microplastics in the Black Sea: River exports and reduction options for zero pollution.

The Black Sea receives increasing amounts of microplastics from rivers. In this study, we explore options to reduce future river export of microplastics to the Black Sea. We develop five scenarios with different reduction options and implement them to a Model to Assess River Inputs of pollutaNts to seA (MARINA-Global) for 107 sub-basins. Today, European rivers draining into the Black Sea export over half of the total microplastics. In 2050, Asian rivers draining into the sea will be responsible for 34-46% of microplastic pollution. Implemented advanced treatment will reduce point-source pollution. Reduced consumption or more collection of plastics will reduce 40% of microplastics in the sea by 2050. In the optimistic future, sea pollution is 84% lower than today when the abovementioned reduction options are combined. Reduction options affect the share of pollution sources. Our insights could support environmental policies for a zero pollution future of the Black Sea.

Modelling global river export of microplastics to the marine environment: Sources and future trends.

Microplastics, transported by rivers to oceans, are triggering environmental concern. This study aims to better understand river export of microplastics from land to sea. We developed the Global Riverine Export of Microplastics into Seas (GREMiS) model, a global, spatially explicit model for analysing the annual microplastics export to coastal seas. Our results indicate that riverine microplastics export varies among world regions, with several hotspots, e.g., South East Asia, and, depending on the 2050 scenario, may be doubled ('Business as usual') or halved due to improved waste management ('Environment profits'). Globally, our model simulations indicated fragmentation of macroplastics as the main source of microplastics, but this result heavily depends on the assumed fragmentation rate. Sewerage discharges contributed only 20%, ranging from 1% (Africa) to 60% (OECD countries) and decreasing by 2050 as a result of improved sanitation. We conclude that, combating microplastics in the aquatic environment requires more region-specific analyses.

River export of triclosan from land to sea: A global modelling approach.

Triclosan (TCS) is an antibacterial agent that is added to commonly used personal care products. Emitted to the aquatic environment in large quantities, it poses a potential threat to aquatic organisms. Triclosan enters the aquatic environment mainly through sewage effluent. We developed a global, spatially explicit model, the Global TCS model, to simulate triclosan transport by rivers to coastal areas. With this model we analysed annual, basin-wide triclosan export for the year 2000 and two future scenarios for the year 2050. Our analyses for 2000 indicate that triclosan export to coastal areas in Western Europe, Southeast Asia and the East Coast of the USA is higher than in the rest of the world. For future scenarios, the Global TCS model predicts an increase in river export of triclosan in Southeast Asia and a small decrease in Europe. The number of rivers with an annual average triclosan concentration at the river mouth that exceeds a PNEC of 26.2ng/L is projected to double between 2000 and 2050. This increase is most prominent in Southeast Asia, as a result of fast population growth, increasing urbanisation and increasing numbers of people connected to sewerage systems with poor wastewater treatment. Predicted triclosan loads correspond reasonably well with measured values. However, basin-specific predictions have considerable uncertainty due to lacking knowledge and location-specific data on the processes determining the fate of triclosan in river water, e.g. sorption, degradation and sedimentation. Additional research on the fate of triclosan in river systems is therefore recommended. CAPSULE: We developed a global spatially explicit model to simulate triclosan export by rivers to coastal seas. For two future scenarios this Global TCS model projects an increase in river export of triclosan to several seas around the world.

Coastal eutrophication in Europe caused by production of energy crops.

In Europe, the use of biodiesel may increase rapidly in the coming decades as a result of policies aiming to increase the use of renewable fuels. Therefore, the production of biofuels from energy crops is expected to increase as well as the use of fertilisers to grow these crops. Since fertilisers are an important cause of eutrophication, the use of biodiesel may have an effect on the water quality in rivers and coastal seas. In this study we explored the possible effects of increased biodiesel use on coastal eutrophication in European seas in the year 2050. To this end, we defined a number of illustrative scenarios in which the biodiesel production increases to about 10-30% of the current diesel use. The scenarios differ with respect to the assumptions on where the energy crops are cultivated: either on land that is currently used for agriculture, or on land used for other purposes. We analysed these scenarios with the Global NEWS (Nutrient Export from WaterSheds) model. We used an existing Millennium Ecosystem Assessment Scenario for 2050, Global Orchestration (GO2050), as a baseline. In this baseline scenario the amount of nitrogen (N) and phosphorus (P) exported by European rivers to coastal seas decreases between 2000 and 2050 as a result of environmental and agricultural policies. In our scenarios with increased biodiesel production the river export of N and P increases between 2000 and 2050, indicating that energy crop production may more than counterbalance this decrease. Largest increases in nutrient export were calculated for the Mediterranean Sea and the Black Sea. Differences in nutrient export among river basins are large.