Modelling a microplastic-free Black Sea: strategies to lower waste from feeder rivers

This research aims to find the most effective strategy to lower microplastic (MP) pollution in the sea, by modelling different riverine MP pollution-reduction scenarios for 2050. These scenario insights can inform policy development, to aid realisation of a zero-pollution future for the Black Sea.

Plastic pollution in our seas and rivers worldwide is a global problem, with the Black Sea an example of where microplastics particularly accumulate, as it is semi-enclosed. The Black Sea is quite unique, as it has a large drainage area (2.5 million km²), with waterways flowing into it from more than 20 countries in Europe and Asia. Three large rivers feed into the sea – the Danube, Don and Dnieper – after flowing through many countries and accumulating plastic pollution. 

This study considers microplastics in rivers (<5mm diameter) from diffuse sources (such as the breakdown of macroplastics, e.g. from plastic bottles or agricultural film) and from point sources (a single identifiable origin of pollution – such as a sewage plant).

The study used an existing model for studying river pollution into the sea, which was updated to include all locations and plastic types, covering point and diffuse sources, for the 107 sub-basins that drain into the Black Sea. The researchers suggest the results from this analysis will aid the creation of effective policies to regulate the MP load entering the seas via large rivers, such as the Danube, that cross multiple countries.

The researchers developed five scenarios, with different riverine plastic pollution-reduction options, and implemented them using a pre-existing ’Model to Assess River Inputs of pollutaNts to seA’ (MARINA), across all waterways draining into the Black Sea. The researchers incorporated diffuse sources of plastic waste on land into the model and updated the data on car-tyre wear, laundry fibres and personal care products for point sources of plastic pollution.

The researchers then projected river exports of MP into the Black Sea until the year 2050, by source and sub-basin, and comparing this with actual data from 2010. Hydrology aspects and retention of MP in rivers were also added to the model – these are both factors which could be impacted by climate change, which influences water availability in rivers. Lastly, new scenarios were developed with more recent shared socioeconomic pathways (SSPs – scenarios of projected socioeconomic global changes used to establish greenhouse gas emissions scenarios under different climate policies) and representative concentration pathways (RCP – a greenhouse gas concentration trajectory adopted by the IPCC), with one scenario being modified as a baseline for the Black Sea.

The researchers examined five scenarios:

1. The baseline scenario – plastic waste management and treatment efficiencies follow current trends.
2. Improving waste-water treatment – MP from sewage is reduced.
3. Lowering MP through sustainable consumption and production of plastics – a 50% per-person reduction in MP during 2010–2050.
4. Lowering MP through better waste collection – collecting more plastic waste, and handling it better, resulting in a 90% collection rate.
5. An optimistic future incorporating scenarios 1–4. The ‘zero pollution targets’ of the EU are important, with this option lowering MP from diffuse and point sources.

The scenarios 2–5 are alternative versions of the baseline scenario and assume improvements in the waste-water treatment in 2050.

The study found that European rivers draining into the Black Sea export over half of the total microplastics to the sea, with both diffuse and point sources important contributors of MP. By 2050, Asian rivers draining into the sea will be responsible for 34–46% of MP pollution – depending on the scenario examined. Under the baseline scenario, river export of MP will increase, especially for Asian rivers and the upstream Danube sub-basin. Implementing advanced treatment technologies will reduce point-source pollution, but not for all rivers.

Reduced consumption or better collection of plastics will reduce 40% of MPs in the sea by 2050, compared to 2010. In the optimistic futures scenario (5), sea pollution was found to be 84% lower than today.

The researchers suggest that results from the MP-reduction scenarios, could support environmental policies for a ‘zero-pollution’ future of the Black Sea. The study’s scenarios are based on existing European ambitions, to support sustainable development goals including clean water, improved waste-water treatment, reduced plastic production/consumption and improving mismanagement of waste. The researchers posit that it is possible to achieve the European target to reduce microplastics in the environment by 30% by 2030 under a number of different reduction scenarios. However, they note that cleaning up the Black Sea will require co-ordinated efforts by both European and Asian countries, such as Türkiye.

Source:

Strokal, V., Kuiper, E. J., Bak, M. P., Vriend, P., Wang, M., Van Wijnen, J., & Strokal, M. (2022) Future microplastics in the Black Sea: River exports and reduction options for Zero pollution. Marine Pollution Bulletin, 178: 113633.

To cite this article/service:

“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.