Based on data for 3,525 wastewater treatment plants and literature data, the team calculated that about 67 trillion microplastic particles of the previously mentioned size enter the Baltic Sea each year. The simulations used for the calculations based on three-dimensional flow models also provided an insight into the time spent by the particles in the sea and identified major deposition sites. According to the figures from the scientific team, the majority of the particles are deposited, within a relatively short residence time of around 14 days, on the coasts near to the emission points such as river estuaries. It can be assumed that on average around one million particles are deposited per meter of coastline every year.
Against this background, the results also show clearly what efficient monitoring could look like. Because the highest deposition rate is on the coasts near emission sources, it is here that the level of pollution of the Baltic Sea with microplastic can best be recorded through regular monitoring, says Gerald Schernewski, head of the Coastal and Marine Management working group at the IOW. Particularly recommended would be a monitoring strategy that prioritizes the banks of fjords, bays and lagoons. According to the calculations, these can serve as efficient traps for microplastics and thus protect the open Baltic Sea from pollution.
In a further study, the team examined, with the help of various scenarios, the effectiveness of reduction measures at individual sources and found that the greatest effect could be achieved by establishing sewage separation with retention units. As a result, the total quantity of microplastic discharged into the Baltic Sea could be halved. A reduction of a further 14 % would be attained if all wastewater were processed by treatment plants with a third treatment stage.
To the original publications:
- IOW press release of 25.2.2021
- Photo: @ Pixabay