Simulation study on 3H behavior in the Fukushima coastal region: Comparison of influences of discharges from the Fukushima Daiichi and rivers

The release of tritium (³H) to the ocean is planned on the coastal environment in the Fukushima coastal region from Spring or Summer of 2023. Before its release, we evaluate the effect of ³H discharges from the port of Fukushima Daiichi and rivers in the Fukushima coastal region using a three-dimensional hydrodynamic model (3D-Sea-SPEC). The simulation results showed that discharges from the port of Fukushima Daiichi dominantly affected the ³H concentrations in monitoring points within approximately 1 km. Moreover, the results indicate that the effect of riverine ³H discharge was limited around the river mouth under base flow conditions. However, its impact on the Fukushima coastal regions under storm flow conditions was found, and the ³H concentrations in seawater in the Fukushima coastal region were formed around 0.1 Bq/L (mean ³H concentrations in seawater in the Fukushima coastal region) in the near shore.

Hydrodynamic modelling of traffic-related microplastics discharged with stormwater into the Göta River in Sweden

Microplastics (MP) are transported from land-based sources from rivers to marine waters. However, there is currently little knowledge about MP fate from land sources to marine waters. Traffic is estimated to be one of the largest sources of MP; hence, stormwater is expected to be an important transportation route of MP to marine waters. The aim of this study was to investigate the effect of the size and density of tyre wear particles in road run-off on their fate in the Göta River in Sweden using hydrodynamic modelling. The model of the stretch of Göta River, Sweden's largest river, passing through Gothenburg (Sweden's second largest city) and out to the sea, was set up using MIKE 3 FM software. Literature data were used to define the MP characteristics: concentrations in stormwater, prevalent particle sizes, density of MP commonly occurring in road run-off and settling velocities. Results show that higher concentrations of MP are found on the south side of the river, compared with the north side, due to higher annual average daily traffic loads along the south side of the river. The mixing processes in the river and the MP concentrations were generally influenced by the vertical water density gradient caused by saline water from the Kattegat strait. While most MP with higher density and larger size settle in the river, smaller MP with density close to 1.0 g/cm³ do not settle in the river and therefore reach the Kattegat strait and the marine environments. Further research is needed to describe the fate and transport of microplastics in the stormwater system, including treatment facilities, i.e. biofouling, aggregation, degradation and/or further fragmentation and settling.