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

Abstract

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 runoff 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 runoff 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/cm 3 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.

Microplastics in freshwater fishes: Occurrence, impacts and future perspectives

“…Microplastics in freshwaters tend to move and behave according to plastic particle properties such as size, shape or polymer density as well as features and processes within the system (Bondelind et al, 2020; Figure 1). MPs may be transported floating, in the water column or carried along the bottom sediments and may have variable residence times in the environment, depending on whether MPs are ingested, impeded or sink and settle onto or into bottom sediments (Daily & Hoffman, 2020;Hoellein et al, 2019;Song, Jongmans-Hochschulz, et al, 2020).…”

“…Microplastics trapped within sediments may eventually permeate into groundwaters or aquifers before re‐joining the water cycle (O’Connor et al, 2019; Re, 2019), or may be freed by storm and rain events that may resuspend trapped MPs and introduce them back into aquatic systems (Bondelind et al, 2020; Ockelford et al, 2020; Piñon‐Colin et al, 2020). Since freshwater and climatic factors may vary seasonally, there can also be some temporal variation, with environmental MP loadings typically being higher during wet seasons (Campanale et al, 2019; Eo et al, 2019; Kurniawan & Imron, 2019; Weideman et al, 2019; Yuan et al, 2019).…”

“…The foraging habitats of freshwater fish should also impact MP encounter rates, given MP distributions and loadings differ, with typically higher loadings in sediments compared to overlaying surface waters (Bondelind et al, 2020; Boucher et al, 2019; Li, Geng, et al, 2019). Consequently, within a given location, pelagic species ought to encounter fewer floating MPs (e.g.…”

“…and aquatic processes (e.g. water currents and storm events) (Bondelind et al, 2020; Li, Zhang, et al, 2020). The ultimate fate of MPs is to accumulate in sinks, such as river sediments (Simon‐Sánchez et al, 2019; de Villiers, 2019).…”

Combined Approaches to Predict Microplastic Emissions Within an Urbanized Estuary (Warnow, Southwestern Baltic Sea)

“…Here MP emissions per area within the land use categories can vary over time and region. Our utilized MP values are rather conservative, considering reports of on average 7,713 to 111,000 MP/m 3 (>20 μm) in stormwater (Bondelind et al, 2020). Further, tire and road wear particles which can exhibit a significant share were not included in the study by Liu et al (2019) and are accordingly not represented by our results.…”