Session D2 - Pollution: sources and characterisation

Urban stormwater systems have been identified as a major pathway by which microplastics escape into the environment. Our study surveyed stormwater management practices in seven European countries to evaluate awareness, regulatory frameworks, treatment facilities, and monitoring related to microplastic pollution. The findings reveal a significant gap: no country currently enforces specific regulations or standards for microplastics in stormwater, and intentional removal of microplastics is virtually absent across all surveyed nations. Stormwater treatment infrastructure (e.g. sedimentation tanks, ponds, filters) is in place to varying degrees, but these are designed for “conventional pollutants” (like suspended solids) with removal rates < 50 % (sedimentation) and especially sedimentation is not suitable for microplastic capture. Awareness of the microplastic issue is growing among water professionals and the public, but practical actions lag behind. Monitoring of microplastics in runoff is rare, resulting in scarce data and uncertainty about removal efficiencies. These results highlight an urgent need for developing guidelines, improving treatment technologies, and implementing monitoring programs for microplastics in urban stormwater. Bridging this regulatory and knowledge gap is crucial for reducing emissions of microplastics.

Urban stormwater runoff contains pollutants that deteriorate the quality of surface and groundwater when discharged untreated. To prevent pollution and to develop treatment facilities, understanding the sources of hazardous substances is essential. While the leaching behavior of metal roofs is well investigated, the contribution of non-metal roofing materials, especially for inclined roofs, to stormwater contamination is still poorly investigated. Based on a market and literature study to determine the most used non-metal roofing materials in Germany, laboratory leaching tests were conducted in the first step with 15 selected roofing materials: clay tiles, concrete tiles, wood shingles, fiber cement panels, bitumen shingles, and plastic tiles. The eluate of the lab test has been analyzed for different organic and inorganic parameters that occur in urban stormwater. The laboratory test results provided the basis for the subsequent field test. For a period of one year, pilot-scale roofs (triplicates) were exposed to weathering, and runoff from all rain events were collected and analyzed for the parameters found in the lab test. Results showed that several materials release environmentally relevant concentrations of hazardous substances in the lab and field: treated wood shingles are a strong source of B, Cu, and NH4+. Concrete tiles release the biocide terbutryn and associated transformation products, and clay tiles leach V. These findings highlight the role of non-metal roofing materials as pollutant sources in urban runoff.

Most research on roadside infiltration and pollutant accumulation in roadside soils has focused on metals, despite growing evidence that road runoff contains a broader range of pollutants of emerging concern. Among these, PFASs in stormwater are attracting increased interest. This study aims to investigate and compare the accumulation of PFASs and metals in roadside soils to assess similarities and differences of their occurrence, concentration, and distribution with depth and distance from the road. Roadside soil samples were taken along 12 roads in Sweden and Germany. Metal accumulation patterns in the soil were in consistent with previous studies: concentrations were generally higher along roads with higher traffic intensities and decreased with increasing distance from the road and sampling depth. In contrast, PFOS, the most frequently quantified PFAS compound, showed increasing concentrations with distance from the roads and no considerable variation between sampling depths, indicating its persistence and mobility. Elevated concentrations in reference samples suggest background contamination in densely populated areas rather than traffic related sources in road runoff as specific source. 

The presence of microplastics in gully pot has been little studied to date, even though they are the primary entrance for solid particles into the stormwater system. This study focuses on a predominantly industrial catchment that discharges into a detention basin. Eight gully pot were selected for a more detailed study to better understand the contribution of the associated sub-catchments. Four sediment samples were collected from the bottom of each gully pot after rainfall events, and the microplastics and tire road wear particles were analyzed. The results highlight a heterogeneous spatial distribution of microplastics within the catchment area, in contrast to a less variable distribution for tire road wear particles. Microplastic loads and fluxs were also estimated at the sub-catchment scale. To explain these variations within the catchment area, potential emission sources were identified, taking into account the activities present within the sub-catchment areas. This work has highlighted the importance of influencing factors such as the porosity between private and public spaces with regard to the transfer of microplastic particles. Initial information on emission sources could guide public policies for reduction at source in industrial areas.