Environmental risk assessment of stormwater run-off from central Gothenburg to Göta älv

Abstract

An environmental risk assessment of stormwater run-off from central Gothenburg was conducted for the Göta älv river catchment located between the estuary of the Säveån river and the Älvsborg bridge. The run-off from the catchment was modeled based on standard pollutant concentrations for each land-use type present within its geographical limits. Other sources, such as tributaries, wastewater treatment plants, and combined sewer overflow were modeled from measured concentrations. The environmental fate model was based on the GREAT-ER model. The assessed pollutants were selected on the basis of municipal prioritization and data availability. The pollutants were PFOS, tributyltin, trichloroethylene, benzene, benzo[a]pyrene, copper, zinc, chromium, arsenic, lead, cadmium, mercury, and nickel. No risk was observed for any individual substance in the risk assessment, with risk character-ization ratios (RCR) below the risk threshold value of 1. However, the combined mixture toxicity RCR of the assessed substances showed that risk was present in the catchment. The metals zinc, copper, and nickel were found to be the key contrib-utors to the mixture toxicity RCR. Bioretention cells were found to be an efficient measure in reducing the run-off pollutant load from central Gothenburg. However, it was shown that the reductions had a relatively low influence on the pollutant con-centrations in the river catchment. The influence of the bioretention cells achieved a maximum RCR reduction of 5.8%. This suggested that such measures could be more efficient if implemented in catchment areas further upstream.