Background, aim, and scope The aim of this paper is to highlight a not yet recognized hazard for mass failure (landslides) of contaminated soils into rivers and to provide an understanding of important interactions of such events. A first effort to investigate the problem is made focusing on the south eastern part of the Göta Älv river valley, in Sweden, by combining geographical information on potentially contaminated sites with slope stability levels on maps. The objectives of this study were to: (1) Review current Swedish risk assessment methodologies for contaminated areas and landslides, and analyze their capability to quantify the risk of contaminated areas being subject to landslides. (2) Investigate the presence of contaminated areas at landslide risk along the Göta Älv river valley. (3) Provide an overview of the national methods for landslide risk analysis and for environmental risk classification, followed by a comparison between the methods and the results from the superposition of the two methods for the study site. (4) Make a first attempt to conceptualize the release and transport mechanisms. Materials and methods Environmental risk assessment data of the study site was combined with data on slope stability levels. Conceptual issues of the release and transport scenario were identified and a first conceptual model was created. ResultsOf 31 potentially contaminated sites, eight had moderate to high probability for landslide, and of these eight sites, five were classified as having a high or very high environmental risk. These findings had not been revealed when the data had only been considered separately. The 'actual' risk could hence be even higher than the highest environmental risk class actually suggests. By visualizing results from the landslide risk analysis with the results from the environmental risk classification of contaminated sites, a better understanding of the potential hazard involved is obtained. Discussion The release mechanisms as a result of a landslide into surface water were conceptualized using two time scales: the instantaneous and the long-term release. It is clear that the Swedish method for landslide risk assessment and for environmental risk assessment of contaminated soil considers hazard events that are characterized by different time scales. The method for landslide risk assessment addresses events that are rapid (occurring over minutes) with instantaneous impact and consequences. Measurements are made within a short time after the event (days to months). The environmental risk assessment is done with respect to events that are slowly evolving (over years or decades) and any possible consequence materializes after a long period of time. Conclusions The combined data provided a more solid basis for decisions; however, inherent difficulties when combining data based on different methods were revealed. Separate assessment methodologies executed by different authorities may lead to incorrect assessments and inappropriate protective measures.Recommendations and perspective...