Environmentally hazardous substances (HS) are released to coastal waters from point sources such as wastewater treatment plants, industries, precipitation-related overflow, dredging of contaminated sediments, aquaculture, harbours, dockyards, and fire drills (Table 1 and 2). HS may pose a direct toxic threat to marine organisms. Further, due to bioaccumulation of the HS in the food web, humans consuming mussel, crustacean, and fish may also be at risk. This exposure has led to emerging concern among local citizens regarding the health and use of their local coastal area. Present environmental monitoring only considers a limited number of HS at very few stations and, thus, overlooks the spatial distribution, possible overlap, and combined effects of the HS discharged from different point sources. High concentrations of HS are often allowed in the mixing zone near the outlet. This solution seems less costly than improving cleaning facilities or than implementing discharge bans with the risk of losing jobs. The old narrative that ‘the sea dilutes it all’ is, however, questionable as the HS may be accumulated over time, both in sediments and biota near the discharge site, and/or exported to neighbouring areas contributing to the cumulative pressures on marine ecosystems.

Table 2. Overview of different Hazardous substances and their chemical properties, which define their potential effects on marine organism and humans (EQS dossiers, 2005-2012).