Scotland's seas are mainly clean and safe, although there are some localised areas where there is contamination or hazards to human health. For example, sediments in several harbours and estuaries remain contaminated with hazardous substances, a legacy of past industrial discharges. Water quality in the Forth and Clyde estuaries is compromised by discharges of industrial effluent and treated sewage although effluent treatment has improved, resulting in returning populations of residential and migratory fish. The use of historical contaminants such as polychlorinated biphenyls (PCBs) and tributyl tin (TBT) has been banned, and monitoring continues to assess their continued environmental decline.
Information is being gathered on a range of other contaminants, including endocrine disrupters and brominated flame retardants, to assess their environmental effects. Diffuse inputs of nutrients and bacteria have given rise, respectively, to some localised issues in small east coast estuaries and at bathing beaches. Action plans have been put in place to tackle these issues. Concerns such as marine litter and underwater noise have become more broadly recognised and will be addressed through the operational response to the Marine Strategy Framework Directive. Generally the effects of noise remain unquantified and unknown.