An Assessment of the Contamination and Toxicity of Marine Sediments in the Holy Loch, Scotland

Following the closure of the United States Navy Submarine Base in 1992, video surveys revealed that a considerable amount of debris, largely scrap metal, was present on the bed of the Holy Loch. A working group was set up to examine ways of ‘cleaning-upʹ the loch. Consultants were employed by the UK Ministry of Defence to carry out an environmental survey of the Holy Loch, including an assessment of the consequences of lifting the debris from the loch bed. This survey revealed that a number of contaminants were present at high concentrations in the bed sediments. These contaminants included persistent, toxic and bioaccumulable substances such as trace organic contaminants and trace metals. Concern was expressed that the debris removal operation may lead to the release of sediment-bound contaminants, which may in turn exert toxic effects on local flora and fauna. Consequently, the Scottish Environment Protection Agency carried out a survey to verify the levels of persistent organic contaminants and trace metals in the sediments, to set these in context on a UK scale, and to assess the toxicity of sediment/water mixtures. Contamination of Holy Loch sediments by polychlorinated biphenyls (PCBs) and by trace metals, especially copper and zinc, was confirmed as severe but localized. Sediment bioassays indicated that acute water column toxicity was unlikely to arise from the release of sediment-bound contaminants during the debris removal operation. Contaminant levels in mussels collected before and after the initial phase of the debris removal operation showed little change, suggesting no impact on local flora and fauna.