Petroleum oil and mercury pollution from shipwrecks in Norwegian coastal waters

•There are about 2100 wrecks within the Norwegian coastal waters and ca. 2000 t of oil salvaged from these wrecks.•Sediment PAH concentration is about 100 times higher than the background concentration of 0.6 mg/kg d.w.•About 0.03 km2 area of the seabed sediment around U864 wreck has Hg concentration exceeding 1.0 mg/kg.

Worldwide there are tens of thousands of sunken shipwrecks lying on the coastal seabed. These potentially polluting wrecks (PPW) are estimated to hold 3-25 million t of oil. Other hazardous cargo in PPW includes ordnance, chemicals and radioactive waste. Here, we present and discuss studies on mercury (Hg) and oil pollution in coastal marine sediment caused by two of the > 2100 documented PPW in Norwegian marine waters. The German World War II (WWII) submarine (U-864) lies at about 150 m below the sea surface, near the Norwegian North Sea island of Fedje. The submarine is estimated to have been carrying 67 t of elemental Hg, some of which has leaked on to surrounding sediment. The total Hg concentration in bottom surface sediment within a 200 m radius of the wreckage decreases from 100 g/kg d.w. at the wreckage hotspot to about 1 mg/kg d.w. at 100 m from the hotspot. The second wreck is a German WWII cargo ship (Nordvard), that lies at a depth of ca. 30 m near the Norwegian harbor of Moss. Oil leakage from Nordvard has contaminated the bottom coastal sediment with polycyclic aromatic hydrocarbons (PAH). The findings from this study provide useful insight to coastal administration authorities involved in assessing and remediating wreck-borne pollution from any of the tens of thousands of sunken shipwrecks.

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