Mercury in water and sediments of the southern Baltic sea.

Total mercury concentrations [HgT] were measured in samples of water and sediments collected from the southern Baltic Sea from the period 1993-1995. Picomolar concentrations of HgT were found in offshore surface water. Higher levels were measured in samples from the plum of the Vistula. An exceptionally high concentration of mercury (25 pM HgT, 5 pM methylmercury) was measured in the near bottom, quasi-anoxic water of the Gdañsk Deep and explained by the release of mercury from fine grained sediments covering the bottom. In the sediments, the largest contents of HgT were found in fine grained, organic rich deposits of the Baltic deeps. The increase in mercury contents in the upper layers of sediments deposited within the last 100-150 years was attributed to the anthropogenic load of mercury and its increased scavenging to sediments with organic matter.