Ž . The Science of the Total Environment 213 1998 185192 Mercury in water and sediments of the southern Baltic Sea J. Pempkowiak a,  , D. Cossa b , A. Sikora a , J. Sanjuan b a Department of Marine Chemistry and Biochemistry, Institute of Oceanology, PO Box 68, 81-712 Sopot, Poland b IFREMER, Centre de Nantes, BP.21105, F.44311 Nantes Cedex 03, France Abstract   Total mercury concentrations Hg were measured in samples of water and sediments collected from the southern T 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 Ž . mercury 25 pM Hg , 5 pM methylmercury was measured in the nearbottom, quasi-anoxic water of the Gdansk ˜ T Deep and explained by the release of mercury from fine grained sediments covering the bottom. In the sediments, the largest contents of Hg were found in fine grained, organic rich deposits of the Baltic deeps. The increase in T 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.  1998 Elsevier Science B.V. Keywords: Mercury; Dissolved; Total; Water; Enriched; Sediments; Baltic Sea 1. Introduction The Baltic Sea is a semi-enclosed water body Ž surrounded by highly industrialised countries Fig. . 1 . The Baltic Sea is characterised by two main features. The surface waters are brackish as a result of riverine inputs and there is a permanent halocline at approximately 60  80 m, causing oxy- gen depletion and anoxia in sub-halocline waters  Corresponding author. Tel.: 48 58 5517281; fax: 48 58 5512130; e-mail: pempa@iopan.gda.pl of the central basins. The trace-metal cycles in the Baltic Sea are expected to be strongly influ- enced by the anthropogenic activities since the Ž beginning of the 20th century Borg and Jonsson, . 1996 . Previous studies have indicated ‘dissolved’ Hg Ž . concentrations at a level of 10 pM 5  50 pM Ž without any significant spatial trend Brugmann, ¨ . 1982 . However, considering strong stratification of water masses, vast areas of both sediments and overlying water permanently depleted of oxygen and a number of large rivers draining industri- alised regions and discharging water into the 0048-969798$19.00  1998 Elsevier Science B.V. All rights reserved. Ž . PII S0048-9697 98 00091-6