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Toxic metals in bottom sediments and ferromanganese concretions of the Southern Baltic Sea

Szefer P.

Oceanological Studies

2000

Vol. 29, No. 1

31-55

Horizontal and vertical distributions of micro- and macroelements in sediment from the Southern Baltic (including the Vistula Lagoon) are discussed. Variations of concentrations of trace metals and rare earth elements (REE) in ferromanganese concretions sampled from Słupsk Furrow in the Polish Exclusive Economic Zone are characterized. The lack of positive cerium anomalies in the concretions from Słupsk Furrow indicates that they were formed under less oxidizing conditions than spheroidal concretions from the Gulf of Bothnia. Mössbauer studies indicate that poorly crystalline lepidocrosite is the principal iron oxyhydroxide mineral present in these concretions. It is concluded that Ag, Cd, Pb, Zn and possibly Cu are anthropogenic in origin. The concentrations of these elements decrease sharply with depth in the sediment column and the elements are preferentially enriched in the 2 ľm size fraction of the sediment. The anthropogenic elements show no systematic decrease in concentration with depth in a sediment core collected near the mouth of the Vistula River. This reflects the higher sedimentation rate there such that the entire upper 20 cm of the core was deposited during the major, post-war period of industrialization in Poland. It is suggested that the heavy metals are mainly adsorbed on Fe oxyhydroxide particles with diameters greater than 2 ľm at the hydrological front where the Vistula River waters mix with brackish Baltic waters. It appears that heavy-metal pollution of sediments in some parts of Puck Bay may be greater than that near the mouth of the Vistula River which may reflect, in part, the higher sedimentation rate near the mouth of the Vistula River. The mode of incorporation of heavy metals into the sediments in the two areas may also be different. It is speculated that Cu, Zn and Ag have been introduced recently into the sediments of the Gulf of Gdańsk principally from the Vistula River, whereas Cd and Pb have been transported, in part, from the atmosphere. Cd like Pb is a volatile element easily subjected to atmospheric transport. The dual source of Cd and Pb (atmospheric and riverine) reaching the Gulf of Gdańsk may explain the complex interelement relationships displayed by these elements in the sediments of this region. Ag, on the other hand, is introduced into the marine environment mainly with sewage sludge.