On Trace Metals Geochemistry in the Danube River and Western Black Sea.

Trace metal concentrations were measured in the Danube River estuary and in the shelf area of the north-western Black Sea. Total dissolved concentrations (<0.45 omicron M) of the freshwater in the river end-member were found to be: Cd=117pM, Pb=81pM, Co=266pM, Zn=6nM, Mn=19nM, Ni=15nM, Cu=36nM, Al=38nM and Fe=20nM. These concentrations are surprisingly low for an area where serious contamination has been suspected. This is particularly true of Cd, Pb and Zn, which are generally anthropogenic in polluted regions. The observed low concentrations, in particular for Fe, Mn, Co and Al can be attributable to the precipitation of hydrated oxides as a consequence of high pH of the Danube river. Concentrations of metals in the particulate fraction are similar to those in other major rivers of the world. the evolution of the total dissolved trace metal concentrations in the surface waters within the salinity gradient suggest: (1) no noticeable exchange between the particulate and the dissolved fraction for Cu, Ni and Zn and (2) evidence for a low solid to liquid exchange for the other metals (Cd, Fe, Mn, Co and Pb) which brings about a two-fold increase in their concentrations from lower to higher salinity. Another source of dissolved material is suspected at around salinity 15: this source may be from localised-patches in the sediment where specific redox conditions may induce a vertical flux of dissolved materials: the bottom waters above these patches are characterised by a diminution of the dissolved O2 and high concentrations of metals.

GUIEU C.;  MARTIN Jean Marie;  TANKERE S.P.C.;  MOUSTY Francis;  TRINCHERINI Pier Renato;  BAZOT M.; 

1998-06-23

JRC16676

https://publications.jrc.ec.europa.eu/repository/handle/JRC16676,