Historical pollution of seldom monitored trace elements in Sweden—Part A: Sediment properties and chronological indicators

Abstract

Sediment cores from four small oligotrophic boreal lakes, with minor acidification, in remote regions of central Sweden were used for historical interpretation of their metal content, with focus on Cu, Cd, Pb and Zn in Lake Stensjön, which has the longest sediment record (at least two centuries according to ²¹⁰Pb dating). Comparison is made with the other three lakes. Major and trace elements in lake water, porewater and the acid-leached (HNO₃) solid sediment phase was analysed with ICP-MS. In addition, general lake water chemistry, TOC and principal anions were measured in the aqueous phases. Redistribution processes were interpreted from geochemical modelling. The solid/solution distribution of pe/pH sensitive elements, indicates a minor diagenetic redistribution and the concentration profiles are therefore suitable for chronological evaluation. The ratios of Al, Ti, Sc and V, indicated a qualitative shift of sedimenting material a century ago, which did not have any impact on the retention of trace elements. Lead had a concentration profile, supported by the ²⁰⁶Pb/²⁰⁷Pb ratio, where it was possible to distinguish preindustrial conditions, early industrialisation in Europe, industrialisation in Sweden, and the use of leaded petrol after the Second World War. Cadmium showed a similar concentration pattern. The zinc profile resembled that of cadmium, but with less enrichment. Local lithogenic sources are believed to be quantitatively important. The solid/solution distribution (K_d) was independent of depth for all four elements. The sediment concentrations of copper and zinc are not related to early industrialisation but its concentration has doubled since the Second World War.