Sediment chronologies of As, Bi, and Ga in Sweden—impact of industrialisation

Abstract

The acid-leachable amount and pore water concentration of As, Bi and Ga in sediment cores from four remote lakes in a south to north transect in Sweden were used to recapitulate the pollution history of the elements. The diagenetic impact on the element distribution was elucidated from their solid/solution partition and relationships to elements indicative for diagenesis. Dating was made by their acid-leachable lead content in combination with the 206Pb/207Pb ratio. In one of the lakes this approach was validated against dating with 210Pb. The impact of diagenesis on the sediment distribution of theses elements was found to be low enough for a chronological interpretation of the sediment profiles, as evidenced by their ratios to elements indicative of the geological background. A closer examination of the diagenetic impact would however be required if a more detailed chronology is desired. This study has demonstrated that atmospheric deposition of arsenic, bismuth and gallium contributes to the sediment inventory of these elements. The major part of the deposition of arsenic and bismuth took place after the Second World War. For gallium no concentrations exceeding background were detected before circa 1930. Increased levels of arsenic are traceable to circa 1850. For bismuth increased levels are concluded to extend before 1790, i.e., background concentrations were not reached in the present cores. For all elements the atmospheric deposition has been lower towards the north.