Speciation of heavy metals in bottom sediments of a drinking water reservoir for Gdańsk, Poland – changes over the 14 years

Eliza Kulbat

doi:10.5004/dwt.2020.25003

Speciation of heavy metals in bottom sediments of a drinking water reservoir for Gdańsk, Poland – changes over the 14 years

Abstrakt

There was conducted a comparative study of the concentrations of heavy metals (Zn, Cu, Pb, and
Cd) in the surface layer of sediments collected in two investigation periods: 1999–2000 and 2013.
The results demonstrated that the degree of metals pollution decreased over time. The contamination
factors (Cf) calculated for Zn, Cu, Pb, and Cd were respectively 3.63, 3.86, 3.23, and 3.25 in the
first period of research and 1.35, 3.42, 1.98, and 1.43 in the second one. The metal speciation analysis
indicated that Zn was mainly associated with the Fe–Mn oxides fraction and the residual fraction,
and Cu – with the residual fraction and the organic fraction in both periods of investigation, while the
percentage of geochemical fractions in binding of Pb and Cd changed in time. The share of fractions
Fe–Mn oxides/carbonate increased in the case of Pb, and carbonate/exchangeable fractions in the case
of Cd. The risk assessment code (RAC) decreased in the following order: Cd > Zn > Pb > Cu and was
higher in 2013 - achieved the very high-risk category in the case of Cd. Thus, despite the decrease
of sediment pollution, RAC for Cd increased due to changed geochemical speciation.