Heavy metals in coastal sediments of the Ligurian sea off Vado Ligure

Abstract

This paper combines data from a survey on heavy metal contamination of surficial sediments and the analysis of a short sediment core (30 cm) carried out in 1999 and 2001, respectively. Heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) and Al were analysed by AAS after complete dissolution of the samples. Surficial sediments are particularly rich in Cr, Cu, Hg and Pb, which reach concentrations of 322, 47.0, 5.85 and 145 mg/kg, respectively. While most metals show high concentrations close to the built-up area, the maximum values of Cr characterise offshore samples, thus suggesting a different origin. Sediment accumulation rates and chronologies were calculated on the basis of both 137 Cs and 210 Pb activity-depth profiles. The depth distribution of Al is peculiar, showing several peaks (from ca. 17 to ca. 106 mg/g) that are not justified by changes in sediment grain size and mineralogical composition. Very recent inputs of Cr and Ni are accounted for by surficial peak values, whereas Hg and Cu reach high concentrations at depth in core (before the early 1960s) and then decrease. Cu shows also a recent peak. Sediment grain size as well as organic carbon content do not seem to be correlated and significantly influence the metal distributions. Hg concentrations exceed the ERM guidelines all over the study area, whereas Cr is higher than the ERM at the top of the core. Only Cd is always lower than the ERL guidelines.