Sediment quality assessment in an industrialized Greek coastal marine area (western Saronikos Gulf)

Abstract

Eight sediment cores from the coastal marine area of the western Saronikos Gulf have been analysed for grain size and geochemistry. The concentrations of eight metals (Al, Fe, Mn, Cu, Cr, Ni, Pb and Zn) were measured along with total organic carbon (TOC) and carbonate content. The cores are fairly homogeneous in terms of carbonates and the downcore variability of TOC percentage (% TOC) and are characterized by high surficial values that decrease with depth. Metal concentrations from both geological (Al, Mn, Cr, Ni) and anthropogenic origin (Cu, Pb, Zn) are higher in the muddy fraction than in the sand fraction of sediments. The spatial distribution of Al, Fe, Mn, Cu, Pb and Zn in surface sediments presents increasing concentrations from the northeast to the southwest part of the study area and from the shallow to the deeper parts in contrast to Cr and Ni, which are increased in the northern nearshore stations. Based on the vertical distributions, the metal to Al ratios of Cu, Pb and Zn show a constant decrease over depth along most cores, indicating the anthropogenic effects to surface sediments, while Fe/Al is constant. Spearman's correlation analysis performed among the fine-grain metal contents demonstrated a strong positive correlation (r>0.5, p<0.05) between Al, Fe, Mn, Cu, Pb and Zn. The calculated enrichment factors indicate minimal to moderate pollution. The concentrations of Cr at most surface sediments are higher than the “effects range low” (ERL) value (81 mg kg−1) but below the “effects range median” (ERM) value (370 mg kg−1), and the concentrations of Ni are always higher than the ERM value (51.6 mg kg−1). In contrast, the concentrations of Cu, Pb and Zn at most surface sediments are below ERL values. The mean effects range medium quotients (mERMq) of surface sediments, based on the overall metal concentrations, indicated that the surface sediments of most cores are moderately toxic. The levels of Cr, Ni, Mn and Zn at most stations are decreased in 2017, but the concentrations of Pb and Cu are increased in 2017, compared to a previous study of 2007. The concentrations of Cu, Pb and Zn in the surface sediments of the western Saronikos Gulf are lower than levels reported for the inner Saronikos Gulf, Elefsis Bay and other polluted hotspot areas in Greece, owing to a lower degree of urban and industrial development.