Effects of anthropogenic activities on the levels of heavy metals in marine surface sediments of the Thessaloniki Bay, Northern Greece: Spatial distribution, sources and contamination assessment

Surface marine sediments act as important repository of heavy metals (HMs) and play a significant role in their transport and possible release. The anthropogenic contribution to heavy metal contamination and the associated ecological and health risks should be evaluated in studied areas. The objectives of this study were to investigate the presence and spatial distribution of heavy metals (Cr, Ni, Cu, Mn, Cd, Zn, Fe and Pb) in surface marine sediments located in the Northern Thermaikos Gulf, which is an area of increased ecological, financial and social significance, using a sensitive and reliable analytical method and to evaluate the anthropogenic contribution and ecological risks related to the presence of heavy metals. The mean HM concentrations, in the sediments of Thermaikos Gulf exhibited a decreasing order: Fe > Mn > Zn > Cr > Pb >= Ni > Cu > Cd. A very strong correlation was demonstrated between Cu, Ni, Pb and Zn indicating that these elements originate from common anthropogenic sources. This was also supported by Enrichment Factors (EF) and I-geo values, which revealed that almost 50% of the sediments were characterized as heavily to extremely polluted concerning Cd, while almost 30% and 20% of the sampled sediments were characterized as moderately to heavily polluted with regards to Pb and Zn, respectively. Pollution Load Index (PLI) for almost all samples exhibited values > 1 indicating anthropogenic pollution. Ecological Risk (Er) values for Cd indicated high to extreme risk for 50% of the samples. Cr, Cu and Pb concentrations for 74%, 95% and 74% of the samples, respectively, indicated occasional association to toxic biological effects on aquatic organisms. For Ni, 87% of the sediments frequent association with adverse biological antic effects. Contamination Severity Index (CSI) showed that 22% of the samples reflected a moderate to high severity of contamination. Two of the samples near the industrial and shipping zone, exhibited the highest CSI values. The highest total Toxic Units (Sigma TUs) were calculated in sediment samples affected by industrial wastewater and shipping activities, with Ni presenting the higher TUs compared to the rest of the HMs and contributed the most (37%) to the overall TUs revealing its high potential toxicity for the marine ecosystems in Thermaikos Gulf. The Total Risk Index (TRI) for each HM exhibited a decreasing order of Ni (3.9) > Cu (3.0) > Cd (2.6) > Pb (2.0) > Cr (1.6) > Zn (1.4). The area exhibiting the highest impact of anthropogenic HMs, coincides with the Thessaloniki's port broad area, where the industrial and shipping activities have been taking place for several years, indicating the cumulative effect of the anthropogenic load from the activities on urban coastal regions.