Lithogenic and anthropogenic contributions of trace metal(oid)s in coastal sediments near the Port of Trieste (northern Adriatic Sea): A geochemical normalisation approach based on regional background values

Metal(oid) concentrations in coastal sediments are often due to the contribution of anthropogenic inputs to the local geochemistry. This study aims to assess the source (lithogenic or anthropogenic) of metal(oid)s in the surface sediments of the eastern sector of the Gulf of Trieste, which is the area most impacted by urban and industrial activities. A comparison with the environmental quality standards (EQSs) defined by the legislation showed that threshold levels were exceeded for Cr, Ni, Hg, Pb, As and Cd. Since the EQS values do not take into account the natural site-specific geochemical features of sediments, a normalisation procedure was applied to quantify the real anomaly. Aluminium (Al) was identified as an ideal proxy element due to its excellent correlation with the muddy fraction and regional functions for metal(oid)s were determined using sediments from a core collected in the central sector of the Gulf as a baseline in order to calculate enrichment factors (EFs). Negligible or low contamination was found for sediments far from the urbanised and industrialised areas, whereas the EFs were higher near the coast, revealing notable isolated anomalies. The highest enrichment was found for Hg, whose average EF value was 14 times higher than the local baseline, followed by Cu > Cd > Mo > Pb > Zn. On the contrary, Cr and Ni are, in fact, not enriched although showing concentrations higher than the EQS values. This is due to the effectively lithogenic nature of these two elements which occur in the sediments of the Gulf in relation to the particular lithogenic characteristics of the area.