Supervisors info:
Εμμανουήλ Δασενάκης, Καθηγητής Τμήματος Χημείας, ΕΚΠΑ
Σεραφείμ Πούλος, Καθηγητής Τμήματος Γεωλογίας, ΕΚΠΑ
Ελένη Καμπέρη, Ερευνήτρια Β', ΕΛ.ΚΕ.Θ.Ε
Summary:
Marine sediments are considered as “traps” for major elements and trace metals and at the same time may act as a secondary source of diffuse pollution. The aim of this work is to assess the levels and distribution of metals in surface and short cored sediments of the Elefsis Gulf, which has been characterised as one of the most heavily industrialized areas in Greece. With this aim, the concentrations of Al, Fe, Mn, Cu, Hg, Ni, Pb, Zn, organic and inorganic carbon contents, as well as magnetic parameters, were determined in surface and cored sediments. The highest concentations of ferrimagnetic minerals were determined at the stations, situated near the steelworks. The concentrations of metals in surface sediments were compared with ecotoxicological ERL and ERM values. The results showed that the metals, which are likely to cause adverse effects on benthic biota, are zinc (Zn) and mercury (Hg). Furthermore, the assessment of potential sediments contamination by anthropogenic activities, was accomplished by the use of enrichment factors (ΕF). The results showed that in surface sediments, the highest contamination was caused by Pb, Cu, Zn and Hg. Extraction by cold, dilute acid (0,5 M HCl) in the surface sediments showed high concentations of labile fraction and high extractability of metals Pb, Zn and Cu, implying that these metals are potentially mobile and more bioavailable. A method of sequential extractions was first applied in the sediments of Elefsis Gulf, in order to establish the degree of pyritization (%DOP) and the degree of trace metal pyritization (%DTMP). Pyrite is, thermodynamically, the most stable form of sulfides, thus, the association of Fe and trace metals with this phase, could greatly reduce their mobility. In the surface sediments, the highest DOP values were determined in the western part of the gulf, where seasonal anoxia of bottom water is encountered. The incorporation of trace metals into pyrite (%DTMP) is low (with the exception of Hg). In cored sediments, Mn, Cu, Pb and Zn prevail in the «reactive», labile fraction (low DTMP values). Iron and Ni prevail in the fraction of clay minerals. On the other hand, Hg shows high 'preference' to the fraction of pyrite (high DTMP values). However, this may indicate a more general degree of mercury sulphide mineral associations and not incorporation of mercury into pyrite, since Hg sulphides are not completely extracted by the “reactive” fraction. Finally, the process of sequential extractions BCR was applied in cored sediments collected from the close vicinity of steelworks, in order to investigate the forms of metals in the sediments. The results were commented according to the plant production activity and the adoption of best available techniques.
Keywords:
trace metals, sediments, marine pollution, sequential extractions, pyrite
