Temporal changes of metal and trace element contamination in marine sediments due to a steel plant: The case study of Bagnoli (Naples, Italy)

Marine sediments are the final sink of most contaminants produced via anthropogenic activities in coastal areas. Therefore, these sediments may be a useful archive for the investigation of past contamination patterns. To determine the contamination extent, it is necessary to compare present impacted conditions with reference conditions recognizable in the deeper levels of marine sediment. Three sediment cores collected in 2005 in the marine area of Bagnoli (Naples, Italy) close to an important steel plant working from 1910 to 1990 were analysed for grain size and chemical composition (trace elements, PAHs and PCBs). Concentration profiles and enrichment factors (EF) were used to assess the anthropogenic contribution for several elements (Cd, Cu, Hg, Pb and Zn) responsible for contamination of the marine area together with PAHs and PCBs. Conversely, generalized high As concentrations were primarily attributed to hydrothermal submarine springs. Compared to PAHs, PCBs and the content of pelite profiles, EF profiles produced a historical reconstruction of the environmental patterns. The start of the concurrent increase of trace elements and PAHs at 139 cm was attributed to the beginning of the steel plant activity in 1910, while the successive increase of PCBs at 89 cm was associated with the use of these compounds in the electrical equipment in the second half of the 20th century. The highest EFs of Cu, Pb and Zn, between 99 and 29 cm depth, are associated with the time interval of the 1950s–1980s when the highest production levels were attained. A significant decrease of most trace elements (Cu, Hg, Pb and Zn) starting at 29 cm and successively of Cd and PCBs (above 7 cm) mark the gradual decrease of industrial activities and the final closure of the plant. However, contaminants maintain considerable concentrations up to the top of the core, which indicates recent contribution to the marine environment. A new survey would be useful to verify if natural recovery in the area due to the deposition of recent sediment is currently occurring.