Pollutant trends and hazard ranking in Elefsis Bay, Greece

This study investigates the trends in pollutant distributions in Elefsis Bay and establishes an approach to rank contaminants according to their potential hazard. Sampling locations include points along the coast and within the bay. The investigation focuses on four metals, lead (Pb), zinc (Zn), chromium (Cr) and copper (Cu). Temporal trends are investigated by comparing average yearly concentrations for an 18-year long record. Only Cr in seawater exhibits a clear decreasing trend, both at the coast and within the bay. Spatial trends are studied by plotting average yearly concentrations along the coast for every year in the record. Only Cr exhibits systematically peak concentrations in water samples close to a stream outfall and periodic peaks in the sediment at the same location. Periodic peaks of Cu, Zn and Pb are also detected in both water and sediment samples obtained close to the two shipyards of Elefsis Bay. A comparative study of spatial trends confirms that the areas by the two shipyards are the most heavily impacted. Finally, the four metals are ranked by defining a hazard index as the ratio of the 95 percentile for the pollutant concentration and an allowable concentration for each pollutant. According to this ranking, the order of the four metals in seawater is: Pb, Cu, Cr, Zn. The respective ranking in sediments gives: Cu, Zn, Pb, Cr. These results indicate that if the priority is on improving water quality, the focus should be on lead. If, on the other hand, the two hazard indices are considered jointly, then copper becomes the highest-ranking metal, while lead is second.