Cadmium, copper, lead and zinc in Saronikos Gulf in 2004

Cadmium, copper, lead and zinc were measured in the framework of the monitoring project MED-POL MAP/UNEP Environmental Monitoring Program carried out during 2004 in Saronikos Gulf, a marine embayment affected by anthropogenic inputs from the nearby metropolitan area of Athens, approximately a decade after the establishment and operation of the sewage treatment plant of Athens located at Psytalia. The project was running in Greece from 1986 until 1999 and was reactivated in 2004. Two samplings were carried out, in May and September in a grid of fifteen sampling stations. For both samplings, dissolved cadmium ranged between 5.0 and 63 ng/l, lead between 0.05 and 0.60 mu g/l, copper between 0.03 and 0.72 mu g/l and zinc between 0.13 and 8.3 mu g/l. The highest values of dissolved zinc and copper were observed within the Gulf of Elefsis, which is an embayment with restricted water circulation surrounded by urban and industrial areas. The surface distribution of dissolved cadmium and lead did not show any particular pattern. The influence of the treated effluents originating from the wastewater treatment plant of Psytalia was visible at the deepest layers, below the thermocline, during September, demonstrated by relatively high trace metal concentrations. Comparing the results produced in 2004 with those obtained from the corresponding seasonal samplings of 2000, it is shown that zinc levels have decreased from 2000 to 2004, excluding the Gulf of Elefsis. On the contrary, lead levels demonstrate a significant decrease within the Gulf of Elefsis, whereas outside the Gulf they appear to be higher compared to those of 2000. Dissolved copper concentrations appear to remain at the same levels. In general the concentrations of cadmium, copper, lead and zinc during 2000 and 2004 are among the lowest detected in Saronikos Gulf ever since the beginning of the monitoring program MED-POL. Despite the significant four-year gap in monitoring data, the most recent values of 2004 confirm a relatively stable pollution level compared to the situation before 2000, implying that the marine environment of the Saronikos Gulf is possibly reaching a steady state, concerning trace metal pollution. Further research would be required in order to evaluate eventual further improvements following the establishment and operation of the secondary treatment plant inaugurated in 2004. The presence of other coastal and marine sources of metals, in the area must also be studied, as it is possible that their contribution to the metal load of the gulf becomes now comparable or even exceeds the impact of the treated sewage effluents.