Heavy metals behaviour and distribution in a shallow Mediterranean lagoon

Korissia lagoon is located on the southwest coast of Corfu Island, Greece. It is a shallow coastal ecosystem of great ecological importance and is included in the Natura 2000 network of protected areas. The lagoon, whose depth varies between 0.5 and 1.2m, is connected to the sea by an artificial channel. During summer it is hypersaline (the salinity exceeds 50 p.s.u.) while the surface temperature ranges between 23.6 C and 26.1 C. In the winter the salinity falls to about 19 p.s.u. and the surface temperature is between 13.5 C and 16.2 C. Zinc, copper, lead and cadmium were measured in the dissolved phase and particulate material of water samples from the lagoon and adjacent wells, collected during two sampling periods; September 2005 and March 2006. The levels of dissolved Zn, Pb and Cd were controlled by environmental conditions; water inflow, salinity and possibly by human activity in the surrounding area. Maximum values were measured in summer and at the shallowest sampling points. Copper concentration seemed to be related to seasonal and spatial nutrient distribution with maximum values determined in winter and in the central parts of the lagoon. The heavy metal load of the suspended material was grain size-dependent and seasonally variable. Total values (sum of dissolved and total suspended) of the various metals were as follows: zinc 0.08-4.77 kg/1, copper 0.25-0.67 kg/1, lead 0.08-0.59 kg/1 and cadmium 0.00-0.05 kg/1. Copper and cadmium were mostly found in the dissolved phase (61.6-87% and 69.5-87.6% respectively) while lead and zinc in the coarse particulate material (67.4-74.9% and 68.8-75.1% respectively). The metal concentrations in the wells were generally higher than in the lagoon and according to EU criteria, the water of certain wells was inappropriate for human consumption because of increased copper values.