METAL ACCUMULATION IN A BIOLOGICAL INDICATOR (ULVA-RIGIDA) FROM THE LAGOON OF VENICE (ITALY)

Ulva rigida (C. Agardht) was collected from the Palude della Rosa (lag oon of Venice), a particular area characterized by a salinity gradient , from December 1991 to June 1993. Metal contents (Al, Mn, Fe, Cu, Zn, Cr, Co, Ni, Cd, and Pb) were determined by atomic absorption spectrop hotometry and statistically analysed for differences between months an d sampling sites. The mean seasonal variability is very significant (p < 0.001) for all studied metals. Seasonal trends are comparable for g roups of metals according to possible functional similarities. A signi ficant positive correlation was calculated for the pairs Fe-Al and Fe- Pb. Mechanisms regulating metal uptake are discussed, particularly the role of Fe and its linear relationship with Al. Metal concentrations in relation to salinity also were studied. Larger amounts of Fe, Zn, a nd Cd accumulated in correspondence of lower salinity, may be owing to both higher metal activity and burden of bioavailable metals in fresh water flowing into the Palude. Calculation of concentration factor (CF ) indicates that U. rigida specifically accumulates Fe. CF linearly co rrelates with dissolved metal concentrations, suggesting that U. rigid a is a good bioindicator of metal bioavailability, although seasonal a ctive accumulation occurs in some cases (Mn). Metal concentrations det ermined in this macroalga support the conclusion that the studied area is rich in bioavailable Fe and poor in toxic metals. In any case, a g reat affinity for Al in U. rigida may be proposed.