Seasonal variations in metal content of two Unio pictorum mancus (Mollusca, Unionidae) populations from two lakes of different trophic state

To assess the impact of lake trophy on trace element accumulation by Unio pictorum mancus, a population from the mesooligotrophic Lake Maggiore was compared with a population from the eutrophic Lake Candia. The element content in soft tissue and shell biomass, the seasonal variations of element concentrations in soft tissues and shell, and the relationship between element concentrations in the water and those in the tissues were estimated in pursuit of this objective. Thirteen mussel samplings were performed in Lake Maggiore between May 2003 and September 2004 and in Lake Candia between June 2003 and August 2004. Filtered water samples were collected seasonally. Water, shell and soft tissue samples were analysed by ICP-OES and ICP-MS for the measurement of following elements: Zn, Cu, Fe, Mn, Ni, As, Pb, Co, Cr, Mo, V, Cd, Be and Ca. The element concentrations in the mussel tissues and shell from Lake Maggiore were higher than those from Lake Candia. Due to the higher population density and higher element concentrations in the mussels of Lake Maggiore, the element content in the biomass per m2 in this lake far exceeded that in Lake Candia.