Seasonal variations of total mercury in foliar tissues of Posidonia oceanica

Cold vapour atomic absorption spectrophotometry (CV-AAS) was used to evalua te total mercury concentrations in Posidonia oceanica, after initial minera lization of the samples in a microwave oven. Measurements were taken of thr ee leaf tissue types: the adult leaf blade, the adult leaf sheath, and the intermediate leaf blade. Plants were sampled monthly over a one year period at two sites presenting different degrees of pollution: Rosignano (Tuscany , Italy) and Tonnara (Corsica, France). The mercury concentrations recorded in the different P. oceanica tissues we re systematically higher at the more contaminated of the two sites, thus co nfirming the value of this plant as a biological indicator. The mercury con centrations observed exhibit seasonal variations, with higher concentration s recorded in winter than in summer. These variations seemed to be negative ly correlated to the plant's phenology. Also, the mean mercury concentratio ns were generally lower in young tissue (intermediate leaf blade) than in t he older tissue (adult leaf blade).