Relationships between sediment physico-chemical characteristics and heavy metal bioaccumulation in Mediterranean soft-bottom macrophytes

Abstract

Concentrations of Hg, Cd, Pb and Zn in the two seagrasses ( Posidonia oceanica and Cymodocea nodosa), green alga Caulerpa prolifera and sediment and some physico-chemical characteristics of the sediment (organic matter, fine fraction (particles <63 μm), carbonates and cation exchange capacity (CEC)) were quantified in a field study along the Mediterranean Spanish coast. Significant correlations between the concentrations of metals in the plants and sediment (alone or normalized with respect to the physico-chemical characteristics) were usually found for Hg and Zn. For Pb only C. prolifera fractions were correlated to the Pb content of the sediment. For Cd no significant correlations were obtained between the metal in the plants and sediment. The concentration factors of the metals in the plants with respect to sediment were usually negatively correlated with the fine fraction, organic matter and CEC of the sediment for Hg, Pb and Zn in Posidonia and Cymodocea, and for Hg and Zn in Caulerpa. This suggests that these variables of the sediment increase the retention of these metals in the sediment and reduce their availability to the plants. Stepwise multiple regression analyses yielded only three equations with at least two independent variables in the model: the Hg concentration in leaves and roots of Posidonia oceanica is explained by the Hg concentration of the sediment and organic matter of the sediment. The Hg concentration in the fronds of Caulerpa prolifera is explained by the Hg concentration in the sediment and by the carbonate content of the sediment.