Chapter 8 - Speciation and bioavailability of trace metals (Cd, Cu, Ni, Pb, Zn) in the rhizosphere of contaminated soils

Abstract

The unique characteristics of the rhizosphere, combined with the relevance of its function in the soil:plant system, greatly contribute to the marked interest in this microenvironment. Specific changes occur in the rhizosphere as a consequence of root activity, which in turn impact on the speciation and bioavailability of nutrients and trace metals. In order to better understand the processes involved in the fractionation of trace metals in the rhizosphere, the chapter aims (i) to contrast the solid phase fractionation of trace metals (Cd, Cu, Ni, Pb, and Zn) between the inner rhizosphere, the outer rhizosphere, and the bulk components of forest mineral soils along a soil contamination gradient and, (ii) to determine Cu2+ activity in the liquid phase and establish the relationships with pH, dissolved organic carbon (DOC), and total dissolved Cu. Three sites located at distances of 2.5, 15, and 43 km from a Cu-Ni smelter in the Sudbury area of Ontario, Canada, were selected on the basis of their level of soil contamination. The fine roots of a number of white birch trees (Betula papyrifera Marsh.) were sampled in the B horizon along with the bulk soil (n = 6, 4, and 3 at sites 1, 2, and 3, respectively). The partition of the rhizosphere material from the roots was performed in the laboratory where the rhizosphere was separated into two components: the outer and the inner rhizosphere.