Natural enrichment of Cd and Tl in the bark of trees from a rural watershed devoid of point sources of metal contamination.

To help understand the bioaccumulation of Cd and Tl in beaver tissue, we examined the enrichment of these metals in vegetation available to the animals. Bark was collected from 40 species of trees and shrubs, along with a complete soil weathering profile, within a small watershed devoid of trace metal contamination. Weathering resulted in a 5x enrichment of Cd in the soils relative to the underlying sediments, and a 6x Tl depletion: while Cd was lost from calcite and accumulates in the organic matter and oxyhydroxide fractions, Tl occurred only in the residual fraction.