| http://www.w3.org/ns/prov#value | - Various metals, e.g. Zn, Cu and Mn, are essential at low concentrations but become toxic at increasing concentrations, other metals have never been shown to be essential for the development of living organisms and are toxic even at very low concentrations e.g. Hg, Cd, Pb (Trevors et al., 1986; Hall, 2002).
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