ABSTRACT
The term trace e1 ement is used to denote a group of otherwise unrelated chemical elements present in the natural environment in low concentrations. In smal 1 quantities, many elements (e. g, F, Si, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, Sn, I, Cl, B) are essential to biological growth. At a slightly higher concentration, many elements may become toxic to plants and/or animals. There are also elements (e.g., As, Cd, Pb, Hg) that have no known physiological function and are always considered biologically harmful.
