are essential to healthy functioning and reproduction of microorganisms,
plants and animals (includingman). However, at high concentrations,
these same essential elements may cause direct toxicity or
reproductive effects. Some elements are also non-essential (e.g. As,
Pb and Hg) and even low concentrations of these elements in the
environment can cause toxicity to both plants and animals (Nagajyoti
et al., 2010).