ABSTRACT
Trace elements may be present in solution with positive or negative charges and in di¦erent redox states. ¤ey occur predominantly in cationic form (Pb, Cu, Zn, Ni, Cd, Hg, Cr(III), Co), but some are present in anionic form (As, Se, Cr(VI), Mo, and B). Heavy metals and metalloids have critically important biological e¦ects, both benecial and harmful. In trace amounts, many of these elements (e.g., Cu, Zn, Co) are essential to living organisms, but they become poisonous when their concentrations in the environment and in organisms are su¬ciently high. Some elements (e.g., Hg and Pb) are not known to perform any essential biochemical functions and then are injurious or lethal to living organisms even at very low ambient concentrations (Jackson, 1998). Due to industrial development and disposal activity, trace elements are considered to be among the most important environmental contaminants that a¦ect all ecosystem components in natural environments. Concerns about these contaminants are justied in view of the
evidence that trace elements are continually accumulating in the food chain (Iskandar and Kikham, 2001).
