1. Introduction
Human cells employ metals such as zinc, copper and iron
to control significant metabolism and signling functions
making them essential for life [1]. Many heavy metals
play an important biological role, the particular importance
of iron and copper ions in biological processes [2].
Redox-active metals such as iron, copper and chromium
undergo redox recycling to produce free radicals. In contrast
cadimium and mercury are redox-inactive metals
that challenge antioxidant defenses by binding to thiols
in cell [3,4]. The natural aquatic systems may extensively
be contaminated with heavy metals released from domestic
industrial and other man made activities [5]. The
toxic effect of heavy metals usually involves an interaction
between the heavy metal ion and specific target protein
resulting in a change in protein structure and function
[6]. Chromium in its hexavalent form which is the
most toxic species of chromium is used extensively in
some industries such as leather processing. The toxicity
of chromium stems from its tendency to be corrosive and
to cause allergic reactions. Chromium is a carcinogen,
particularly of the lung through inhalation. Cell toxicity
caused by heavy metal ions is attributed to oxidative and
nitro sativa stress [7], defined as an oxidants over antioxidants.
Macro molecules in cell are damaged by metals-induced
production oxygen and nitrogen-containing
free radicals (oxidants) and/or metal induced depletion of
the cells antioxidant defense programmed cell death or
necrotic cell death are usual consequences [8]. Oxidative