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replacement of essential metals in pigments or enzymes disrupting their function
(Prasad and Freitas 2003). Thus higher proportion of heavy metal contamination
destroys the biodiversity by making the area inappropriate for propagation of life
forms. A number of these metals, due to their toxicity, are found in the top 20 on the
2007 CERCLA Priority List of Hazardous Substances, including arsenic (ranked
first), lead (ranked second), mercury (ranked third), cadmium (ranked seventh), and
chromium (ranked 17th) (CERCLA 2007).

7.2 Heavy Metals as Contaminants of Environment
and Its Effects

Both natural and anthropogenic sources are responsible for release of heavy metals
into the environment. Dumping of untreated industrial wastes and different metal
mining operations are the major concern of heavy metal pollution (Hutton and
Symon 1986; Nriagu 1989). Even long after the dumping activities have ceased, the
released metals continue to persist in the environment and gradually contaminating
all the downstream water bodies, like rivers and streams or run-off to the sea
(Nriagu 1989). The metals may then be accumulated in sediments of water bodies
or seep into the underground water thereby contaminating the underground water
resources.
Widespread heavy metal pollution due to industrial activities has been reported
from different parts of the world. An estimated 52 million hectares in the EU
alone—more than 16 % of the total land area—are affected by some level of soil
degradation (Peuke and Rennenberg 2005). Reports suggest that many countries
like Japan, Indonesia, China (with Cd, Cu and Zn), Greece (Cu and Pb), and
Australia (Cu, Pb, Cu, Ni, Zn, and Cd) are contaminated with heavy metals
(Herawati et al. 2000; Zantopoulos et al. 1999). In India, according to the published
information, several places are contaminated with metals due to industrial activities
causing a major environmental problem. States in India with major industries like
Gujarat, Maharashtra, and Andhra Pradesh have been reported to add almost 80 %
of hazardous waste (including heavy metals) in India (INSA, A Position Paper
2011). In general, heavy metal toxicity can cause chronic degenerative diseases
with symptoms like, pain in muscle and joints, gastro-intestinal disorders, vision
problems, chronic fatigue, susceptibility to fungal infections, mental disorders,
genotoxicity, and cancers (Shanker et al. 2005; Nath et al. 2005). Industrial
workers, malnourished people, and pregnant women are vulnerable to the toxicity
of the heavy metals. Crippling effects of fluoride and arsenic toxicity due to
nonavailability of safe water for drinking and farming has now become a major
public health problem.
Our present understanding suggests that heavy metals like arsenic (As), lead
(Pb), mercury (Hg), and cadmium (Cd) do not possess any significant biological
functions (Nriagu and Pacyna 1988; Duruibe et al. 2007; Chetia et al. 2011). As for
example, in the environment, Pb is known to be toxic to plants, animals, and