Introduction heavy metal pollution

HEAVY METAL POLLUTION
Metals are found naturally in soil, water and sediments in background concentration and have been used by humans for thousands of years. Human activity releases them into the environment in much higher concentration that may have adverse impact on ecosystem functioning. Metals with atomic mass over 20 and specific gravity above 5 g cm^-3 are known as heavy metal. They can be metalloids that have toxic effect on biological components of an ecosystem even at low concentration. Metals in soil may range in different concentrations from less than one to as high as 100000 mg kg⁻¹ (Pal and Rai, 2010). Although some metals viz., Co, Cu, Fe, Mo, Mn, Zn and Ni are essential for cell as they are required for normal growth and metabolism for all life forms, while other (e.g. As, Cd, Hg, Pb, and Se) are toxic and/or non essential due to complex compound formation within the cell. Once introduced into the environment heavy metals cannot be degraded easily and persist indefinitely for longer period and pollute the ecosphere.

Rapid industrialization and consumerist life style has led to an unprecedented increase of such toxic substances in natural environment. Although several long term health effects of heavy metals are well known for a long time, exposure to these toxic substances is continue and even increasing in some parts of the world, particularly in developing and less developed countries. Heavy metal pollution occurs both at the industrial production level as well as the end use of products and run-off. They enter the human body through food, water and inhalation of polluted air, use of cosmetics, drugs, poor quality herbal formulations particularly ‘Ayurvedic/Sidha bhasamas’, (herbo-mineral preparations) and `Unani’ formulations, and even items like toys which have paints containing lead (INSA, 2011). Some industrial sources of heavy metal pollution are presented in table 1.

Injudicious applications of synthetic fertilizers such as phosphate have deposited heavy metals in much higher concentrations on earth surface than natural background sources. Phosphate fertilizers show big source of cadmium. For example in Scandinavia, cadmium concentration in agriculture soil increases by 0.2 % per year (Mohammed et al. 2011). In recent years the use of energy-saving CFL bulbs has increased enormously. According to a report CFL bulbs production has increased 500 million in 2010 from 19 million in 2002. These bulbs can prove to be a major health hazard as each contains 3-12 mg of mercury, with no system to recover these bulbs and safe disposal (INSA, 2011).