Where metals meet
The environmental impact of heavy metals always goes unnoticed and is rarely catastrophic to merit immediate measures. Except for the recent report on arsenic poisoning in West Bengal, no major episode of metal toxicity has been recognised in India (see box: Arsenic poisoning ). It took decades of research to establish the cause and source of cadmium poisoning along the Jinzu river in Japan (see box: Brittle bones ). Besides, sophisticated equipment and rigorous controls of laboratory conditions are needed to analyse heavy metal impacts. Such facilities in India are either non-existent or are very inferior.
air : A human being breathes in 12,000 litres of air each day, yet keeps on using the atmosphere as a refuse bin. Approximately 734,000 tonnes of heavy metals are released into the atmosphere every year worldwide. According to N Manivasakam, of the Princial Public Health Laboratory in Coimbatore, the main sources of atmospheric metal pollution are mining, smelting and refining of metals; burning of fossil fuels; production and use of metallic commercial products; and, vehicular exhaust.
The available data for air concentrations for India reveal consistently higher values (see chart: Dirty air ) compared to the World Health Organisation ( who) standards. The data represents atmospheric concentrations in Ludhiana in Punjab.
water: Drinking is one of the key routes of intake of heavy metals by the human body. The who has laid down several guidelines for heavy metal content in drinking water. Yet, approximately 1,108, 000 tonnes of heavy metals are released into the water every year worldwide. The main sources of water pollution are domestic sewage and industrial effluents; power plants; and atmospheric fallout.
According to the National Environmental Engineering Research Institute ( neeri ), Nagpur, 70 per cent of India's inland water is unfit for consumption. All major rivers contain metals in excess of the prescribed limit (see chart: Watered down ).
A cpcb study reported that the river Yamuna, even before it reaches Delhi, contains a host of heavy metals. A glass of water from the Yamuna contains 0. 01 nanogramme/litre (n/l) of chromium, 0.01ng/l of cadmium, 0.02ng/l of nickel and 0.02ng/l of zinc, says Devika Nag, head of the department of neurology, King George Medical College, Lucknow.
The sewage treatment plants
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