Lead story
Heavy metals get deposited in the kidneys, liver and bones. They act as systematic toxins and disrupt metabolic functions of the body. Although most heavy metals are toxic, emphasis has been on lead all over the world. Lead pollution is, by far, the most common form of heavy metal contamination.
Children are known to be most susceptible. In India, Veena Kalra of the department of paediatrics at the Delhi-based All India Institute of Medical Sciences studied the blood levels of 100 schoolchildren from two areas in Delhi: Siri Fort and Bahadur Shah Zafar Marg, ITO. The lead content in the blood of children in the Siri Fort area was 79 microgrammes per decilitre (mg/dl) while those from ITO had a high of 408 mg/dl. The permissible limit is 10 mg/dl.
Besides absorption of lead through inhaling or ingestion, in a foetus or a new-born, the intestinal barrier, which is not fully developed, allows five times more lead to pass through than in an adult. While there may be no clear symptoms, likely effects include low intelligence levels, abnormal neurobehaviour and impaired growth.
Transfer of lead from the mother to the foetus or the infant also takes places via the placenta or breast milk. In 1997, S Shrimachari, from the Institute of Pathology, Safdarjung Hospital, New Delhi, randomly selected placental tissues from deliveries at the hospital. The mean values of arsenic, cadmium and lead from 26 samples were 0.35, 0.06 and 0.07 mg/gramme respectively, which is higher than normal. It suggests higher environmental pollution.
D K Saxena from the Industrial Toxicology Research Centre, Lucknow, also found that mean values of lead in mothers with normal delivery were 19.4mg/dl, while in cases of abnormal delivery, it was 22.5mg/dl. It has been diagnosed that lead in maternal blood above 15mg/dl poses greater risk to foetuses and infants than pregnant women. Lead in breast milk was also found to be higher than it was 30 years ago. In industrialised countries, average lead levels in breast milk were 5-20 mg/l. In polluted areas it was 20 times higher.
Depending on the type of heavy metal, exposure period and concentration, heavy metals exhibit different effects leading to different types of diseases (see table: Killing fields ).
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