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Byline: DR. SM ALAM

Lead is a metal which is easily extracted from its ore. It is found in nature in form of sulfate, sulfide, and carbonate. It is soft, malleable bluish grey metal with little tensile strength. Lead is reactive metal and it is used extensively in the production of tetraethyl lead, which is used to increase the efficiency of petrol.

Lead vapor is discharged from the exhaust of the automobiles into the atmosphere. This causes pollution in the environment as lead and its compounds are poisonous. Lead is also used in car batteries and for the manufacture of paints such as white lead chromate and other pigments.

Lead is one of the most dangerous environmental pollutant. It has adverse effect as it accumulates in the body, especially of children and pregnant women. It can lead to behavior disorders, anemia, mental retardation and permanent nerve damage. Most lead accumulates in bone and kidney.

Man-made sources of lead include lead smelting and refining, the combustion of leaded fuel, the production of storage batteries, the manufacture of alkyl lead and lead paints and the application of lead-based pesticides. Lead pipes, lead-glazed earthenware and flaking lead points are possible sources of lead in the domestic environment. The predominant source of atmosphere lead appears to be from the use of 'antiknock' agents in petrol.

Food is the major source of lead intake in adults who are not occupationally exposed or have high concentration of lead in drinking water. The contribution of airborne lead to the total daily absorption as compared to average dietary intake is more difficult to estimate, as it depends on the concentration, particle size and solubility of the lead. Some scientists suggest that airborne lead is much more dangerous and that about 50 per cent of it may be absorbed on inhalation.

Young children in urban and industrial areas are much more prone to lead poisoning than other sectors of the population. Such children may ingest lead from paint, roadside dust, vehicle exhaust emissions and industrial pollution.

According to a scientist at London University, pollutants like lead are already affecting the intelligence of one in 10 British children, and as much as 90 per cent of children in some African countries.

Lead contributes to the high rate of osteoporosis, the brittle-bone disease that bends the backs, shortens the stature and breaks the hips of many older women. At high levels, lead in the blood of a pregnant woman can lead to a miscarriage or premature birth and at lower levels it can hold back the development of an unborn baby's nervous system and brain. Soft (acidic) water in areas with lead plumbing can be hazardous to bottle-fed babies. Childhood is a risky time because exposure to lead during the first four years can damage nerve cells and retardation. Students with high levels of lead are more likely to be distracted and easily bored. Hyperactivity in a young child often turns out to be a symptom of lead poisoning, and hyperactive children are more likely to become delinquent.

Lead is a poisonous metal that can damage nervous connections (especially in young children) and causes blood and brain disorders. Lead poisoning typically results from ingestion of food or water contaminated with lead but may also occur after accidental ingestion of contaminated soil, dust, or lead based paint. Long-term exposure to lead or its salts can cause nephropathy and colic-like abdominal pains. The effects of lead are the same whether it enters the body through breathing or swallowing. Lead can affect almost every organ and system in the body. The main target for lead toxicity is the nervous system, both in adults and children. It may also cause weakness in fingers, wrists, or ankles. Lead exposure also causes small increases in blood pressure, particularly in middle-aged and older people and can cause anemia. Chronic, high-level exposure can reduce fertility in males.

Most cases of adult elevated blood lead levels are workplace-related. Adults may suffer high blood pressure, hearing and vision impairment and nerve damage. High blood levels are associated with delayed puberty in girls. Lead has been shown many times to permanently reduce the cognitive capacity of children at extremely low levels of exposure. There appears to be no detectable lower limit below which lead has no effect on cognition. In children lead exposure can cause hyperactivity, anemia, brain damage and mental retardation.

By the mid-1980s, a significant shift in lead end-use patterns had taken place. Much of this shift was a result of the US lead consumers' compliance with environmental regulations that significantly reduced or eliminated the use of lead in non-battery products, including gasoline , paints, solders, and water systems. Lead may still be found in harmful quantities in stoneware, vinyl (such as that used for tubing and the insulation of electrical cords), and brass manufactured in China. Between 2006 and 2007 many children's toys made in China were recalled, primarily due to lead in paint used to color the product. In recent years, international studies have shown that lead-base paints are a major contributor in creating lead- contaminated dust, which represents a major pathway of exposure to children.

Many others sources of lead in the environment include petrol, water, food, cosmetics and lead glazed ceramics. Lead- based paints are also used in manufacturing toys in many countries, causing slow poisoning among children. The health risks posed by-products containing lead have led many developed countries to either limit or banned use of lead in paints in recent years. Lead and its compounds are used in paints to impart good color, bring durability and to improve drying. The common lead compounds such as lead acetate and lead nitrate are very dangerous because of their high solubility in water.

Distemper of paints contain high amount of lead from 195mg/kg to 785mg/kg. Older houses may still contain substantial amounts of lead paint.

Lead as a soil contaminant is a widespread issue, since lead is present in natural deposits and may also enter soil through (leaded) gasoline leaks from underground storage tanks. It is rapidly absorbed into the bloodstream and is believed to have adverse effects on the central nervous system, the cardiovascular system, kidneys, and the immune system. Depending on one's location on the face of the planet, the food and water supply as well as the air we breathe expose us to lead.

Areas of particular risk are places where the drinking water is obtained from geologic strata with significant lead content. Areas which have deposits of gold, zinc, and other economically useful metals, also have lead as an ore contaminant and the "tailings" of the mining and purification of the ore often have a very high lead content. Before the systematic reduction of lead content in regular gasoline, the lead in the atmosphere in high automobile traffic areas was hazardous especially to small children.
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Publication:Pakistan & Gulf Economist
Date:Jun 27, 2010

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