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Lead


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Lead a soft, heavy, malleable and ductile isometric mineral, the native metallic element Pb. It is silvery when freshly cut, but tarnishes readily in moist air to dull grey. Lead rarely occurs in native form, being found mostly in combination (as in galena, cerussite and anglesite). Lead is a term sometimes applied to graphite. It is used in insecticides, car batteries, in roofing, as a radiation shield, in high-octane gasoline and mixed with other metals to form alloys. As a cumulative poison, lead enters the body from lead water pipes, lead based paints, and leaded petrol. In humans exposure to lead shortly after birth is associated with impaired mental health between the ages of two and four. Emission into the atmosphere due to increase use of fossil fuel and coal and an increase production of waste by the industries, worldwide output of lead has been rising steadily. Automobile exhaust accounts for about 50% of the total inorganic lead absorbed by humans. In Bangladesh leaded gasoline is in common use. Distribution of total lead level in road-dust of Dhaka City has been determined, which ranges from 9 to 1437 mg kg -1. [M Qumrul Hassan]