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Human beings are made up of millions of cells arranged in a complex manner. Protoplasm (a thick, jelly-like fluid), the basis of all cells, in turn, is composed of several elements. About 99 per cent of the cells comprise elements like oxygen, hydrogen and carbon. The remaining one per cent is made up of trace elements like nitrogen, calcium, phosphorus, iron, sulphur, zinc, chromium, cobalt, fluorine, iodine, manganese, molybdenum and selenium.
Lead is noticeably missing from this list as it is not present on the earth’s surface in its free state; it is obtained exclusively by mining. Its absence in our biosphere before societies learnt to mine has meant that there was no need for developing any mechanism to assimilate, utilise or eliminate it. Hence, whenever lead enters the body through the skin, inhalation, or by ingestion, it gradually accumulates in our system till it reaches toxic levels.
Lead is found in gasoline and is released in its exhaust. India has adopted the “green policy” and switched over to “lead free” gasoline which has a lower lead content. But the inefficient engines of our automobiles, trucks and two-wheelers negate the effects of the cleaner fuel. Children, especially those residing in urban areas, inhale the lead in the air.
Batteries, both the AA and AAA batteries used in gadgets and toys and the large ones used in the automobile industry, contain lead. Although manufacturers are supposed to buy back old automobile batteries and dispose them without polluting the environment, this is seldom done. The by-lanes of cities are full of “battery experts” who earn a livelihood “reconditioning” old batteries. The waste is discharged into the sewage, which then contaminates the soil and groundwater.
We have a penchant for wrapping cooked and uncooked food in old newspaper. But we must remember that newsprint also contains lead, which leeches out and contaminates the food. Cows and goats eat waste printed paper, thereby contaminating both their milk and meat.
Traditionally, water and food are stored in containers made of copper, brass, steel or aluminium. Some of these may be lined with lead. Also, we often get these containers soldered if they develop holes. Lead is a major constituent of the soldering material. This, too, makes us susceptible to lead poisoning.
Waste industrial oils, often recycled in the community and used as a cheap, smoky cooking fuel, contains lead. Unscrupulous traders, too, use lead illegally as it is a cheap adulterant that can easily be added to food to increase the weight.
Paints used in non-commercial areas like homes, for furniture and toys, and the colours used during festivals like Holi and to paint clay Ganeshas are legally supposed to be “lead free”. This, however, is seldom the case.
Inexpensive makeup contains lead-based colour. The metal gets absorbed through the skin. Surma and kajal, used to line the eyes, also contain lead.
The level of lead in blood should not exceed 600 µg (microgram) in men and 300 µg in women. In children aged between one and five years, the blood lead levels should not be greater than 10 µg. Tests done on blood samples of children in several areas in India (especially in the cities) reveal levels higher than the prescribed norm.
Lead causes problems because of its affinity for sulphur. It immediately combines with the sulphur present in the enzymes in our bodies, causing disruption and a wide range of malfunction. It gradually displaces the calcium in our bones and interferes with the haemoglobin synthesis thereby causing anaemia. It also damages kidney cells causing nephritis and, eventually, renal failure. It affects nerve conduction causing tingling, numbness and loss of sensation in the extremities. It crosses the blood-brain barrier — as it reaches the brain cells, there is a slow deterioration in mental function. (A rise to 100 µg is associated with a 4.6 point decrease in IQ.) Eventually, there may be encephalopathy seizures and coma.
Symptoms of lead poisoning are initially vague as many enzymes are involved, affecting all the organs in the body. Anaemia is one of the early manifestations and the diagnosis may be confused with iron deficiency. Lead poisoning may also mimic renal disease.
As more and more essential enzymes are affected, there may be lethargy, headache, aches and pains and difficulty in concentration. There may be unexplained mental deterioration and poor academic performance. The abdomen may get bloated with constipation and cramps.
Lead poisoning is suspected if the person has blue “lead lines” on the gums, anaemia with a typical “basophilic stippling” and X-rays showing “dense lead lines” in the bones. Diagnosis is confirmed by estimating the blood lead levels.
Treatment with chelating agents (substances whose molecules can form several bonds to a single metal ion) is possible and curative. It will, however, succeed only if repeated environmental exposure to the toxic metal is avoided.
Dr Gita Mathai is a paediatrician with a family practice at Vellore. Questions on health issues may be emailed to her at firstname.lastname@example.org