ISBN 0070349223
Description
Lead is a highly toxic trace mineral. In recent years, human exposure to lead poisoning has changed in origin and probably has increased in magnitude.
The human body can tolerate only 1 to 2 milligrams (about 0.00003 ounce) of lead without suffering toxic effects. Two pounds of food contaminated by only 1 part per million of lead contain almost a milligram of lead, so there is not a very wide margin of safety.
Absorption and Storage
Lead contained in food is poorly absorbed and excreted mainly in the faeces. It enters the body via the skin and the gastrointestinal tract. The lead that is absorbed enters the blood and is stored in the bones and the soft tissues, including the liver. Up to certain levels of consumption, lead excretion keeps pace with ingestion so that retention is negligible. The lead that builds up in the body is retained in the central nervous system, bones, brain, glands, and hair.
Dosage and Toxicity
Critical levels of intake, above which significant lead retention occurs, cannot be quoted with any accuracy. Toxic intake can come from consumption of moonshine whiskey and foods stored in lead-glazed earthenware pottery that has been fired at too low a temperature, preventing sufficient fixation of the lead, which allows it to leach out. Regulations now have lowered the acceptable amount of lead in pottery, but foreign products are not covered in these regulations.
Some supplemental sources of calcium in the form of bone meal may be contaminated with lead. Sources of poisoning include drinking water that is soft and acidic and that erodes lead from lead piping built into homes before 1930; the solder used to connect copper pipes in homes until 1986; food from lead-soldered containers (all but 15.9% of manufacturers in the U.S. have, as of 1987, complied with the recommendation to use other forms); lead-based paint, cosmetics, and cigarettes (because of the lead-containing insecticide applied to tobacco); the burning of coal; peeling lead-based paint or plaster; and motor vehicle exhausts. The accumulation of lead in the body from motor vehicle exhausts is caused directly by inhalation and indirectly through deposition in the soil and plants along highways and in urban areas. We now have a certain amount of protection because of catalytic converters; however, there is still a limited amount of leaded gasoline available. Even though the level of lead pollution in the air has been lowered, there remains the 4 to 5 million metric tons accumulated in the soil before the 1970s. Those living near roads or highways who grow food might want to test the soil.
Acute lead toxicity is manifested in abdominal colic, encephalopathy (dysfunction of the brain), myelopathy (any pathological condition of the spinal cord), and anemia. Lead is able to cause abnormal brain function by competing with and replacing other vital minerals, such as zinc, iron, and copper, which regulate mental processes. High levels of lead attack the central nervous system and cause hyperactivity. Low levels of lead cause learning disorders, reading problems, slower reflexes, poor eye-hand coordination, and behavioral problems. Even small levels will contribute to these conditions.
A definite relationship has been established between lead ingested from soft drinking water and mental and growth retardation in children. The lead from drinking water ingested by pregnant women can cross the placenta and settle into the brain of the fetus. An estimated 90% of the lead stored in the mother's body is free to cross the placenta. Some 16% of all children are thought to have levels of lead that exceed the acceptable amount. Unusually high levels have been found in those who have died from sudden infant death syndrome (SIDS).
Lead intoxication can result from a condition in children called pica, the eating of lead-containing dirt, paper, and paint. Depression is a symptom of chronic lead poisoning, as are headaches, restlessness, irritability, inability to concentrate, impairment of memory, insomnia, hallucinations, muscular weakness, muscular aches, nausea, and indigestion. Gums can turn blue; paralysis of the extremities, blindness, mental disturbances, and even insanity can occur. Impotence in men has been found along with infertility and anemia. Consumption of alcohol allows higher levels of lead to settle in soft tissues, including the brain. Damage is most prevalent in the heart, liver, kidneys, and nervous system. High levels can cause a protein deficiency, and if vitamin E is also deficient, toxicity is more likely.
The usual treatment for lead poisoning during acute stages consists of a diet high in calcium plus injections of a calcium chloride solution and administration of vitamin D. Sufficient calcium prevents the accumulation of lead in the body by reducing its absorption from the intestinal tract. Too little calcium in the body results in higher levels of lead in the blood, bone, and soft tissues. Vitamin C at doses up to 6 grams per day can help lead excretion. The amino acids cysteine and methionine and supplementation of all essential minerals also help. Thiamine produces a powerful effect against this toxin.
An effective way that may prevent lead poisoning is to include a small amount of algin in the daily diet. Algin is a nonnutritive substance found in Pacific kelp, which is sometimes used as a thickening agent in the preparation of various foods. It attaches itself to any lead that is present and carries it harmlessly out of the system.
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