Lead in the Inner Cities by Howard Mielke
1. Introduction / 2. Sources of Lead / 3. Health Consequences / 4. Re-evaluations / 5. Children at Risk / 6. Prevention
2. Sources of Lead [600 words]
Lead is versatile and formulated into many products. Some products, such as common
lead-acid batteries used in cars, trucks, boats, motorcycles and the like, are sealed and
if appropriately recycled, should not be the cause of poisoning of ordinary citizens.
Other products allow lead to be released into the pathway of human exposure. Lead solder
was used to seal seams in the canning industry until it was voluntarily withdrawn, first
from baby food containers and then all canning facilities in the early 1980s. The same
canning solder is used in other countries, and imported canned food continues to be
tainted with lead. Some brightly colored ceramic plates and cups as well as leaded crystal
may, in the presence of acidic foods (tomatoes, pineapple, wine etc.), release lead and
contaminate the food. Lead-based paint was banned for household use in 1978, but lead is
still an ingredient of “specialty” paints. Leaded gasoline was banned in 1986,
although lead additives are still in use in racing fuels (up to 6 grams per gallon), boat
fuels, farm tractors and personal watercraft fuels despite the fact that they are not
required in any of these applications. Alternative octane boosters are available.
Lead acetate, or “sugar of lead,” is water-soluble and one of the most bioavailable forms of lead. It is an ingredient in some hair-coloring cosmetic products. The Food and Drug Administration allows up to 6,000 parts per million of lead acetate in cosmetics. Several brands of slow-acting hair-coloring cosmetics are used daily by a sizable number of people with graying hair in many homes both in the U.S. and abroad. When users pour the cosmetic into their bare hands to rub into their hair, they become conveyers of a very toxic substance. Some lead acetate may be spilled on the sink, and it is indistinguishable from drops of water. On the hands it can be easily transferred to other items such as toothbrushes, faucet handles, combs and dental floss. It can be absorbed through the skin and shows up in sweat and saliva, but not in blood, as does ingested lead. Many plastics and vinyl products contain lead as a stabilizer or coloring agent. Products become a hazard if they deteriorate into fine dust particles or otherwise directly release lead onto hands (or paws), from which it is transferred into the mouths of unsuspecting creatures, including people.
Lead in paint and gasoline together accounts for most of the lead now in the human environment. In terms of raw tonnage, the amount of lead in gasoline over only the 57 years of its use from 1929 to 1986 roughly equals all of the lead in paints in 94 years of lead-paint production, from 1884 to 1978. The peak use of lead-based paint came during the 1920s when the U.S. economy was largely agrarian and rural. Most lead paints still exist as a thin mass on the walls and structures of older buildings. Deteriorated or sanded and scraped paint contributes to lead dust accumulation in the soil.
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| Figure 3. Lead use in paint peaked
in the U.S. in the mid-1920s and then gradually died out, just as the use of leaded
gasoline was on the rise. The use of leaded gasoline reached its peak in the 1970s and
then declined until Congress banned it in 1986. There is a common perception that
lead-based paints alone account for the amount of lead in the environment. In reality, both sources of lead contribute to the problem. |
In contrast, the use of leaded gasoline peaked early in the 1970s, a time during which the U.S. economy had become industrial and urban and reliant on automobiles for transportation. About 75 percent of gasoline lead was emitted from exhaust pipes in the form of a fine lead dust (the remaining 25 percent of the lead ended up in the oil or was trapped on the internal surfaces of the engine and exhaust system). It is estimated that the use of 5.9 million metric tons of lead in gasoline left a residue of 4 to 5 million metric tons in the environment. From these facts, we expected to find that lead would be disproportionately concentrated along roadways with the highest traffic flows -- those running through cities.
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| Figure 5. Two different-sized lead particles are spewed into the air when leaded gasoline is used. The trajectory of a typical particle is indicated by the blue arrows (top). Larger, heavier particles settle near the street. Smaller particles are carried by the wind until they meet a barrier, such as a tree or a house, to which they stick. Eventually, they are washed into the soil by rain. Lighter particles can be carried a greater distance and are eventually scavenged by precipitation and then fall to the ground. Assuming unpainted homes, the graph (bottom) generalizes the quantity of lead in the soil around an inner-city home situated about 7 meters from a heavily traveled road versus around a home more than 25 meters |
� American Scientist 1999
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