Health and Environment
Health and Environmental Impacts
Human Health Effects
Chronic (long-term) exposure to lead in humans results in effects on the blood, central nervous system (CNS), blood pressure, kidneys, and Vitamin D metabolism. Children are particularly sensitive to the chronic effects of lead, with slowed cognitive development, reduced growth and other effects reported. Reproductive effects such as decreased sperm count and spontaneous abortions have also been associated with high lead exposure. The developing fetus is at particular risk from maternal lead exposure, with low birth weight and slowed postnatal neurobehavioral development noted. Human studies are inconclusive regarding a link between lead exposure and cancer.
Acute (Short-Term) Health Effects
Brain damage, kidney damage, and gastrointestinal distress (such as colic) are seen from acute exposure to high levels of lead in humans.
Death from lead poisoning is likely to occur in children who have blood lead levels greater than 125 micrograms per deciliter of blood (μg/dL). Effects on kidney function, neurodevelopment, and blood pressure are evident when blood lead levels are below 10 μg/dL.
The most sensitive targets for the toxic effects of lead are the kidneys and the hematological, cardiovascular, and nervous systems. Because of the multiple modes of action of lead in biological systems, lead could potentially affect any system or organ in the body.
Chronic (Long-Term) Health Effects
Human studies are inconclusive regarding lead exposure and the potential for increased cancer risk. Animal studies have reported kidney tumors in rats and mice exposed to lead via the oral route. EPA considers lead to be a Group B2, probable human carcinogen. International Agency for Research on Cancer (IARC) considers inorganic lead compounds to probably be carcinogenic to humans (Group 2A), and organic lead compounds to be not classifiable as to their carcinogenicity to humans (Group 3).
Studies on male workers using lead have reported severe depression of sperm count and decreased function of the prostate and/or seminal vesicles at blood lead levels of 40 to 50 μg/dL. Occupational exposure to high levels of lead has been associated with a high likelihood of spontaneous abortion in pregnant women. Exposure to lead during pregnancy produces toxic effects on the human fetus, including increased risk of preterm delivery, low birthweight, and impaired mental development.
Chronic exposure to lead in humans can affect the blood and the nervous system. Neurological symptoms have been reported in workers with blood lead levels of 40 to 60 μg/dL. Slowed conduction in peripheral nerves has been reported in adults with blood lead levels of 30 to 40 μg/dL. Children are particularly sensitive to the neurotoxic effects of lead.
Other effects from chronic lead exposure in humans include effects on blood pressure and kidney function, and interference with vitamin D metabolism. Animal studies have reported effects similar to those found in humans, with effects on the blood, kidneys, and nervous, immune, and cardiovascular systems noted.
Human exposure to lead occurs through a combination of inhalation and oral exposure, while dermal absorption of inorganic lead compounds is reported to be much less significant. Inhalation generally contributes a greater proportion of the dose for occupationally exposed groups, and the oral route generally contributes a greater proportion of the dose for the general population.
Potentially high levels of lead occur in the following industries: primary and secondary lead smelting and refining industries, steel welding or cutting operations, battery manufacturing plants, construction, rubber products and plastics industries, printing industries, firing ranges, radiator repair shops, and other industries requiring flame soldering of lead solder. In these work areas, the major routes of lead exposure are inhalation and ingestion of lead-bearing dusts. In the smelting and refining of lead, historical mean concentrations of lead in air have been measured at 4,470 μg/m3; in the manufacture of storage batteries historical mean airborne concentrations of lead from 50 to 5,400 μg/m3 have been recorded. While these values are based on older manufacturing processes (i.e., from the 1970s), they are significant when considering that the recommended upper exposure limit of lead in the air is 100 μg/m3.
The largest source of lead in the atmosphere has historically been from leaded gasoline combustion, but with the phase out of lead in automotive gasoline in the 1970s through 1980s, air lead levels have decreased considerably. On-going airborne sources include combustion of solid waste, coal, and oils, emissions from iron and steel production and lead smelters, emissions from general aviation aircraft and racing vehicles, combustion of marine fuels, and tobacco smoke.
Exposure of the general population to lead is most likely to occur through the ingestion of contaminated food and drinking water, and by the inhalation of lead particulates in ambient air. Fruits, vegetables, and grains may contain levels of lead in excess of background levels as a result of plant uptake of lead from soils and direct deposition of lead onto plant surfaces. A common source of lead exposure for children is from lead-based paint that has deteriorated into paint chips and lead dusts. Common sources of lead exposure for adults include occupational and non-occupational exposures from activities such as do-it-yourself paint scraping, renovations, and castings. For example, using heat guns or dry scraping of old lead containing paint during home reconstruction and remodeling can result in lead exposure.
Exposure to lead can also occur from food and soil. Children are also exposed by handling and mouthing lead-stabilized PVC plastics and lead alloy jewelry and toys. Lead exposure to the general public can also occur during the use of inadequately glazed or heavily worn earthenware vessels for food storage and cooking, as well as by engaging in certain hobbies such as using recreational shooting ranges, stained glass making, or using molten lead in casting ammunition, fishing weights, or toy figurines.
Lead particles are removed from the atmosphere by precipitation and dry deposition. The average residence time of lead in the atmosphere is ten days, during which long distance transport reaching thousands of kilometers may take place. Elemental lead is by nature extremely persistent in both water and soil. The presence of lead and compounds in these media varies widely, however, depending on such factors as temperature, pH, and the presence of humic materials (i.e., dark colored organic material associated with the biological breakdown of living matter).
Biologists have studied the effects of lead sinkers and jigs on waterfowl, such as loons and swans, since the 1970s. A single fishing sinker swallowed with food or taken up as grit could be fatal to waterfowl. Lead adversely affects the function and structure of the kidney, central nervous system, bones, and production and development of blood cells in waterfowl. Exposure to lead, such as through ingestion of fishing sinkers, can cause lead poisoning in waterfowl, producing convulsions, coma, and death. A study of 522 loons found dead in New England was conducted between 1987 and 2000. The study revealed that for breeding adult loons, confirmed and suspected lead poisoning from ingested fishing weights accounted for almost half of the adult deaths.
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