Lead

Sources

Lead is the most abundant toxic heavy metal. World production exceeds 3.5 million tons per year. Major industrial sources of lead emissions include:

• Waste oil and solid waste incineration.
• Iron and steel production.
• Lead smelting.
• Battery and lead alkyl manufacturing.

The lead content of motor vehicle emissions (at one time the major source of lead) has dropped by 89% since 1983, due primarily to reductions from automobile emissions. This was originally brought about by the increased use of unleaded gasoline after federal legislation mandated the phaseout of leaded gasoline, which fouls the catalytic converters used to meet federally mandated emission limits. At the same time, the lead content of leaded gasoline was decreasing, as was the number of vehicles using leaded gasoline. In 1993, 99.4% of the gasoline sold nation-wide was unleaded and by 1996, the production of leaded gasoline became illegal. However, lead additives can still be purchased and added to unleaded gasoline for engines that still require that type of fuel combustion. (Source: Annual SIGMA Statistical Report).

Health Effects

Exposure occurs from lead's presence in air, food, water, soil, dustfall, paint, and other materials. Lead is readily absorbed by the body via the primary routes of entry, inhalation and ingestion. Studies indicate that 10% to 20% of inhaled lead enters the blood stream. In children, approximately 50% of ingested lead is absorbed as compared to 8% to 10% for adults. This is especially significant since much of children's lead exposure is caused by their normal habits of mouthing dirty hands, objects and materials. (A growing body of research suggests there may be no safe level of lead ingestion.)

Within the body, lead is found in circulating red blood cells, soft tissues (liver and kidney), and bone (where lead is accumulated). Blood lead concentrations are the most reliable indicator of recent lead exposure. Known health effects of lead poisoning include:

• Anemia.
• Brain and nervous system damage, which can include permanent mental and motor retardation and in extreme cases, death.
• Severe kidney injury or failure.
• Injury to the gastrointestinal system and the heart.
• Damage to the reproductive system, including:
  • Ovarian and testicular dysfunction.
  • Impaired fetal blood synthesis, premature births, and other delivery complications.

Long-term, low level lead exposure causes learning deficits and behavioral problems in children. The major source to children is through contact with the dust or chips from old lead-containing paint. However, significant airborne exposure may occur near manufacturing facilities emitting large amounts of lead.

At present, a child with blood lead levels over 10 micrograms per deciliter (µg/dl) is considered lead-poisoned. Exposure to air containing 1 µg/m³ of lead is associated with a 5 µg/dl increase in blood lead; thus, long-term exposure to air containing over 2 µg/m³ could cause a child to become lead-poisoned.

Recent studies suggest that lead may be a factor in high blood pressure and subsequent heart disease in middle-aged white males.

Effects on Plants and Animals

At common low ambient concentrations lead does not usually pose a threat to plants and animals. However, exposure to high concentrations has adversely affected domestic animals, wildlife, and aquatic life. Areas near major emission sources, such as lead smelters, are most susceptible. In past years, small animals trapped near highways showed high lead levels.

Lead shot ingestion is a serious health problem in waterfowl. This has prompted legislation to require waterfowl hunters to use steel shot, as well as studies on various other shot types.

Health Effects of Air Pollutants || Air Quality & Health