Lead and other heavy metal exposure

Neurotoxic substances are chemical compounds that, depending on the dose, may have harmful effects on brain function and interfere with the workings of the nervous system. Neurotoxics may affect intelligence, language ability, and attention. They may cause behavioral problems and affect mood and social adjustment. At very high doses, neurotoxics may produce such effects as coma, convulsions, respiratory paralysis, and death. Lead, mercury, and polychlorinated biphenyls (PCBs) are among the substances suspected of having harmful and possibly permanent neurological effects on children.

Abnormal development is a major concern in children because it may result in birth defects and lasting changes in intelligence, behavior, and reproductive capability. A child's nervous system, reproductive organs, and immune system grow and develop rapidly during the first months and years of life. As organ structures develop, vital connections between cells are established. These delicate developmental processes in children may easily and irreversibly be disrupted by toxic environmental substances, such as lead.

Neurotoxics that may have only a temporary ill effect on an adult brain can cause enduring damage to a child's developing brain^. The immaturity of children's internal systems especially in the first few months of life, affects their ability to neutralize and rid their bodies of certain toxics. If cells in the developing brain are destroyed by lead, mercury, or other neurotoxic chemicals, or if vital connections between nerve cells fail to form, the damage is likely to be permanent and irreversible. This may mean a loss of intelligence and alteration of normal behavior.

Lead is a neurotoxic metal that affects areas of the brain associated with regulating behavior by altering the output of neurotransmitters and disrupting the development of nerve cells. Lead poisoning in children may cause lowered intelligence, reading and learning disabilities, impaired hearing, reduced attention span, hyperactivity, and antisocial behavior. Pregnant women exposed to lead may transfer the metal to a developing fetus resulting in developmental problems. While the fetus is developing, there are critical periods for each organ system, including the nervous system. During these critical periods, the cells of the body are especially sensitive to environmental toxics that may interfere with the normal development of organ structure and function.

A growing body of evidence suggests a number of synthetic and naturally occurring organic chemicals may disrupt the endocrine (hormonal) systems of humans and wildlife. A variety of chemicals cause endocrine disruptions in laboratory animals and some scientists have hypothesized that these effects also may occur in humans. Although further research is needed before such effects can be either demonstrated or ruled out, theoretically children would be at particular risk from very low levels of endocrine disrupting chemicals because of the important role the endocrine system plays in development. Concern exists about the potential for adverse developmental effects because chemicals that block or "mimic" reproductive and thyroid hormones may determine the course of prenatal development.  

Lead

Lead is an international problem because of transnational movement of lead released into the air from stationary and mobile sources; because of trade in products containing lead, such as food and painted objects; and because of the movement of lead-containing discards (Silbergeld, 1995).

Lead released from cars first enters the air, where it may be an immediate source of lead exposure by inhalation. Most lead from this source is deposited close to roadways, where it contaminates dusts and soils. This contamination may affect the food supply, particularly foods grown exposed to air; drinking water; and dusts and soils in houses, schools, and other environments.

Lead exposures related to use of leaded gasoline are highest in urban environments. Residents of intense vehicular traffic areas generally have blood lead levels much higher than populations exposed to less vehicular traffic. The populations of Latin America and the Caribbean are primarily urban – 75 percent of all people in the region live in urban zones, and this percentage is expected to increase in the coming years.

Besides lead from vehicular emissions, other sources of lead exposure in LAC require consideration: Lead emitted into the air by fixed sources such as smelting, petrochemical processing, and mining is considered to be an important health hazard. Lead-based paint, lead-glazed ceramicware and varnishes are also considered to be a significant source of lead exposure. Battery recycling is also considered a health hazard. For countries like Mexico, Peru, Ecuador and Honduras, where lead-containing varnishes are used as a glaze for ceramics used in food preparation, contamination of food also constitutes a source of exposure. Finally, dust and water pollution may be considered a problem.

 Mercury

Mercury is another neurotoxic substance that can produce a wide range of health effects depending on the amount and timing of exposure. Mercury is a liquid at room temperature but vaporizes readily; in vapor form it is readily absorbed through the lungs. Repeated exposures to low levels of mercury vapor over long periods have been associated with tremors, irritability, impulsiveness, drowsiness, impaired memory, and sleep disturbances. These effects may occur at lower levels of exposure in children than adults.

When mercury attaches to an organic molecule, it may be absorbed into the body through the digestive tract. Methylmercury, which is produced naturally by certain bacteria, is such a molecule. It can cross the placenta and enter the brain, causing severe brain damage in fetuses. High mercury levels in fish consumed by pregnant women have been linked to severe brain damage and cerebral palsy in newborns.

Children are exposed to mercury primarily from eating contaminated fish. However, children eating soil contaminated with mercury or accidental exposures to mercury, also have been documented.