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Children are not generally exposed to lead from paint while the paint is still in the can or when the paint is being newly applied to a previously unpainted or uncoated surface. Rather, lead exposure generally occurs after the lead paint has already dried on the wall or on the article that has been painted.
Over time, paint on a surface will chip, wear and deteriorate. This happens more quickly when the surface is exposed to sunlight or is subject to friction and impact (such as with windows and doors). Any lead that was present in the deteriorating paint is released to dust and soil in and around the home, school or other location where lead paint was used. When a surface that was previously painted with lead paint is sanded or scraped in preparation for repainting, very large amounts of lead-contaminated dusts are produced and spread.
Children playing indoors or outdoors get house dust or soil on their hands and then ingest it through normal hand-to-mouth behavior. If the house dust or the soil is contaminated with lead, the children ingest lead. Hand-to-mouth behavior is especially prevalent in children aged six years and under, the age group most easily harmed by exposure to lead. A typical one- to six-year-old child ingests approximately 100 milligrams of house dust and soil each day. In some cases, children pick up paint chips and put them directly into their mouths. This can be especially harmful because the lead content of chips can be much higher than what is typically found in dust and soils. When toys, household furniture or other articles are painted with lead paint, children may chew on them and directly ingest the lead-contaminated dried paint. Nonetheless, the most common way that children ingest lead is through lead-contaminated dust and soil that gets onto their hands.
While lead exposure is also harmful to adults, lead exposure harms children at much lower doses, and the health effects are generally irreversible and can have a lifelong impact. The younger the child, the more harmful lead can be, and children with nutritional deficiencies absorb ingested lead at an increased rate. The human fetus is the most vulnerable, and a pregnant woman can transfer lead that has accumulated in her body to her developing child. Lead is also transferred through breast milk when lead is present in a nursing mother.
Once lead enters a child’s body through ingestion or inhalation or across the placenta, it has the potential to damage a number of biological systems and pathways. The primary target is the central nervous system and the brain, but it can also affect the blood system, the kidneys and the skeleton. It is generally agreed that one key element in lead toxicity is its capacity to replace calcium in neurotransmitter systems, proteins and the bone structure, altering their function and structure and thereby leading to severe health impacts.
Lead is also known to affect and damage the cell structure. Children are more sensitive to the harmful effects of lead than adults for several reasons, including:
- A child’s brain undergoes very rapid growth, development and differentiation and lead interferes with this process. For example, it has been shown that moderate lead exposure (5 to 40 ug/dL) during early childhood is connected to region-specific reductions in adult gray matter volume. Moderate blood levels have been linked to an increased likelihood of impaired cognition and executive function, impulsiveness, aggression and delinquent behavior. The loss of grey matter in the brain constitutes a potential explanation for cognitive and behavioral problems associated with lead exposure. Brain damage caused by chronic, low-level exposure to lead is irreversible and untreatable.
- Exposure to lead early in life can re-program genes, which can lead to altered gene expression and an associated increased risk of disease later in life. For example, gene alterations caused by prenatal lead exposure have been implicated in the development of Alzheimer’s disease.
- Gastrointestinal absorption of lead is enhanced in childhood. Up to 50 percent of ingested lead is absorbed by children, as compared with 10 percent in adults. (Pregnant women may also absorb more ingested lead than other adults.)
Evidence of reduced intelligence caused by childhood exposure to lead has led the World Health Organization (WHO) list “lead caused mental retardation” as a recognized disease. WHO also lists it as one of the top ten diseases whose health burden among children is due to modifiable environmental factors and has called on countries to strengthen national actions to eliminate lead. In recent years, medical researchers have been documenting significant health impacts in children from lower and lower lead exposures. In response, the U.S. Centers for Disease Control and Prevention (CDC) and other authorities have concluded that there is no known acceptable lead exposure level for children.