Lead Information Package - Some Commonly Asked Questions About Lead and Human Health

Exposure and Human Health

• What are the health effects at different lead levels?
• What are the routes of exposure to lead for children and adults?
• How is inhaled or ingested lead absorbed into the blood?
• Where is lead stored in the body?
• How is lead excreted from the body?
• How do calcium and iron deficiencies affect lead absorption?
• Why might blood lead levels be higher in women after menopause?
• What is lead "poisoning" compared to lead "exposure"?
• Is lead poisoning a common problem in Canada?
• Are there noticeable and visible signs/symptoms of lead poisoning to look for?
• How do I find out if I have been exposed to high lead levels? Is there a medical test to show whether I've been exposed to lead?
• What type of treatment exists to remove lead from blood?
• How do pregnancy and breastfeeding affect blood lead levels?
• Why are children and the developing fetus at a greater risk for adverse health effects associated with blood lead levels?
• What are the blood lead levels in Canadian children? Should children be screened?
• Where can I get more information?

What are the health effects at different lead levels?

The latest medical and scientific research shows that absorption of even very low levels of lead into the blood may have harmful health effects on the intellectual and behavioural development of infants and young children. Blood lead levels in the range of 10 to 15 micrograms per decilitre in fetuses, infants, and children have been associated with adverse neurobehavioural and cognitive changes. At levels above 40 micrograms per decilitre, there is a decrease in the body's capacity to produce red blood cells.

What are the routes of exposure to lead for children and adults?

Lead may enter the body through: the mouth (ingestion), the lungs (inhalation) or the skin (dermal route). The growing fetus may also be exposed to lead from the mother via the placenta. For the general population in Canada, the main exposure routes are through ingestion or inhalation. The most common route of entry is ingestion, except in industrial environments, where inhalation of lead fumes may play a larger role. Absorption of lead through the skin is rare.

Children are at greater risk of ingesting lead due to their frequent hand-to-mouth activity and normal tendency to mouth or chew objects they come into contact with (especially non-food products such as paint chips, furniture or toys).

How is inhaled or ingested lead absorbed into the blood?

In adults with a normal diet, 3-15% of ingested lead is absorbed into the blood by the intestine. Less than 5% of absorbed lead stays in the body. Depending on such factors as particle size, solubility, density and the individual's ventilation rate, approximately 30% to 50% of the airborne lead particulate inhaled by an adult are retained, of which nearly all (80%) are absorbed into the blood.

In children, the percent of lead absorbed and retained is much greater. Children eight or younger absorb 40-50% of ingested lead.

Where is lead stored in the body?

Regardless of the route of entry, lead is absorbed directly through the blood into tissue. Lead has no known biological function in the body. Once absorbed, it circulates in the bloodstream and either accumulates in tissues or is excreted as waste. Some of it is absorbed into soft tissue such as the liver, kidneys, pancreas and lungs. A very high proportion of absorbed lead is transferred to bone (hard tissue), where it accumulates over time and remains for long periods. The half-life (time for the body to excrete half the accumulated lead) is about 25 years. Therefore, high lead concentrations can stay in the body for many years after exposure to lead has stopped.

During periods of physiological stress (pregnancy or serious illness, for example), or when bone mass decreases with aging, the minerals stored in bones, including lead, go back into the bloodstream. An individual may therefore be at risk for release of stored lead into the bloodstream throughout a lifetime.

How is lead excreted from the body?

Lead is excreted from the body mainly through the kidneys and the intestine.

How do calcium and iron deficiencies affect lead absorption?

Studies indicate that deficiencies in some mineral nutrients, specifically calcium, iron and zinc, may increase the amount of lead absorbed, since lead molecules will attach at sites in body cells which these mineral nutrients would otherwise fill.

Why might blood lead levels be higher in women after menopause?

After menopause, women often develop osteoporosis, which is a progressive and serious loss of bone mass. As a result of loss of bone mass, lead stored in bone may be released into the blood.

What is lead "poisoning" compared to lead "exposure"?

Lead exposure refers to the entry of lead into the body, through ingestion, inhalation, the skin or the placenta. Lead poisoning occurs when there are adverse health effects due to lead in the body.

Is lead poisoning a common problem in Canada?

Very few cases of lead poisoning are documented in Canada each year. However, since low-level lead poisoning is often unrecognized, it is difficult to determine the number of Canadians affected by exposure to low levels of lead.

Are there noticeable and visible signs/symptoms of lead poisoning to look for?

Some of the more prominent symptoms of lead poisoning include headaches, irritability, abdominal pain, vomiting, anaemia (general weakness, paleness), weight loss, poor attention span, noticeable learning difficulty, slowed speech development and hyperactivity. However, at very low exposure levels, lead may not produce specific symptoms, but still can produce subtle adverse effects on children's development.

How do I find out if I have been exposed to high lead levels? Is there a medical test to show whether I've been exposed to lead?

Through a simple blood test, a family doctor can determine your blood lead level and therefore how much lead you have been exposed to. This is the most useful screening and diagnostic test for lead exposure. For more information contact your doctor or the Poison Information Centre in your area.

What type of treatment exists to remove lead from blood?

Chelation therapy is a drug therapy to remove lead from the body by binding it firmly to a chemical agent. Since this therapy is costly, burdensome to families and poses significant risk of side effects, it is usually only considered when lead levels in the blood are very high. It should be used only with caution in young children with blood lead levels below 45 ug/dl.

Children and Pregnant Women

How do pregnancy and breastfeeding affect blood lead levels?

Since lead can be found everywhere in our environment, it is impossible for pregnant women or women who are breastfeeding to avoid all exposure to lead and to avoid passing lead on to a fetus through the uterine wall or through breast milk. Despite this fact, Health Canada still recommends breastfeeding as the optimal method of feeding infants.

There are a number of actions pregnant or breastfeeding women can take to avoid unnecessary exposure. For example, they should not drink beverages from leaded crystal, use candles with lead core wicks, or inhale dust generated by the removal of leaded paint.

For additional advice and information, women should contact their health care practitioner.

Why are children and the developing fetus at a greater risk for adverse health effects associated with blood lead levels?

There are a number of reasons why a child and developing fetus are at greater risk for higher blood lead levels than adults. Because children are developing rapidly, they have a higher metabolic rate. As a result, they are more efficient at absorbing and retaining substances, including lead, than adults. Additionally, children have an increased soft tissue lead burden because their smaller skeletons store less lead. Compounding this, the developmental organs and systems of children are incomplete, making them less able to eliminate lead. Studies suggest that children are most susceptible to the neurological effects of lead in the first three years of life.

What are the blood lead levels in Canadian children? Should children be screened?

Blood lead levels of Canadian children are generally low, less than 10 micrograms per decilitre (ug/dl). In fact, there are very few documented cases in Canada of blood lead levels that require intervention of some form. In areas where there are unusual sources of lead exposure, such as a historic or ongoing problem of soil contamination from a smelter, higher blood lead levels have been observed. Routine blood lead testing may be necessary in these communities. If you live in one of these communities, you can contact your local medical officer of health for more information.

Where can I get more information?

Please refer to Health Canada's website at http://www.hc-sc.gc.c