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The U.S. Consumer Product Safety Commission recently initiated a recall of crayons imported from China because they contained enough lead to present a poisoning hazard to children who might eat or chew on them.

This is just one more instance that points out the hazards of lead in the environment. Lead is toxic. It can cause a variety of health problems, particularly in infants and children, including stomach pain, irritability, vomiting and anemia. Lead poisoning has been associated with learning disorders and at high levels can cause brain and kidney damage and can even be fatal.Lead is everywhere. It is a natural element, one of the heavy metals that have been used in manufacturing and industrial processes for centuries. There are many sources of hazardous lead in the environment, including some drinking water tainted by lead pipe and solder and some industrial emissions.

From time to time we hear warnings about lead used in pottery glazes that make dishes unsafe for food. Crystal, fishing weights, spent ammunition and wine bottle seals have also been implicated in lead poisoning. And, of course, there were the crayons that caused recent problems.

A major source of hazardous lead is soil contaminated by gasoline residues. Tetraethyl lead has been largely phased out as a gasoline additive, but lead residues from gasoline remain in the soil along many heavily traveled streets and highways.

Another source mentioned frequently is old, lead-based paint. In the paint industry's early years, lead carbonate (white lead) was considered the best white pigment available. In combination with linseed oil, white lead might constitute as much as 50 percent or more of the contents of a can of paint.

But the industry began to look for acceptable substitutes early in this century. But 1953, industry consensus standards limited lead use in interior house paints to not more than one percent by weight in the dry paint film; by 1962 it was reduced even further. In 1978 CPSC banned the use of lead in consumer paints altogether.

The National Paint and Coatings Association points out that the mere presence of lead-based paint is not hazardous in itself, however. To present a problem, lead has to get into the body through ingestion or inhalation.

If the old paint is chipping or peeling, so that children can chew on or mouth the paint chips, or if there are large amounts of lead-contaminated dust that they may inhale or get onto their hands and into their mouths through normal hand-to-mouth activity, it can be a dangerous source of exposure.

How much lead is too much? Lead poisoning is diagnosed by measuring blood-lead content, in micrograms per deciliter of whole blood. In 1970 the levels set by the U.S. Centers for Disease Control as the threshold for poisoning was 60 micrograms. But more recent research has caused that level to be reduced. In 1991, the CDC issued guidelines setting tiered "levels of concern" starting at 10 micrograms per deciliter. Lead at levels as low as 10, says the CDC, might not in themselves be a problem, but they might be an indication of progressive exposures and cumulative effects, leading to adverse effects on children's health.

Should children be routinely screened for lead poisoning? There is much debate on that question, with some advocates calling for universal screening. Many physicians and clinics are reluctant to test a child's blood, however, unless there is reason to suspect abnormal lead exposure: a family member with an elevated level, or who is exposed to lead in the workplace; old lead-based paint in poor condition in the home, school or day-care centers.

In the meantime, here are some other suggestions for dealing with lead hazards in the environment:

- Take a good look at your child's environment. If your home is near a major highway or traffic artery, you might consider having the soil tested.

- If the home was built prior to the 1950s, it may contain old, lead-based paint. Lead paint in good condition - smooth, tight to the walls, not chipped or peeling - may not pose a risk, but make sure the child can't pick off the old paint and eat it or chew on painted surfaces such as windowsills. (For more suggestions of dealing with paint, see sidebar.)

- Check to make sure that any pottery you buy is safe for food. If you don't know (souvenirs bought in foreign countries, for example), don't take a chance.

- Buy only crayons and other children's art materials that have this label: "Conforms to ASTM D-4236" (or similar words), which means that a toxicologist has reviewed the formula or the art material for chronic hazards. If you recently purchased crayons that were imported from China, discard them or take them back to the store to see if they are part of the recall.

- Beware of lead-removal scams. From time to time, problems crop up where unscrupulous lead "experts" go door to door offering to test for lead content. For example, there is a testing method knows as X-ray fluorescence, or XRF. XRF spectrometers are difficult to use outside a controlled laboratory setting, and therefore the accuracy of a home test could be in question. But that doesn't stop some people from renting them and claiming to be experts on lead testing.