Paint in houses built before 1978 is thought to be the major source of lead exposure for children, but the debate now is whether exposure at much lower levels is really that harmful
December 9, 2013 12:00 AM
Osceola Parklet in Bloomfield might be near lead contamination, but the area hasn't been tested yet.
By Cristy Gelling / Pittsburgh Post-Gazette
At the turn of the 20th century, "female pills" containing lead -- a toxic heavy metal -- were used for inducing abortions. As the popularity of the method grew, dozens of cases of lead poisoning in England were traced back to abortion pills.
Werner Troesken, an economist at the University of Pittsburgh, has estimated that a woman living in certain cities in Massachusetts around the same time would have received a similar dose of lead just by drinking a 5-ounce glass of tap water.
It is now known that generations of Americans were slowly poisoned by lead in the water, the air and in their houses, but at the time the effects were largely invisible. Although people knew that lead was poisonous, few people thought the small amount that leached into the water from the plumbing was enough to cause health problems.
In comparison, the average person today is exposed to a miniscule amount of lead. But as lead levels in the environment have plummeted over the past few decades, so too has the threshold that health authorities consider hazardous. In the 1960s, 60 micrograms of lead per deciliter of blood was considered a dangerous reading for a child. In the 1970s, anything over 30 micrograms per deciliter was the official CDC definition for elevated childhood levels; in 1985 it dropped to 25, and in 1991 it dropped to 10. Last year, the CDC endorsed a recommendation to use a shifting definition that would be lowered every four years, stating it cannot pinpoint a particular level of lead that is "safe."
The implication is that even the low levels of exposure that are common today may still be high enough to affect child development in subtle ways. Many researchers argue that lead is harmful at any concentration and because lead exposure is highest for the children with the lowest socioeconomic status, the ultimate target should be zero exposure.
Others disagree. They say that the evidence for these low-level effects is uncertain, and the cost of eliminating the last traces -- particularly for old industrial towns like Pittsburgh -- is prohibitively high.
It has been long known that lead is fatal in large doses, causing debilitating symptoms like muscle weakness, pain, vomiting and anemia. But lower levels of lead were not considered dangerous during the 19th and early 20th centuries, when lead plumbing was widely used. Mr. Troesken and his colleagues examined historical records and found that people who grew up in cities with the most lead in their water suffered higher mortality, scored lower on Army intelligence tests and suffered from more low-level health problems, like hearing loss, in their old age. "This was an effect of the same order of magnitude as typhoid fever," Mr. Troesken said, one of the biggest health concerns of the time.
Yet by the standards of the day, he said, the lead in tap water was considered inconsequential.
In the 1970s and 1980s, researchers like the University of Pittsburgh's Herbert Needleman found that much lower doses were also harmful to children, without causing obvious symptoms. These studies found that children with higher exposure to lead tended to have lower IQs and were more likely to have attention and behavior problems.
Children are thought to be particularly sensitive to lead at low doses because their brains are still developing.
Some estimate that the average child growing up in the 1970s was exposed to enough lead to decrease his or her IQ by a few points. But regulations that phased out lead from gasoline and paint in the 1970s have helped reduce childhood lead exposure dramatically since then. Today, the average blood lead level of children ages 1-5 is about 90 percent lower than in the 1970s; the latest estimate is around 1.3 micrograms per deciliter, while in 1976 it was greater than 15.
But the correlation between higher lead exposure and low IQ didn't disappear after the 1970s. As average blood lead levels in children dropped below the lowest levels seen in older studies, researchers continued to find that the children with lower lead levels tended to score better in cognitive tests.
For example, a study published this May showed that children with higher blood lead levels had lower reading readiness scores on entering kindergarten. The reading readiness test measures skills that children need before they can learn to read. It's an important benchmark for childhood development and for future success in school, said Patricia McLaine, a community public health researcher at the University of Maryland. "Learning to read is key to reading to learn, which is the next step of education," she said.
Although the average blood lead level in the children was around 4 micrograms per deciliter, much higher than the national average, it was still well below the cutoff of 10 micrograms per deciliter that the CDC considered the "level of concern" until last year.
This study is one of many over the last decade or so that have suggested lead is harmful at levels below 10 micrograms per deciliter.
Last year, the CDC accepted the recommendations of a federal advisory committee -- the Advisory Committee on Childhood Lead Poisoning Prevention. The committee recommended a new framework with a moving target; every four years the lead level that triggers public health intervention should be revised downward. The new reference level would be adjusted so that roughly 2.5 percent of children would always be above the cutoff. The level is currently set at 5 micrograms per deciliter. By this definition, more than 500,000 children ages 1 to 5 are estimated to have elevated blood lead levels.
But one member of the committee, Rutgers University epidemiologist George Rhoads, voted against the recommendations. Dr. Rhoads, the committee chair, said that although he acknowledges lead is a serious toxin in small amounts, he is not convinced that current evidence shows there is harm below 10 micrograms per deciliter.
He argues that just because IQ is correlated with blood lead levels, this doesn't mean that lead itself causes low IQ. For example, lead exposure is more common in socially disadvantaged children, and it might be this disadvantage that leads to low IQ, he said.
"Parents who let their children eat off the floor or who don't have as well-manicured a home may also be the parents who don't have time to read to their children at bedtime and do other things that help children to develop the kinds of skills that help on IQ tests," Dr. Rhoads said.
He also said that children with very low IQs might more frequently put their hands and toys in their mouth, which would increase their exposure to lead from soil and dust.
"I fully support the level of 10 but not the notion that you just have to keep going lower and lower, and there's no end to how low you have to go," said Dr. Rhoads. "If you keep taking these observational studies at face value without being critical, I think it's going to lead to a lot of worry for parents and a lot of expenditure for the health care system for environmental issues that are probably not very harmful."
Another member of the committee, neurotoxicologist Deborah Cory-Slechta, of the University of Rochester Medical Center, disagrees.
"Think of the philosophy that we accept by saying that it's OK to lose a few IQ points, that we have to accept that for economic reasons," she said. "It says to me that children with low socioeconomic status, typically minority children, don't deserve improvements in their environment."
She argues that blood lead and IQ are correlated even after correcting for the effect of socioeconomic status. Toxicity at low lead levels is consistent with data from animal experiments, she said.
But even though the CDC has now formally accepted the committee's view of low blood lead levels, federal budget cuts mean they don't have enough money to fully implement the recommendations. In 2012, the healthy homes and childhood lead poisoning budget was cut by more than 90 percent, and CDC had to slash funding for state and local childhood poisoning prevention programs.
Because of the cuts, Allegheny County Health Department has stopped handling the medical case management of children with elevated blood lead levels. "We expect that doctors are doing the testing and that they mandatorily report results to us," said director Karen Hacker.
The department now focuses its resources on environmental risk assessments of the homes of children with high blood lead. If lead hazards are found, the department issues orders for the homeowner to eliminate the risk. Currently, these investigations are triggered when a child tests with blood lead greater than 15 micrograms per deciliter, which is still the current CDC guideline.
Dr. Hacker advised parents concerned about lead to have their children tested and to make sure that they are not exposed to lead paint during renovation work. Lead paint in houses built before 1978 is thought to be the major source of lead exposure for children.
One other possible source in Pittsburgh is contamination from former industrial sites.
Children in Allegheny County are at greater risk than average because most housing here was built before 1978. In 2011, less than 2 percent of children tested in Allegheny County had blood lead levels above 10, according to figures provided by Dr. Hacker. Although the Health Department recommends that all children be tested for elevated blood lead between the ages of 1 and 2, at the moment most doctors in Allegheny County only screen a portion of children, she said.
Lead screening rates in many places are quite low, said Ms. Cory-Slechta, but preventing lead exposure in the first place is even more important than screening.
"We can talk about how much it costs, but if a child does poorly in school in the first and second grade -- which is what we know is going to happen -- that child is really unlikely to be the class valedictorian in high school," Ms. Cory-Slechta said. "This problem has a way of amplifying itself over a lifespan."
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