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Environmental connections to public health >>

Scientists: Lead contamination in drinking water is never safe.

Monday, February 2, 2009

When are traces of lead in drinking water dangerous?

The better question is, when aren't they?

That question became personal back in early 2004, when the Washington Post disclosed that, beginning in 2001, Washington D.C.'s drinking water had been contaminated with rising levels of lead, flushed from aging pipes by a new treatment process.

Last week, in Environmental Science and Technology, a research team led by Marc Edwards, a professor of civil and environmental engineering at Virginia Tech whose tests helped uncover the lead crisis, reported that the number of babies and toddlers with elevated lead levels in their blood increased more than 400 percent between 2001 and 2004 period. The study, based on blood tests of more than 28,000 children seen at the Children's National Medical Center in Washington, was the first to draw a strong correlation between the city's water contamination and elevated lead blood levels in young children from the hardest-hit neighborhoods.



But what does it mean for the hundreds, or possibly thousands, or even tens of thousands of D.C.'s children exposed to minute quantities of lead in their drinking water? As with most subtle, long-acting environmental toxins, there are more questions about lead than answers. But what we do know isn't reassuring.

The smartest take on the significance of early childhood exposure to lead contamination in Washington D.C.'s drinking water comes from Washington Post health and science reporter David Brown, a physician, who reports that most experts do not believe that IQ losses suffered by individual D.C. children are likely to be dramatic. "Studies have shown that lead exposure explains less than 4 percent of the variation in intelligence among individuals," he writes. "In contrast, societal and parenting factors account for more than 40 percent."

Dana Best, a pediatrician at Children's who co-authored the new study with Edwards and Simoni Triantafyllidou of Virginia Tech, told Brown that "in the worst-case scenario a child might have lost three to four IQ points, " harm that could be offset, she said, by good education.

Even so, Brown cited some studies that have demonstrated a paradoxical phenomenon: low exposures to lead can cause more intense damage than higher exposures, so any blood lead level greater than zero cannot be dismissed. "On a microgram-by-microgram exposure, lead has a greater effect on IQ at low concentrations than at high concentrations," Brown wrote. "In other words, the brain is more sensitive to small doses than to large ones, even though large ones ultimately do more damage. The consequence of this counterintuitive fact is that a child whose blood lead rises from two micrograms to five micrograms for several years might not only be affected, but that the effect might also be more exaggerated than one would expect."

The outsize impact of the first few micrograms of lead was the subject of a pioneering 2003 study by a team led by Richard Canfield, a senior researcher in Cornell's Division of Nutritional Sciences, with scientists from the Cincinnati Children's Hospital, the University of Rochester, the National Institutes of Health and the University of Washington. The study, published in the April 17, 2003 issue of the New England Journal of Medicine, found that children suffer intellectual damage at a blood-lead concentrations below the level of 10 micrograms per deciliter (mcg/dl), or 100 parts per billion. That number is significant because the Centers for Disease Control and Prevention (CDC) calls for public health action if a child's blood-lead measurement is above the 10 mcg/dl level.

But, Canfield said, the study found that "most of the damage to intellectual functioning occurs at blood-lead concentrations that are below 10 mcg/dl. The amount of impairment was also much greater than the researchers had expected. "

The implications for D.C.'s children are uncertain, as the Post's Brown points out. What is clear is that we need to know much more about what's in our water supply, and we need to prevent another lead contamination crisis from happening in D.C., and everywhere else.

Image by Sebarex

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