|Vol. 1, No. 3 , 1995, Page 4|
While the United States is making strides in reducing lead pollution -- primarily by phasing out leaded gasoline and paint -- a recent report notes that "an estimated 3 to 4 million American preschool children have blood lead levels above 10 micrograms/dl, a level now recognized to be associated with subclinical neurologic impairment." The report, by Philip Landrigan and Andrew Todd, adds that as many as 68% of poor, minority children in inner cities may have unsafe lead levels.
That's alarming news, because research suggests lead poisoning is a major risk factor for behavior problems and criminality. One study by Deborah Denno, in fact, found that lead poisoning was the strongest predictor of disciplinary problems in school, which in turn were the strongest predictor of arrests between the ages of 7 and 22. Another study, of 501 boys in Edinburgh, Scotland, found that blood lead levels correlated strongly with measures of psychological deviance.
The lead-crime connection isn't surprising, because lead poisoning causes the types of cognitive problems most strongly linked to criminal behavior. A large-scale study by Herbert Needleman et al., who excluded children with overt lead poisoning, found that children with elevated lead levels suffered from reduced IQ, attention deficits, and poor school performance, and a recent follow-up study found that they were seven times as likely as other children to fail to graduate from high school. Other studies have linked elevated lead levels to hyperactivity, impulsivity, and low frustration tolerance.
It's no surprise that high lead levels are a risk factor for crime and delinquency, because lead poisoning causes the cognitive problems most strongly linked to criminal behavior: impulsivity, low I.Q., hyperactivity, and low frustration tolerance.
There is new evidence that high lead levels may harm some individuals more than others. A recent study by Karl Kelsey et al. found that about 15 percent of whites, but virtually no blacks, carry a mutant gene that may help keep lead from entering the brain, where it can reduce IQ and impair neurological functioning.
Unfortunately, research suggests that current estimates of "safe" lead levels are far too high -- meaning that most children at risk of lead-caused brain dysfunction may go undiagnosed. One study, by D. A. Cory-Slechta and Bernard Weiss, found that rats show aberrant mental functioning at lead concentrations "approaching those of many suburban children," and several other studies have found subtle signs of mental impairment in lead-industry workers with body lead burdens well below levels considered toxic.
Yet, while millions of children may have unsafe lead levels, and more than a million adults work in jobs that increase their risk of lead exposure (battery making, smelting, soldering, demolition, stained glass manufacturing, etc.), Landrigan and Todd note that "great gaps exist in our knowledge of the chronic toxicity of lead." But the researchers say a new diagnostic technology, known as x-ray fluorescence (XRF), may help fill in those gaps.
XRF measures the lead in bones rather than blood, they say, "tak[ing] advantage of the fact that absorbed lead is stored in bone and has a half-life in dense cortical bone of at least 25 years." One form of this technique (KXRF) can accurately measure cumulative exposure to lead, while another form (LXRF) may help researchers measure changing lead levels.
The researchers believe XRF technology will be useful in "assessing the contribution of lead to neurological and psychological dysfunction in adolescents and young adults who manifest symptoms of developmental delay, dyslexia, or criminality."
"Direct measurement of lead in bone: a promising biomarker," Philip J. Landrigan and Andrew C. Todd, Journal of the American Medical Association, Vol. 271, No. 3, Jan. 19, 1994, pp. 239-240.
"Lead poisoning," Philip J. Landrigan and Andrew C. Todd, Western Journal of Medicine, Vol.
"Influence of blood lead on the ability and attainment of children in Edinburgh," M. Fulton, G. Thomson, R. Hunter, G. Raab, D. Laxen, and W. Hepburn, Lancet, 1987, i: 1221-6.
"The long-term effects of exposure to low doses of lead in childhood: an 11-year follow- up report," Herbert Needleman, Alan Schell, David Bellinger, Alan Leviton, and Elizabeth Allred, New England Journal of Medicine, Vol. 322, No. 2, January 11, 1990.
"Delayed behavioral toxicity of lead with increasing exposure concentration: a systematic replication," D. A. Cory-Slechta and B. Weiss, The Toxicologist, 2, 81, 1982.
"Gene appears to alter lead's toxicity," J. Raloff, Science News, Vol. 147, March 11, 1995.