Lead poisoning, one of the most persistent environmental threats faced by many young Americans, may also contribute to the incidence of murder in some communities, according to a new nationwide study.
Researchers found that counties that have high levels of lead in their air also have higher homicide rates. Homicide rates were estimated to be nearly four times higher in counties with the highest levels of lead than those locations with the lowest lead levels.
The study, published online this week by the American Medical Association's Archives of Pediatric and Adolescent Medicine, supports an emerging view among some scientists that lead exposure can predispose some individuals to committing crimes and displaying violent behaviors.
Until recently, lead exposure has been tied mainly to developmental disorders and learning disabilities in children, and high blood pressure and nervous disorders in adults. And the biggest threat in most settings has been thought to be exposure to dust or chips from lead paint or other materials in the home and workplace, rather than general exposure to airborne lead.
But the new study's results "indicate that these additional environmental pathways may be more ubiquitous than imagined, affecting patterns of serious forms of violence such as homicide," said Paul Stretesky, a sociologist at Colorado State University who co-authored the report with Michael Lynch, a criminologist at the University of South Florida.
The researchers stress that their findings are only an association between lead exposure and murder rates during their study period - 1989-1991 - but that their evidence isn't strong enough to say that more lead actually causes more murders. That would require testing individuals for lead exposure.
Still, if more research confirms the connection, "the findings may have important policy implications that link the need for continued efforts toward lead abatement, human health and behavior and crime control."
Several other studies have found an increased tendency toward aggressive and delinquent behavior among teens who had high exposure to lead as children. And a study published last year also found a link between the use of leaded gasoline and violent crimes in the United States, as well as a connection between lead paint use and murder from the late 19th century through 1961.
The new study used 1990 data from the Environmental Protection Agency on the estimated concentration of airborne lead in all 3,111 counties of the lower 48 states. The researchers then matched those estimates with homicide counts for the counties maintained by the National Center for Health Statistics.
A third of the counties didn't have a murder during the study period, and air lead concentrations and other pollutants were also within the recommended toxicological bounds in most places.
But the researchers found that air concentrations of lead and murder rates tracked closely. Then they factored in 15 additional air pollution and social factors to their statistics to shake out any bias against the mostly urban areas where murders and air pollution are most commonplace. That adjustment produced more conservative numbers, but still showed the fourfold difference between murder rates in counties with the lowest and highest lead concentrations.
However, the scientists also point out that their study did not consider other possible sources of lead exposure, such as soil or water, since that information wasn't available for all the counties.
The EPA has determined that since leaded gas has been eliminated, most of the lead in the air now comes from smelters, battery plants and other industrial plants that process lead.
Stretesky said the results underscore the importance of continued national efforts to monitor lead. Last month, the Bush administration announced it would leave in place new rules set by the Clinton administration that require more businesses to report their releases of lead or lead compounds into the environment.
The regulations, strongly opposed by industry groups, will require a facility to report releases if it emits at least 100 pounds of lead a year. Current rules require an emissions report only from a plant that processes more than 25,000 pounds of lead or compounds or uses 10,000 pounds in a year.
EPA officials say the new regulations impose reporting on at least 9,800 more industrial facilities.
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