It has long been known that exposure to lead has harmful effects on judgment, cognitive function and the ability to regulate behavior, but according to two new studies, children exposed to lead early in life are likely to develop criminal behavior in adulthood.

The studies also found that, despite the efforts of the federal government and cities to minimize exposure to lead, this continues to be a problem.

Between 1979 and 1984, Dr. Kim Dietrich a professor of environmental health at University of Cincinnati and colleagues recruited pregnant women in poor areas of Cincinnati, known for high concentration of older lead-contaminated housing. About 250 out of the 376 newborns recruited into the study were included in the final analysis.

The researchers measured blood lead levels during pregnancy and then regularly until the children were six and a half years old, as an indication of their lead exposure. The level of lead exposure was then correlated with local criminal justice records on how many times each of the recruits had been arrested between becoming 18 years old and the end of October 2005.

The study found that 55 percent of the subjects (63 percent of males) had been arrested at least once and that the average was five arrests between the ages of 18 and 24. In fact, the higher the blood lead level at any time in childhood, the greater the likelihood of arrests was.

“There are some data that suggest that in fact lead does run in parallel with crime trends over the past several decades. Lower income, inner-city children remain particularly vulnerable to lead exposure,” Dietrich said in a telephone interview with Reuters.

A second study by a team of UC researchers led by Kim Cecil of Cincinnati Children’s Hospital Medical Center examined a “representative sample” of 157 members of the same group using whole brain MRI scans. The findings showed that those with the highest blood levels of lead during childhood had the smallest brain volume. Brains were about 1.2 percent smaller in participants with average lead level. The most affected regions of the brain were those involving decision-making, impulse control, attention, error detection, monitoring completeness of a task and reward-based decision-making. Men were far more affected than women.

“The most important message is that lead affects brain volume, independent of demographic and social factors that are often used to explain away poor outcomes. This is independent biological evidence showing that the brain is affected by lead,” Cecil said.

About 310,000 children between the ages of 1 and 5 have blood lead levels above the federal guideline of 10 micrograms per deciliter nationwide.

“It’s a national disgrace that so many children continue to be exposed at levels known to be neurotoxic. The associations observed by Cecil and colleagues provide a clear warning sign that early lead exposure disrupts brain development in ways that are likely to be permanent,” Dr. David C. Bellinger of the Harvard Medical School wrote in an editorial accompanying the new reports in the online journal Public Library of Science Medicine.

The two studies seem to have a clear warning: “It doesn't take a lot of imagination to suspect that this [level of exposure] will also cause problems and affect conduct later on,” Dietrich said.

The studies were funded by grants from the National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency.