The Star Tribune recently reported that the Minneapolis crime rate was dropping to its lowest levels in 30 years ("City crime level 2nd lowest since 1983," Jan. 6). Mayor R.T. Rybak attributed this decline to "effective partnerships between police and community."

This report is great news for our city, but the mayor may be missing the real explanation about why crime has declined so much over the last two decades here and across the country.

The January/February edition of Mother Jones carries a vastly more important story about crime. In "America's Real Criminal Element: Lead," Kevin Drum details fascinating new research that strongly points to lead in the environment as the hidden villain behind violent crime, lower IQs and even the ADHD epidemic (attention deficit hyperactivity disorder). It is a must-read.

Our city and the entire country experienced a horrific increase in crime from the late 1950s until the early 1990s. Since 1990, crime rates, particularly for violent crime, have fallen dramatically here and throughout America and even around the world. The question is why.

For nearly half a century, police, politicians, sociologists, criminologists and ordinary Americans have debated the causes of crime and strategies to combat it. Economics, particularly the concentration of poverty, have often been seen as a primary culprit. Changes in the number of young males in the population have been another favorite.

Various strategies to reduce crime also have been advanced: stricter law enforcement; longer jail terms; greater community engagement; smarter policing; antiviolence programs, more social and economic opportunities for youths, and even the legalization of drugs.

There has been, in short, a tremendous amount of noise on the topic. Perhaps now a clear signal has been found, and it turns out an important cure may have been put in place decades ago.

The Mother Jones story details the 2000 and 2007 research of Rick Nevin, an economist who worked for the federal Department of Housing and Urban Development, on the effects of lead in the environment. Nevin set forth a startling hypothesis: Lead in the environment generated by the internal combustion engine directly correlates to the dramatic increase in crime this country experienced from 1960 to 1990.

Nevin's research, along with work done in 2007 by Jessica Wolpaw Reyes, an Amherst professor, argues persuasively that the elimination of lead in gasoline through EPA regulations and the catalytic converter beginning in the 1970s is the primary reason we have seen the dramatic decline in crime rates since 1990.

In the 1920s, General Motors developed tetraethyl, a lead-based additive to gasoline. Lead became prevalent in gasoline beginning in 1940 into the mid-1970s, with a concomitant dramatic rise in lead levels in the environment peaking in the mid-'70s. The brilliance of Nevin's theory was to overlay the levels of lead in the environment with the scale of the crime epidemic, staggered by an interval of 23 years (the midpoint in the most crime-prone years of life: ages 15 to 30).

Persons born during the expansion of lead in the environment, from 1940 to 1975, came of age between the 1950s to 1990. That coincides with the crime epidemic.

Research shows that lead in the bloodstream lowers IQ and essentially corrodes the brain. Basically, lead-addled brains are dumber and more dangerous.

As lead levels in the environment (and human bloodstreams) have dropped, so have the crime rates among young people reaching the most crime-prone period in their lives, and in society as a whole.

Nevins and Wolpaw Reyes examined international trends as well. Studies done in Europe, Scandinavia, Canada, America and Australia all show similar trends -- a decline in crime corresponding to declining levels of lead as the affected children become young adults. Most interesting is that the murder rate, often the strongest evidence of social dysfunction, has equalized between urban and rural areas, just as lead levels have equalized in these areas.

In "The Signal and the Noise," Nate Silver explains how good research and analysis is critical to separate meaningful numbers from useless statistics. The accomplishment on the Minneapolis crime rate is wonderful, but Mayor Rybak and Police Chief Janeé Harteau may well be just talking about the "noise." Nevin and Wolpaw Reyes may have found the most important "signal" on crime we've heard in this 50-year debate.

Crime has been with us since Cain killed Abel and always will be part of society, requiring effective crime-fighting strategies. So the Minneapolis Police Department should continue its efforts. However, the crime epidemic this country suffered from 1960 to 1990 could well have been environmental in origin.

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Brian F. Rice is a Minneapolis attorney.