PCB pollutant levels decline quite slowly.

• Position: YOUR LIFE - Polychlorinated biphenyls

It has been almost 35 years since the manufacture of polychlorinated biphenyls was banned in the U.S., but the chemicals, known as PCBs, still are very much with us. A series of policy briefs describes findings from the Integrated Atmospheric Deposition Network (IADN), a U.S.-Canada project that has measured pollution in the Great Lakes region for the past 20 years.

"PCB concentrations in the atmosphere are decreasing very slowly, if at all, even though their production was banned in 1976," writes Ronald A. Hites, coauthor of the research, whose analysis demonstrates that it takes 30 years for PCB concentrations to decrease by half. A statistical analysis of IADN data by Hites considers the influence of urbanization, temperature, wind speed and direction, and regulation on concentrations of several persistent organic pollutants.

In addition to PCBs, IADN has traced combustion-related pollutants such as polycyclic aromatic hydrocarbons (PAH), chlorinated pesticides like lindane, chlordane, DDT, and, more recently, brominated and chlorinated fire retardants. Air samples have been collected every 12 days at five...