Airborne urban dust contains harmful lead.

• Position: Blood Poisoning

A mysterious seasonal fluctuation in blood lead levels--observed in urban areas throughout the U.S.--results from resuspended dust contaminated with lead, according to a study in Environmental Science &.Technology. This has implications for government efforts to control childhood exposure to lead, which can have serious health consequences.

Shawn P. McElmurry, a professor in the Department of Civil & Environmental Engineering at Wayne State University, Detroit, Mich., and colleagues point out that average blood lead levels in the U.S. have declined following the elimination of lead from gasoline, paint, water pipes, and solder used to seal canned goods.

Much of the current lead in major urban areas is from those "legacy" contaminants. Modern human exposure takes the form of fine particles, deposited in the soil years ago, that are swept up into the air. Past research identified a seasonal trend in blood lead levels in children in multiple cities, including New York; Washington, D.C.; Chicago, III.; and Milwaukee, Wis. Those levels increase, often by more than 10%, in July, August, and September. Blood lead levels then decrease during winter and spring.

Scientists set out to test...