Airborne lead is still a health problem, the U.S. Environmental Protection Agency (EPA) tells us. The secondary lead industry still has 21 smelters in the United States, according to the U.S. Geological Survey, so the secondary lead industry must rank first or second as a source or airborne lead, right? Wrong.

Secondary lead smelters are listed as sixth, contributing only 3.2 percent of the lead getting into the air, according to a set of EPA estimates. Ahead of secondary lead smelters in the ranking are iron and steel foundries (second), primary lead smelting (third), industrial/commercial/institutional boilers and process heaters (fourth) and hazardous waste incineration (fifth).

First place: Piston-engine airplanes using leaded aviation gas (avgas) to power propellers. But aren't corporate airplanes all jet propelled now? Think Walter Matthau's day job when he played a bank robber in Charley Varrick. Crop dusting. You don't hear much about that industry, but it does burn gasoline and it does have a National Agricultural Aviation Association.

"Avgas is commonly used in piston engines, which account for approximately 54.66 percent of agricultural aircraft," according to that trade group. "Although no...