Decades ago, aviation gasoline contributed a tiny percentage of the overall lead pollution in the United States. But after EPA standards were installed in 1978, other sources-most profoundly, leaded auto fuel-were outlawed, leaving aviation fuel as one of the top lead polluters. Though avgas today still represents a tiny fraction of what was emitted 30 years ago, new standards are aiming to cut current lead pollution by up to 90 percent overall. The new limit of .15 micrograms per cubic meter is 10 times as low as the 1978 standard. According to the Associated Press, there are 16,000 sources of lead pollution, including smelters, mines and incinerators. In recent years, there has been strong interest in weaning general aviation piston engines off of their lead diet. A meeting at this year's EAA AirVenture in Oshkosh addressed the issue and outlined a plan of action to evaluate options for converting the fleet to unleaded fuel, whether a refined form of today's automotive unleaded or a diesel/jet fuel program.