A lot of lead in an aero engine never makes it into the atmosphere, which is what they were talking about
About 3/4 makes it into the air, so your figure was still out by several orders of magnitude.
Vehicular air pollution: experiences from seven Latin American urban centres. Volumes 23-373 pg. 20. Published by the World Bank, 1997 Authors: Bekir Unursal and Surhid Gautam (found on google books)
Here's another question - are they still manufacturing engines that cannot currently run on any form of unleaded fuel. I'm suspecting the answer is 'yes'.