The two papers (plus others) taken together suggest that the impact is measurable (paper 2), perhaps to the tune of one or two IQ points on average per person exposed (me drawing a line from paper 1).
Granted, the latter point is my extrapolation, but there's enough of a foundation now for policy decisions to be made in advance of explicit research connecting these dots.
The largest result in the avgas paper, for children living within 500m of an airport, put their lead levels at 0.043 micrograms/dl higher than the general population.
From this paper[1], "An increase in blood lead from 10 to 20 micrograms/dl was associated with a decrease of 2.6 IQ points". So while there is an impact on lead levels, it is not nearly large enough to lead to the loss of 1-2 IQ points.
I'm not saying we shouldn't get rid of leaded avgas, but it accounts for about 0.1% of gasoline used in the US so the impact will be much smaller than banning leaded fuel for cars was.
* March 2022 - https://www.pnas.org/doi/full/10.1073/pnas.2118631119 - "Half of US population exposed to adverse lead levels in early childhood"
* October 2011 - https://ehp.niehs.nih.gov/doi/10.1289/ehp.1003231 A Geospatial Analysis of the Effects of Aviation Gasoline on Childhood Blood Lead Levels
The two papers (plus others) taken together suggest that the impact is measurable (paper 2), perhaps to the tune of one or two IQ points on average per person exposed (me drawing a line from paper 1).
Granted, the latter point is my extrapolation, but there's enough of a foundation now for policy decisions to be made in advance of explicit research connecting these dots.