Those emissions are going to be concentrated around airports, not distributed evenly amongst the population. Also, a tiny amount of lead can lead to drops in IQ and long-term problems.
The question you need to answer is whether the amount of lead being released is safe or not; the proportions don't matter:
According to one 2003 estimate, published in The New England Journal of Medicine, blood lead levels below the supposedly âoesafeâ limit of 10 micrograms per deciliter still produced a reduction in IQ of around 7 points. (Approximately 1 in 50 American children has lead levels above that threshold.)
Others are saying the same thing:
After taking account of factors likely to influence the results, they found that blood lead levels at 30 months showed significant associations with educational achievement, antisocial behaviour and hyperactivity scores five years later.
With lead levels up to five microgrammes per decilitre, there was no obvious effect.
But lead levels between five and 10 microgrammes per decilitre were associated with significantly poorer scores for reading ( 49% lower) and writing (51% lower). A doubling in lead blood levels to 10 microgrammes per decilitre was associated with a drop of a third of a grade in their Scholastic Assessment Tests (SATs).
5 mcg/dl is 50 ppb, if I'm not mistaken. Intuitively, do you think that the people working around airports who are exposed to aircraft exhaust would get levels above that? Remember, too, that lead persists in the environment, collects in dirt, is kicked up in dust, etc.
And the effects are truly felt throughout life. Indeed, there is convincing evidence that the crime wave of the 80s was due to lead in cars:
We now have studies at the international level, the national level, the state level, the city level, and even the individual level. Groups of children have been followed from the womb to adulthood, and higher childhood blood lead levels are consistently associated with higher adult arrest rates for violent crimes . All of these studies tell the same story: Gasoline lead is responsible for a good share of the rise and fall of violent crime over the past half century.