We knew it was dangerous within a year of it being introduced, even if we didn't publish widespread clinical studies before the 60s. Its creator, Thomas Midgley Jr, was diagnosed with lead poisoning multiple times.
> Warnings about the toxicity of tetraethyllead came to Midgley from various sources. The letter of Erich Krause concerning its toxic effects, quoted in part in part 1,2 written on November 30, 1922, to George Calingaert (then at M.I.T.) was forwarded to Midgley in December 1922 by W. G. Whitman, Assistant Director of the M.I.T. Research Laboratory of Applied Chemistry. However, despite his own health problems and these early warnings, Midgley did not appear to be overly concerned about the health issues associated with the handling and use of tetraethyllead.
https://pubs.acs.org/doi/10.1021/om030621b
There's also some discussion at https://en.wikipedia.org/wiki/Tetraethyllead#Initial_controv... suggesting that early studies may have been suppressed by the lead industry.
> In the years that followed, research was heavily funded by the lead industry; in 1943, Randolph Byers found children with lead poisoning had behavior problems, but the Lead Industries Association threatened him with a lawsuit and the research ended.
Right, so we figure these things out within 100 years or so at most. We've been dealing with hunger for millions of years, you'd expect there to be something in the Torah about how no man shall act as a judge before he's had lunch.
Until when do they sit in judgment? ? Rav Sheshet said: Until mealtime, noon. Rav Ḥama said: What is the verse that alludes to this? As it is written: “Woe to you, land that your king is a lad and your ministers eat in the morning. Happy are you, land that your king is free and your ministers eat on time in strength and not in drunkenness”
-Shabbos 10a