Well, organometallic molecules are famously way more dangerous to us (e.g. mercury vs dimethylmercury), so it’s not really controversial to say that pumping tons of tetraethyl lead directly into the air people breathe may have been worse than whatever can leach out of lead pipes or dishware.
Now that leaded gasoline is mostly phased out (except for avgas), I imagine the prevalence of lead poisoning will settle closer to what it may have been a millennia ago
I also didn’t downvote, but maybe you would want to convey the information to your players that creatures here can use that spell without outright killing a PC in the first battle? Like “you guys should really watch your health points in this area” type of thing