The minimum level of lead we can measure is dangerous. Your claim is that there is some level that is safe, but there is absolutely no evidence for that. Each time we get better at measuring smaller and smaller lead levels in people, we find a correlation between lead levels and negative outcomes. There is literally zero evidence that supports a "safe" level of lead.

We also understand the mechanisms in which lead acts on the body. We know it's harmful in any amount. There is no safe level of lead.

My claim was that with small enough lead exposure there will be certainly no observable risk to your expected health outcomes.

Take your correlation, straight line it as a linear effect, and find the point where the effect size is less than we can observe. Ta dah.