Plant-based products still have non-zero contamination because lead is still allowed in things like avgas, so we keep putting more in the environment. In theory, leaded avgas is finally starting to get phased out but this has been an excruciatingly slow process.
The good news is that if and when we eliminate lead totally from its remaining uses, we won't have to wait too long to see the benefits. IIRC people's blood lead levels started dropping pretty quickly after we phased out leaded gasoline.
How are we going to remove all the existing contamination? Soil lead levels in old residential areas are still high from when leaded gas was in use. To the point where people with chickens or vegetable gardens at home need to be testing for lead.
