Two of the articles cited that found Pb in eggs concluded the Pb source was the soil the birds were kept on.I’ll post a link to a few of the articles that I read. There were a few peer reviewed journal articles detailing lead in oyster shell, but I had read enough at that point to convince myself that it could be true.
One of the articles cited found that the birds were exposed to Pb-based paint.
The article discussing the accumulation of Pb in oyster shells was indicating that oysters could be used as a biomarker for Pb contamination in the oceanic sediment the oysters inhabit in the wild.
Most of the oyster shells that are available for Ca supplementation come from farm raised oysters, oysters that would not have been exposed to Pb.
If you do not have Pb contaminated soil that your chickens are on or Pb-based paint your chickens have access to, I think the big debate over the dangers of Pb accumulation in your chickens eggs, you and your children is over.