Research studies, in my opinion, serve as the main purpose to gather more money for the chosen subject, and for the team to use as they wish, to collect data which will prove they are correct.
I read, study, learn new words and processes, always good.
When my life shows the opposite, or close to, I tend to believe my eyes, body, ears, and brain. Damaged as it is.
I am sure, (opinion), that excessive, very large amounts of lead, either in the body, or ingested over a long period of time may cause damages to the human body. Some of the article seems to state that the lead must be ingested to get lead poisoning. Maybe too many of us with lead in our organs and muscles, with no ill side effects to use as uncontrovertible data.
I remember where the anti-hunting and gun haters were using the California Condor deaths, and reduced young as a tool to do their best to stop hunting and lead bullets. Lead bullets at that time, as the California Condors haunt the forested mountains, above the bird hunting areas.
It was very impressive.
Then it was found that DDT was the actual culprit. DDT was outlawed, in almost totality.
The antis mentioned above completely forget to update the public on the new and conclusive findings. They still did their best to continue the fight against lead pellets, bullets, and hunting.