There are currently four questions tagged lead and five questions tagged lead-poisoning, one of which is tagged with both.
All of the questions tagged with lead are about lead poisoning, which means that if both tags were worth keeping, they’d all ought to have both tags, which means one of them is redundant.
I think we should get rid of the lead-poisoning tag, in case someone wants to ask a question which is about lead, but isn’t about lead poisoning.