What is the limit of lead poisoning for it to be deadly?

Lead poisoning: Depends. There is no safe amount of lead for humans. All lead is toxic. Children are more suseptable than adults and the lethal level can vary.

Lead toxicity: Varying levels of lead exposure cause symptoms at different levels in kids and adults. The national health and nutrition examination survey concluded blood levels as low as 5-9 micrograms/deciliter were associated with increased risk of death from all causes, cardiovascular disease and cancer. Point: stay clear from lead, and if exposed get treated to remove it from your body. Hope this helps.