I get this from a web, it's for humans, but if newts are small, and breathe from the skin, they can be affected sooner and higher (I believe).
"Lead is a highly toxic metal, producing a range of adverse human health and environmental effects, particularly in children and fetuses. Lead has the ability to impede the development and function of every organ and system in the body. Once it enters the body, lead travels through the bloodstream. A small portion of the ingested lead remains in the bloodstream, while some is deposited and stored in the kidneys and brain. Most, however, is stored in the bones. This lead moves in and out of the bones as the body absorbs nutrients and grows. Lead stays in the body for a long time. Therefore, one can be lead poisoned through high exposure to lead during a short time period or through low exposure over a long period of time."