I'm referring to the paper on it that states lead has a benign interaction with air or water. I'm pretty sure both mediums become toxic after exposure to molten lead. And it seems corrosion resistance is a problem when using lead as a coolant and they still haven't quite figured that out yet.Actually Chernobyl used lead as a coolant. Lead cooling is not necessarily dangerous or unsafe, just different. Chernobyl lacked a containment building and cut many, many corners.