lead is a natural element that we mine from the earth so i don't see a huge problem.
Well, lead is not naturally as concentrated as we use it. The problem is that lead is a a heavy metal and is toxic for the animals and humans. If there is too much lead in your food or drinking water, you may be very sick.
"Lead has no known biological role in the body. The toxicity comes from its ability to mimic other biologically important metals, the most notable of which are calcium, iron and zinc. Lead is able to bind to and interact with the same proteins and molecules as these metals, but after displacement, those molecules function differently and fail to carry out the same reactions, such as in producing enzymes necessary for certain biological processes."
"The symptoms of chronic lead poisoning include neurological problems, such as reduced IQ, nausea, abdominal pain, irritability, insomnia, excess lethargy or hyperactivity, headache and, in extreme cases, seizure and coma. There are also associated gastrointestinal problems, such as constipation, diarrhea, abdominal pain, vomiting, poor appetite, weight loss, which are common in acute poisoning. Other associated affects are anemia, kidney problems, and reproductive problems."
http://en.wikipedia.org/wiki/Lead_poisoning