Many folks are raising backyard chickens for meat and eggs as they are trying to get a safer alternative to commercially produced eggs.  However, Dr. Radford Davis at Iowa State indicates that there are some concerns that the birds can be exposed to heavy metals such as lead, and they could pass toxic lead on to people in the eggs or meat. 

The chickens may pick up lead from sources like contaminated water or food, but the most likely source of lead is contaminated soil.  Soil can be contaminated by flakes of lead-based paint that may have come off older buildings or even be contaminated if guns were shot nearby in the past.  A study out of California recently looked at lead exposure in backyard chickens and lead contamination of eggs, which can affect human health.  Livers from about 1500 backyard chickens were tested for a 1-year period and over 3% were positive for lead. Most lead-positive chickens were from urban areas, not rural ones. The chickens with the highest lead concentration would lay eggs that would double the recommended amount of lead for a child under 6 years old, and liver exposure in children can lead to behavior disorders, attention deficit disorders, decreased brain volume and decreased IQ.  Even at lower levels, repeated consumption of lead can cause a problem as lead was found in chicken feed, paint chips and blood from other chickens in the flock.  Most chickens did not have clinical signs although still had enough lead in their bodies to contaminate meat and eggs and potentially cause illness in humans. 

To prevent this, check your soil for lead (ask your veterinarian how to do that in your area) and also check lead levels in eggs before feeding them to your family.