A new study by Northwestern University researchers shows that edible plants grown in urban gardens could contain potentially hazardous amounts of lead. Chicago has one of the highest rates of lead poisoning in the United States, an extremely persistent health problem that particularly plagues urban areas. While the majority of the lead was concentrated in the roots, some lead was detected in shoots, which is often the portion of the plant that people eat. Much of the soil's lead contamination comes from deteriorated paint, past use of lead-containing gasoline and industrial air pollution.