Cycling of Lead in Soils: The Environment and Health

Lead contamination of urban soils is a widespread problem. Urban environments often have lead levels > 1000 mg/kg and reported values as high as 50,000 mg/kg while natural soil levels are below 50 mg/kg.  The commonly recognized sources for lead exposure include lead contaminated paint, dust and water.  However, recent concerns include contributions to blood lead levels from urban soils, and several studies have found that soil lead is an important contributor to children’s blood lead levels and lead poisoning. In fact, environmental health researchers acknowledge that urban soil is a significant sink of bioavailable lead that has not been regulated or included in a comprehensive prevention strategy, and is thus a public health issue. The primary sources of lead in the soil are deteriorating and flaking lead-based paint, lead emissions from motor vehicles and industrial activities.  In some cases lead contaminated soils have contaminated vegetable crops in backyard gardens. ingestion of lead from fruits and vegetables grown in backyard gardens is also a source of exposure that has received less attention, but may prove to be a persistent, long term and recurring source of lead for both children and adults, contributing to elevated body burdens of lead. The highest concentrations of Pb have been found in leafy vegetables, such as spinach and lettuce, with the lowest concentrations in grain. Certain species of plants, known as hyperaccumulators, can accumulate very high levels of metals in their tissues without showing signs of toxicity.  Such plants can be used to clean up heavy metal polluted soils if their biomass and metal content are large enough to complete remediation within a reasonable period of time. Phytoremediation has been used cost effectively to remove lead from soil at firing ranges and industrial sites as well as from residential yards.