The Presence and Effects of Lead in Soil

Lead poisoning is a major health risk, especially for children and infants. Along with water, food, and paint; soil is one of the leading sources of lead exposure. Lawns and gardens should have lead levels tested and taken care of before children are allowed to play or gardens are planted in the area.

Lead poisoning is harmful because the heavy metal affects most of the systems in the body including the cardiovascular, reproductive, nervous, and gastrointestinal systems. Overexposure to lead can cause such symptoms as headaches, irritability, abdominal pain, seizures, and in severe cases, death.

Children and infants are at an elevated risk for several reasons. Because of their developing nervous system, harm that occurs there has much more of an impact on physical and mental development suppressing growth to various degrees based on age and levels of exposure. Children are also more affected by lead in soil because they are at a stage in life where they put many inappropriate things in their mouths. While lead in soil does not typically soak through skin, when children play in the soil and then put their hands in their mouths the lead enters their body through ingestion. Another factor in this is that children’s gastrointestinal systems absorb lead and heavy metals faster and in higher quantities than a developed adults system, so not only do children ingest more lead, but their bodies soak it in more efficiently putting children at a much higher risk of overexposure and poisoning than adults.

Lead is present in soil from multiple environmental sources. There is some lead present in all soil (about 50 micrograms per gram (mg/g)) but not in levels that are harmful or toxic to children. Lead concentration is increased beyond safe levels in areas where there is lead mining, construction, a focus on agriculture, or heavy traffic. Lead mining and smelting releases lead particles into the air which then settles as dust in the soil. Areas of construction are also generally high in lead soil content because of lead released from equipment and during demolition of old houses. Houses before 1978 were painted using mostly lead-based paint which can flake off and get in the soil when they are torn down. Farming acts as a source of lead in soil primarily through fertilizer that contains lead and lime. Waste disposal can also contribute to increased lead levels in these areas. In areas of high traffic lead from gasoline that is pumped into the air settles as dust on soil and pollutes the ground.

In general the most concentrated levels of lead in soil will be in the top 2-5 cm of soil. In areas of farming and construction, the soil is often turned up and pushed around mixing lead much deeper into the soil. Because it is a heavy metal, lead does not biodegrade or decay so once it is deposited in soil it remains there until an outside effort is made to remove it. Lead also presents a danger of leaching into water supplies. Especially in areas where the soil is overturned frequently, or where there is heavy rainfall. Lead can soak deep to water stores or be washed into lakes and creeks and pollute the water source.

Before children are allowed to play in exposed soil, or gardening occurs, lead levels should be tested by a certified specialist. If levels are higher than the safe level, especially if they approach or pass 200 mg/g, measures should be taken to protect people from the heavy metal. Thick grass could be planted to cover the affected area but it would be best to remove the top few inches of soil and replace it with uncontaminated soil.

While lead levels and cases of lead poisoning have been on the decline since the late 1980’s and 1990’s, there is still a danger in areas of construction and farming especially if children are present. Precautions should be taken to avoid exposure to lead in the soil to prevent lead poisoning and the harmful effects of overexposure.

Sources:

Blumenthal H.T. and R. Mayfield An update on blood lead levels in pediatric patients of a neighborhood health center and an analysis of sources of exposure.. Journal of the National Medical Association. 87(2): 99–104. February 1995

Lynch, Robert A., Lorraine Halinka Malcoe, Valerie J. Skaggs, Michelle C. Kegler; The Relationship between Residential Lead Exposures and Elevated Blood Lead Levels in a Rural Mining Community. Journal of Environmental Health, Vol. 63, 2000

Environmental Protection Agency. Lead in paint, dust, and soil. Retrieved from http://www.epa.gov/lead/pubs/leadinfo.htm#where (2009, June 16).