Do You Have to Remove Contaminated Soil Before Planting a New Yard?

Soil Contaminants

• There are many different substances that can potentially contaminate soil. In fact, really any substance that occurs in a high enough concentration to cause harm to human health, animal health or plant life can be considered a contaminant. Some of the most common soil contaminants that occur in home soil are heavy metals like lead, mercury, arsenic and cadmium. Not only are these substances harmful to humans, plants and animals in large concentrations, but the potential household sources of contamination are many.

Sources of Heavy Metal Contamination

• In their soil contamination fact sheet, the State of Washington Department of Ecology lists some of the most common household products that can make their way to outside soil and contaminate it. Products such as lead-acid batteries, consumer electronics, glass and ceramics, plastics, soldered cans and pigments can lead to lead the contamination of garden soil. Household batteries, electric lighting, paint residues, fever thermometers, miscellaneous electronics and pigments are all common sources of mercury contamination. Cadmium contamination was found to stem from household batteries, plastics, consumer electronics, appliances, pigments and glass and ceramics. Chipped lead-based interior paint, lead in tap water due to deteriorating lead plumbing and lead dust in air from industrial pollution may also contribute to lead soil contamination.

Treating Contaminated Soil

• Regardless of the source of contamination, contaminated soil needs to be made safe before any plants are cultivated in it. Rarely is contamination so bad in home soil to warrant complete removal of the soil; typically lead contamination levels that occur in home soils can be made safe enough for gardening using some basic soil treatments. In soils with a pH reading above 6.5, lead is rendered "immobile" in soil, meaning that plants will be unable to metabolize it at any level that is dangerous to humans. Therefore raising your pH to this level and maintaining it can help guarantee that plants will not absorb lead in the soil. Adding 1/3 by volume of organic matter to the soil in your garden will also increase lead immobility. To avoid further contamination, locate your garden away from any walls with lead paint, and exposed lead plumbing that may be deteriorating or any other potential sources of contamination.

Health Concerns

• States generally have their own regulations that establish concentration of soil contaminants that are considered safe and concentrations that are believed to present a health risk to humans. Check with a local government office to determine the guidelines that apply to your area. The University of Minnesota Extension advises that in homes with children, soils with heavy metal contamination levels of 100 to 300 parts per million (ppm) should never be used for gardening. Children are more likely to come into direct contact with the contaminated soils and, should the children eat the soil, lead metabolizes in children's intestines at a rate approximately five times higher than in adult intestines.