Contaminated Soil

The presence of toxic and radioactive chemicals in soil at concentrations above trace levels poses potential risks to human health and ecological integrity. Soil can be contaminated by many human actions, including discharge of solid or liquid materials to the soil surface, pesticide and fertilizer application, subsurface release from buried tanks, pipes, or landfills, and deposition of atmospheric contaminants such as dust and particles containing lead.

Contaminants can be introduced into the soil horizon at discrete locations called point sources, or across wide areas called non-point sources. Point source contamination typical of leaking tanks, pipes, and landfills is often concentrated and causes rapid, dramatic effects in a localized region near the original spill or leak. Soil contaminated by a plume emanating from a point source is, however, often easier to identify and remediate than the diffuse pollution caused by non-point sources like agriculture runoff or airfall from coal-burning energy plants. Governmental programs established to cleanup contaminated soil in the United States have made progress in cleaning up the nation's most polluted sites, but the technical difficulty and expense of remediation has made prevention the clear solution to soil contamination issues.

Frequently observed soil contaminants include volatile hydrocarbons such as benzene, toluene, ethylene, and xylene, and alkanes found in fuels. Heavy paraffins used in chemical processing, chlorinated organic compounds such as polychlorinated biphenyls (PCBs) that were used as coolants and lubricants in electrical equipment, pesticides and wood preservatives such as pentachlorophenol, and inorganic compounds of heavy metals like lead, cadmium, arsenic, and mercury, are all additional contaminants found in soil. Soil contaminated with radioactive waste has also been observed. Often, soil is tainted with a mixture of contaminants. The nature of the soil, the chemical and physical characteristics of the contaminant, environmental factors such as climate and hydrology, and proximity to human agricultural and municipal water sources interact to determine the accumulation, mobility, toxicity, and overall significance of the contamination in any specific instance.