There are many different sources of soil contamination. Soil properties vary from place to place and are influenced by many factors. Most potentially harmful substances, however, end up in soils as a result of human activities. Soil properties are affected by past and current land uses, as well as proximity to pollution sources. Some substances, such as pesticides and fertilizers, are intentionally added to soils while other substances, such as commercial and industrial chemicals, cause contamination through accidental spills or leaks. Contaminants can also be spread through the air and are deposited as dust or by precipitation (Shaylor et al., 2009b).