The presence of chemicals, contaminants and pollutants in natural ground. The Earth’s soil is becoming contaminated by pollutants through underground storage tanks, the application of pesticides and the leaching of waste from landfills into the ground. Contaminated soil can harm plants growing in the soil, expose humans to contaminants and harm humans who eat plants and animals that have been exposed. It is unknown exactly how much of the Earth’s land has been contaminated, however the United States is considered to have a large percentage of contaminated soil.