Pollution is the introduction of contaminants into the natural environment that causes harm. It can take the form of chemical substances, noise, heat, or light. Pollutants can be foreign substances or naturally occurring contaminants. Soil pollution occurs when chemicals are added to soil, reducing its productivity. Common causes of soil pollution include excess fertilizers and pesticides from agriculture, acid rain, and urban waste. Soil pollution poses health and environmental risks to humans, animals, and agriculture.