Cadmium is a natural element in the earth's crust. It is usually found as a mineral combined with other elements such as oxygen, chlorine, or sulfur. Most soil and rocks, including coal and mineral fertilizers, contain some cadmium. Cadmium is used in many products, including batteries, pigments, metal coatings, and plastics, and it is found in cigarette smoke. Cadmium enters the environment through mining operations and the action of wind and rain. Forest fires and volcanoes also release some cadmium to the air.