Cadmium does not exist as a single element in the natural world. In natural water, the concentration of Cadmium is very low. Cadmium is an accumulative toxicant. Cadmium poisoning causes itai-itai disease and stimulates the respiratory tract. Long-term exposure to cadmium will cause Ansonia or yellow spots on gums. Cadmium compounds are not easily absorbed by the intestinal tract. However, they can be absorbed by the respiratory tract and accumulate in the liver or kidneys to harm health.