Some forms of cancer are linked directly to metal contamination. Most at risk are the people who work in particular industries or live near plants where production safeguards are inadequate. Arsenic workers have respiratory cancer mortality almost three times the expected rate. That for cadmium smelter workers is more than twice the expected rate, and lead smelter workers' is a third higher than expected. (The excess cancer rate in lead smelter workers may be attributable to the arsenic in the ore rather than to the lead). Lead has been linked to cancers of the respiratory and digestive organs, arsenic to cancer of the skin, mouth, and nose. Other serious and chronic health effects can result from metal poisoning and contamination. Lead and mercury are historically associated with mental disability, lead and arsenic with digestive difficulties, cadmium with kidney disease, and lead with anaemia.