(2) Gold Explanation: Toxic metals are metals that form poisonous soluble compounds and have no biological role, i.e. are not essential minerals, or are in the wrong form. Most often the definition includes at least cadmium, lead, mercury and the radioactive metals. Metals in an oxidation state abnormal to the body may also become toxic: chromium (III) is an essential trace element, but chromium (VI) is a carcinogen. Similarly, cobalt could also be toxic.