Designation for a group of metals, whereby there are many different definitions such as atomic weight, density, chemical properties or toxicity. In colloquial language, heavy metals are often considered "toxic substances". However, this is not correct, as the vital heavy metals include iron, copper, manganese, molybdenum and zinc. Arsenic, lead, cadmium, chromium, nickel and mercury (amalgam) are considered to be dangerous even above a certain amount. However, it depends on the quantity, because in the human body some are required as essential trace elements, for example chromium between 10 and 20 mg for the regulation of the blood sugar level and according to the latest findings also arsenic up to 7 mg for various metabolism processes.