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