Heavy metals such as copper are essential for our biological functioning. Excessive amounts of these metals become, nonetheless, toxic, leading to cellular and tissue damage. There are also non-essential metals such as aluminium and barium which can be toxic even at very low doses. Toxic amounts of heavy metals have been shown to affect cell membranes, their organelles (e.g. mitochondria, nuclei) and enzymes that play an important role in metabolism, detoxification and damage repair.