Heavy metal
Heavy metal refers to any metallic chemical element that has a relatively high atomic mass and density (greater than 5.0 specific gravity), and is toxic or poisonous at concentration. The term "heavy metal" however has never been officially defined by any authoritative body such as IUPAC.[1] Some heavy metals such as cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), vanadium (V), strontium (Sr), and zinc (Zn), are essential to human health in trace amounts. Others are non-essential and can be harmful to health in excessive amounts. These include cadmium (Cd), antimony (Sb), chromium (Cr), mercury (Hg), lead (Pb), and arsenic (As) - these last three being the most common in cases of heavy metal toxicity. Heavy metals also tend to accumulate in food chains (bio-accumulation).