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 pernicious at concentration. The term 'heavy metal' has never been officially defined by any authoritative body such as the International Union of Pure and Applied Chemistry (IUPAC). 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 dosages. Others are non-essential and can be deleterious 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).
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