A heavy metal is a member of an ill-defined subset of elements that exhibit metallic properties, which would mainly include the transition metals, some metalloids, lanthanides, and actinides. In Chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings It commonly refers to any element in Metalloid is a term used in Chemistry when classifying the Chemical elements On the basis of their general physical and chemical properties nearly every element Terminology The Trivial name " Rare earths " is sometimes used to describe all the lanthanoids together with Scandium and Yttrium History of the actinoid series From the earlier known chemical properties of actinium (89 up to uranium (92 indicating a relation to the Transition metals it was generally Many different definitions have been proposed—some based on density, some on atomic number or atomic weight, and some on chemical properties or toxicity.  The term heavy metal has been called "meaningless and misleading" in an IUPAC technical report due to the contradictory definitions and its lack of a "coherent scientific basis".  There is an alternative term toxic metal, for which no consensus of exact definition exists either. Toxic metals are Metals that form Poisonous soluble compounds and have no biological role i As discussed below, depending on context, heavy metal can include elements lighter than carbon and can exclude some of the heaviest metals. One source defines "heavy metal" as ". . . common transition metals, such as copper, lead, and zinc. These metals are a cause of environmental pollution (heavy-metal pollution) from a number of sources, including lead in petrol, industrial effluents, and leaching of metal ions from the soil into lakes and rivers by acid rain. "
Living organisms require varying amounts of "heavy metals. " Iron, cobalt, copper, manganese, molybdenum, and zinc are required by humans. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Manganese (ˈmæŋgəniːz is a Chemical element, designated by the symbol Mn. Molybdenum (məˈlɪbdənəm from the Greek word for the metal " Lead " is a Group 6 Chemical element with the symbol Mo Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Excessive levels can be detrimental to the organism. Other heavy metals such as mercury, plutonium, and lead are toxic metals that have no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of animals can cause serious illness. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Toxic metals are Metals that form Poisonous soluble compounds and have no biological role i Certain elements that are normally toxic are, for certain organisms or under certain conditions, beneficial. Examples include vanadium, tungsten, and even cadmium. Vanadium (vəˈneɪdiəm is a Chemical element that has the symbol V and Atomic number 23 Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Cadmium (ˈkædmiəm is a Chemical element with the symbol Cd and Atomic number 48 
Heavy metal pollution can arise from many sources but most commonly arises from the purification of metals, e. g. , the smelting of ores and the preparation of nuclear fuels. Chemical reduction, or smelting, is a form of Extractive metallurgy. Nuclear fuel is any material that can be consumed to derive Nuclear energy, by analogy to chemical Fuel that is burned to derive energy Electroplating is the primary source of chromium and cadmium. Cadmium (ˈkædmiəm is a Chemical element with the symbol Cd and Atomic number 48 Through precipitation of their compounds or by ion exchange into soils and muds, heavy metal pollutants can localize and lay dormant. Soil contamination is caused by the presence of man-made chemicals or other alteration in the natural soil environment Bay mud consists of thick deposits of soft unconsolidated Silty Clay, which is saturated with Water; these soil layers are situated at the bottom of Unlike organic pollutants, heavy metals do not decay and thus pose a different kind of challenge for remediation.
A well documented environmental disaster associated with heavy metals is the Minamata disease cause by mercury pollution. sometimes referred to as, is a neurological syndrome caused by severe Mercury poisoning.
In medical usage, heavy metals are loosely defined and includes all toxic metals irrespective of their atomic weight: "heavy metal poisoning" can possibly include excessive amounts of iron, manganese, aluminium, or beryllium (the fourth lightest element) or such a semimetal as arsenic as well as heavy metals. Toxic metals are Metals that form Poisonous soluble compounds and have no biological role i Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Manganese (ˈmæŋgəniːz is a Chemical element, designated by the symbol Mn. WikipediaNaming Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 Arsenic (ˈɑrsənɪk is a Chemical element that has the symbol As and Atomic number of 33 This definition excludes bismuth, the heaviest of stable elements, because of its low toxicity. Bismuth (ˈbɪzməθ is a Chemical element that has the symbol Bi and Atomic number 83
Heavy metals in a hazardous materials (or "hazmat") setting are for the most part classified in "Misc. A dangerous good is any Solid, Liquid, or Gas that can harm people other living Organisms property or the environment " on the UN model hazard class, but they are sometimes labeled as a poison when being transported.