![]() Additional compounds often encountered in conservation are also listed. The Chart of Heavy Metals, their Salts, and other Compounds provides a quick reference to the 35 elements and some of their compounds classified and regulated by OSHA as heavy metals 1. Hexavalent chromium, Cr (VI), however, is highly toxic 6 and its compounds, including chromic acid and chromates, are potential carcinogens 22. For example, trivalent chromium, Cr (III), is an essential trace element 6 and its compounds, including soluble chromium salts, are considered to be of low toxicity and are thought to present few industrial hazards 22. The resulting metallic compounds can result in very different properties of solubility and toxicity 5. Metallic compounds such as oxides, sulfides, chlorides, carbonates, nitrates, and other salts are formed when positively charged metals called cations react with negatively charged elements called anions in ionic or covalent bonds. One of the most significant factors about metals is their residual persistence over time. The 35 shaded elements in this periodic table are those regulated by OSHA under the classification of Heavy Metals 1, 2. All metals are characterized by their excellent ability to conduct heat and electricity (the metalloids being semi-conductors), and are malleable, ductile, hard, and shiny, the exception being mercury which is liquid at room temperature.įigure 1. An example of the ambiguity of the term heavy metal is that of molybdenum, a heavy but essential trace element and beryllium, a light but very toxic metal 4. The heavy metals group includes transition metals, some metalloids (elements that exhibit both metal and non-metal properties), some lanthanides and actinides, and often includes reference to certain light and trace metals with an inference to toxicity. Although there are several other definitions of the term there is no specific set of elements that would imply any common set of properties such as high toxicity or high atomic weight 3. The term heavy metal is a loosely used term generally accepted to mean dense metals of relatively high atomic mass, with a specific gravity of 4 or above. 7 A Specific Note About Arsenic as Arsine.Although its form and availability to living organisms may change over time, mercury persists in the environment. It is converted among its various forms through a range of abiotic and biogeochemical transformations and during atmospheric transportation. Since mercury can be adsorbed easily onto small particles of matter, some scientists use the notation Hg(p) to represent elemental mercury attached onto or absorbed into a particle.īecause it is an element, mercury is not biodegradable. Hg 2+ is also found in organic (carbon based) substances like dimethylmercury (Me 2Hg), which is far more toxic than inorganic forms of mercury and bioaccumulates in the tissues of living organisms. The mercuric cation is more stable and is generally associated with inorganic molecules, such as sulfur (in the mineral cinnabar), chlorine (mercuric chloride), oxygen and hydroxyl ions. Mercury is also found in two positively charged, or cationic, states, Hg 2+ (mercuric) and Hg 1+(mercurous). Elemental mercury (Hg 0) has no electric charge. In nature, mercury has 3 possible conditions of electrical charge, or valence states. The metal is a fair conductor of electricity, but a poor conductor of heat. Mercury has a relatively high vapour pressure and the highest volatility of any metal, vapourizing to become a colourless, odourless gas. Fortunately, mercury does not form amalgam with iron, which allows for the element to be shipped in standard iron flasks containing 76 pounds, or 34.5 kilograms, of liquid mercury. The element also combines with other metals such as tin, copper, gold and silver to form mercury alloys known as amalgams. The liquid is highly mobile and droplets combine easily due to low viscosity. Droplets of liquid mercury are shiny and silver-white with a high surface tension, appearing rounded when on flat surfaces. Mercury has a melting point of -38.9 oC, a boiling point of 356.7 oC, and is the only metal to remain in liquid form at room temperature. The element's atomic mass is 200.59 grams per mole and its specific gravity is 13.5 times that of water. ![]() Like cadmium, zinc and lead, mercury is a naturally occurring element known as a "heavy metal" and can be toxic to living organisms.
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