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Arsenic is widespread in the environment where it occurs combined with metals and sulfur and as secondary minerals in combination with oxygen. Its atomic structure allows it to be trivalent or pentavalent, and its properties lead to its classification as a metalloid in the periodic classification of the elements. Arsenic trioxide is a by-product of the smelting of metal sulfide ores and can contaminate other industrial products such as sulfuric acid. Arsenic from mineral deposits can also be solubilized and be present in groundwater, where it presents a health and environmental hazard, and in the sea, where it can be taken up by marine animals in the form of arseno-betaines. Although arsenates resemble phosphates in their chemistry, and can be transported with them in living systems, arsenate cannot replace phosphate in plant and animal metabolism as has sometimes been postulated. |
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