Term (also microelement) for chemical elements that occur only in low concentrations or traces. If the concentration is extremely low, it is also referred to as an ultra-trace element. As a rule, in geochemistry, material components and accompanying elements of rocks and minerals in concentrations below 0.1% or 1000 ppm (millionths) are called trace elements. In analytical chemistry, the threshold value is 100 ppm or 100 µg/g (= 100 mg/kg) or 0.01 %. In biology, essential trace elements are chemical elements that are essential for a living organism (colloquially mostly referring to humans) and occur in mass proportions of less than 50 mg/kg in the organism. These include arsenic (As), chromium (Cr), cobalt (Co), iron (Fe), iodine (I), copper (Cu), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se), silicon (Si), vanadium (V), zinc (Zn) and tin (Sn). They are necessary for the formation of enzymes. In viticulture, any trace elements required are added through fertilisation according to the results of the soil analysis. Trace elements also occur in wine; see ash, total extract and nutrients.
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