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A trace element is present in only a small amount. The amount depends on context.
- In analytical chemistry, it is an element in a sample that has an average concentration of less than 100 parts per million (ppm) measured in atomic count, or less than 100 micrograms per gram.
- In biochemistry, it is one that is needed in minute quantities for the proper growth, development, and physiology of the organism. In biochemistry, a trace element is also referred to as a micronutrient. See Cofactor.
- In geology, its concentration is less than 1000 ppm or 0.1% of a rock's composition. The term is used mainly in igneous petrology.
- H.J.M. Bowen 1976. Trace elements in biochemistry. 2nd ed, Academic Press.