The frequencies of chemical elements differ considerably when their occurrence in the solar system, in the planet Earth, in rocks of the earth’s crust, in the water of oceans or, for example, in the human body is considered. Within the respective frequency distribution, the frequent elements are separated from the rare as bulk elements. 1000 ppm as trace elements, analytical chemistry usually prefers a threshold value of 100 ppm or 100 µg/g or 0.01 %.
Microelements belong to the micronutrients. Essential trace elements for humans Too little or even the lack of essential trace elements causes deficiency diseases in living beings. Such deficiency symptoms – such as anemia due to iron deficiency or an enlargement or underfunction of the thyroid gland due to iodine deficiency – reveal the indispensability of an element. Trace elements are usually absorbed during eating and drinking with food that contains them in traces. Iron is medically classified as a trace element because of its mode of action; in humans it is contained at an average of about 60 mg/kg. Fluoride, on the other hand, is not one of the essential substances, but fluoride has a caries-preventing effect. The Federal Institute for Risk Assessment also recommends an average total daily fluoride intake of 3.1 mg for pregnant and lactating mothers as appropriate for adults. The daily maximum recommended dose is 7 mg for adults or