## 4 Discussion
### Selected Heavy Metals
[26] determined, i.a., the chromium and cobalt contents of three microgreens species to be 0.1923 mg and 0.011 mg per 100 g fresh vegetable matter, respectively. These values were many times higher than those obtained in this work, which were, for chromium, at an average of 0.0004 mg (young safflower and amelina shoots) and 0.0021 mg (young nigella shoots), while for cobalt they were at an average of 0.0001 mg (young safflower and amelina shoots) and 0.0002 mg (young nigella shoots) after their conversion from 100 g dry to 100 g fresh matter. As for manganese contents, [PERSON] et al. [33] found that, for three microgreens species, the results determined by ICP-AES were in the range of 6.4-20.2 mg in 100 g of dry matter, which agrees with most of the results obtained in this study. Copper, an essential micronutrient for plants, plays a key role in a number of biological processes such as photosynthesis and hydrocarbon metabolism. Plants absorb this element from the soil in the form of Cu\({}^{2+}\). As copper is transported to aboveground parts, it can be metabolised to organic forms and, as is the case with zinc, these can be proteins, peptides, amino acids, carotenoids, alcohols, phenolic compounds, flavonoids, glycosides and stilbenoids [21; 51; 52]. As with zinc, the copper content in foods depends on the type of food and its origin. According to [PERSON] et al. [33], the copper content in various microgreens varieties of chicory, lettuce and Brassica species ranged widely, from 0.43 to 1.8 mg per 100 g d.m. In the present study, a considerable number of the results obtained exceeded 1.8 mg per 100 g d.m. ; the highest result, 3.10 mg in 100 g d.m., was found for safflower from the first harvest. Zinc occurs in all the tissue types of various living organisms. This element is essential for the proper functioning of plants, animals and humans. Zinc is a constituent of over 200 enzymes. In food products, its content varies both due to the type of food product, but also due to its origin [53]. Plants can absorb zinc from both the soil and water. Its bioavailability to plants depends on the speciation form of this element, but also on environmental conditions such as soil pH, organic and inorganic matter content and moisture content [21; 51; 52]. [PERSON] et al. [33] determined the zinc and strontium contents in three microgreens species. and the results ranged from 5.4-9.7 and 5.5-8.5 mg per 100 g d.m., respectively. All the results obtained for the zinc content in the microgreens of rare oilseed plants, except for the nigella microgreens from the second harvest, were higher in the present study. Concerning the amounts of strontium in the examined microgreens, only the results of its content in the microgreens of safflower (from the second harvest; 7.20 mg/100 g d.m.) and microgreens of amelina (from the first harvest; 7.27 mg) are consistent with the findings presented by [PERSON] et al. [33]. In turn, [PERSON] et al. [15] estimated the contents of, i.a., copper, zinc and manganese in nine species of summer leafy microgreens and compared them to the content of these aforementioned elements in the mature vegetables. The authors expressed these contents as mg per kilogram of fresh vegetable weight. They observed considerable differences between microgreen species. Copper, manganese and zinc were found in the smallest amount in the microgreens of the poi species, while the highest amounts were noted in the microgreens of bottle gourd (copper), radish (manganese) and amaranthus cv. _Katwa_ (zinc). The contents of the minerals in kale cultivars (_Brassica oleracea_) at the microgreen, young leaf and adult stages were determined by [PERSON] et al. [54]. According to the authors [54], microgreens contained significantly more zinc and copper than their relative adult vegetable. [PERSON] et al. [55], in turn, examined the mineral contents in seeds, seed sprouts and the microgreen stage of the different legumes.