## 4 Discussion
### Selected Heavy Metals

Table 2: The nitrate (NO\({}_{3}\)\({}^{-}\)) and nitrite (NO\({}_{2}\)\({}^{-}\)) contents in the young shoots of nigella (_Nigella sativa L._), safflower (_Carthamus tincorris_ L._) and amelina (_Camelina sativa L._) at different stages of vegetation (mg 100 g\({}^{-1}\) dry matter—d.m.). and 0.0011 (young camelina and nigella shoots), while for lead this was 0.0002 (young safflower shoots), 0.0005 (young camelina shoots) and 0.004 (young nigella shoots), and these were higher for cadmium and lower for lead compared to the values obtained by [PERSON] et al. [26]. Cadmium exhibits very strong toxicity; the ingestion of even small doses of this element can result in serious health effects. The higher risk with cadmium is due to the fact that this element has a toxic effect both when ingested, via the gastrointestinal tract, and also when inhaled, via the respiratory tract. Moreover, cadmium can also accumulate in the lungs [27]. It is assumed that the toxic effect of cadmium is mainly due to the Cd\({}^{2+}\) ion to which cadmium is converted after the intake of cadmium compounds into the body. The biological function of cadmium in plants has not yet been recognised; however, it has been confirmed that this element is taken up from soil and water and can be accumulated in the root and transported to other parts of the plant. As in animal organisms, the cadmium in plants is bound by organic ligands. These are, i.a., phytochelatins, proteins and amino acids [28; 29; 30]. The exact mechanism of cadmium binding depends on the individual plant species. Cadmium can also be absorbed via plant leave leaves. All of the above-mentioned mechanisms of cadmium's uptake and translocation in plants can lead to the accumulation of this element in edible parts of the plant [28; 29; 30]. Minor elements have been rarely measured in microgreens. [PERSON] et al. [31] analysed the cadmium and lead content in 30 vegetable microgreens belonging to the _Brassicaceae_ family and found that these elements were below the detection threshold. Additionally, [PERSON] et al. [32] observed that lead was under the detection limit in some genotypes of microgreens belonging to the _Asteraceae_ or _Brassicaceae_ families. [PERSON] et al. [33] determined the content of 13 elements, including cadmium, manganese, copper, zinc and strontium in microgreens of the _Asteraceae_ and _Brassica_ families. Two measurement techniques were used, i.e., ICP-AES and X-ray fluorescence spectroscopy (XRF), which differed in sample preparation. As far as the absolute level of harmful metals such as cadmium, is concerned, the highest amounts of it, amounting to 0.135 mg in 100 g of d.m., were determined in lettuce of the _'Trocalero'_ variety. In the present work, all the results obtained for the cadmium contents in the examined young shoots were lower than those reported by [PERSON] et al. [33]; the highest cadmium content was in young safflower shoots from the second harvest (0.119 mg in 100 g d.m.). Cadmium, being a contaminant, may cause potential health problems, mainly due to its toxicity to the kidney [34]. The European Food Safety Authority (EFSA) established a tolerable weekly intake (TWI) of 2.5 g/kg b.w. for cadmium based on dietary cadmium exposure, urinary cadmium and urinary beta-2-microglobulin, which is a biomarker associated with effects on renal tubules [24; 34; 35]. It has been found that the half-life of cadmium in the human kidney is up to 15 years. JECFA therefore removed their PTWI of 7 ug/kg of body weight and instead set the provisional tolerable monthly intake (PTMI) at 25 ug/kg of body weight [24; 36]. Lead is not easily absorbed by plants due to the fact that the element is usually strongly bound to the soil via organic matter. Therefore, its transport in the food chain may be limited. As the lead mobility in plants is low, the highest amounts of the element may accumulate in root plants [29]. In the years 2010 and 2011, two institutions (EFSA and JECFA) withdrew their previous Provisional Tolerable Weekly Intake (PTWI) for lead [24; 36; 37].