## 3 Results and Discussion  
### Nitrate Content  
The issue of excessive accumulation of nitrates in plants has been the subject of intensive research worldwide for several decades. Nitrates are essential for plants because they are a nitrogen source and a building block of proteins. Specific amounts of nitrates in plants are related to the natural nitrogen cycle in nature [42]. Unfortunately, the intensification of plant production causes an excessive transfer of these compounds from the soil to the plants. When plants receive too much nitrogen from artificial or organic fertilisers, they cannot use it and store it as nitrites [43]. Consumption of vegetables with excess nitrates does not pose a severe threat to humans because these compounds are absorbed relatively quickly from the digestive tract and excreted from the body unchanged [43]. The harmfulness of nitrates increases after a reduction in nitrites, which occurs during processes occurring after harvesting vegetables and in the digestive tract [44; 45]. The results of nitrate determinations in various types of vegetables are widely presented in the literature, which indicates a considerable scale of exceedances of permissible standards [45; 46; 47]. Polish standards regarding nitrate content for the analysed vegetables are, respectively, [0.4 mg \(\times\) g\({}^{-1}\)] for carrots, parsley, and celery, [0.75 mg \(\times\) g\({}^{-1}\)] for cabbage, onion, and rocket, and [1.5 mg \(\times\) g\({}^{-1}\)] for dill and beet [46; 48]. Considering the above criteria, it can be concluded that the content of nitrogen compounds was within the permissible limits, except for carrots, celery, parsley, and dill bought in a local market, representing the _Apiacea_ family [Figure 1A]. The analyses carried out revealed the highest nitrate content in dill [2.16 mg \(\times\) g\({}^{-1}\)] and the lowest in onions [0.06 mg \(\times\) g\({}^{-1}\)] from conventional crops (local market). In the case of cabbage family vegetables, the lowest nitrate content was recorded for plants from independent agriculture production (local market). Of course, it should be remembered that the distribution of various compounds in plants changes during the growing season. Their concentration in different parts of plants also varies. Moreover, the taller the plants, the fewer nitrates are typically found [49]. For example, the results obtained for beet do not coincide with the data of other authors, who classified beet as a vegetable with an exceptionally high nitrate content [42; 46; 47; 50]. The nitrate levels in all these studies are much higher than the results obtained in this study because nitrate accumulation was examined only in the root. According to [PERSON] [51] and in subsequent studies by [PERSON] and [PERSON] [52], several times higher amounts of these compounds are collected than in the leaves. It is generally known that vegetables with edible roots, stems, and leaves have more nitrates than vegetables with edible fruit [53]. It has been shown that nitrate concentrations differ between edible plant parts [54]. The nitrate content decreases in the following order: leaf > stem > root > infloresence > tuber > fruit > seeds [50]. The results of other authors quoted and discussed in the work usually concern the root part, which was not examined in this study. It should be noted that the exact determination of the nitrate content in vegetables is complicated because it is determined by various factors acting simultaneously [55; 56; 57]. It turns out that the same vegetable, grown in a different place, may differ significantly in terms of nitrate concentration. The factors influencing their level include region and growing conditions, such as season, growth temperature, humidity, pH, and soil composition, including the content of microelements [58]. The plant's age and thermal treatment method have a significant impact, as mentioned in [45; 59] and the works cited therein. The study examined young vegetables purchased in the spring and summer.