## 3 Results and Discussion
### Trace Element Contents in Brassicaceae Species: Conventional Versus Organic
These results are in agreement with those reported by [PERSON] et al. [19], who also found higher Cr concentration in conventional carrots (0.059 ug/g) than in organic carrots (0.046 ug/g). We have presumed that the main chemical form in which Cr is found in _Brassicaceae_ vegetables, would be Cr (III). This chemical form is considered as being a beneficial element for human health, and according to several previous research works [21; 22], it is the main chemical form (unlike Cr(VI) in which Cr is found in waters and foods. Therefore, according to their Co and Cr content, organic turnip greens would not have a higher nutritional value than conventional grown ones. For the same reason as that already mentioned for the previous trace elements, Co and Cr concentrations in turnip tops (_Brassicapa_) also decreased with respect to the corresponding turnip greens (_Brassicapa_) (Farm I, conventional, 0.14 and 0.87 ug/g d.w.); (Farm II, conventional, 0.16 and 0.52 ug/g d.w.); (Farm II, organic, 0.19 and 0.48 ug/g d.w.). Again we find differences in Cr concentrations between turnip tops grown on the two Farms but not between the cropping systems (conventional versus organic). Thus, there were significant statistical differences for Cr contents (_p_ < 0.05) between conventional turnip tops grown on Farm I and conventional turnip tops grown on Farm II. We also found statistically significant differences for Cr contents (_p_ < 0.01) between conventional turnip tops grown on Farm I and organic ones grown on Farm II. Therefore, this again indicates that the total inorganic element content in vegetables does not only depend on the farming system [16]. _Sinapis alba_ showed higher Cr concentrations (_p_ < 0.01) for conventionally produced vegetables (0.51 ug/g d.w.) than organically ones (0.26 ug/g d.w.). Co contents for this _Brassicaceae_ species were below the quantification limit (LOQ < 0.07 ug/g). On the other hand, Co and Cr contents in _Eruca vesicaria_ were Farm I, conventional, 0.39 and 7.17 ug/g d.w; Farm II, conventional, 0.26 and 3.29 ug/g d.w, and, Farm II, organic 0.44 and 5.17 ug/g d.w. Cr contents in _Eruca vesicaria_ are slightly higher with those reported in a previous study (2.59 ug/g) [3]. In addition, there were no statistically significant differences for both elements between organic and conventional _Eruca vesicaria_. Previous studies have reported that there is no clear trend in this matter. Thus, [PERSON] et al. [18] gave higher Co contents in conventional potato, onion, tomato and carrot versus organic ones, whereas Cr contents were higher for organic onion, carrot and potato. Regarding Fe, we found statistically significant differences (\(p<0.01\)) between organic turnrip greens (_Brassica rapa_) (0.10 mg/g d.w.) and conventional ones (0.19 ug/g d.w.) from Farm II; and between organic _Sinapis alba_ (0.07 mg/g d.w.) and conventional one (0.15 mg/g d.w.) from Farm II (Table 3). Similarly, [PERSON] et al. [19] have also reported higher Fe content for conventional carrots (5.24 ug/g) versus organic ones (4.96 ug/g). Nevertheless, for the rest of the vegetable _Brassicaaceae studied_, the differences between conventional and organic cultivation were scant. In relation to this latter aspect, [PERSON] and [PERSON] [9] observed only minor variations in Fe concentrations between tomatoes and lettuce cultivated on organic and conventional farms. While the above trace elements have a clear nutritional role, Pb and Cd are considered to be heavy metals that have harmful effects on the environment and human health. With respect to Ni, although the nutritional and/or toxicologic role of Ni in humans is unclear, in animal models, severe Ni deficiency can affect vision, Fe metabolism, and Na homeostasis [23]. However, high concentrations of this element can also affect vital processes in plants and induce toxic effects at morphologic, physiologic and biochemical levels [24].