## 4 Discussion  
### Effect of Immobilizing Agents on Bioconcentration Factors (BCF)  
Despite the fact that some metals perform important metabolic functions, their excessive amounts pose a significant health hazard for humans [29]. Thus, the need to improve  
Figure 10: Estimated daily intake (EDI) and health risk index (HRI) calculated for women (W) and men (M) for Zn in oat;* for descriptions see Material and Methods. Statistically significant differences and \(p\)-value are presented in Table 3.  
Figure 9: Estimated daily intake (EDI) and health risk index (HRI) calculated for women (W) and men (M) for Cu in oat;* for descriptions see Material and Methods. Statistically significant differences and \(p\)-value are presented in Table 3.  
soil conditions and mitigate heavy metal mobility through the use of remediation methods is indicated. Especially inexpensive, natural and/or industrial byproducts may be an effective alternative to conventional immobilization methods [30]. In practice, organic and inorganic substances are usually used as immobilization agents. The most popular organic immobilizing agent are composals, manure, and biochar [7; 9; 11; 13; 14; 15]. In turn, mineral substances proposed for remediation purposes include natural zeolites, lime, phosphorus [15; 30], and fly ash [13; 14; 31]. It is worth emphasizing that the abovementioned substances not only immobilize metals, but also fertilize (especially compost and manure), modifying the physicochemical properties of fertilized soils, first of all pH, OM, TOC and CEC, which consequently mitigates the bioavailability of heavy metals for plants [7; 9]. The bioconcentration factor (BCF) is widely used to assess the toxicity of heavy metals as well as their translocation from soil to plants [11; 19; 32; 33; 34]. Additionally, [PERSON] et al. [35] stated that the bioaccumulation values rather than the total contents of heavy metals should be taken into consideration. In practices, the bioconcentration factor is usually applied based on the total amount of heavy metals (\(\mathrm{BCF_{T}}\)) in soil and plant tissue. According to [PERSON] et al. [11], the bioaccumulation values rather than the total contents of heavy metals should be taken into consideration, and the authors proposed an additional bioconcentration factor by taking into account the bioavailable amounts of metals. As a result, in this study two separate bioconcentration factors were calculated: \(\mathrm{BCF_{T}}\) and \(\mathrm{BCF_{B}}\). Generally, the applied amendments caused only an increment of Cu and Zn total contents in soil, whereas the other analyzed parameters show a downward tendency in comparison to the control conditions. The applied compost and fly ash similarly influenced most of the tested indices, which resulted in non-significant differences between the values of individual parameters recorded in this study. Heavy metal concentrations in plants are crucial, because they greatly influence the nutritional value. According to [PERSON] et al. [36], the accumulation ability of heavy metals varies among plants, which may be affected by factors related to soil properties as well as differences in the morphology and physiology of plants. Generally, leafy vegetables accumulate greater amounts of metals in comparison to non-leafy vegetables [4; 35]. It is in agreement with findings published by [PERSON] et al. [36], who for leafy vegetables recorded the highest values of BCF for Cu (0.018) and Zn (0.024). Greater values of BCF for Zn (0.1-0.7) and BCF for Cu (0.2-1.0) in vegetables irrigated with different water sources were indicated by [PERSON] and [PERSON] [37]. Comparable values of BCF for Zn in young (0.7) and mature (0.2) tea leaves were found [PERSON] et al. [38]. On the other hand, in the abovementioned paper BCF for Cu ranged from 0.1 (mature tea leaves) to 0.16 (young tea leaves).