However, it simultaneously has some limitations, such as its long duration and low efficiency of the remediation process, application of selected plant species, and formation of toxic byproducts in the ash form after the incination of plant residues. In general, chemical methods are simple operations and provide quick results; however, the production of insoluble precipitates can limit applicability of these methods [8]. The group of chemical methods includes immobilization, stabilization, and solidification. According to [PERSON] et al. [7], in situ immobilization has gained growing attention because of its potential effectiveness, the short duration of the treatment, the low cost, extensive time of action, and the less adverse influence on the environmental health. Hence, in recent years many immobilizing agents, such as red mud, lime biochar, composts, and fly ash have been applied to treat and mitigate heavy metal contamination in soils. Regardless of the used materials, the final effect is similar--reduction in heavy metal mobility and bioavailability for plants. The potential application of organic or alkali substances for remediation processes of soils contaminated with heavy metals has been underlined by various authors [7; 9; 10; 11; 12; 13; 14; 15]. Binding of metals by organic matter or formation of insoluble compounds under alkali conditions leads to restricted metal uptake by plants and consequently prevents the bioaccumulation of heavy metals in the food chain. Bioaccumulation of metals from soil to crops varies across soil-cropping systems and depends on plant variety and metal concentration in soil [3]. The uptake of heavy metals from soil by plants is a significant path to harm human health. It is extremely important in the case of heavy metal-contaminated soils, because it promotes the actual state of metal mobility and the potential uptake by plants. Therefore it is important to control and limit the accumulation of heavy metals both in soil and in plants. Soil assessment of heavy metal contamination has to be based on total amounts of metals. Despite the total metal amounts being a basic criterion, when assessing the heavy metal contamination in soil it may inadvertently overestimate the potential risk [16]. Hence, more adequate and reliable information is provided by the mobile amounts of metals, indicating a risk of potential exposure for the soil-crop-human transfer, which is associated with metal bioavailability. Bioavailability is a very complex concept, but it generally refers to the dissolved metal fraction, which can be taken up by plant roots and soil organisms. Bioavailability is associated with the physical dispersion and chemical mobility of metals as well as the organism's exposure, biological characteristics, and individual sensitivity [16]. Evaluation of bioavailability must be based on more sensitive methods than in the case of total amounts; as a result, greater applicability is ascribed to the chelate DTPA. DTPA-extractable heavy metals mainly exist in water-soluble and ion-exchangeable states, which can be directly adsorbed by plants [9], so it is particularly important in the evaluation of the potential risk of their incorporation into the food chain. Moreover, it is recommended by the International Organization for Standardization [17]. Additionally, the DTPA test has been indicated as the best extractant method for Cu and Zn bioavailability in soil [18]. Based on the amount of metals in the soil and in the plant, the transfer of heavy metals from soil to plants should be assessed, with the bioconcentration factors (BCF) being useful coefficients [11,19]. Furthermore, the probable human risk associated with heavy metals should be calculated on the basis of two indices, such as dietary intake and health risk. These parameters are commonly used in practice as useful and reliable tools when assessing potential negative effects of heavy metals present in soils and plants in relation to their possible influence on human health [2].