Impact of different treatments of DTPA – heavy metal contents
HM toxicity in soil is primarily impacted by the availability of metal forms accessible to plants rather than the overall concentration of metals in the soil (Yin et al., 2016). Zn, Pb, Ni, Cd, Mn, Fe, and Cu concentrations before and after cultivating sorghum plants in Mahad AD’Dahab under various treatment conditions are reported in Table 5. The findings indicate that the use of both tested BC in the soil led to a decrease in DTPA-extractable Zn, Pb, Ni, Cd, Mn, Fe, and Cu (Table 5), which is consistent with the outcomes demonstrated by Yousaf et al. (2016) for Cd and Rehman et al. (2016) for Ni.
Table 5
DTPA- extracted Cd, Cu, Fe, Mn, Ni, Pb, and Zn contents before and after cultivation for 90 days grown in Mahad AD’Dahab used in the pot experiment. (mean ± SD, n = 3)
Treatments | Cd | Cu | Fe | Mn | Ni | Pb | Zn |
| Before cultivation |
K | 2.40 ± 0.17 | 169.52 ± 7.24 | 56.80 ± 4.20 | 78.86 ± 3.48 | 9.25 ± 0.94 | 43.88 ± 4.89 | 116.03 ± 6.84 |
| After Cultivation |
K | 2.12 ± 0.28 | 155.57 ± 5.12 | 49.70 ± 4.10 | 69.80 ± 6.22 | 8.20 ± 1.11 | 39.12 ± 3.09 | 103.76 ± 7.15 |
VW | 2.32 ± 0.36 | 149.38 ± 6.33 | 51.94 ± 4.57 | 67.68 ± 5.45 | 8.71 ± 1.64 | 41.75 ± 3.89 | 104.24 ± 6.24 |
B1 | 1.80 ± 0.22 | 137.44 ± 6.71 | 42.46 ± 3.73 | 60.73 ± 4.90 | 6.84 ± 0.96 | 35.25 ± 3.23 | 94.72 ± 4.44 |
B1 + VW | 1.64 ± 0.19 | 140.11 ± 6.18 | 40.88 ± 2.34 | 61.13 ± 5.46 | 6.25 ± 0.94 | 37.60 ± 3.65 | 91.39 ± 5.25 |
B2 | 1.56 ± 0.14 | 128.10 ± 4.39 | 41.23 ± 3.63 | 59.33 ± 3.84 | 5.97 ± 0.44 | 38.47 ± 2.89 | 93.65 ± 5.84 |
B2 + VW | 1.50 ± 0.16 | 127.19 ± 7.27 | 39.13 ± 3.24 | 57.22 ± 4.90 | 6.05 ± 0.58 | 40.01 ± 3.99 | 96.27 ± 3.61 |
CA | 2.89 ± 0.23 | 188.04 ± 4.61 | 65.97 ± 2.84 | 92.16 ± 5.22 | 10.97 ± 0.60 | 49.32 ± 3.43 | 130.77 ± 5.49 |
CA + VW | 2.80 ± 0.33 | 183.41 ± 7.59 | 64.75 ± 3.94 | 90.41 ± 5.22 | 10.76 ± 1.16 | 47.67 ± 3.53 | 127.81 ± 5.59 |
Similarly, the outcomes show that the bioavailability of Cd, Cu, Fe, Mn, Ni, Pb, and Zn decreased by 18.92%, 25.00%, 25.25%, 22.99%, 26.05%, 19.67%, and 18.37%, respectively, when date palm (BC1) biochar was applied. In contrast, Prosopis biochar (BC2) reduced 35.00%, 24.43%, 27.41%, 24.77%, 35.46%, 12.33%, and 19.29%, respectively (Table 5). These findings confirm that date palm and Prosopis BC have an increased adsorption capacity and the potential to create binding sites for the tested HMs. This finding aligns with previous studies (Zheng et al., 2016; Bashir et al., 2019; Rafique et al., 2021; Ramírez et al., 2022; Wang et., 2022; Alazzaz et al., 2023; Li et al., 2023),
Moreover, the strong affinity of HMs to BC may be another reason for reduced metal availability. BC’s larger surface area and numerous contact sites significantly reduce DTPA-extractable Cu, Cd, Fe, Ni, Mn, Zn, and Pb in the soil (Lu et al., 2017; Naeem et al., 2020). Comparable results have been reported in prior research, where BC from various sources effectively reduced Cd, Cu, Fe, Mn, Ni, Pb, and Zn concentrations in mine-contaminated soil (Xu et al., 2016; Irfan et al., 2021; Alazzaz et al., 2023).
Furthermore, HM bioavailability in soil is crucial for successful phytoremediation (Greman et al., 2001). In this study, the application of 1.5 mol/Kg soil of CA elevated the bioavailability of Zn, Pb, Ni, Mn, Fe, Cu, and Cd by 11.27%, 10.99%, 15.68%, 14.43%, 13.90%, 9.85%, and 16.96% respectively (Table 5). The same results were recorded by Diarra et al. (2021), who found that applying CA released the most elevated Cu and Ni fractions in the soil, accounting for 75.5% and 79.5%, respectively. This finding is compatible with those of Wuana et al. (2010), who revealed a significant decline in Cu and Ni levels through batch soil washing with CA. Furthermore, fractionation patterns revealed that CA primarily targets HMs related to the reducible as well as exchangeable fractions. A smaller proportion of HMs bound to the soil organic matter are also targeted by CA (Wuana et al., 2010).
Impact of various amendments on morphological traits
Plant morphological traits, such as plant height, root length, and plant biomass (both fresh and dry weights), were significantly influenced by various treatments when compared to the untreated treatment (K)(Fig. 3). Root and shoot lengths varied between 9.33–12.83 cm and 76.33-88.00 cm, respectively. The sorghum plants cultivated in untreated soil (K) exhibited the shortest root and shoot lengths, while the application of a combination of CA + VW to the soil led to the longest shoot and root lengths.
Compared to control (K), the implementation of both tested BCs (B1&B2) significantly enhanced sorghum morphological characteristics. The enhancement in plant height, root length, and fresh and dry biomass was 20.61%, 59.72%, 83.06%, and 54.92% for the B1 treatment and 60.98%, 22.87%, 75.28%, and 61.59% for the B2 treatment.
Abbas et al. (2017) demonstrated that the application of BC substantially impacted the root length, plant height, and biomass of wheat plants when exposed to various Cd treatments compared to untreated conditions. BC soil amendment has been shown to promote the growth of numerous species of plants exposed to metal stress (Rizwan et al., 2016; Rehman et al., 2016; Younis et al., 2016; Almaroai and Eissa 2020; Helaoui et al., 2023). In this study, the elevation in these parameters by adding BC may be attributed to increased mineral nutrient availability. Previous research has frequently reported that BC improves plant growth because of improved biological characteristics, increased nutrient content, elevated cation exchange capacity, and pH adjustments (Paz-Ferreiro et al., 2014; Širi’c et al., 2022). Additionally, Irfan et al. (2021) found that applying wheat straw BC in polluted soil significantly enhanced shoot and root lengths and plant biomass in maize plants compared to those grown in contaminated soil without BC. Similar findings were reported by Lu et al. (2014) for edible amaranth, Park et al. (2011) for canola plants, and Ali et al. (2017) for Indian mustard.
In contrast, the application of CA resulted in a significant enhancement of shoot and root lengths, as well as overall plant biomass, in contaminated soil. Fresh and dry weights increased with CA application from 23.5 g and 3.15 g /pot in the K to 48.86 g and 5.85 g/pot. Additionally, sorghum root elongation, plant height, and biomass increased when VW was applied with BCand CA (Fig. 3).
Several researchers have reported that applying CA enhances biomass and plant growth under metal stress in various plant species, including Juncus effusus (Najeeb et al., 2009), Zea mays (Anwer et al., 2012), Iris halophile (Han et al., 2018), and Brassica napus (Afshan et al., 2015). This elevation in biomass and plant growth may be attributed to improved plants’ nutrient uptake (Najeeb et al., 2011) or phytochelatins (PCs) synthesis in plants (Muhammad et al., 2009). Additionally, applying VW promoted all the tested growth criteria, as shown in Fig. 3.
When considering the individual and combined applications of VW and BC, the influence on plant growth followed this order: K > VW > B2 > B1 > B1 + VW > B2 + VW > CA > CA + VW (Fig. 3). VW, a liquid bio-fertilizer with high water content, contains P, K, N, Zn, Ca, plant growth hormones, amino acids, and vitamins (Sundararasu and Jeyasankar, 2014). Rathika et al. (2020) also found that applying VW improved the morphological characteristics of sorghum plants grown in Pb and Ni-polluted soil significantly, and similar results were reported by Naroila and Poonia (2011) for pearl millet.
Impact of various amendments on pigments
The data reveals that treatment with contaminated soil (K), without the addition of BC, substantially (p ≤ 0.05) diminished chlorophyll a, b, levels and total chlorophyll (Fig. 4). However, the addition of both tested BC led to a significant increase in chlorophyll content. The most substantial enhancements in chlorophyll content, specifically a 41% and 28% increase for chl. a, a 43% and 51% increase for chl. b, and a 32% and 29% increase in total chlorophyll were observed at a BC application rate of 1.5% for B1 and B2, respectively (Fig. 4).
Several studies conducted by Bashir et al. (2018), Mehmood et al. (2018), and Helaoui et al. (2023) have reported that the application of BC derived from rice straw can elevate chlorophyll content and mitigate oxidative stress. Conversely, Belhaj et al. (2016) noted a decrease in chlorophyll a and b due to increased HM contents in soil contaminated by mining activities. Additionally, BC appeared to alleviate the stress caused by HMs on sorghum plants through mechanisms such as toxic metal adsorption onto the BC surface (Arabyarmohammadi et al., 2018), enhancement of soil physico-chemical properties, and enhanced nutrient uptake by sorghum (Ok et al., 2015; Younis et al., 2016).
Furthermore, Shahbaz et al. (2018) identified a substantial negative association between nickel concentration in the shoots and sunflower and maize plants as well as their physiological characteristics after incorporating BC. This result indicates that BC may accelerate the adsorption of HMs (through surface interactions), ultimately improving the photosynthetic capacity of the tested plants under HM stress.
Conversely, compared to the K treatment, CA application alone elevated chl. a, b, and total chlorophyll by 86%, 82%, and 81%, respectively. In comparison, the application of VW alone increased these chlorophyll levels by 79%, 58%, and 68%, respectively, in plants subjected to HM stress. However, the most significant increases in chl. a, b, and total chlorophyll, at 105%, 80%, and 91%, respectively, were detected in plants grown (under the combined VW and CA application) (Fig. 4). Afshan et al. (2015) illustrated that CA application significantly increased photosynthetic pigment levels in Brassica napus when grown in soil contaminated by Cr, compared to exposure to Cr alone. This increase in photosynthetic pigments may be attributed to enhanced antioxidant enzyme activity, which reduces the production of malondialdehyde (MDA) and electrolyte leakage. These findings are consistent with those of Mallhi et al. (2019), who found that photosynthetic pigments of castor plants grown in Pb-contaminated soil significantly enhanced after applying CA compared to treatments with Pb alone. The beneficial role of CA in the photosynthetic system of plants exposed to heavy metal stress has been described in numerous studies, including Shakoor et al. (2014), Afshan et al. (2015), and Farid et al. (2017). Applying CA enhances essential nutrients’ uptake and photosynthetic pigments’ formation (Farid et al., 2017).
Impact of various amendments on HMs concentration and uptake
The addition of BC led to improved plant growth and alleviated the tested HM mobility and availability within the plant tissues. The substantial decline (p ≤ 0.05) in HM bioavailable concentration in soil induced the decreased translocation in the root and shoots of sorghum (grown in contaminated soil). For instance, when comparing the contents of Zn, Pb, Ni, Mn, Fe, Cu, and Cd in sorghum plants’ roots, the application of B1 and B2 reduced them from 3.10, 129.29, 170.61, 54.07, 7.96, 47.91, and 115.59 mg/kg to 2.66, 115.08, 149.86, 45.62, 7.19, 39.79, and 103.80 mg/kg, respectively for B1, and 2.66, 116.69, 142.39, 45.70, 7.10, 37.89, and 103.86 mg/kg, respectively for B2 (Table 6).
Table 6
Concentration of Cd, Cu, Fe, Mn, Ni, Pb, and Zn (mg/Kg) on roots and shoots of sorghum plants at different treatments.
Treatment | Root |
| Cd | Cu | Fe | Mn | Ni | Pb | Zn |
K | 3.10 ± 0.54b | 129.29 ± 5.36b | 170.61 ± 6.17b | 54.07 ± 3.46b | 7.96 ± 0.76ab | 47.91 ± 2.54b | 115.59 ± 7.11b |
VW | 2.95 ± 0.28b | 126.86 ± 5.26b | 167.90 ± 7.10b | 56.21 ± 3.80b | 8.13 ± 1.09ab | 45.89 ± 2.78bc | 116.99 ± 6.13b |
B1 | 2.66 ± 0.32c | 115.08 ± 5.89c | 149.86 ± 6.42c | 45.62 ± 2.67c | 7.19 ± 0.72b | 39.79 ± 2.60d | 103.80 ± 4.14c |
B1 + VW | 2.70 ± 0.23c | 115.33 ± 5.00c | 147.24 ± 6.14c | 44.74 ± 2.22c | 7.22 ± 0.86b | 39.00 ± 1.98d | 104.14 ± 4.28c |
B2 | 2.66 ± 0.27c | 116.69 ± 7.13c | 142.39 ± 6.08c | 45.70 ± 3.28c | 7.10 ± 1.03b | 37.89 ± 3.90d | 103.86 ± 4.27c |
B2 + VW | 2.68 ± 0.21c | 116.18 ± 4.24c | 140.79 ± 5.13c | 46.66 ± 3.08c | 7.10 ± 0.87b | 40.89 ± 2.79cd | 102.07 ± 5.28c |
CA | 3.99 ± 0.35a | 142.92 ± 6.36a | 187.15 ± 8.07a | 64.32 ± 3.28a | 9.28 ± 1.10a | 53.77 ± 2.77a | 131.69 ± 6.36a |
CA + VW | 3.90 ± 0.24a | 144.77 ± 5.64a | 184.81 ± 6.13a | 65.36 ± 3.31a | 9.64 ± 1.24a | 56.91 ± 3.87a | 138.38 ± 4.76a |
| | | | Shoot | | | |
| Cd | Cu | Fe | Mn | Ni | Pb | Zn |
K | 1.36 ± 0.12b | 26.41 ± 2.82ab | 38.75 ± 3.25bc | 9.09 ± 0.53b | 3.70 ± 0.11ab | 8.83 ± 1.10ab | 20.78 ± 2.32b |
VW | 1.34 ± 0.05c | 24.54 ± 2.07ab | 39.87 ± 3.45bc | 8.33 ± 0.46bc | 3.78 ± 0.26ab | 8.69 ± 0.99ab | 20.44 ± 1.07b |
B1 | 0.94 ± 0.09c | 22.95 ± 1.12b | 34.89 ± 2.19cd | 7.94 ± 0.22bc | 2.93 ± 0.12c | 7.28 ± 0.20bc | 17.98 ± 1.12c |
B1 + VW | 0.91 ± 0.07c | 23.06 ± 1.09b | 35.02 ± 3.22cd | 7.52 ± 0.57c | 2.99 ± 0.66c | 7.72 ± 1.19bc | 18.22 ± 2.08c |
B2 | 0.96 ± 0.06c | 24.04 ± 1.20b | 32.85 ± 2.87cd | 8.10 ± 0.54bc | 2.85 ± 0.13c | 7.09 ± 1.06bc | 18.14 ± 2.10c |
B2 + VW | 0.93 ± 0.09c | 23.10 ± 2.10b | 33.82 ± 3.26cd | 8.20 ± 1.00bc | 2.92 ± 0.23c | 7.16 ± 0.64bc | 18.50 ± 1.11c |
CA | 1.55 ± 0.06a | 30.59 ± 1.79a | 45.87 ± 2.35a | 11.20 ± 2.15 a | 4.20 ± 0.44a | 10.66 ± 1.13a | 25.44 ± 2.10a |
CA + VW | 1.49 ± 0.06a | 29.37 ± 1.65a | 43.51 ± 2.86ab | 12.02 ± 1.13a | 4.11 ± 0.35a | 11.07 ± 1.22a | 26.09 ± 1.79a |
All the data are presented as mean values of three independent experiments (n = 3). K represents un-amendment (control), VW (addition of vermiwash), B1 (biochar date palm), B1 + VW (biochar date palm + vermiwash), B2 (biochar Prosopis), B2 + VW (biochar Prosopis + vermiwash), CA (citric acid), and CA + VW (citric acid + vermiwash). All the means sharing common letter(s) are insignificantly different at P ≤ 0.05. |
Furthermore, it was observed that both B1 and B2 treatments significantly reduced the concentrations of Cd, Cu, Fe, Mn, Ni, Pb, and Zn in the shoots compared to the control soil. These reductions amounted to 30.88%, 13.10%, 9.96%, 12.65%, 20.81%, 17.55%, and 13.47%, respectively for B1, and 29.41%, 8.97%, 15.23%, 10.89%, 22.97%, 19.71%, and 12.70%, respectively for B2. The results demonstrate that applying BC immobilized HMs such as Cd, Cu, Fe, Mn, Ni, Pb, and Zn in the soil reduces their concentrations in the roots and shoots of sorghum plants. Numerous studies have previously reported similar findings, where BC amendments in heavy metal-contaminated soil resulted in the immobilization of these metals, leading to decreased uptake by plants (Moon et al., 2013; Rehman et al., 2018; Yin et al., 2016; Gascó et al., 2019; Helaoui et al., 2023).
In a study by Abbas et al. (2017), varying rice straw BC levels (0, 1.5, 3.0, and 5% w/w) were applied to Cd-contaminated soil. The outcomes indicated that BC treatments lowered Ni and Cd concentrations in wheat grains, roots, and shoots compared to controls. In addition, Cd concentration in wheat grains declined by 26%, 42%, and 57% following the application of 1.5%, 3.0%, and 5.0% BC, respectively, compared with the control. The reduction in HM concentrations in the roots of sorghum plants may be attributed to the selectivity of plants and metals’ immobilization within the soil, as evidenced by a decrease in DTPA-extracted soil HM levels (Lu et al., 2012). Functional groups in the BC may have immobilized Cu and Pb concentrations (Uchimiya et al., 2011). Immobilization of HMs through BC applications has been previously documented (Ahmad et al., 2016; Jones et al., 2016; Ok et al., 2015). Consequently, applying both tested BCs (B1 and B2) proved more effective in promoting plant growth and reducing metal concentrations in the roots and shoots of sorghum plants (Table 6).
However, the application of 1.5 mM CA to the plants increased the Cd, Cu, Fe, Mn, Ni, Pb, and Zn contents in the roots by 22.31%, 9.54%, 8.84%, 15.94%, 14.22%, 10.90%, and 12.23%, respectively, whereas in the shoots, increased by 12.26%, 13.66%, 15.52%, 18.84%, 11.90%, 17.17%, and 18.32%, respectively, compared to the plants grown in K treatment (Table 6). A comprehensive comprehension of the accumulation of HMs and the transportation behavior of plants is crucial in the process of selecting suitable agents for phytoremediation or enhancing plant stress tolerance. Organic acids have been widely recognized for their dual function in facilitating metal accumulation and acting as allies in the development of stress tolerance in plants involving metal tolerance (Ehsan et al., 2014; Mahmud et al., 2017).
Exogenous application of CA has been shown to enhance HM uptake in numerous plants (Najeeb et al., 2011; Almaroai et al., 2013; Ehsan et al., 2014). CA in this study significantly increased the HM content in the shoots and roots of sorghum, confirming its potential for phytoremediation. The CA application also considerably elevated HM translocation from roots to shoots.
Applying VW alone and combined with BC 1& 2 and CA has no significant effect on tested HM contents compared to treatments with the tested BC and chelating agents alone. The findings of this study provide evidence in favor of the hypothesis that the effectiveness of phytoextraction can be enhanced by augmenting the dry mass and, to a lesser degree, the metal accumulation in the upper parts of the plants (Table 6).
Chelating agents are frequently employed to improve the availability of metals and promote their accumulation in plants. However, this increased metal uptake can lead to decreased plant biomass due to the toxicity associated with excessive metal absorption. Therefore, the simultaneous application of VW and CA represents an optimal approach to address this issue. Moreover, this combination can enhance a plant’s inherent antioxidative defense mechanisms, as suggested by Gao et al. (2010).
Conversely, the efficacy of the phytoremediation procedure, encompassing phytoextraction and phytostabilization, is contingent upon the quantity of biomass produced by the roots and shoots, as well as their capacity to absorb HMs. As a result, the quantification of metal absorption by the roots and shoots of sorghum plants was computed and graphically depicted in Fig. 5. The findings of the study indicated a significant increase (p ≤ 0.05) in the uptake of heavy metals (HMs) by both the shoot and root when exposed to all tested treatments, as compared to the untreated soil potassium (K). The combined application of calcium (CA) and vermicompost (VW) resulted in the highest uptake of heavy metals (HM) in both the shoot and root. This observation can be attributed to the increased dry matter production associated with the application of VW, as compared to K. The concurrent utilization of CA and VW resulted in a significant enhancement in plants’ absorption of various heavy metals. Specifically, the uptake of Cd increased from 4.37 to 11.28 µg/pot, Cu increased from 163.48 to 408.66 µg/pot, Fe increased from 219.82 to 535.79 µg/pot, Mn increased from 66.32 to 179.42 µg/pot, Ni increased from 11.82 to 32.27 µg/pot, lead (Pb) increased from 59.58 to 159.53 µg/pot, and Zn increased from 143.19 to 385.95 µg/pot, respectively, in comparison to the control treatment using K.
However, applying BC and VW improved the sorghum plant’s phytoextraction ability by enhancing plant growth. This study’s findings indicate that using BC in conjunction with nutrient supplements may be a viable approach for enhancing the phytoremediation of heavy metals (HMs) when employing sorghum as a bioenergy crop. The results obtained in this study were consistent with the findings reported by Houben et al. (2013), Fellet et al. (2014), and Houben et al. (2013) also observed the phytostabilization of cadmium (Cd) and zinc (Zn) by Brassica napus plants when BC was applied. A study conducted by Fellet et al. (2014) observed that the application of BC led to increased uptake of lead (Pb) by various plant species. This phenomenon was attributed to plant growth promotion, thereby indicating the potential for phytostabilization. The application of BC frequently leads to enhanced soil water-holding capacity, nutrient retention, microbial community composition, cation exchange capacity (CEC), and plant responses to diseases. The enhanced attributes of the BC ultimately lead to a higher crop output, indicating the BC’s potential as a phytoextractant (Graber et al., 2010; Paz Ferreiro et al., 2014).
Phytoextraction efficiency of metals
The bioconcentration factors (BCF) and translocation factors (TF) for sorghum are presented in Figs. 6&7. Baker (1981) has classified BCF into three distinct categories, which are as follows: Plants exhibiting a BCF below 1 are classified as excluders, while those falling within the range of 1 to 10 are classified as accumulators. Plants with BCF values exceeding 10 are referred to as hyperaccumulators. The HM BCF values for the sorghum plant were observed to follow a decreasing order, with Cd having the highest average value, followed by Cu and Fe, and then Mn, Ni, Pb, and Zn. The mean BCF value across all treatments was found to be below 1 (Fig. 6).
The study findings revealed that the transfer factor (TF) and bioconcentration factor (BCF) values for the various amendments examined were found to be less than one. This suggests that the process of phytoextraction is not viable for the sorghum plants in the present investigation despite their elevated biomass yield (Steve and Zhao, 2003). Metal accumulation by the shoot and root of sorghum plants is depicted in Table 5. The study results indicated that a considerable proportion of the metals was accumulated in the roots, as opposed to the shoots. The results presented in (Figs. 6&7) indicate a decline in the translocation of HMs in the roots, as evidenced by the lower values of TF and BCF. This finding suggests that the phytostabilization process was not as effective in preventing the accumulation of HMs in the roots. Phytostabilization refers to the capacity of certain plant species to effectively accumulate a substantial amount of HMs in their root systems, thereby mitigating the risk of contamination in nearby or underground water sources (Vamerali et al., 2009).
Fellet et al. (2014) and Karami et al. (2011) have documented that BC application has demonstrated suitability for the phytostabilization of certain HMs. Therefore, based on our findings, it can be suggested that the utilization of date palm and prosobis BC demonstrates effective potential for the immobilization of heavy metals in soil. However, the implementation of phytoextraction using sorghum plants in soil contaminated by mining activities is not considered a viable option. According to Goswami and Das (2015), soluble chemical elements have the ability to enter roots through two distinct pathways: the apoplastic pathway, which involves movement through the cell wall-free space, and the symplastic pathway, involving transportation across the plasma membrane of root cells followed by movement through the cytoplasm.
Multiple studies have demonstrated that roots serve as a protective barrier against the translocation of HMs, thereby protecting the stems and other aboveground plant components from contamination and minimizing oxidative stress (Panwar et al., 2002; Liu et al., 2019). The observed variations in HM concentrations in different plant parts indicate the presence of distinct cellular mechanisms responsible for partitioning, translocating, and bioaccumulating these metals within plant systems (Sinha et al., 2007; Sharma and Dietz, 2009). Furthermore, HM translocation and uptake to the shoots are inherently connected to the speciation of soil organic matter, soil pH, SOM, and elements (Kabata-Pendias, 2010).
Multivariate Analysis
A principal component analysis (PCA)
It has been performed to evaluate the effect of different treatments in removing tested HMs (Fig. 8). Metals are correlated negatively with PCA components. In contrast, other metals correlate positively with PCA components. It was shown that some treatments are suitable for removing HMs; on the other hand, some are not suitable according to PCA analysis. B1, B2, B1 + VW, and B2 + VW are negatively correlated with PCA components for removing HMs. Meanwhile, VW, CA, and CA + VW are positively correlated with PCA for removing HMs. The most critical treatment used in this study to remove HMs is Vermiwash (VW), which is effectively necessary for removing Zn. The results indicated that Cu and Zn are correlated positively with PCA. In comparison, Cd and Ni correlated negatively with PCA components (Fig. 8). PCA 1 (91.82%) and PCA 2 (5.5%) explain the majority of the data, so there is no need for the other PCA components.