| چکیده انگلیسی مقاله |
Introduction: Anthropogenic activities have transformed the global geochemical cycling of heavy metals. Mine tailings are of great concern due to the detrimental effects of toxic inorganic elements causing environmental risks. Zinc (Zn) as an essential element is required in small amounts for various biochemical reactions and physiological functions. However, high concentrations of Zn can induce oxidative stress. Applying an organic amendment is a promising, in situ phytostabilization approach to alleviate the phytotoxic effects of heavy metal in contaminated soils. The application of biochar as an amendment may be a solution to reduce the risk of pollutant diffusion. Biochars is a fine-grained biological residue combusted under low oxygen conditions, resulting in a porous, stable carbon-based material. The potential biochar applications include carbon sequestration, soil fertility improvement, and pollution remediation; therefore, it can reduce pollutants mobility and bioavailability. Materials and Methods: Results of this research indicated that biochars decreased Zn concentration in maize shoots and roots. They reduced Zn concentration in the shoot/root of maize. Zinc concentration in shoots and roots of maize (Zea mays L.) harvested at 60 days after sowing, decreased with increasing thermochemical temperature and application rate of biochar. In treated soil with 2% (w/w) biochar prepared at 600 °C, Zn concentration in shoots and roots decreased by 21.6 and 33.0 % respectively (p< 0.05). Physiological responses showed that WB applications improved the shoot/root growth and dry biomass (root and shoot). In comparison with the control, the highest shoot and root dry matter values were found in 2% (w/w) biochar-600 °C treatment by 131.4 and 116.7% respectively (p< 0.05). Zinc bioaccumulation towards plant decreased with increasing thermochemical temperatures and application rate of biochars. Determination of bioaccumulation factor (BF) and translocation factor (TF) indicated that bioaccumulation factor is higher than translocation factor in maize planting. For the treatment biochar produced at 600 °C, BF, and TF were 0.132 and 0.117 respectively. Thereby maize can be considered as a potential phytostabilizer. At the same time efficiency of phytostabilizing nature of maize can increase together with the application of biochar. The results showed that water and DTPA-extractable Zn concentrations were significantly (p < 0.05) lower in Walnut leaves biochars treated soils than those in unamended soils. Bioavailable Zn concentration (soluble and DTPA-extractable Zn) decreased by increasing WB thermochemical temperature and application rate.In comparison with the control, the 2% biochar-600 °C significantly reduced soluble and DTPA-extractable Zn by 63.1 and 34.9 % respectively (p< 0.05). A significant positive correlation coefficients was found between soluble Zn and Zn concentrations in plant shoot and root (0.72, 0.70, p < 0.01), and between DTPA-extractable values and shoot and root Zn concentrations (0.90, 0.81, p < 0.01, respectively). There is a negative correlation between soluble Zn and shoot and root dry weight (-0.78, -0.79, p < 0.01 respectively), and between bioaccessible Zn and shoot and root dry weight (-0.88, -0.87, p < 0.01, respectively). Importantly, the results of the Pearson correlation analysis revealed a negative relationship between biochar surface area (and production temperature) and DTPA-extractable Zn in the soil, suggesting biochars produced at higher temperature played a more important role in immobilizing heavy metals. Results and Discussions: The results indicated that biochars decreased Zn concentration in maize shoots and roots. Zinc concentration in shoots and roots of maize (Zea mays L.) harvested at 60 days after sowing date, decreased with increasing thermochemical temperature and application rate of biochar. In treated soil with 2% (w/w) biochar prepared at 600 °C, Zn concentration in shoots and roots decreased by 21.6 and 33.0 %, respectively (p< 0.05). Physiological responses showed that WB application improved the shoot/root growth and dry biomass (root and shoot). In comparison with the control, the highest shoot and root dry matter values were found in 2% (w/w) biochar-600 °C treatment by 131.4 and 116.7%, respectively (p< 0.05). Zinc bioaccumulation towards plant decreased with increasing thermochemical temperatures and application rate of biochars. Determination of bioaccumulation factor (BF) and translocation factor (TF) indicated that bioaccumulation factor is higher than translocation factor in maize planting. For the treatment biochar produced at 600 °C, BF and TF were 0.132 and 0.117, respectively. Therefore, maize can be considered as a potential phytostabilizer. The efficiency of phytostabilizing nature of maize can be increased by application of biochar. The results showed that water and DTPA-extractable Zn concentrations were significantly (p< 0.05) lower in the soils treated by Walnut leaves biochars as compared with those in unamended soils. Bioavailable Zn concentration (soluble and DTPA-extractable Zn) decreased by increasing WB thermochemical temperature and application rate. In comparison with the control, the 2% biochar-600 °C significantly reduced soluble and DTPA-extractable Zn by 63.1 and 34.9 %, respectively (p< 0.05). A significant positive correlation coefficient was found between soluble Zn and Zn concentrations in plant shoot and root (0.72, 0.70, p< 0.01), and between DTPA-extractable values and shoot and root Zn concentrations (0.90, 0.81, p< 0.01, respectively). There was a negative correlation between soluble Zn and shoot and root dry weight (-0.78, -0.79, p< 0.01 respectively), and between bioaccessible Zn and shoot and root dry weight (-0.88, -0.87, p< 0.01, respectively). Importantly, the results of the Pearson correlation analysis revealed a negative relationship between biochar surface area (and production temperature) and DTPA-extractable Zn in the soil, implying the fact that the biochars produced at higher temperature played a more important role in immobilizing heavy metals. Conclusions: Our results denote that WB application to a contaminated soil has the potential of in situ remediation by immobilizing Zn, thereby reducing metal availability to maize. Given that Walnut leaf is a readily available agricultural residue, we suggest that its conversion to biochar and incorporation into a contaminated soil can be an achievable and cost-effective approach to mitigate metal exposure of maize. The WB has the potential to significantly affect the behavior of Zn in soil by altering its solubility and availability. In conclusion, these results highlight the biochar potential to mitigate the metals phytoaccumulation and reduce metal exposure of maize. Further experiments are needed not only to define the biochar potential in phytoremediation but also to better understand the criteria for choosing the best ingredient. The results of this pot experiment are encouraging and need to be confirmed with the long-term field experiments. |