Tobacco (Nicotiana tabacum L.) is a crop that is able to accumulate metals. In this study, humic acid was selected as a Cd, Cu, Pb, and Zn passivator, and added to calcareous field soil in amounts of 6.4, 10.3, and 14.8 kg·ha⁻¹. Its impact on the soil fractions of the metals in the soil was extracted by the Community Bureau of Reference (BCR) sequential extraction method, and their accumulation of the metals in tobacco leaves was investigated. Application of 14.8 kg·ha⁻¹ humic acid decreased the DTPA-extracted concentrations of Pb, Cd, Zn, and Cu by 39%, 37%, 29%, and 18%, respectively, as compared with untreated soil. The fractions of Cd, Pb, Cu, and Zn in soil were extracted by the BCR sequential extraction method, and the relationship between the difference metal fractions in the soil and the metal contents in the plant materials were analyzed. The exchangeable fractions of Cd, Pb, Cu, and Zn and the reducible fractions of Pb and Cu are the main bioavailable fractions. Additionally, the reducible fractions of Cd and Zn, the oxidizable fractions of Pb, Cu, and Zn, and all residual fractions of metals were nonbioavailable fractions in the soil. The soils were treated with humic acid (HA) to shift bioavailable metals to stable phases that were less bioavailable. The available Cd, Pb, Cu, and Zn were strongly retained in the soil after the application of humic acid, which decreased the uptake in tobacco in the upper, middle, and lower leaves.

Excessive accumulation of cadmium (Cd) and arsenic (As) in rice (Oryza sativa L.) poses a potential health risk to populations. Cd and As exhibit opposite geochemical behavior in paddy soil, using appropriate remediation materials to reduce their migration and inhibit their uptake by rice is a great challenge. A pot culture experiment was conducted to investigate the effects of application of silkworm excrement biochar (BC) and ferrous sulfate (Fe(II)) on available Cd and As in paddy soils and their uptake by rice. Results showed that the application of BC + Fe significantly accelerated the tillering of rice plants, and the addition of BC alone to soil did not have a significant effect on the pH of soil, while applied 1% (w/w) BC and 1% (w/w) Fe(II) (1BC-1 Fe(II)) treatment could markedly reduce the soil pH. BC+Fe(II) could reduce the content of available Cd (reduced by 10%–23%) and As (reduced by 6%–33%) in soil. BC+Fe(II) has a distinct decreasing effect on the available As, thus inhibiting As uptake in rice tissues, and the effect was more obvious with an increasing mass ratio of Fe in BC+Fe(II) treatment. BC+Fe(II) decreased bioaccumulation factors (BF) of As compared to control and BC alone treatments. Compared with As, Cd was more readily transferred from the root to the shoot and accumulated in rice eventually. These findings provide a safe and reliable remediation strategy though application of BC+Fe(II) in Cd and As co-contaminated soil. However, the improvement effect of amendments should be paid a special attention on soil pH.

A 56d incubation experiment was conducted to explore the effects of the silk-worm excrement biochar (500 °C, BC) combined with different iron-based materials (FeCl₃, FeSO_4, and reduced iron powder) on the speciation of cadmium (Cd) and lead (Pb) in a contaminated soil. Application rate of BC and iron-based materials is 1% (W/W) and 0.2% (W/W) of the soil, respectively. At the same time, the soil physicochemical properties, such as pH, cation exchange capacity (CEC), and the structure of soil, were determined in order to explore the influence mechanism of amendments to forms of Cd and Pb in soil. The results show that the stabilization effects on Cd is (BC + FeSO₄) > (BC + FeCl₃) > (BC + Fe) > (BC) and Pb is (BC + Fe) > (BC + FeSO₄) > (BC + FeCl₃) > (BC) at the end of incubation, compared with the effect of the control group. The treatment of (BC + FeSO₄) is the most effective in terms of the stabilization of Cd and Pb, which makes the percentages of organic-bound and residual Cd and Pb increase by 40.90% and 23.51% respectively. In addition, with different ways of treatment, the pH value and CEC of soil see a remarkable increase by 1.65–2.01 units and 2.01–2.58 cmol·kg⁻¹ respectively. X-ray diffraction (XRD) patterns show that the soil imprisons Cd and Pb in different mineral phases. As such the treatment of (BC + FeSO₄) can significantly improve soil environment, increase soil pH value & CEC and exert a relatively good stabilization effect on both Cd and Pb.

In this study, biochar (BC) was prepared from bagasse and then successfully loaded with nanoscale zerovalent iron (nZVI) to produce BC-supported nZVI, termed nZVI@BC. Satisfactory results were obtained using a nZVI@BC-activated persulfate (PS), termed nZVI@BC/PS, to remediate total petroleum hydrocarbons (TPH)-contaminated water. The effects of three influencing factors—the dosage of nZVI@BC, D_nZVI@BC, the concentration of PS, C_PS, and the initial pH, pH_i—on TPH removal were examined through single-factor and batch tests. The results show the following. Each factor considerably influenced the performance of the prepared nZVI@BC/PS reaction system in removing TPH. The TPH degradation process conformed to a first-order kinetic model. The response surface method (RSM) was used in tandem with a Box–Behnken design to optimise the variables involved in TPH degradation. The three influencing variables (i.e., D_nZVI@BC, C_PS, and pH_i) were set in the range of 0.4–1.0 g/L, 20–160 g/L, and 2.21–9.42, respectively, during the experiment. An optimised quadratic model used to fit the experimental data displayed a high level of significance (p < 0.0001) with a very high regression value (R² = 0.9906; adjusted R² = 0.9786). Analyses of regression and variance revealed that the quadratic model sufficiently explains the TPH degradation rate. An electron paramagnetic resonance (EPR) spectroscopic analysis of the nZVI@BC/PS system revealed that SO₄⁻·, ·OH, O₂⁻·, and ¹O₂ participated in the activation and degradation processes. The results of this study show that nZVI@BC-activated PS systems possess great potential for applications in TPH-contaminated wastewater treatment and environmentally sustainable development.

In this study, maize plant was cultured in soil contaminated with different levels of crude oil. The purpose was to investigate the change of soil properties, leaf physiological and chemical parameters, and phenanthrene content in the leaf. Results showed that soil water content significantly increased when the levels of total petroleum hydrocarbons were 3700–17,800 mg/kg in soil, and soil electrical conductivity significantly increased compared with the control. In maize leaf, stomatal length and density, as well as K and Na contents decreased in contaminated treatments compared with the control. Stomatal length has a significant positive correlation with K content in leaf (r = 0.92, p < 0.01), while stomatal density was negatively correlated to the crude oil level in soil (r = −0.91, p < 0.05). Accumulation of phenanthrene in maize leaf was mainly through the foliar uptake pathway. Phenanthrene concentrations of maize leaf in oil-treated soil were less than that of the control, which exhibited a significant positive relationship with stomatal length (r = 0.98, p < 0.01). This study demonstrated that the stomata structure of maize could be influenced by crude oil and thus possibly controlling the accumulation of polycyclic aromatic hydrocarbons in aerial tissues. Based on these results, controlling stomata movement will be beneficial to phytoremediation of contaminated soil.

The aim of this study was to explore the feasible measurement of the control of cadmium (Cd) and arsenic (As) accumulation in rice grains. A field experiment was carried out to research the effect of different treatments, including spraying silicon (Si)/selenium (Se) foliar fertilizers, the application of lime (CaO), water management (continuous flooding), and the co-application of foliar fertilizers and flooding, on Cd and As accumulation in rice grains in Guangxi Province. The results indicate that Cd accumulation in rice grains decreased under different treatments and Cd content in rice grains reached the threshold of 0.2 mg kg⁻¹. In the single technical treatments, CaO application, flooding, spraying foliar Se fertilizer, and spraying foliar Si fertilizer decreased Cd content by 73.15%, 60.44%, 45.76%, and 36.07%, respectively. However, flooding and CaO amendment enhanced As accumulation in rice grains. The co-application of flooding and spraying foliar fertilizer can simultaneously reduce Cd and As in rice grains. In addition, they resulted in lower Cd content than the single technical treatments. Among the treatments, the lowest bioaccumulation factors of Cd and As were found after the co-application of flooding and Si foliar fertilizer, which decreased these factors by 74.02% and 22.72%, respectively. These results suggest that spraying foliar Si fertilizer combined with flooding may be a promising method to synchronously inhibit the accumulation of Cd and As in rice.