Many organic materials have been used to decrease heavy-metal bioavailability in soil via in-situ remediation due to its high efficiency and easy operation; meanwhile, cheap materials have also been pursued to decrease the cost of remediation. Agricultural wastes exhibit their potential in remediation materials due to their low cost; however, raw agricultural wastes have a low ability to immobilize heavy metals in soil. Attempts have been made to modify agricultural wastes to improve the efficiency of heavy-metal passivation. In this study, novel agricultural waste-based materials, raw sugarcane bagasse (SB), citric acid modified (SSB) and citric-acid/Fe₃O₄ modified (MSB) sugarcane bagasse at 0.5% and 1% addition rates, were compared for their effectiveness in soil Cd passivation and Cd accumulations in pakchoi plants in a 30-day pot experiment. The addition of SB did not decrease soil bioavailable Cd effectively and slightly decreased Cd accumulation in plant roots and leaves. In comparison, SSB and MSB exhibited a great potential to decrease the transformation, translocation and accumulation of Cd with the decrease being greater at 1% than 0.5% rate in the soil-pakchoi system. For example, the addition of SSB and MSB at 0.5% decreased the concentration of Cd in leaves by 10%, and 16%, and at 1% decreased the concentration by 25% and 30%, respectively. High pH and abundant functional groups of three amendments played important roles in Cd immobilization. The enhanced microbial activities might also contribute to Cd passivation. However, plant growth was decreased in the amended treatments except SSB at 0.5% rate. The results suggest that citric-acid-modified sugarcane bagasse at addition rate of 0.5% has a potential to immobilize Cd in soil and decrease Cd accumulation in edible part of pakchoi effectively without decreasing vegetable growth.

Cadmium (Cd) is a major pollutant in farmland, which not only greatly restricts crop production, but also brings a serious threat to human health through entering the food chain. Our previous study showed that hemin treatment could reduce the accumulation of Cd in pak choi seedlings. However, the underlying mechanism remains unclear. In this study, we used non-invasive micro-test technology (NMT) to detect the real-time Cd²⁺ flux from pak choi roots and demonstrated that hemin treatment decreased Cd uptake rather than its translocation within plants. Moreover, through comparing the responses of different chemical treatments in pak choi seedlings and Arabidopsis wild-type and heme oxygenase-1 (HO-1) mutant, we provided evidence that hemin-decreased Cd uptake was HO-1 dependent. Furthermore, analyses of hemin degradation products suggested that the hemin-derived suppression of Cd uptake suppression was probably relying on its degradation by-products, ferrous iron (Fe²⁺) and carbon monoxide (CO), via repressing the expression of a Fe²⁺/Cd²⁺ transporter BcIRT1 in pak choi roots.

Heavy metal contamination has been threatening the health of human beings. To decrease the bio-toxicity of heavy metals, a thiol-functionalized nano-silica (SiO₂-SH) was adopted to remediate the soil contaminated by lead (Pb), cadmium (Cd) and copper (Cu). The remediation effect of SiO₂-SH on contaminated soils was investigated by the uptake of the heavy metals into lettuce and pakchoi in pot experiment. The bio-toxicity of the SiO₂-SH was evaluated, and its immobilization mechanisms were proposed by the fraction distribution of Cd, Pb and Cu. It was found that the SiO₂-SH can significantly reduce the uptake of Cd, Pb, Cu into pakchoi by 92.02%, 68.03%, 76.34% and into lettuce by 89.81%, 43.41%, 5.76%, respectively. The chemical species analyses of Cd, Pb, Cu indicate SiO₂-SH can transform the heavy metal in acid soluble states into reducible fraction and oxidizable fraction, thereby inhibiting the extraction of heavy metals into soil solution. The concentrations of microbial biomass carbon, organic matter, and cation exchange capacity of the soil increased while the soil bulk density decreased after remediation. Those changes demonstrate that SiO₂-SH not only has no bio-toxic impact on the soil environment but also improves the soil environment, which proves the prepared SiO₂-SH is environmental-friendly. The SiO₂-SH could be a promising amendment for heavy metal contaminated soils.

Current understanding of biochar's effect on antibiotic resistance genes (ARGs) in soil is limited, and whether the effect could change after long-term field aging remains largely unknown. In this study, we employed high-throughput quantitative PCR to assess the effect of biochar amendment on soil resistome as affected by three years of field aging. Application of fresh biochar significantly elevated the number and abundance of ARGs in the manured soil, but did not show such effect under pakchoi cultivation. The presence of aged biochar caused a marked reduction of ARGs only in the planted manured soil. Results of principal coordinate analysis and structural equation modeling indicate that biochar's effect on soil ARG profile was changed by field aging through altering soil microbial composition. These results highlight the necessity of considering aging effect of biochar during its on-farm application to mitigate soil antibiotic resistance.

Cadmium (Cd) is the most concerning soil pollutant, and a threat to human health, especially in China. The in-situ immobilization of Cadmium by amendments is one of the most widely adopted methods to remedy soil contamination. The study was designed to evaluate the effect of organo-chemical amendments on soil Cd bioavailability and nitrogen cycling microbes under continuous planting of rice (Oryza sativa) and pak choi (Brassica chinensis L.). The experiment was carried out using four amendments, Lime, Zeolite, Superphosphate, and Biochar, at two different ratios; M1: at the ratio of 47:47:5:1, and M2 at the ratio of 71:23:5:1, respectively. Moreover, both M1 and M2 were enriched at four levels (T1: 0.5%; T2: 1%; T3: 2%; T4: 4%). Results showed that compared with CK (Cd enriched soils), the yield of rice under treatments of M1T1 and M2T1 increased by 8.93% and 8.36%, respectively. While the biomass (fresh weight) of pak choi under M1 and M2 amendments increased by 2.52–2.98 times and 0.76–2.89 times respectively, under enrichment treatments T1, T2, and T3. The total Cd concentrations in rice grains treated with M1T3 and M2T3 decreased by 89.25% and 93.16%, respectively, compared with CK. On the other hand, the total Cd concentrations in pak choi under M1T3 and M2T2 decreased by 92.86% and 90.23%, respectively. The results showed that soil pH was the main factor affecting Cd bioavailability in rice and pak choi. The Variance partitioning analysis (VPA) of rice and pak choi showed that soil pH was the most significant contributing factor. In the rice season, the contribution of soil pH (P) on Cd bioavailability was 10.14% (P = 0.102), and in the pak choi season, the contribution of soil pH was 8.38% (P = 0.133). Furthermore, the abundance of ammonia oxidation and denitrifying microorganisms had significantly correlation with soil pH and exchange Cd. In rice season, when the enrichment level of amendments increased from 0.5% (T1) to 2% (T3), the gene abundance of AOA, AOB, nirK, nirS and nosZ (І) tended to decrease. While in pak choi season, when the enrichment level increased at the level of 0.5% (T1), 1% (T2), and 2% (T3), the gene abundance of AOB, nirS, and nosZ (І) increased. Additionally, the gene abundance of AOA and nirK showed a reduction in the pak choi season contrasting to rice. And the mixed amendment M2 performed better at reducing Cd uptake than M1, which may have correlation with the ratio of lime and zeolite in them. Finally, we conclude that between these two amendments, when applied at a moderate level M2 type performed better than M1 in reducing Cd uptake, and also showed positive effects on both gene abundance and increase soil pH.

Planting leafy vegetables, especially pakchoi, in cadmium (Cd) polluted farmland is easy to lead to excessive Cd content in edible parts, which results in high risk of food chain. In this study, a field experiment was carried out to study the effects of intercropping of pakchoi with Cd hyperaccumulator Sedum alfredii Hance, and the roles of endophytic bacterium SaMR12 was also investigated. When intercropping with Sedum, the growth of pakchoi was not affected but their Cd concentration and accumulation were significantly increased, while which were obviously decreased by SaMR12 inoculation. After intercropping, the biomass of Sedum was significantly reduced, but their Cd concentration increased. SaMR12 inoculation significantly increased Cd accumulation of Sedum, and which increased to 3 times in Sedum monoculture. Those results showed that although intercropping with hyperaccumulator could lead to higher risk of pakchoi in Cd polluted field, intercropping with SaMR12 inoculated Sedum can decrease Cd concentration of pakchoi and promote Cd absorption of Sedum, which indicated that this endophyte can be made into a microbial inoculum as a soil additive for the safe production of vegetables and the soil Cd pollution remediation.

Coupling with triolein-embedded cellulose acetate membrane (TECAM) technique, hydroxypropyl β-cyclodextrins (HPCD) extraction method, and the greenhouse pot experiments, the influences of biochars on polychlorinated biphenyls (PCBs) bioavailability in soil to plant (Brassica chinensis L. and Daucus carota) were investigated. Addition of 2% biochars to soils significantly reduced the uptake of PCBs in plant, especially for di-, tri- and tetra-chlorobiphenyls. PCBs concentrations in the roots of B. chinensis and D. carota were reduced for 61.5–93.7%, and 12.7–62.4%, respectively in the presence of biochars. The kinetic study showed that in the soils amended with/without biochars, PCBs concentrations accumulated in TECAM, as well as in the HPCD extraction solution, followed significant linear relationships with those in plant roots. Application of biochars to soil is a potentially promising method to reduce PCBs bioavailability whereas TECAM technique can be a useful tool to predict the bioavailability of PCBs in soil.

Contamination of soil with heavy metals seriously harms the growth of crops. Silicon fertilizer is known to promote growth of crops and alleviate heavy metals stresses in vegetables. However, little is known about the effects of silicon fertilizer on pakchoi vegetable growth and soil microbial community in soil contaminated with multiple heavy metals. In order to elucidate this question, current study was designed to analyze the impact of different silicon fertilizer doses on the growth of pakchoi, heavy metals accumulation in pakchoi, and diversity and composition of bacterial community in heavy metals contaminated soil. Results of the study showed that, silicon fertilizer application significantly improved the yield of pakchoi and reduced the content of heavy metals in pakchoi. Moreover, the silicon fertilizer led to the heterogeneity of bacterial community structure in soil. Linear discriminant analysis (LDA) effect size (LEfSe) test showed the change of soil bacterial community structures under the higher silicon fertilizer doses (0.8–3.2%). Similarly, soil bacteria associated with heavy metal resistance and carbon/nitrogen metabolism showed a more active response to medium fertilizer dose (0.8% w/w). In addition, Mantel test and Redundancy analysis (RDA) showed that both the soil bacterial community structures and pakchoi growth were significantly correlated with soil EC, available K and pH. Study suggested that the application of silicon fertilizer provided richer bacteria associated with heavy metal resistance and plant growth, and more favorable soil physicochemical environment for the growth of pakchoi under multiple heavy metal contamination, and the impact was dependent on fertilizing dose.

Biochar sequesters cadmium (Cd) by immobilisation, but the process is often less effective in field trials than in the laboratory. Therefore, the involvement of soil components should be considered for predicting field conditions that could potentially improve this process. Here, we used biochar derived from Spartina alterniflora as the amendment for Cd-contaminated soil. In simulation trials, a mixture of kaolin, a representative soil model component, and S. alterniflora-derived biochar immobilised Cd by forming silicon-aluminium-Cd-containing complexes. Interestingly, the biochar recalcitrance index value increased from 48% to 53%–56% because of the formation of physical barriers consisting of kaolinite minerals and Cd complexes. Pot trials were performed using Brassica chinensis for evaluating the effect of S. alterniflora-derived biochar on plant growth in Cd-contaminated soil. The bio-concentration factor values in B. chinensis were 24%–31% after soil remediation with biochar than in control plants. In summary, these results indicated that soil minerals facilitated Cd sequestration by biochar, which reduced Cd bioavailability and improved the recalcitrance of this soil amendment. Thus, mechanisms for effective Cd remediation should include biochar-soil interactions.

There is a lack of understanding about the potential accumulation of antibiotics in plants exposed to low-dose contaminated soil. 12 Brassica rapa subsp. chinensis cultivars were used to investigate the different accumulation capacities of sulfamethoxypyridazine, tetracycline, ofloxacin, norfloxacin and difloxacin from the soil. The results showed a significant variation (p < 0.05) among the 12 cultivars in the accumulation of antibiotics. Cultivars Y1 and Y2 had the highest accumulation capacity with average concentrations of 3.26 and 3.00 μg kg⁻¹, respectively, while cultivars Y4 and Y9 had the lowest accumulation capacity with average concentrations of 0.83 and 0.89 μg kg⁻¹. The average antibiotic concentration in all edible part samples (2.74 μg kg⁻¹) of the treatment group was about 3.0-fold of that of the control group (0.93 μg kg⁻¹). The average bioconcentration factors of sulfamethoxypyridazine, tetracycline, ofloxacin, norfloxacin and difloxacin were 0.051, 0.031, 0.017, 0.036 and 0.034, respectively, indicating a higher uptake of sulfamethoxypyridazine compared to ofloxacin. And the mobility of antibiotics in soil is a main factor affecting the bioavailability for plants. The average concentration of antibiotics in edible parts of cultivar Y12 on the 25th and 45th day were 1.52 and 1.73 μg kg⁻¹ and that of the roots were 3.73 and 6.61 μg kg⁻¹, respectively. The concentrations of tetracycline and difloxacin in the edible parts and roots significantly increased with growing time, while the concentration of sulfamethoxypyridazine and ofloxacin changed little throughout the growing period. The potential risks of antibiotics in vegetables on human health cannot be ignored. Overall, attention should be paid to the translocation of antibiotics from soil to plants.