At present, the application of phytoremediation technology in the ecological remediation of heavy metal tailings is receiving more and more attention. In this study, the physiological and biochemical response and tolerance mechanism of woody plant Nerium indicum to Pb and Zn under different proportions of inorganic modifier calcium carbonate (C1: 5%, C2: 10%, C3: 15%) and organic modifier mushroom residue (M1: 10%, M2: 20%, M3: 30%) was compared. The results showed that the pH value has a trend of C group > M group > CK group and organic matter has a trend of M group > CK group > C group. Phosphatase activity and catalase activity has a trend of M group > C group > CK group, but catalase was more vulnerable to the calcium carbonate concentration. Both modifiers can promote the transformation of Pb, Zn, Cu, and Cd in tailings to more stable organic bound and residual states. However, the stabilization effect of mushroom residue is better, and its stability is Pb, Zn > Cd, Cu. Both modifiers can increase the biomass of Nerium indicum and the modification effect of mushroom residue is better than calcium carbonate. Pb/Zn content and accumulation in Nerium indicum organs showed root > stem > leaf in all groups. Compared with the CK group, the enrichment coefficient of Pb/Zn in C1 and M1 groups decreased, while the translocation factor of Pb/Zn in C1 and M1 groups increased. With the increase in modifier concentration, the enrichment coefficient increases about 1.75~52.94%, but the translocation factor decreases rapidly (20.01~64.46%). Clearly, both the calcium carbonate and mushroom residue amendment could promote the growth ability of Nerium indicum in lead–zinc tailings and strengthen the phytoremediation potential.

Phytoremediation could be an alternative strategy for lead (Pb) contamination. K. paniculata has been reported as a newly potential plant for sustainable phytoremediation of Pb-contaminated soil. Physiological indexes, enrichment accumulation characteristics, Pb subcellular distribution and microstructure of K. paniculata were carefully studied at different levels of Pb stress (0–1200 mg/L). The results showed that plant growth increased up to 123.8% and 112.7%, relative to the control group when Pb stress was 200 mg/L and 400 mg/L, respectively. However, the average height and biomass of K. paniculata decrease when the Pb stress continues to increase. In all treatment groups, the accumulation of Pb in plant organs showed a trend of root > stem > leaf, and Pb accumulation reached 81.31%~86.69% in the root. Chlorophyll content and chlorophyll a/b showed a rising trend and then fell with increasing Pb stress. Catalase (CAT) and peroxidase (POD) activity showed a positive trend followed by a negative decline, while superoxide dismutase (SOD) activity significantly increased with increasing levels of Pb exposure stress. Transmission electron microscopy (TEM) showed that Pb accumulates in the inactive metabolic regions (cell walls and vesicles) in roots and stems, which may be the main mechanism for plants to reduce Pb biotoxicity. Fourier transform infrared spectroscopy (FTIR) showed that Pb stress increased the content of intracellular -OH and -COOH functional groups. Through organic acids, polysaccharides, proteins and other compounds bound to Pb, the adaptation and tolerance of K. paniculata to Pb were enhanced. K. paniculata showed good phytoremediation potential and has broad application prospects for heavy metal-contaminated soil.

Cadmium (Cd) in paddy soil is one of the most harmful potentially toxic elements threatening human health. In order to study the effect of lime combined with intermittent and flooding conditions on the soil pH, Cd availability and its accumulation in tissues at the tillering, filling and maturity stages of rice, as well as enzyme activity and the microbial community in contaminated soil, a field experiment was conducted. The results showed that liming under flooding conditions is a more suitable strategy for in situ remediation of Cd-contaminated paddy soil than intermittent conditions. The availability of Cd in soils was closely related to the duration of flooding. Liming was an effective way at reducing available Cd in flooding soil because it promotes the transformation of Cd in soil from acid-extractable to reducible fraction or residual fraction during the reproductive growth period of rice. Compared with control, after liming, the concentration of Cd in brown rice was reduced by 34.9% under intermittent condition while reduced by 55.8% under flooding condition. Meanwhile, phosphatase, urease, and invertase activities in soil increased by 116.7%, 61.4% and 28.8%, and 41.3%, 46.5% and 20.8%, respectively. The high urease activity in tested soils could be used to assess soil recovery with liming for the remediation of contaminated soil. Soil microbial diversity was determined by the activities of soil acid phosphatase, urease and available Cd by redundancy analysis (RDA). The results indicated that the problem of Cd-contaminated paddy soil could achieve risk control of agricultural planting by chemical treatment such as lime, combined with various water regimes.

Rapid industrial development increases soil contamination risks in suburban agricultural areas; however, the extent and sources of heavy metal(loid)s pollution in the soil during this process are not well understood. This study investigated the concentrations, spatial distribution, and potential risks of heavy metal(loid)s (As, Hg, Cd, Cr, and Pb) in soil and wheat samples from an agricultural area. The study found that soil Cd was the main pollutant with the highest enrichment factor of 15.9 with 21.6% of the wheat samples having Cd concentrations exceeding the China's limit of 0.1 mg/kg. Soil As, Cd, Hg, and Pb were concentrated in the northwest, while Cr was high in the southeast. Soil Cd contamination is more severe than other heavy metal(loid)s and poses a slight ecological risk. Monte Carlo simulations showed that the hazard quotient for all five heavy metal(loid)s in wheat was less than 1, with Cd being the highest. 1.35% of children and 0.87% of adults exceeded the carcinogenic risk level for Cd, while 0.54% of children exhibited above the threshold for Cr. Children were the most sensitive to heavy metal(loid)s exposure in contaminated areas, with heavy metal(loid)s) concentration in wheat being the key factor influencing health risks. Source apportionment via the PCA-APCS-MLR model and correlation analysis revealed that the soil Cd originated from agricultural activities and industrial-traffic. This study assessed soil heavy metal(loid)s pollution, ecological risks, sources, and health risks to residents from wheat consumption, providing evidence for managing soil contamination and food safety.

Nitrogen (N) fertilizer affects the migration and transformation of arsenic (As) in soil and rice. We conducted pot experiments and studied the effects of 0.1, 0.2, and 0.4 g∙kg⁻¹ N levels of NH₄Cl, (NH₄)₂SO₄, and NH₄NO₃ fertilizers on the As bioavailability in the As-contaminated inter-rhizosphere soil and As accumulation in the rice organs. The results showed that the concentration of bioavailable As in the rice rhizosphere soil was significantly negatively correlated with pH under the 0.4 g∙kg⁻¹ N level of each fertilizer. At the same N level, while the As concentration was maturity stage > tillering stage in rice stems and leaves treated with NH₄Cl and (NH₄)₂SO₄, it was the opposite in roots. This suggests that the transfer of As from roots to stems and leaves mainly occurs in the late stage of rice growth under the condition of only NH₄⁺-N fertilizer applying. The As concentration in rice aboveground organ (grains and stems–leaves) decreased with the increasing N application under the same N fertilizer treatment condition during the mature stage. In addition, the As concentration in rice grains treated with (NH₄)₂SO₄ was the lowest. This result indicated that SO₄²⁻ and NH₄⁺-N had a significant synergistic inhibition on the As accumulation in rice grains. It was concluded that appropriate (NH₄)₂SO₄ levels for As-contaminated paddy soils with high sulfur (S) contents would obtain rice grains with inorganic As concentrations below 0.2 mg·kg⁻¹.