[In-situ Remediation Effect of Cadmium-polluted Agriculture Land Using Different Amendments Under Rice-wheat Rotation].

Exploring the effects of one-time amendment treatments on cadmium (Cd)-contaminated farmland soils is beneficial for providing a theoretical basis to effectively prevent Cd pollution in farmland soils and ensure the safe production of crops. Five amendments, including straw biochar, fly ash, sepiolite, white marble powder, and shale (particle size <0.2 mm, application rate 2.25 kg·m-2), were applied to the Cd-contaminated farmland soils. The soil nutrients, pH, soil available Cd, and Cd chemical forms in the soils and grain Cd concentration in the planted crops were determined to investigate the effects and persistence of one-time applications of the five amendments. The results showed that:① the application of the five amendments had little effect on soil nutrient content, but all of them could increase soil pH. Amendment treatments improved the transfer of Cd from the acid extraction fraction to residue fraction and further reduced the Cd availability in the soil. The decreasing amplitudes of straw biochar and white marble powder soil conditioner were 20.42%-22.53%, which was higher than those in the other treatments. ② The grain Cd concentrations in rice and wheat were significantly decreased under the amendment treatments with the decreasing amplitudes of 19.88%-48.77% and 5.06%-24.00%, respectively. The Cd concentrations in rice grains under the treatments of straw biochar, fly ash, and white marble powder soil conditioner were 0.195, 0.196, and 0.223 mg·kg-1, respectively, which were lower than those under the other treatments and were close to or approached the National Standard of Food Safety(GB 2762-2017)(0.2 mg·kg-1). ③ The immobilization effects on Cd in farmland soils were decreasing with time under one-time application of the amendments. The available Cd concentrations in the soil and Cd concentrations in crop grains were still lower than those in the control after three rounds of rice-wheat rotation. The straw biochar and white marble powder soil conditioner had a good and long-term effect on reducing Cd availability in soils and Cd concentrations in crop grain, making them ideal materials for safe production in Cd-contaminated soils.

[Stabilization Characteristics of Exogenous Cd in Different Types of Soil].

To clarify the characteristics of stabilization and availability of exogenous cadmium (Cd) in different types of soils, six main agricultural soils in Sichuan province, including acidic purple soil, neutral purple soil, calcareous purple soil, gray fluvo-aquic soil, typical yellow soil, and rinsed yellow soil, were used in this study. A soil culture experiment was conducted to explore the differences in stabilization time, chemical form, and effective Cd content between the six types of soils. Additionally, the effects of exogenous Cd on the growth and Cd accumulation of cabbage growing in different soils was discussed. The results showed the following: 1 with exogenous Cd treatment, the available Cd content of the six soils decreased sharply within 15 d after Cd addition and then tended to be flat. After 30 d, there was no significant difference. The available Cd contents of rinsed yellow soil and acidic purple soil were significantly higher than that of the other four soils, and the content of calcareous purple soil was significantly lower (1.01 mg·kg-1). 2 After stabilization, exchangeable Cd was the main Cd form in the six soils, up to 42.51%-56.07%. The relative proportions of other Cd forms differed greatly between different soils. The proportion of iron and manganese oxides in the rinsed yellow soil and typical yellow soil was higher, whereas organic complex Cd, residual Cd, and carbonate-bound Cd were higher in the gray fluvo-aquic soil, neutral purple soil, and calcareous purple soil, respectively. 3 The characteristics of availability and bioavailability of Cd among different soils were significantly different with different exogenous Cd doses. With the lowest Cd dose (0.5 mg·kg-1), compared with that in the control, there was no significant decrease in Cd content in the edible parts of the cabbage, but Cd accumulation in the edible parts differed. The Cd contents of edible parts of the cabbage growing in typical yellow soil and rinsed yellow soil were significantly higher than that of the other soils. With the highest Cd dose (2.0 mg·kg-1), the growths of cabbage growing in all six soils were significantly inhibited. The available Cd contents of rinsed yellow soil and acidic purple soil were significantly higher than that of the other four soils, which is consistent with the Cd content in the edible parts of the cabbage. The available Cd contents and the Cd content in the edible parts of the cabbage in calcareous purple soil were the lowest, and acidic soils, especially in rinsed yellow soil, had the highest.

Dissipation of available benzo[a]pyrene in aging soil co-contaminated with cadmium and pyrene.

A microcosm experiment was conducted to investigate the dissipation of available benzo[a]pyrene (BaP) in soils co-contaminated with cadmium (Cd) and pyrene (PYR) during aging process. The available residue of BaP in soil was separated into desorbing and non-desorbing fractions. The desorbing fraction contributed more to the dissipation of available BaP than the non-desorbing fraction did. The concentration of bound-residue fraction of BaP was quite low across all treatments. Within the duration of this study (250 days), transformation of BaP from available fractions to bound-residue fraction was not observed. Microbial degradation was the dominant mechanism of the dissipation of available BaP in the soil. The dissipation of available BaP was significantly inhibited with the increment in Cd level in the soil. The addition of PYR (250 mg kg(-1)) remarkably promoted the dissipation of available BaP without reducing Cd availability in the soil. The calculated half-life of available BaP in the soil prolonged with the increment in Cd level; however, the addition of PYR shortened the half-life of available BaP by 13.1, 12.7, and 32.8% in 0.44, 2.56, and 22 mg Cd kg(-1) soils, respectively. These results demonstrated that the inhibiting effect of Cd and the promoting effect of PYR on the dissipation of available BaP were competitive. Therefore, this study shows that the bioremediation process of BaP can be more complicated in co-contaminated soils.

Simultaneous removal of cadmium and sulfamethoxazole from aqueous solution by rice straw biochar.

The simultaneous sorption behavior and characteristics of cadmium (Cd) and sulfamethoxazole (SMX) on rice straw biochar were investigated. Isotherms of Cd and SMX were well modeled by the Langmuir equation (R(2)>0.95). The calculated maximum adsorption parameter (Q) of Cd was similar in single and binary systems (34129.69 and 35919.54 mg/kg, respectively). However, the Q of SMX in a binary system (9182.74 mg/kg) was much higher than that in a single system (1827.82 mg/kg). The presence of Cd significantly promoted the sorption of SMX on rice straw biochar. When the pH ranged from 3 to 7.5, the sorption of Cd had the characteristics of a parabola pattern with maximum adsorption at pH 5, while the adsorption quantity of SMX decreased with increasing pH, with maximum adsorption at pH 3. The amount of SMX adsorbed on biochar was positively correlated with the surface area of the biochar, and the maximum adsorption occurred with d 250 biochar (biochar with a diameter of 150-250 µm). Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) showed that the removal of Cd and SMX by rice straw biochar may be attributed to precipitation and the formation of surface complexes between Cd or SMX and carboxyl or hydroxyl groups. The results of this study indicate that rice straw biochar has the potential for simultaneous removal of Cd and SMX from co-contaminated water.

Bioremediation of Cd-DDT co-contaminated soil using the Cd-hyperaccumulator Sedum alfredii and DDT-degrading microbes.

The development of an integrated strategy for the remediation of soil co-contaminated by heavy metals and persistent organic pollutants is a major research priority for the decontamination of soil slated for use in agricultural production. The objective of this study was to develop a bioremediation strategy for fields co-contaminated with cadmium (Cd), dichlorodiphenyltrichloroethane (DDT), and its metabolites 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethylene (DDE) and 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethane (DDD) (DDT, DDE, and DDD are collectively called DDs) using an identified Cd-hyperaccumulator plant Sedum alfredii (SA) and DDT-degrading microbes (DDT-1). Initially, inoculation with DDT-1 was shown to increase SA root biomass in a pot experiment. When SA was applied together with DDT-1, the levels of Cd and DDs in the co-contaminated soil decreased by 32.1-40.3% and 33.9-37.6%, respectively, in a pot experiment over 18 months compared to 3.25% and 3.76% decreases in soil Cd and DDs, respectively, in unplanted, untreated controls. A subsequent field study (18-month duration) in which the levels of Cd and DDs decreased by 31.1% and 53.6%, respectively, confirmed the beneficial results of this approach. This study demonstrates that the integrated bioremediation strategy is effective for the remediation of Cd-DDs co-contaminated soils.

The impact of EDTA on lead distribution and speciation in the accumulator Sedum alfredii by synchrotron X-ray investigation.

The in vivo localization and speciation of lead (Pb) in tissues of the accumulator Sedum alfredii grown in EDTA-Pb and Pb(NO(3))(2) was studied by synchrotron X-ray investigation. The presence of EDTA-Pb in solution resulted in a significant reduction of Pb accumulation in S. alfredii. Lead was preferentially localized in the vascular bundles regardless of treatments but the intensities of Pb were lower in the plants treated with EDTA. Lead was predominantly presented as a Pb-cell wall complex in the plants regardless of its supply form. However, a relatively high proportion of Pb was observed as Pb-EDTA complex when the plant was treated with EDTA-Pb, but as a mixture of Pb(3)(PO(4))(2), Pb-malic, and Pb-GSH when cultured with ionic Pb. These results suggest that EDTA does not increase the internal mobility of Pb, although the soluble Pb-EDTA complex could be transported and accumulated within the plants of S. alfredii.

[Research advances in plant lead tolerance and detoxification mechanism].

To have an overall understanding about the physiological mechanisms of plants in their lead (Pb) absorption, transportation, accumulation, and detoxification is the prerequisite of the phytoremediation of Pb-polluted soil. This paper reviewed the research advances in the mechanisms of plant Pb-adaptation and recovery, including the functions of cell wall and vacuole in Pb-inactivation and sequestration in plant cells, the effects of plant root exudates on Pb bioavailability, the roles of antioxidative enzymes dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione reductase (GR), and ascorbate peroxidase (APX), and of antioxidants phytochelatins (PCs) and glutathione in Pb detoxification, and the expression and function of metallothionein and Pb-specific genes. The further researches on the plant's Pb-tolerance and detoxification mechanisms as well as the technologies for phytoremediation of Pb-contaminated environments were prospected.

[Effects of exogenous Ca2+ on the growth and Zn accumulation of two Sedum alfredii Hance ecotypes].

A hydroponic study was conducted to investigate the biomass, root morphology, and zinc (Zn), calcium (Ca) and sulfur (S) contents of two Sedum alfredii ecotypes under effects of different concentration calcium (Ca2+) addition. The results showed that with increasing exogenous Ca2+ concentration, the dry mass of the two S. alfredii ecotypes increased, and the shoot dry mass of hyperaccumulation ecotype increased significantly (P <0.05). The root length and root surface area of hyperaccumulation ecotype increased with increasing exogenous Ca2+ concentration, while those of non-hyperaccumulation ecotype were in adverse. The Zn accumulation in the root, stem and leaf of hyperaccumulation ecotype was increased with increasing exogenous Ca2+ concentration though the differences among Ca2+ treatments were not significant (P >0.05), while the Zn accumulation in the shoot of non-hyperaccumulation ecotype was significantly low (P <0.05). The Ca accumulation in the root, stem and leaf of non-hyperaccumulation ecotype had a significant positive correlation with the concentration of exogenous Ca2+ (P <0.05), so as the S accumulation in the root of hyperaccumulation ecotype (P <0.01). Exogenous Ca2+ promoted the Zn absorption and accumulation of hyperaccumulation ecotype, while inhibited the Zn accumulation of non-hyperaccumulation ecotype. Appropriate concentration of exogenous Ca2+ could promote the growth of hyperaccumulation ecotype S. alfredii, and improve its ability of accumulating more zinc.