Simultaneous alleviation of cadmium and arsenic accumulation in rice by applying zero-valent iron and biochar to contaminated paddy soils.

The fates of cadmium (Cd) and arsenic (As) in paddy fields are generally opposite; thus, the inconsistent transformation of Cd and As poses large challenges for their remediation. In this study, the impacts of zero valent iron (ZVI) and/or biochar amendments on Cd and As bioavailability were examined in pot trials with rice. Comparison with the untreated soil, both Cd and As accumulation in different rice tissues decreased significantly in the ZVI-biochar amendments and the Cd and As accumulation in rice decreased with increasing ZVI contents. In particular, the concentrations of Cd (0.15 ± 0.01 mg kg-1) and As (0.17 ± 0.01 mg kg-1) in rice grains were decreased by 93% and 61% relative to the untreated soil, respectively. A sequential extraction analysis indicated that with increasing Fe ratios in the ZVI-biochar mixtures, bioavailable Cd and As decreased, and the immobilized Cd and As increased. Furthermore, high levels of Fe, Cd, and As were detected in Fe plaque of the ZVI-biochar amendments in comparison with the single biochar or single ZVI amendments. The ZVI-biochar mixture may have a synergistic effect that simultaneously reduces Cd and As bioavailability by increasing the formation of amorphous Fe and Fe plaque for Cd and As immobilization. The single ZVI amendment significantly decreased As bioavailability, while the single biochar amendment significantly reduced the bioavailability of Cd compared with the combined amendments. Hence, using a ZVI-biochar mixture as a soil amendment could be a promising strategy for safely-utilizing Cd and As co-contaminated sites in the future.

Qiao JT ，Liu TX ，Wang XQ ，Li FB ，Lv YH ，Cui JH ，Zeng XD ，Yuan YZ ，Liu CP ... -  《-》

Pristine/magnesium-loaded biochar and ZVI affect rice grain arsenic speciation and cadmium accumulation through different pathways in an alkaline paddy soil.

Cadmium (Cd) and arsenic (As) co-contamination has threatened rice production and food safety. It is challenging to mitigate Cd and As contamination in rice simultaneously due to their opposite geochemical behaviors. Mg-loaded biochar with outstanding adsorption capacity for As and Cd was used for the first time to remediate Cd/As contaminated paddy soils. In addition, the effect of zero-valent iron (ZVI) on grain As speciation accumulation in alkaline paddy soils was first investigated. The effect of rice straw biochar (SC), magnesium-loaded rice straw biochar (Mg/SC), and ZVI on concentrations of Cd and As speciation in soil porewater and their accumulation in rice tissues was investigated in a pot experiment. Addition of SC, Mg/SC and ZVI to soil reduced Cd concentrations in rice grain by 46.1%, 90.3% and 100%, and inorganic As (iAs) by 35.4%, 33.1% and 29.1%, respectively, and reduced Cd concentrations in porewater by 74.3%, 96.5% and 96.2%, respectively. Reductions of 51.6% and 87.7% in porewater iAs concentrations were observed with Mg/SC and ZVI amendments, but not with SC. Dimethylarsinic acid (DMA) concentrations in porewater and grain increased by a factor of 4.9 and 3.3, respectively, with ZVI amendment. The three amendments affected grain concentrations of iAs, DMA and Cd mainly by modulating their translocation within plant and the levels of As(III), silicon, dissolved organic carbon, iron or Cd in porewater. All three amendments (SC, Mg/SC and ZVI) have the potential to simultaneously mitigate Cd and iAs accumulation in rice grain, although the pathways are different.

Zhang C ，Shi D ，Wang C ，Sun G ，Li H ，Hu Y ，Li X ，Hou Y ，Zheng R ... -  《Journal of Environmental Sciences》

Effect of sulfur and sulfur-iron modified biochar on cadmium availability and transfer in the soil-rice system.

Cadmium (Cd) contamination in paddy soils has aroused global concern. Sulfur modified biochar (BC) could combine the benefits of BC and S for Cd remediation. However, no information is available on the impact of sulfur modified biochar on Cd phytoavailability in paddy soils. In this study, a pot experiment was conducted to investigate the effect of sulfur modified biochar (S-BC) and sulfur and iron (Fe) modified biochar (S-Fe BC) on Cd mobility and Cd transfer in the soil-rice system. The application of S-BC and S-Fe BC effectively reduced pore water Cd in the rhizosphere and non-rhizosphere pore water throughout the rice growth stages. S-BC and S-Fe BC addition increased the total chlorophyll content, as well as the root, shoot and grain biomasses of rice. Furthermore, S-BC and S-Fe BC amendments greatly increase the formation of Fe plaque on rice root surface, thus decreasing Cd accumulation in different rice tissues. In particular, S-Fe BC supplementation significantly reduced the Cd concentration in rice grains to 0.018 mg kg-1 in Cd-contaminated soil, which was lower than the China National standard for food contamination limit (0.2 mg kg-1 Cd). Sequential extraction results showed that S-BC and S-Fe BC can promote the transfer of exchangeable Cd to Fe-Mn oxide, organic and residual bound forms which reduce Cd in paddy soils. Thus, the amendment of S-Fe BC to Cd-contaminated paddy soil is an effective strategy to decrease Cd accumulation in rice grains and thereby protect public health.

Rajendran M ，Shi L ，Wu C ，Li W ，An W ，Liu Z ，Xue S ... -  《-》

Goethite modified biochar simultaneously mitigates the arsenic and cadmium accumulation in paddy rice (Oryza sativa) L.

Cadmium (Cd) and arsenic (As) contamination of paddy soils is a serious global issue because of the opposite geochemical behavior of Cd and As in paddy soils. Rice plant (Oryza sativa L.) cultivation in Cd- and As- contaminated paddy soil is regarded as one of the main dietary cause of Cd and As entry in human beings. This study aimed to determine the impact of goethite-modified biochar (GB) on bioavailability of both Cd and As in Cd- and As- polluted paddy soil. Contrary to control and biochar (BC) amendments, the application of GB amendments significantly impeded the accumulation of both Cd and As in rice plants. The results confirmed an obvious reduction in Cd and As content of rice grains by 85% and 77%, respectively after soil supplementation with GB 2% amendment. BC 3% application minimized the Cd uptake by 59% in the rice grains as compared to the control but exhibited a little impact on As accumulation in rice grains. Sequential extraction results displayed an increase in immobile Cd and As fractions of the soil by decreasing the bioavailable fractions of both elements after GB treatments. Fe-plaque formation on the root surfaces was significantly variable (P ˂ 0.05) among all the amendments. GB 2% treatment significantly increased the Fe content (10 g kg-1) of root Fe-plaque by 48%, which ultimately enhanced the sequestration of Cd and As by Fe-plaque and minimized the transport of Cd and As in rice plants. Moreover, GB treatments significantly changed the relative abundance of the microbial community in the rice rhizosphere and minimized the metal(loid)s mobility in the soil. The relative abundance of Acidobacteria, Firmicutes and Verrucomicrobia increased with GB 2% treatment while those of Bacteroidetes and Choloroflexi decreased. Our findings confirmed improvement in the rice grains quality regarding enhanced amino acid contents with GB application. Overall, the results of this study demonstrated that GB amendment simultaneously alleviated the Cd and As concentrations in edible parts of rice plant and provided a new valuable method to protect the public health by effectively remediating the co-occurrence of Cd and As in paddy soils.

Irshad MK ，Noman A ，Wang Y ，Yin Y ，Chen C ，Shang J ... -  《-》

Effect of calcium and iron-enriched biochar on arsenic and cadmium accumulation from soil to rice paddy tissues.

Arsenic (As) and cadmium (Cd) are nonessential toxic metal(loids) that are carcinogenic to humans. Hence, reducing the bioavailability of these metal(loids) in soils and decreasing their accumulation in rice grains is essential for agroecology, food safety, and human health. Iron (Fe)-enriched corncob biochar (FCB), Fe-enriched charred eggshell (FEB), and Fe-enriched corncob-eggshell biochar (FCEB) were prepared for soil amelioration. The amendment materials were applied at 1% and 2% application rates to observe their alleviation effects on As and Cd loads in rice paddy tissues and yield improvements using pot trials. The FCEB treatment increased paddy yields compared to those of FCB (9-12%) and FEB (3-36%); this could be because it contains more plant essential nutrients than FCB and a lower calcite content than that of FEB. In addition, FCEB significantly reduced brown rice As (AsBR, 29-60%) and Cd (CdBR, 57-81%) contents compared to those of the untreated control (CON). At a 2% application rate, FCEB reduced the average mobility of As (56%) and Cd (62%) in rhizosphere porewater and enhanced root Fe-plaque formation (76%) compared to those of CON. Moreover, the enhanced Fe-plaque sequestered a substantial amount of As (171.4%) and Cd (90.8%) in the 2% FCEB amendment compared to that of CON. Pearson correlation coefficients and regression analysis indicated that two key mechanisms likely control AsBR and CdBR accumulations. First, rhizosphere soil pH and Eh controlled As and Cd availabilities in porewaters and their speciation in the soil. Second, greater Fe-plaque formation in paddy roots grown in the amended soils provided a barrier for plant uptake of the metal(loids). These observations demonstrate that soil amendment with Fe-enriched corncob-eggshell biochar (e.g., 2% FCEB) is a prospective approach for the remediation of metal accumulation from the soil to grain system while simultaneously increasing paddy yield.

Islam MS ，Magid ASIA ，Chen Y ，Weng L ，Ma J ，Arafat MY ，Khan ZH ，Li Y ... -  《-》