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》

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 ... -  《-》

Iron-modified phosphorus- and silicon-based biochars exhibited various influences on arsenic, cadmium, and lead accumulation in rice and enzyme activities in a paddy soil.

Contamination of paddy soils with potentially toxic elements (PTEs) has become a severe environmental issue. Application of functionalized biochar for rice cultivation has been proposed as an effective means to reduce environmental risks of these PTEs in paddy soils. This work was undertaken to seek the positive effects of a rice husk-derived silicon (Si)-rich biochar (Si-BC) and a pig carcass-derived phosphorus (P)-rich biochar (P-BC), as well as their Fe-modified biochars (Fe-Si-BC and Fe-P-BC) on the enzyme activity and PTE availability in an As-Cd-Pb-contaminated soil. A rice cultivation pot trial was conducted using these functionalized biochars as soil amendments for the alleviation of PTE accumulation in rice plants. Results showed that Si-BC decreased the concentrations of As in rice grain and straw by 59.4 % and 61.4 %, respectively, while Fe-Si-BC significantly (P < 0.05) enhanced plant growth, increasing grain yield (by 38.6 %). Fe-Si-BC significantly (P < 0.05) elevated Cd and Pb accumulation in rice plants. P-BC enhanced the activities of dehydrogenase, catalase, and urease, and reduced grain-Pb and straw-Pb by 49.3 % and 43.2 %, respectively. However, Fe-P-BC reduced plant-As in rice grain and straw by 12.2 % and 51.2 %, respectively, but increased plant-Cd and plant-Pb. Thus, Fe-modified Si- and P-rich biochars could remediate paddy soils contaminated with As, and enhance the yield and quality of rice. Application of pristine P-rich biochar could also be a promising strategy to remediate the Pb-contaminated paddy soils and limit Pb accumulation in rice.

Yang X ，Wen E ，Ge C ，El-Naggar A ，Yu H ，Wang S ，Kwon EE ，Song H ，Shaheen SM ，Wang H ，Rinklebe J ... -  《-》

Comparison of Four Amendments for Arsenic and Cadmium Combined Contaminated Soil.

Li Y ，Wen J ，Shen P ，Zhou Y ，Shen J ，Jiang J ，Kong X ，Gu X ... -  《-》

[Using Biochar and Iron-calcium Material to Remediate Paddy Soil Contaminated by Cadmium and Arsenic].

Wu QC ，Wu JZ ，Zhao KL ，Lian B ，Yuan F ，Sun Q ，Tian X ... -  《-》