| Summary: | Biochar plays an essential role in soil remediation, but its effect on the arsenic remediation has been controversial. In this study, hexadecyl trimethyl ammonium bromide (HDTMA-Br) modified or unmodified biochar on As mobility and bioavailability in soil were studied. The sequential extraction experiment showed that As in the original soil mainly existed in the occluded form (78.24%), followed by Fe‒As (20.72%) and Al‒As (0.88%) forms. With the addition of the modified and unmodified biochars, the contents of Ca‒As and Fe‒As increased by 0.36 – 0.95% and 2.06 – 3.36%, respectively, suggesting the increased potential toxicity of As. The NaH2PO4 extraction result showed that the unmodified biochar increased the As availability by 3.23 – 22.76%, whereas the HDTMA-modified biochar reduced the As availability by 4.80 – 13.41%. Pot experiment showed that the unmodified and modified biochar increased the biomass of Brassica pekinensis, and the modified biochar (HB5) decreased the uptake of As by plants by 80.77% compared to the unmodified biochar. In particular, the plant achieved better growth in the modified biochar treatment (average height 8.31 cm) than in the unmodified biochar treatment (average height 6.97 cm). Therefore, both biochars facilitated phase transformation of As from the stable to the mobile states in the soil. Nevertheless, the HDTMA-modified biochar had an effect on alleviating As bioavailability and toxicity.
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