Persistence of Hg-Contaminated Soil Stabilization in Typical Areas of Dehua County, Fujian Province, China

The in-situ stabilization remediation of Hg-contaminated soil in Qianyang, Dehua County, Fujian Province, was studied through the pre-experiments (stabilization orthogonal experiment and pot experiment) and field plot experiments for two consecutive years. The pre-experiments results showed that the main factors of the stabilization were the initial concentration of Hg in the soil and the amount of amendment added, followed by the amendment type, while the aging time had less effect. When the initial concentration of Hg in the soil was less than 10 mg·kg−1 and the amendment (modified biochar with modified attapulgite) added ratio was 0.2–0.4%, indicating optimized stabilization effect. After one-time application of 6750 and 11,250 kg·hm−2 amendment in low (1.38 mg·kg−1), medium (2.46 mg·kg−1), and high (8.52 mg·kg−1) Hg-contaminated soils, it could accelerate the transformation of Hg from exchangeable to residual and oxidizable Hg, enhance the activities of catalase, urease, and invertase in the soil. After one year of remediation, the case of adding 6750 kg·hm−2 amendment showed a significant stabilization effect. Compared to the control group, the available Hg content in the soil and Hg content in the water spinach reduced to 52.1–62.0% and 58.2–66.6%, respectively. When the application amount was increased to 11,250 kg·hm−2, the reduction rates were 43.2–46.0% and 58.2–62.0%, respectively. After two years of remediation, the stabilization effect was weakened, but the available Hg content in the soil and the water spinach was still significantly lower than that of the control, indicating that the persistence of the stabilization was good. For the soil contaminated slightly by Hg, the Hg content in the water spinach within two years was lower than the limit value of the Chinese standard (0.01 mg·kg−1). Although the Hg content in the water spinach for the soil contaminated highly by Hg was higher than the limit value, it could reduce to 67.3%, indicating an acceptable stabilization effect on heavily contaminated soil.