铬在铁合金厂周边土壤-蔬菜系统中的迁移转化及健康风险

分析湖南省某铁合金厂附近重金属铬在土壤中的分布及迁移特征,在土壤-植物系统中的迁移转化规律,以及铬污染蔬菜对人体的健康风险。结果表明：铁合金厂外排污口、污灌区和对照区土壤的铬含量平均值分别为2239.5,995.33和104.9mg/kg。总铬在排污口附近土壤中主要富集在地表下200-400mm;在污灌区,主要富集于地表下0-200mm;而在对照区,铬浓度从上至下逐渐降低且各层之间富集浓度相差不大。结果也表明芹菜、莴苣和白菜均能够把土壤中吸收的致毒性较强的六价铬转化成低毒的三价铬,且蔬菜中的铬含量平均值为11.95mg/kg。铬在土壤–蔬菜中的生物富集因子大小依次为：白菜〉莴苣〉芹菜。居民每天摄入的铬含量严重超过食物中最大铬允许摄入量,表明铬污染对当地居民存在一定的健康风险。     

Optimization of Cr（VI） bioremediation in contaminated soil using indigenous bacteria

Bench-scale soil column experiments were carried out to evaluate the effectiveness of Cr(VI) bioremediation process in soils by using indigenous bacteria with the addition of bacteria nutrient media. Effects of particle size, spray intensity, initial Cr(VI) concentration, circulation mode and soil depth on Cr(VI) remediation were studied. Results show that soils after 6 d remediation with spray intensity controlled in the range of 29.6-59.2 mL/min could well fulfill the requirement of concrete aggregate and roadbed material usage, for the leaching toxicity concentration of the Cr(VI) in treated soils under the chosen condition is far less than 5 mg/L. The leaching toxicity and fractions of both hexavalent chromium and trivalent chromium from remediated soils were determined and compared with that of untreated soil. The results show that water soluble Cr(VI) declines from 1520.54 mg/kg to 0.68 mg/kg, exchangeable Cr(VI) decreases from 34.83 mg/kg to 0.01 mg/kg and carbonates-bonded Cr(VI) falls from 13.55 mg/kg to 0.68 mg/kg. Meanwhile, a corresponding increase in carbonate-bonded Cr(III), Fe and Mn oxides-bonded Cr(III) and organic matter-bonded Cr(III) are found. It reveals that indigenous bacteria can leach out water soluble Cr(VI), exchangeable Cr(VI) and carbonates-bonded Cr(VI) from contaminated soil followed by converting into carbonate-bonded Cr(III), Fe and Mn oxides-bonded Cr(III), organic matter-bonded Cr(III) and residual Cr(III).