Microbial and Abiotic Interaction in Transformation of Reducible Pollutants on the Interface of Subtropical Soil Clays and Water
Subtropical soil clays contain a large amount of free iron oxides and the geochemistry and biogeochemistry of Fe species should be special. Therefore, the transformation of reducible pollutants should be strongly depend on the biogeochemistry of Fe species, and is resulted in microbial and abiotic interactions. 1) The interaction between polycarboxylic acids (root exudates) and iron oxides. The enhancement effect of polycarboxylic acids on reductive dechlorination transformation of pentachlorophenol (PCP) reacting with iron oxides was studied in anoxic suspension. Batch experiments were performed with three species of iron oxides (goethite, lepidocrocite and hematite) and four species of polycarboxylic acids ( oxalate, citrate, succinate, and tartarate) through anoxic abiotic reactors. The chemical analyses and morphological observation showed that different combinations between polycarboxylic acids and iron oxides produced distinct contents of Fe ( II )-polycarboxylic ligand complexes, which significantly enhanced PCP transformation. The results suggest that surface-bound Fe( II ) formed on the iron oxides surface appears to be a key factor in enhancing PCP transformation. The enhancement mechanism attributes to strong nucleophilic ability and low reductive potential of the = Fe (II) -polycarboxylate complexes. The interaction between polycarboxylic acids and subtropical soil colloids was also investigated. Our results showed that the transformation rate was significantly accelerated by 1. 2 - 9.4 times when either oxalic acid or Fe (II) was added into the reaction suspension to increase the concentration of surface-bound Fe( II ) species. PCP transformation was affected by the soil properties, such as the type of parent material, pH, BET surface area, Fe content of soil colloids. Soil colloids developed from Basalt presented higher PCP transformation rate than those developed from Sandshale and Quaternary Period red earth. 2) The interaction between dissimilatory iron-reducing bacteria (DIRB) and iron oxides. A fermentative facultative anaerobe, which was able to reduce Fe ( III) oxide and carbon tetrachloride (CT) , was newly isolated from ancient subterranean forest in China, and identified as Klebsiella pneumoniae strain L17 by 16S rRNA sequence analysis. Citrate, glycerol, glucose and sucrose are available electron donors for the reduction of various Fe (III) oxides, including hydrous ferric oxide, goethite, lepidocrocite and hematite. The reduction rate of Fe(III) oxides was influenced by the crystal structure of Fe(III) oxide, the type of electron donor and the fermentative metabolic status of strain L17. The reduction rate can be significantly accelerated by the addition of anthraquinone-2, 6-disulfonate (AQDS). The strain L17 can dechlorinate CT to chloroform, and the dechlorination rate can be accelerated in the presence of Fe(III) oxide and AQDS. The mechanism of dechlorination in strain L17/Fe(III) oxide suspension included two processes; the biotic dechlorination by strain L17 and the abiotic dechlorination by the sorbed Fe( II ) formed from microbial Fe (III) oxide reduction. And AQDS might accelerate the dechlorination rate by indirect electron transfer from strain L17 to AQDS to Fe(III) oxide to CT. The results will be helpful to understand the natural attenuation of reducible pollutants in anoxic soil environments containing Fe(III) oxides and humic substances.
Fangbai Li Shungui Zhou
Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environment and Soil Sciences, Guangzhou 510650, China
国际会议
The 7th International Symposium on Plant-Soil Interactions at Low pH(第七届低pH条件下植物-土壤交互作用国际研讨会)
广州
英文
213-214
2009-05-17（万方平台首次上网日期，不代表论文的发表时间）