铁基生物炭降低稻田砷镉有效性的化学和微生物机制

The environmental behavior of arsenic (As) and cadmium (Cd) is different in the rice paddy field. The use of biochar can reduce the bioavailability of Cd but improve the mobility of As. It is difficulty that how to reduce simultaneously the bioavailability of As and Cd. The bioavailability of As can be effectively reduced by the regulation of iron cycle. Previous studies have found that biochar-supported zero-valent iron (biochar-Fe) materials reduce simultaneously the bioavailability of Cd and As in the rice paddy field, but the mechanism is not clear. The object of this project is the As and Cd co-contaminated rice paddy soil. This project focus on the rule of morphological transformation of Fe, As and Cd in the paddy soil using simulation and pot experiment. The technique about chemical analysis and molecular biology will be used. The content of As and Cd in rice，the structure and properties of biochar-Fe materials, the morphology of As and Cd will be analyzed for these relationship. So the chemical mechanism that biochar-Fe materials reduce simultaneously the bioavailability of Cd and As in the rice paddy soil will be illustrated. The experiments will be conducted about the structure of microbial community with each system, the microbial and gene abundance of Fe-oxidizing/reducing bacteria and As-oxidizing/reducing bacteria. And the microbial mechanism will be clarified by analying the relationship that the content of As and Cd in rice, the property and structure of biochar-Fe, the morphology of As and Cd, the abundance of function microorganism and gene. The results of this project could provide a new theoretical basis to repair the As and Cd co-contaminated rice paddy field.

稻田砷镉环境行为差异大。采用生物炭能降低镉有效性，但提高砷在土壤中的流动性。如何同时降低稻田镉砷有效性是个难点。铁循环调控可有效降低砷有效性。前期研究发现，铁基生物炭可同时降低稻田砷镉有效性，但其机制尚不明确。本项目以砷镉复合污染水稻土为对象，采用室内模拟与盆栽试验，综合运用化学形态分析与分子生物学手段，重点研究铁基生物炭作用下，模拟体系水稻土、盆栽试验水稻重要生育期整体土壤与根际土壤中砷镉铁形态转化规律，分析稻米砷镉含量与铁基生物炭结构性质、砷镉形态之间的关系，阐明其化学机制；以及研究各体系土壤微生物群落结构，铁还原与氧化功能微生物丰度，砷还原与氧化功能微生物与基因丰度，分析稻米砷镉含量与相关功能微生物与基因丰度之间的关系，阐明其微生物机制；分析稻米砷镉含量与铁基生物炭结构性质、砷镉铁形态、功能微生物与基因丰度之间的关系，阐明其作用机制。可为稻田砷镉复合污染控制提供新的理论依据。

生物炭在土壤重金属修复方面受到极大的重视和广泛的研究，但铁基生物炭降低稻田砷镉有效性的机制尚不明确。本研究以棕榈丝生物质为原料，硝酸铁为铁源，通过高温碳化方法，制备铁基生物炭材料，铁颗粒尺寸约为20nm。通过吸附实验发现，铁基生物炭对As3+和As5+具有快速和较强的吸附能力，随着铁含量和使用量的增加，吸附量也相应增加。相同浓度下铁基生物炭对As5+的吸附能力优于As3+，并且可以将As3+氧化为As5+。添加不同温度制备的铁基生物炭到土壤中发现，土壤中微生物的砷还原基因表达水平显著提高，导致土壤中As3+含量升高，As5+含量降低。铁基生物炭加入镉砷污染土壤后，促进了铁还原相关微生物的活性，促进了土壤固相中铁的活化，进而通过电子穿梭体加快As5+的还原。铁基生物炭加入土壤后，土壤pH和Fe-DCB含量均升高，促进了镉的水解平衡，通过络合和沉淀作用降低了镉的生物有效性。同时，由于铁的存在，进一步钝化了土壤中的镉，最终降低了稻米中砷镉含量，为稻田砷镉复合污染控制提供新的理论依据。