结构改良剂对污染水稻土重金属形态和有效性的影响机理

Heavy metal contamination in paddy soil is a major environmental problem in China. Properly techniques should be used to decrease the hidden trouble of heavy metal in the contaminated paddy soils, and to increase rice yield and ensure the food safety. Previous works on the remediation of heavy metal contaminated soils usually focused on soil chemistry, the relations between soil structure (aggregate) and heavy metal fractions were seldom considered. In this project, a heavy metal contaminated red paddy soil was chosen as study material, pot experiment, incubation experiment, and some advanced analysis technologies such as XRF, TEM-EDX, XANES, and EXAFS were used to determine the effects of soil conditioners on the fractions distribution and position of heavy metal between soil aggregate interior and exterior from the molecular level, to reveal the relationship between soil aggregate structure and fractions distribution of heavy metal, and to clarify the mechanisms of soil conditioners affecting fraction and availability of heavy metal in the contaminated paddy soil. Hopefully the results of this study would have instructional significance on the remediation of heavy metal contaminated soils and the increase of rice yield and quality.

水稻土的重金属污染是当前我国面临的一个重要环境问题。为了提高水稻产量、保证粮食安全，必须采取适当措施对重金属污染水稻土进行改良修复，以降低其安全隐患。当前研究大多从土壤化学的角度开展重金属污染土壤的改良修复工作，极少考虑土壤结构（团聚体）与重金属形态的关系。本项目以重金属污染红壤性水稻土为研究材料，采用水稻盆栽和室内培养相结合的方法，利用XRF、TEM-EDX、XANES和EXAFS等先进分析技术，从分子水平研究结构改良剂对重金属在土壤团聚体内外不同部位形态分布与定位的影响，揭示土壤团聚体结构与重金属形态分布之间的关系，阐明结构改良剂对污染水稻土重金属形态和有效性的影响机理。研究结果对重金属污染土壤的实际改良修复、水稻产量和质量的提高具有指导意义。

本项目以重金属污染红壤性水稻土为研究对象，采用水稻盆栽实验和室内培养实验研究结构改良剂对污染土壤重金属形态分布和有效性的影响机理。结果表明，结构改良剂的施用显著增加了土壤> 0.25 mm水稳性团聚体含量，但显著降低了0.053~0.002 mm粒级和< 0.002 mm粒级团聚体含量。说明结构改良剂的施用改善了土壤结构，进而促进水稻根系和地上部的生长。各结构改良剂处理水稻株高和秸秆干重均显著高于对照处理。与对照处理相比，结构改良剂的施用降低了> 2 mm、2~0.25 mm和0.053~0.002 mm粒级团聚体中的Cu、Cd含量，但增加了0.25~0.053 mm和< 0.002 mm粒级团聚体中的Cu、Cd含量。与此同时，结构改良剂降低了2~0.25 mm和0.053~0.002 mm粒级团聚体中交换态和铁锰氧化物结合态Cu、Cd的比例，但增加了有机结合态和残渣态Cu、Cd的比例，0.25~0.053 mm和< 0.002 mm粒级团聚体中交换态Cu、Cd的比例也有不同幅度的增加。结构改良剂的施用显著降低了水稻根、秸秆和稻米中的Cu、Cd含量，说明结构改良剂能够通过影响Cu、Cd在土壤团聚体结构中的形态分布来降低它们的生物有效性，抑制水稻对Cu、Cd的吸收，达到改良修复重金属污染土壤的目的。