Effects Of Heavy Metals On Dissimilitary Iron Reduction In Paddy Soils

Heavy metal pollution in paddy soils of China has become serious; it induced crop reduction of output, crop bad and endangered people's health through food chain. Iron oxide reduction is an important process when paddy soil flooding, because the process may influence methane production and the change of phosphorus's and some heavy metals'validity in paddy soil. Now some research said the process of iron oxide anaerobic reduction is mainly a microbial dissimilatory iron reduction. Iron oxide is also an important absorption of heavy metals. In heavy metal pollution paddy soil, heavy metals may restrict dissimilitary iron reduction, and iron oxide can absorb heavy metals strongly. Some research said heavy metals might come in solution when iron oxide reducing and ferrous ion may co-deposition heavy metals with some negative ions in soil, such as carbonic acid and phosphorus acid. In heavy metal pollution paddy soil, when flooding, the influence of heavy metals in dissimilatory iron reduction and transform of heavy metals'fractions has important environmental meaning in repairing heavy metal pollution in paddy soils.In this study, the effects of different heavy metals on dissimilatory iron reduction and the results was discussed through anoxic incubation experiment which used paddy soil solutions as microbe inoculation solutions, added different heavy metals, used different carbon sources and added AODS as electron shuttle. The effect of excessive copper on iron reduction on paddy soils and the change of copper fractions under flooding were also discussed through anoxic incubation experiment that added different concentrations of copper on paddy soils and at the same time added ferrihydrite to observe its effect. Some conclusive results were obtained as following.(1) Different heavy metals (As(V),Pb²⁺,Cd²⁺,Zn²⁺,Cu²⁺ and Hg²⁺)in the same concentration restricted iron reduction on different extent, they increased the time before iron reduction happened and decreased the rate of iron reduction, As(V) and Pb²⁺ did not restrict dissimilatory iron reduction, Cd²⁺ and Zn²⁺ restricted it, Cu²⁺ and Hg²⁺ restricted the most. When the concentrations of Cu²⁺ and Hg²⁺ increased, the restriction on iron reduction increased, iron reduction would not happen when the concentrations of Cu²⁺ï¹¥0.1 mmol/L and Hg²⁺ï¹¥0.04 mmol/L. The rate of iron reduction in Sichuan paddy soil incubation was faster than Jiangxi paddy soil and the same heavy metal restricted iron reduction stronger in...