Effects Of Organic Materials On Transformation Of Arsenic Species In Paddy Soil

Arsenic(As)is one of the carcinogens identified by the International Agency for research on cancer(IARC).With the rapid development of industry,agriculture and chemical industry,burning of fossil fuels and excessive use of As-containing pesticides,As was gradually accumulated in the soil,causing different levels of As contamination and entering the food chain through the soil-plant system,which could cause damage to the human gut,skin,and nervous system.Organic matters contains a lot of nutrients as well as beneficial microorganisms and enzymes for crop growth.It can improve soil fertility and increase crop yield,however,the effect of organic manure application on As transformation and the microbial mechanism are not clear.Moreover,the carbon source is not only an important component of organic matter,but also an important component of soil,the change of carbon source has obvious effect on soil microbes,and the change of carbon source availability by exogenous carbon input not only directly affects the carbon cycle of soil microbes in paddy soil and influence the emission of carbon dioxide(CO2)and methane(CH4),it also restricts the demand of soil for other nutrients.Different carbon sources also have different effects on the transformation of As in soil,due to the utilization of different carbon sources is different of As transformation microorganisms.In this study,the effects of input of organic matter and carbon source and methane production on arsenic speciation transformation in soil were studied.In this study,different As-polluted paddy soils were selected.Firstly,we studied the effects of organic fertilizer application on As release and methylation in different paddy soils.Then the effect of different carbon sources on As transformation were also studied.Moreover,the methaneproducing inhibitor(BES)and coenzyme M(CoM)was added to study the effect of methanogenesis on transformation of As in soil.The diversity and abundance of functional genes in soil were analyzed by real-time quantitative PCR(qPCR)and high-throughput sequencing,to study the microbial mechanism of methanogenesis on As moblization and transformation.The main findings are as follows:1.The effect of organic fertilizer on the transformation of As were studied.It was found that the contents of total As in soil solution were influenced by the total As contents of soils.Addition of organic fertilizer significantly increased As mobility in soils with higher As contents(>30mg kg1).The contents of total Fe and total Mn in soil solution were the main factors affecting the total As.Moreover,organic fertilizer addition promoted As methylation in all soils.2 The effects of different carbon sources on the As transformation and methanogenesis werestudied.The addition of carbon source significantly increased the contents of DOC in soil,especially the addition of glucose.Besides,the addition of carbon source significantly increased the release of CH4 and CO2.Pyruvate was preferred for Fe(Ⅲ)reduction by microorganisms in the experiment.As(Ⅲ)was the main species of As in soil solution,followed by As(V).Glucose treatment promoted the release of As mainly by increasing DOC contents in soil solution.3.The effect of methanogenesis on transformation of As in soil was studied.It was found that the addition of coenzyme M(CoM)promoted the release of methane and the methylation of As,and the addition of 2-bromoethanesulfonate(BES)inhibited the release of methane,while the addition of CoM increased the concentration of DOC and Fe(Ⅱ).The addition of CoM may contribute to the As methylation by by increasing the relative abundance of arsM-harboring As(Ⅲ)methylators,such as Rhodomicrobium,Gaiella and Bellilinea,and arsM-harboring methanobacter,such as Methanbacterium,Methanosarcina.