Reductive Transformation Of Chlorinated Acid Herbicide In Paddy Soils

Widely distributed in southern China,red paddy soils are facing potential ecological environment risks associated with large-scale use of herbicides and pesticides.The degradation and transformation of organic pollutants in agricultural soils has been a great concern in the field of soil environmental chemistry.In this study,the degradation of 2,4-dichlorophenoxyacetic acid?2,4-D?,a typical chlorinated acid herbicide,in iron-rich red paddy soils from southern China,was investigated.The microbial driving force was focused on,and the batch anaerobic experiments were conducted to investigate the degradation kinetics and microbiology mechanism of 2,4-D of red paddy soil.We focus on the changes of iron species,and the response mechanism of microbial communities in different periods,and their impacts on the pathways of degradation and transformation of 2,4-D under different incubation conditiions.By simulating the typical agronomic practices in southern China,the differences in degradation and transformation kinetics of 2,4-D,combined with the composition and structural changes of soil dominant microbial communities were evaluated under the conditions via adding different exogenous substances.Results from our study are expected to reveal the inherent nature of the degradation and transformation of 2,4-D under anaerobic conditions in red paddy soils.Main conclusions were shown as follows:?1?The transformation of 2,4-D is a interaction of biological and abiotic process with microbes as the main driving force,not just a simple biological or chemical reaction.2,4-D with an initial concentration of 20 mg l^-1 can be degraded and transformed completely under anerobic incubation conditions for 45 days,while no reductive degradation of 2,4-D were observed in the sterilized treatments.?2?During anaerobic incubations,2,4-D was degradated into 4-CPA,4-CP,and chloride.In this study,two possible degradation pathways were recommended:one is that 2,4-D was dechlorinated to 4-CPA which was subsequently hydrolyzed to 4-CP,the other parthway is that 2,4-D was simultaneously hydrolyzed and dechlorinated to 4-CP.?3?Under anaerobic incubation conditions,the microbial degradation of 2,4-D was significantly affected by different exogenous substances.The addition of AQDS(0.1mmol l^-1),sodium nitrate and sodium sulfate all significantly inhibited the degradation of 2,4-D in anaerobic incubation system,where the inhibitation effects was strengthened with the increasing e concentration of sodium sulfate.The addition of Fe₃O₄nanoparticles(20 mg kg^-1)could promote the degradation of 2,4-D in the incubation system.The addition of sodium lactate and glucose both significantly accelerated the degradation of 2,4-D,however,the high concentration of glucose(25 mmol l^-1)significantly inhibited the transformation of 2,4-D.?4?During anaerobic incubations,there was significant difference in abundance and communities of bacteria between the treatments with lactate or glucose and the control treatments,where Proteobacteria was the most dominant bacteria.There were significant correlations between the abundance and communities of bacteria and the pH value,iron species,2,4-D and their degradation intermediates in the incubation system.