Different Iron-containing Substances Shape Roxarsone Biotransformation

Roxarsone?3-nitro-4-hydroxyphenylarsonic acid?,which widely used as the feed additives in livestock and poultry breeding industry,is an organoarsenicals.It exists in livestock waste and goes into the natural environment in its original form,which may cause arsenic pollution of soil and water.It is important to explore the way of transformation for roxarsone in the environment in order to identify its'potential pollution risk.Shewanella oneidensis MR-1,a kind of facultative anaerobe which can make use of a variety of electron acceptor,such as Fe³⁺,NO₃^-,NO₂^-and heavy metal ions to conduct metabolism and electron transport in anaerobic conditions,was selected as model bacteria in this study,to investigate biotransformation process of roxarsone at the condition of different kind of iron minerals.The result shows that iron ion and minerals containing iron have substantial influence on the reduction of roxarsone by S.oneidensis.The main conclusions are listed as follows:?1?The result of effect of dissolved Fe???on S.oneidensis MR-1 mediated roxarsone biotransformation shows that S.oneidensis MR-1 could reduce roxarsone to4-hydroxy-3-aminophenylarsonic acid in aqueous anaerobic environment.Dissolved Fe???could improve the reducing rate of roxarsone by S.oneidensis MR-1.One mmol/L Fe???could improve transformation rate by almost one order of magnitude compared with the control.Small amount of soluble Fe???can promote the biotransformation of roxarsone.When the Fe???concentration reach 6 mmol/L,the growth rate of S.oneidensis is slow down.It is illustrated that transformation rate is not proportional to Fe???concentration.And high concentrations of soluble Fe???may hinder the biotransformation process.?2?The influence of ferrihydrite absorbed roxarsone for the reduction by S.oneidensis MR-1.The result shows that ferrihydrite has good adsorption on roxarsone,and the maximum product formation rate increase with the ferrihydrite weight.The influence of phosphate for ferrihydrite shows that phosphate could compete with roxarsone for absorption spot,causing the decrease of arsenic on the surface of ferrihydrite.Ferrihydrite could form vivianite in aqueous phosphate condition.?3?The biotransformation process of roxarsone at the condition of different kind ofminerals.The result shows that S.oneidensis could reduce roxarsone under the condition of iron-containing minerals existence.Reduction rate is related to minerals'crystalline state.There is secondary mineralization in this process,forming vivianite in aqueous phosphate.