Formation Of Natural Organohalogens Catalyzed By Chloroperoxidase

As a typical environmental pollutant,Organohalogens(OHs)are arousing more and more concern all over the world.Studies of recent decades have confirmed the existence of natural sources of halogenated organic contaminants in the environment,and the detected types of natural OHs have been continuously increasing.However,research in related fields at both regional and international level has just started.This article summarizes the marine,land and other sources of natural OHs and the background concentrations of several representative compounds.This thesis explained the biotic and abiotic process to form OHs,interpreted the migration,transformation and fate of natural OHs in the environment,and discussed the research progress of chloroperoxidase.In this paper,with phenol acts as organic substrate,we explored the formation of natural halogenated organic compounds under the catalysis of chloroperoxidase(CPO).The qualitative and quantitative analyses of the structure of the products were performed by liquid chromatography-mass spectrometry(LC-MS/MS)and high performance liquid chromatography(LC-HPLC),respectively.The effects of the concentration of the reactants,pH,and reaction time on the enzymatic reaction were also investigated.To further explore the formation of natural halogenated organic compounds under the catalysis of CPO when considering natural organic matter as a precursor,we characterized the structural of five types of dissolved organic matter in soil by means of elemental analysis,infrared spectrum analysis and ultraviolet spectrum analysis.Fourier transform ion cyclotron resonance mass spectrometry(FT-ICRMS)was also used to analyze the change of the structure and species of that organic matter during experiments.The main conclusions and innovations achieved in this study are as follows:(1)It was proved that under the catalysis of CPO,when H2O2 is present,phenol and inorganic chloride ions can be halogenated to produce chlorophenols,while the dominate products are composed of p-chlorophenol and o-chlorophenol,and during this process,hydrolysis and polycondensation of the benzene ring would occur.The toxicity evaluation experiment of Vibrio fischeri confirmed that the toxicity of the substrate after the enzymatic reaction was significantly enhanced.The pH value has a significant effect on the catalytic reaction of CPO.The acidic condition is more conducive to the progress of the reaction,while under alkaline condition the reaction can barely process.The lower the pH,the higher the yield of chlorophenol products.The concentration of each reactant may directly affect the yeilds of the product.When the concentration of phenol increased,the production of p-chlorophenol and o-chlorophenol first increased and then decreased.When the concentration of chloride and hydrogen peroxide increased,the amount of product increased at beginning and then stabilized.The production of chlorophenols can be detected even when the substrate concentrations are extremely low.However,phenols,inorganic chlorides,H2O2 and CPO are ubiquitous in the environment indicating that the formation of OHs of this pathway can commonly occur in environment.Being different from other synthesis and degradation reactions of microorganisms in nature,this enzymatic reaction does not cost a long period of time.Therefore,the formation of natural OHs may bring great environmental risks.(2)It was ascertained how the structure and composition of natural organic matter changes before and after reaction under the catalysis of chloroperoxidase in the presence of H2O2 and inorganic chloride ions by FT-ICR-MS.Three representative DOM samples were analyzed and there is a background OHs in each soil sample.The total amount of organic matter and chlorine-containing organic matter in sediment sample was the largest,followed by aging plants sample,and the least in fresh plants sample.Because the sediments submerged in water,of which the degree of humification is the highest.The distribution of organic matter in three soil samples was mainly categorized into two areas of highly unsaturated phenolic compounds and plant-derived polyphenols.After the reaction,a considerable amount of inorganic chlorine is converted to Organochlorine,leading to the OHs increased by 19.7-137.6%above the original background value,and the formed chlorine-containing organic matter is mainly distributed in two areas of highly unsaturated phenolic compounds and plant polyphenolic compounds.The lake soil sample,which is rich in aromatic benzene rings produces the most abundant natural OHs.Finally,according to the toxicity evaluation experiment of Vibrio fischeri,in the process of CPO enzyme catalyzing natural organic matter to form natural Organohalogens,the organic toxicity increases,so the process would pose certain environmental risk.