Photogeneration Of Environmentally Persistent Free Radicals From Granular Natural Organic Matter(NOM) In Water

Environmental Persistent Free Radicals?EPFRs?are a new kind of environmentally harmful substances,which are widely distributed in the environment and are even ubiquitous.They can induce the production of reactive oxygen species?ROS?and have a strong risk.Water,as one of the three major environmental factors in the world,contain large number of particulate organic matters,transition metal ions,and substituted aromatic compounds,which provide sufficient conditions for the formation of EPFRs.However,the study of EPFRs in water is absence at present.Therefore,it is of certain environmental significance to study the environmental origin and distribution of EPFRs and to provide new ideas for the generation of ROS on granular organic matter by investigating the production of EPFRs on particulate organic matter in water under natural light.In this study,we used montmorillonite?Mnt?and humic acid?HA?to represent the minerals and the NOM in the water respectively.And the montmorillonite-humic acid composite particles?Mnt-HA?were obtained by adsorption experiments to represent particulate organic matters.Through the laboratory simulated light experiments,we studied the generation of EPFRs and ROS in HA and Mnt-HA composite particles under light conditions by electron paramagnetic resonance techniques,and the influence of different environmental factors on the formation of EPFRs on Mnt-HA composite particles,such as HA content,metal ions and halogenated phenolic compounds.The main contents are as follows:1)HA contains EPFRs with a g-value of 2.00373 and line width??H?of 5.65 G,and irradiation can promote the production of EPFRs on HA;HA adsorbed with 2,4-DCP and?or?Cu²⁺can generate EPFRs under light conditions;2)The HA and HA+Cu²⁺+2,4-DCP systems both exist e^-and·OH without light.Under light conditions,e^-,·OH,and ¹O₂ were formed in the HA and HA+Cu²⁺+2,4-DCP systems.3)The EPFRs on Mnt-HA composite particles consist of two parts:one is generated by HA itself,the other is formed by Mnt-HA adsorbed with 2,4-DCP and?or?Cu²⁺under light conditions;irradiation also can promote the production of EPFRs on Mnt-HA.4)The higher the O/M,the more EPFRs are formed on the Mnt-HA composite particles;the lower the Cu²⁺concentration,the more EPFRs generates on Mnt-HA;at the same adsorption concentration,the ability of Cu²⁺,Fe³⁺,Zn²⁺,and Mn²⁺to generate EPFRs as follow:Fe³⁺>Zn²⁺>Cu²⁺>Mn²⁺;2 mM 2,4-DCP generated the most EPFRs,and too high and too low concentration of 2,4-DCP are not conducive to the generation of EPFRs;at the same adsorption concentration,bromophenol is more likely to generate EPFRs than chlorophenol,and 2-BP generated more EPFRs than 2,4-BP.5)By EPR spin trapping agents and spin labels techniques,it was found that e^-and·OH exist in the Mnt-HA-Cu²⁺-2,4-DCP system in the absence of light,but only e^-is present in the Mnt-HA system.Under light conditions,e^-,·OH and ¹O₂ were formed both in the Mnt-HA and Mnt-HA-Cu²⁺-2,4-DCP systems.