Mechanism On Photochemical Transformation Of Dibutyl Phthalate Plasticizer And Its Metabolites In Aqueous Solution

Phthalate esters（PAEs）are widely used as plasticizers in various plastic products.The environmental pollution levels,ecotoxicology and behavior fate have caused serious concern of experts.Most of them,however,focuses on the analysis of the concentration of free-body pollutants in environmental media and effects of the toxicological on organisms.It is few reports that states the environmental behavior of their conjugated states.According to latest toxicological research results,the conjugated PAEs organic pollutants and their metabolites may have stronger bioavailability.Thus,they may have greater impact on the aquatic environment.Photodegradation is the main removal pathway of phthalates and their metabolites in natural water,but their photochemical conversion mechanism is still unclear.Dibutyl phthalate（DBP）,monobutyl phthalate（MBP）and phthalic acid（PA）are taken as representatives and are systematically explored the photodegradation process of DBP,MBP and PA under the condition of ultraviolet light or simulated sunlight and the influence of concentration,p H,photosensitive substances(FA,NO₃^-,Fe³⁺,Fe³⁺-FA complex)on the photodegradation in this article.The results show that DBP,MBP and PA cannot undergo direct photolysis under simulated sunlight,but can undergo indirect photolysis in the presence of Fe³⁺or Fe³⁺-FA complexes as photosensitizer and the photodegradation rate increases with the increase of the concentration of photosensitive substances.Hydroxyl radicals（·OH）is the main reactive species of the photosensitization of and Fe³⁺or Fe³⁺-FA complex and ³FA^*is also contribute to the photodegradation in the presence of FA.It is more effective in alkaline environment conducive to the direct photodegradation of DBP under ultraviolet light and more conducive to the direct photodegradation of MBP and PA under acidic environment.·OH also plays a crucial role of promoting photodegradation of DBP,MBP and PA in NO₃^-aqueous solutions.FA at low concentration has positive effect on the photodegradation of three substances above,but and significantly inhibits the photodegradation of DBP,MBP,and PA because of light shielding effect caused by high concentration of FA.Through the qualitative analysis of photoactive substances using LFP and ESR,it is further verified that the ³FA^*and·OH produced during the reaction are the main substances that promote the phototransformation of dibutyl phthalate and its metabolites.This study clarified the photodegradation pathway and mechanism of dibutyl phthalate and its metabolites in natural water and provides a theoretical support so that comprehensively and objectively evaluate the environmental effect and behavior of dibutyl phthalate as well as its metabolites in environment.