Influence Mechanism Of Dissolved Organic Matter On Photodegradation Of Polycyclic Aromatic Hydrocarbons

Dissolved organic matter (DOM) is ubiquitous in aquatic environment and has special photochemistry properties. Recent studies showed that DOM could affect photochemical behavior of coexisted organic pollutants. Polycyclic aromatic hydrocarbon (PAHs) is a class of persistent organic pollutants which have caused intensive attentions due to their carcinogenicity, terato genicity and mutagenicity. A series of studies indicated that DOM could affect photodegradation of PAHs, but the mechanisms are not well defined. To clarify environmental fate and ecological risk of PAHs more clearly, it is necessary to conduct further study of mechanisms and effects of DOM on the photodegradation of PAHs. Therefore, acenaphthene (Ace) and pyrene (Pyr) were selected as model compounds. Simulate solar photolysis experiments of acenaphthene and pyrene were conducted with a500W Hg lamp as light source, and roles of reactive oxygen species (ROS) and binding effect were examined.Photodegradation of Ace was promoted by DOM and photolysis rate constants of Ace in DOM solutions are different. The photolysis of Ace in LHA, EHSA, NAHA, ALHA, SRFA were2.32,1.78,1.43,1.26,1.12times of that in pure water. ROS generated by DOM were responsible for the promotion effect and contribution of reactive oxygen species depended on the origin of DOM. The contribution of singlet oxygen and hydroxyl radical of ALHA, LHA, EHSA, NAHA, SRFA were40.3%and23.0%.29.4%and2.2%,36.3%and6.0%.26.2%and16.9%.31.4%and14.1%respectively. EPR spectra of DOM indicated that singlet oxygen and hydroxyl radical were detected in all DOM solution.Inhibition effects were observed in photodegradation of Pyr in DOM solutions. Photolysis rate constants of Pyr in pure water, LHA, EHSA, NAHA, ALHA, SRFA were0.88,0.42,0.46,0.55,0.68,0.74h-1respectively.The influence of reactive oxygen species on the photodegradation of Pyr was not obvious compared with Ace. Light screening and quenching by DOM is the main mechanism of inhibition. Effects of DOM on the photodegradation of PAHs depends on reaction rate constant of reactive oxygen species and binding constants of PAHs.Except for light sheiding, quenching of excited states of Pyr was caused by interaction with DOM. A combined quenching of dynamic and static mechanism was observed in quenching of Pyr, and the contributions of dynamic and static quenching were different in different DOM. The inhibited effect of DOM on photodegradation of Pyr demonstrated strong concentration-dependent. In addition, another Hydrophobic organic compound(BDE-47) was selected to verify the mechanism further. Results indicated that quenching effect of DOM to BDE-47was static quenching and increased with the binding ability of DOM.