腐殖质的光化学降解及其对环境污染物环境行为的影响

摘要

腐殖质是地表环境中最重要的有机组分，也是生态环境中最主要的吸光物质之一，对环境污染物的形态、迁移、毒性和生物可利用性有着重要的影响。文章综述了腐殖质的结构特征和光化学降解反应过程和机理，指出腐殖质的光敏化和光化学降解过程对环境污染物的环境行为和归宿有重要的影响。通常，腐殖质的光敏化作用在低质量浓度下，尤其在一定铁离子的协同作用下可促进有机污染物的降解，但高质量浓度的腐殖质由于其本身的吸光作用以及参与自由基的竞争则抑制有机污染物的降解。腐殖质的光化学降解过程降低了环境体系的pH和腐殖质的分子量、破坏了腐殖质的芳环结构、改变了紫外和可见光区域的吸收等，导致其与重金属离子和有机污染物结合能力的下降，造成水体或颗粒态中游离的污染物质量浓度增加，对生态系统将造成更大的危害。目前对腐殖质和环境污染物本身的光化学降解机理已较为清晰，今后应加强对自然水体或土壤系统中腐殖质光化学降解的影响因素，腐殖质光化学降解过程中结构特性的变化机理，以及腐殖质的结构特性与环境污染物结合性质之间的构效关系等方面的研究。特别是随着平流层臭氧空洞的增加，增强了到达地球表面的紫外线强度，研究紫外线增强对腐殖质和有机污染物的降解以及对生态系统的影响可进一步深刻理解太阳光辐射对污染物环境行为和归宿的影响。%Humic substance is the key organic component, and also one of the main light absorbents in ecosystem, which impacts on the environmental pollutants’ conformation, migration, toxicity and bioavailability significantly. This paper reviews the structure, and photochemical degradation reaction process and mechanism of humic substance. In general, humic substance promotes the photodegradation of pollutants at low concentration, especially with certain iron. However it depresses the photodegradation at high concentration due to the competition of sunlight and reactive oxygen species. Photodegradation of humic substance results in the decrease of molecular weight, aromatic ring and changes of absorbance of ultraviolet and visible region which lead to the lower binding capacity of pollutants and the higher free pollutant concentration. It would be more harmful to the ecosystem. Although it is clear of the mechanism of photodegradation of humic substance and pollutants, more attentions should be paid on the factors of humic substance photodegradation in water and soil system, the mechanism of photosensitive reaction and photodegradation of humic substance, and the relationship between the structure of humic substance and binding capacity of pollutants in the near future. With the increase of stratospheric ozone hole, it enhances the intensity of ultraviolet radiation to the earth's surface. To study the influences of ultraviolet radiation enhancement on the photodegradation of humic substance and pollutants and their impacts on the ecosystem would deep our understandings to the environmental pollutant behavior caused by sunlight radiation.