腐殖酸的光化学过程模拟及其对五氯苯酚结合系数的影响

Simulated photochemical process of humic acid and its effects on binding of pentachlorophenol

研究了2种有代表性的腐殖酸:美国Swuannee河提取的腐殖酸(国际腐殖酸协会标准)和德国森林土壤腐殖酸,在模拟太阳光照射过程中不同照射时间、溶解氧浓度和入射光波长范围对五氯苯酚结合性质的影响。结果表明腐殖酸经模拟太阳光照射后,其与五氯苯酚的结合系数Koc下降。光化过程中腐殖酸的分子量或SUVA270与lg(Koc)之间有良好的线性关系。溶解氧浓度的升高能加速腐殖酸的光氧化,使结合系数进一步下降。氮气饱和条件下照射则使腐殖酸与五氯苯酚的结合系数升高。UV-B、UV-A和可见光部分对Swuannee河腐殖酸与五氯苯酚的结合系数Koc的下降的贡献分别为18%、47%和35%。

The impact of photo-oxidation of German soil humic acid and Suwannee river humic acid(IHSS standard) on their affinity for binding pentachlorophenol(PCP) was studied.The effects of O_2 abundance,wavelengths of incident light,and pH value on photo-alteration of binding coefficient(K_(oc)) were discussed.Solar-simulated irradiations substantially decreased the PCP binding affinity to humic acids.After 24 hours of irradiation,K_(oc) decreased by 48% and 39%,for SRHA and FSHA respectively.The decreases of K_(oc)(corrected for photo-induced pH value changes) were positively correlated with the decreases of the molecular weight and aromaticity of humic acids in the time-course of irradiation.Increasing O_2 abundance accelerated the decreases of the binding affinities as a result of enhanced photo-degradation of humic acids while increased the K_(oc) under N_2-saturated irradiations.For the decrease of K_(oc) in SRHA,the relative contribution in ascending order was UV-B(18%),visible(35%),and UV-A(47%).Visible light played a more important role in reducing the molecular weight and aromaticity of humic acid(and hence its binding affinities) than in reducing the content of dissolved organic carbon(DOC) while vice versa for UV radiation,indicating that photochemical reduction of the binding affinities may occur in natural waters at depths deeper than UV radiation can reach.