Characterization Of HA Fractions Fractionated From Soil Humic Substance And Study On Their Photochemical Effects

Humic substances, the most widespread organic compounds in nature, account for 50～80 percent of the total organic compounds in the soil, hydrosphere and ecosphere. Previous studies revealed that, humic substances play important roles in the environmental behaviour of organic contaminants. Obviously, the environmental behaviour of humic substances is interrelated closely with their structures. However, humic substances are ununiform organic compounds with complex structure and high molecular weight. So it is necessary to fractionate the humic substances to relatively uniform fractions, which can help us understand this kind of substances and their behaviour.In this study, HAs extracted from conifer forest soil in Dalian, Liaoning Province and deciduous forest soil in Jilin Province using standard method proposed by IHSS, were fractionated by SDS-polyacrylamide gel electrophoresis and chromatography, and the apparent molecular weights of the HAs and their fractions were calculated by gel chromatography. The effect of HAs and their fractions on phenol photodegradation under high-pressure mercury and xenon lamps were also investigated.The results indicated that â‘  the extracted HAs were devided into 4 fractions with apparent molocular weights of 16531, 32084,49223, and 77678 respectively. â‘¡ The UV-Vis spectra showed that the absorbency of HAs and their fractions decreased with increasing wavelength, and at the same concentration (expressed by TOC), the absorbency of HA fractions increased with increasing apparent molecular weight. â‘¢ E₄/E₆ was negatively relative to the apparent molecular weight of HA fractions, with R² = 0.9824. â‘£ FTIR spectra revealed that the four HA fractions had different molecular structures. Fractions with lower apparent molecular weight have more oxygen, aromaticity groups and less aliphatic groups. However, the higher molecular weighted fractions behaved on the contrary. ⑤ HAs, at different concentrations, inhibited phenol photodegradation under high-pressure mercury and xenon lamp, and the inhibition became more significant when HA concentration increased. The inhibition was attributed to the competition to absorb photons and the shield for phenol by HAs.â‘¥At the same concentration of HAs, the inhibition of HA fractions with higher apparent molecular weight was more significant than that of lower apparent molecular weighted ones, which was due to the stronger shield for phenol by larger moleculars.