Study On Isolation Of Organic Matter Subfractions Obtained From Soil And Intetaction With Carbamate Pesticides

Humic substances (HS) is a mixture of various organic substances including organic macromolecules derived from the remains of plants and animals through complicated physical, chemical and biological processes, widely occurring in environmental such as atmosphere, water, soils, sediments and so on. In accordance with its varying solubility under different acidity and alkalinity conditions, HS can be separated into fulvic acid (FA, soluble at all pHs), humic acid (HA, insoluble at pH1), and humin (HM, insoluble at all pHs). As the important part of the natural organic material, HS not only the main places of hydrophobic organic contaminants, but also the important complexing agent or adsorbent of environmental pollutants, as well as, its had potential effects on environmental behavior, toxicity and bioavailability of various pollutants. Recently, HS has become the theoretical basis of the research focus and environmental pollution control and treatment technology concern.In this paper, soil was collected from the Jiufeng Mountain forest in North China Plain with typical characteristics of yellow soil region. The XAD-8adsorption technique coupling with stepwise elution using pyrophosphate buffers with initial pH3,5,7,9, and13was developed to fractionate the FA into five sub-fractions. Six sub-fractions of HA were isolated by adding0.02mol/L Na4P2O7,0.05mol/L Na4P2O7,0.1mol/L Na4P2O7,0.05mol/L NaOH,0.1mol/L NaOH, and0.25mol/L NaOH tandem. The sub-fractions of FA and HA were characterized by elemental analysis, Fourier transform infrared, UV-visible spectroscopy,13C-NMR, high performance size exclusion chromatography, fluorescence spectroscopy and potentiometric titration technique. Fluorescence quenching titration method was used to study the interactions between HS with carbamate pesticides and the mechanisms of the interactions were discussed. Fluorescence quenching titration method was used to study the interactions between FA, HA, sub-fractions of FA and HA with carbamate pesticides and the mechanisms of the interactions were discussed. The followings results can be summarized: 1、The XAD-8adsorption technique coupling with stepwise elution using pyrophosphate buffers with initial pH3,5,7,9. and13was developed to fractionate the FA into FApH3,FAph5, FApH7, FAph9and FApH13. the mass ratio of FA subfractions was42:36:14:5.0:2.5. FA subfractions accounted for about97.0%～98.5%of total FA in weight compared to FA isolated using the method recommended by IHSS. The mass ratio of HA1, HA2, HA3, HA4, HA5and HA6were26:16:12:25:11:9eluted with0.02mol/L Na4P2O7,0.05mol/L Na4P2O7,0.1mol/L Na4P2O7,0.05mol/L NaOH,0.1mol/L NaOH, and0.25mol/L NaOH tandem.2、The O contents, polarity, SUVA280. molecular weight, the content of carboxylic groups and total acidity decreased, and the C contents,ratio of H/C and amounts of aliphatic carbon increased for sub-fractions of FA and HA with elution sequence,the protein-like materials in FApH7, FApH9, and FApH13. The separation mechanism of stepwisely elute FA adsorbed on XAD-8according to the difference of deprotonization at different pH values for carboxylic and phenolic groups, the difference of isoelectric points for different protein-like substances, and size exclusion interaction. With different concentration of Na4P?O7/NaOH may be extracted different composition and chemical structure of the HA sub-fractions from the same soil FA and HA further separation will be beneficial for FA and HA complex chemical structures and interaction with environmental pollutants.3、The intrinsic fluorescence of carbofuran and carbaryl were quenched by the FA and HA,as well as, the intrinsic fluorescence of carbaryl were quenched by the FA fractions and HA fractions, and static quenching was the primary mechanism. The association constants (1g K) were estimated using fluorescence static quenching model(FSQM) and1g K ranged from3.92～4.96,1g K was correlated with aromaticity,alkyl, total acity and O contents. The hydrophobic force is the main interactions between carbamate pesticides with HS, hydrogen bonding slightly affects the bonding of carbamate pesticides and humic substances. HS bounded carbamate pesticides about32%～61%was evaluated in the natural water.