Chemical Extractions Affect the Structure and Phenanthrene Sorption off Soil Humin

摘要

Humin is a major fraction of soil organic matter and strongly affects the sorption behavior and fate of organic contaminants in soils and sediments.This study evaluated four different extraction methods for soil humins in terms of their organic carbon structural changes and the consequent effects on phenanthrene sorption.Solid-state ~(13)C NMR demonstratedthat 0.1 M NaOH exhaustively extracted humin and humin extracted with 6 M HF/HCI at 60 deg C had a relatively high amount of aliphatic components as compared with 1 M HF-extracted humin.The treatment of 6 M HF/HCI at 60 deg C greatly reduced carbohydrate components(50-108 ppm)from humin samples,i.e.,more than 50% reduction.In addition,the humin from this 6 M HF/HCI treatment contained relatively more amorphous poly(methylene)domains than the humins extracted by other methods.With the respect to phenanthrene sorption,the linearity of sorption isotherm(N)and sorption affinity(K_(oc))varied markedly among the humin samples extracted by different methods.The NaOH exhaustively extracted humin had the most nonlinear sorption isotherm and the HF-extracted humin had the lowest K_(oc).It is concluded that humin samples from different extraction procedures exhibited substantial differences in their organic carbon structure and sorption characteristics,even though they were from the same soil.Therefore,one needs to be cautious when comparing the structural and sorption features of soil humins,especially when they are extracted differently.The 6 M HCI/HF extraction at elevated temperature is not encouraged,due to the modifications of chemical structure and physical conformation of organic matter.