Characterization of the sorption of an anthranilate fungicide in soil using thermal analytical and mineralogical techniques

The sorption of pesticides to soil particles has implications for their distribution and fate in the soil environment. A batch equilibrium technique was used to investigate sorption of the fungicide AEC623892 to intact and hydrogen-peroxide-treated whole soils and several particle-size fractions isolated from them. Sorption of AEC623892 to the soil as a whole was low. K(f oc) values measured in the whole soils were 169.2 and 41.9 ml g(-1) for Soil A and Soil B respectively. The highest values of K(f oc) were measured in soil particle-size fractions <53 microm (266.5 ml g(-1) in the 2-20 microm fraction of Soil A; 471.9 ml g(-1) in the 20-53 microm fraction of Soil B). Sorption was most irreversible in the 2-20 microm fractions. Overall, treatment of soil particle-size fractions with hydrogen peroxide resulted in lower values of K(f oc) (112.3 ml g(-1) in Soil A whole soil and 30.9 ml g(-1) in Soil B whole soil). In both soils, the maximum sorption among hydrogen-peroxide-treated samples was observed in the <2 microm fraction (166.6 and 311.0 ml g(-1) for Soil A and Soil B, respectively). Investigation of the mineralogical composition of the soils suggested that the clay mineralogy (dominated by kaolinite and illite) is less likely to account for the differences in sorption observed than differences in the characteristics of the soil organic matter. Thermal analysis of the different soil fractions indicated that hydrogen peroxide treatment preferentially removed aliphatic fractions of organic matter, but had less effect on lignin-like, aromatic fractions.