Sorption and desorption of diuron on Typic Argiudoll, Oxic Argiudoll and on their clay fractions: environmental aspects

Abstract The sorption and desorption of diuron by soil samples from Horizons A and B (HA and HB) and by their different clay fractions were investigated, using two soil samples, classified as Typic Argiudoll and Oxic Argiudoll. The sorption and desorption curves were adjusted to the Freundlich model and evaluated by parameters Kf, Kd and Koc. Based on the data of groundwater ubiquity score (GUS), leachability index (LIX) and hysteresis index (HI), the risk of groundwater pollution was evaluated. The Kd values obtained for soil samples were between 4.5 mL g−1 (Oxic Argiudoll – HB) and 15.9 mL g−1 (Typic Argiudoll – HA) and between 1.13 and 14.0 mL g−1 for the different mineral fractions, whereas the Koc values varied between 276 (Oxic Argiudoll – HB) and 462 (Typic Argiudoll – HA). According to the parameter GUS, only Oxic Argiudoll – HB presented leaching potential, and based on the LIX index this same soil presented the highest leaching potential. Some samples presented low LIX and GUS values, indicating no leaching potential, but none presented HI results indicative of hysteresis, suggesting weak bonds between diuron and the soil samples and, hence, the risk of groundwater pollution by diuron.