Soil hydrophobicity: a contribution of diuron sorption experiments

Abstract

Retention processes play a major role in the fate and impact of organic contaminants in soils. The main goal of this study was to determine the influence of soil hydrophobic properties on the retention of diuron by using plots of a long-term experiment in Versailles. We selected seven plots with pH 3.4 to 8.2 and low organic content. Sorption isotherms were obtained on soil slurries and kinetic measurements of diuron sorption were performed on undisturbed soil samples. The results showed that the Freundlich coefficient k f decreased as pH increased and that the K oc coefficient, k f /TOC, was linearly related to the contact angle measured on the clay fraction over a wide range of pH. A low initial adsorption rate and low adsorption equilibrium were observed for the plot treated with NaNO 3 . In this case, the structure in micro-aggregates was assumed to limit the accessibility of adsorption sites. The CaCO 3 and CaO treated plots had similar organic matter contents, pHs, CECs and bulk densities, although their < 2 mm:C ratio differed. The higher retention of diuron in the CaCO 3 plot is attributed to the higher hydrophobicity of the < 2 mm fraction, probably masking part of the permanent clay negative charges. Thus, in addition to the different treatments, organic matter composition and distribution should also be included as specific soil properties. We conclude that the sorption properties of pesticides such as diuron can be a good tool to obtain greater understanding of soil properties and the degree of soil hydrophobicity/hydrophilicity in particular.

Sorção e dessorção do diuron em quatro latossolos brasileiros

“…A taxa de sorção nos solos decresce com o aumento da concentração do diuron no solo, pois há diminuição da disponibilidade dos sítios de sorção deles. Os resultados encontrados estão de acordo com os de outros estudos, que demonstraram a adequação da equação de Freundlich Cs (mg kg para descrever a sorção do diuron nos solos (Inoue et al, 2006;Yu et al, 2006;Chaplain et al, 2008).…”

Sorção de Diuron em minerais da fração argila

“…Neste caso, também há favorecimento, além das ligações de H, de interações dipolo-dipolo (van der Waals), pois essas associações são mais significativas para moléculas em contato mais próximo com a superfície adsorvente. 47 A capacidade de adsorção maior em pH 7,0 em relação a pH 3,5 difere de resultados obtidos por outros pesquisadores, 17,56,57 que observaram maior adsorção de Diuron quanto maior a acidez. Porém, as condições de adsorção foram diferentes: Bailey et al 56 estudaram apenas esmectita, a qual apresentou condições intermediárias no presente estudo quando comparada aos óxidos de Fe; Chaplain et al 57 e Liu et al 17 estudaram solos (terra fina seca ao ar) com a presença de matéria orgânica, o que pode dificultar bastante a comparação, visto que os coloides orgânicos, além de apresentarem outros mecanismos de adsorção, podem cobrir as superfícies minerais alterando, portanto, o processo de sorção.…”

Fate of Pesticides in Soils: Toward an Integrated Approach of Influential Factors

“…The cosθ is related to the liquid and solid interactions by the Young-Dupré equation and the polar and apolar components of these interactions can be measured using appropriate solvents (Van Oss, 1994). We suggest that diuron can be used as a reference pesticide to characterize the global hydrophobicity of soil due to its high chemical stability in a large range of pH (Chaplain et al, 2008). Finally, as drying is known to enhance soil hydrophobicity (Diehl et al, 2009), an increase in the sorption of pesticide by re-wetting soils is expected but this is poorly described (Lennartz & Louchart, 2007).…”

“…Pesticide movement through aggregated soils is mainly controlled by kinetic sorption and diffusion (Beulke et al, 2004). In static conditions, the rate of pesticide adsorption decreases when the density of soil aggregates increases (Chaplain et al, 2008). In dynamic conditions, retention depends on transport parameters such as pore water velocity and residence time (Pot et al, 2005;.…”

“…High molecular weight and high surface area confer to the organo-clay complex a major role towards the retention of pesticides in soils. For example, the wettability of the clay fraction, characterized by the contact angle θ of water drop deposed on a thin air dried film, is directly related to the retention of diuron by the soil (Chaplain et al, 2008). The cosθ is related to the liquid and solid interactions by the Young-Dupré equation and the polar and apolar components of these interactions can be measured using appropriate solvents (Van Oss, 1994).…”