Pesticide adsorption and degradation in fine earth and rock fragments of two soils of different origin C. Vischetti a, ⁎, G. Corti a , E. Monaci a , S. Cocco a , L. Coppola a , A. Agnelli b a Dipartimento di Scienze Ambientali e delle Produzioni Vegetali, Università Politecnica delle Marche, via Brecce Bianche, 60131 Ancona, Italy b Dipartimento di Scienze Agrarie ed Ambientali, Università degli Studi di Perugia, Borgo XX Giugno, 06121 Perugia, Italy abstract article info Article history: Received 29 June 2009 Received in revised form 25 September 2009 Accepted 6 November 2009 Available online 27 November 2009 Keywords: Pesticides Rock fragments Adsorption Degradation The soil skeleton (larger than 2 mm fraction) can provide a source of organic carbon which may represent an unexplored possibility of adsorbing and degrading pesticides. The present paper reports a laboratory experiment on the adsorption of metobromuron and terbuthylazine on the skeleton and fine earth of two Italian soils derived from two parent rocks, a calcareous marl and a sandstone. K F values of 1.30 and 2.22 for metobromuron and 1.24 and 2.21 for terbuthylazine were found in the fine earth of sandstone and calcareous marl, respectively. Surprisingly, the soil skeleton, intended as the 2–10 mm fraction, showed a good adsorption capacity of about 40% and 20% with respect to the fine earth fraction for sandstone and calcareous marl soils, respectively. The derived K oc values for the skeleton turned out to be much higher than those of the fine earth indicating an adsorption activity of organic carbon in the skeleton higher than that of the fine earth. Pesticide degradation followed first order kinetics in all samples and half-life values in the skeleton were in the same range as those in the fine earth demonstrating a biodegradation activity of this substrate. A degradation trial in sterilized skeleton of the two soils supports the previous statement, since degradation was almost absent. The experiment performed indicated a possible contribution of the soil coarse fraction to pesticide adsorption and degradation, helping in their disappearance from the environment. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Adsorption and degradation of pesticides in soils have been studied over the last few decades as the main processes aimed to reduce the available concentration responsible for environment contamination. Usually, laboratory studies are carried out in batch equilibrium experiments to determine adsorption parameters such as K oc , K F and 1/ n, and incubation over time to determine degradation parameters such as k and t 1/2 . All these parameters were useful to evaluate pesticide persistence and mobility through the soil profile and to improve pesticide fate models that either provide predicted environmental concentrations or simulate environmental fate of pesticides (FOCUS, 2000; Footprint, 2009). These studies started from the assumption that the adsorption and degradation phenomena are limited to the interaction between pesticides and fine earth through the formation of several physical, physico-chemical and chemical interactions of electrostatic, chelating and hydrophobic nature (Wauchope et al., 2002) and through the action of soil microbial biomass able to degrade and transform the parent molecules. Soil skeleton is the fraction that comprises particles larger than 2 mm and its prominent inorganic nature usually leads to neglect its presence in soil for aspects related to soil fertility and biological activity. Nonetheless, many studies have demonstrated the capacity of soil skeleton to supply a pool of available nutrients (Ugolini et al., 2001; Holscher et al., 2002; Heisner et al., 2004), and this would be expectable as, at least in some cases, the rock fragments manifest a cation exchange capacity similar to that of the fine earth, less than 2 mm soil fraction (Ugolini et al., 1996; Corti et al., 1998). On the contrary, not many studies have explored the possibility of soil skeleton supplying an additional source of organic carbon. Corti et al. (2002) studied 26 soils with different skeleton content coming from different parts of the world and found that rock fragments may contain substantial amounts of organic carbon. These findings suggest a possible effect of the soil skeleton on adsorption and degradation of pesticides, especially in the case of porous rock fragments such as those that form soils coming from volcanic and sedimentary parent materials. This research deals with the evaluation of adsorption and degradation of two commonly used pesticides (metobromuron and terbuthylazine) by fine earth and the rock fragments of two soils Geoderma 154 (2010) 348–352 ⁎ Corresponding author. Tel.: +39 071 2204264; fax: +39 071 2204856. E-mail address: c.vischetti@univpm.it (C. Vischetti). 0016-7061/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2009.11.006 Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma