Graber, E.R., Institute of Soils and Water, Volcani Center, ARO, P.O. Box 6, Bet Dagan 50250, Israel
Sluszny, C., Institute of Soils and Water, Volcani Center, ARO, P.O. Box 6, Bet Dagan 50250, Israel
Gerstl, Z., Institute of Soils and Water, Volcani Center, ARO, P.O. Box 6, Bet Dagan 50250, Israel

Abstract. The aim of this work was to examine the effect of organic soil amendments (municipal sewage sludge and composted municipal sewage sludge) on transport ideality, sorption equilibrium, and s-triazine (atrazine, simazine, ametryn, and terhuthylazine) retardation compared with nonamended soil. Organic-matter amendment resulted in increased nonequilibrium sorption effects, including early breakthrough, increased breakthrough, and elution front-tailing. Organic amendments likewise caused greater solute retardation compared with transport in nonamended soil columns. AS the organic matter content increased, retardation increased and the desorption rate constant decreased. The fraction of fast sorption sites also decreased, resulting in greater sorption non-equilibrium. In a given column, the fraction of fast sorption sites was essentially equal for she different s-triazine compounds. The desorption rate constant decreased as the organic carbon partition coefficient (K(oc)) increased in the order atrazine > simazine ≤ ametryn > terbuthylazine. Soil amendment with sludge and compost resulted in some nonideal physical transport, which was negligible compared with sorption nonideality effects. The linear sorption isotherm nonequilibrium (LNE) model adequately simulated the measured breakthrough curves. The breakthrough curve for ametryn in an amended, nonrinsed column was identical to that in an amended, rinsed column, indicating that sludge-/soil-derived dissolved organic carbon did not affect ametryn sorption and transport in this system.