In many countries around the world, municipal sewage and industrial wastewaters are typically treated, or sometimes only partially treated, prior to their discharge into surface waters. A major anionic surfactant, Linear Alkyl benzene Sulfonate (LAS), and a degraded product of a non-ionic surfactant, Nonylphenol (NP), are frequently found in municipal wastewaters. When wastewater containing such surfactants and their degraded products is used for irrigation, it can have an effect on the sorption/desorption and movement of pesticides in soils. Therefore, a lysimeter study was conducted, in summer 2004, to assess the effect of LAS and NP on the movement of agricultural herbicides through a sandy loam soil. The degradation of the herbicides was studied in lysimeters over a ninety-day period. Irrigation water with a concentration of 12 mg L -1 of LAS and NP was used to assess their effect on the leaching of atrazine, metolachlor, and metribuzin. Moreover, a laboratory sorption experiment was undertaken to estimate the partition coefficients (kd) of the three herbicides with water containing the same concentrations of LAS and NP. Irrigation water containing low concentrations of surfactants (LAS and NP) did not increase leaching of the three herbicides. Therefore, these results would reduce the concerns regarding pesticide leaching through sandy soil brought on by LAS and NP in wastewaters for irrigation, which is becoming more important due to increasing water scarcity in the dry climate regions of the world. / Beside the lysimeter study, mathematical models can be used effectively and economically in a very short period of time for simulating herbicide concentrations into soil. PESTFADE, a one dimensional transient flow model, was used, in this study, to simulate the fate of the three herbicides in sandy soils. Another model, Artificial Neural Network (ANN), was also used over mathematical modeling due to its faster execution period and less input parameter requirements, for predicting the concentrations of the three herbicides in a sandy loam soil. The predicted concentrations, from both models were compared with the experimental results from the lysimeter study. Although slight overestimations and underestimations were observed, both models simulated herbicide concentrations in the soil profile satisfactorily.

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