Desorption of organo phosphorous pesticides from soil with wastewater and surfactant solution

Surfactants can be introduced in the environment by wastewater discharge, point-charge pollution or deliberate action, e.g. to remediate contaminated soil or groundwater. The irrigation of soil with wastewater containing surfactants may modify pesticide desorption from soil, thus affecting their environmental fate. Desorption from soil of the plain of Granada (South-eastern Spain) of two organophosphorous pesticides, diazinon and dimethoate, differing in solubility and hydrophobicity, has been evaluated in the presence of different surfactant aqueous solutions and municipal wastewater. Soil was added with both insecticides and aged during two weeks. Batch experiments were performed for seven surfactants: a cationic (HDTMA), three anionic (Aerosol 22, Biopower and SDS), and three non ionic (Tween 80, Triton X-100 and Glucopone 600), municipal wastewater (MWW) from a secondary treatment (Granada municipal plant) and MilliQ water as a control. Besides, non ionic/anionic mixed-surfactants solutions were assayed. The insecticides were extracted from the aqueous solutions using microwave assisted extraction and analysed by gas chromatography. For any given solution, the greater desorption rates corresponded to the most polar insecticide, dimethoate. Single surfactant solutions affected insecticide desorption mainly depending on the surfactant type. When compared with MilliQ water the cationic surfactant enhanced both insecticides retention on soil, while the anionic and non ionic ones increased desorption rates for the most polar insecticide, dimethoate, decreasing those for diazinon. Additionally, the maximum percentage of insecticide extracted to the aqueous phase for non ionic and anionic surfactants was determined through linear regression. Non ionic/anionic mixed-surfactant solutions assayed, at concentrations including those normally found in wastewater, enhanced desorption rates for dimethoate. Desorption performed with MWW did not largely modify the desorption rate for both pesticides with regard to control water and for the assayed soil:solution ratio. The data obtained will require further consideration before establishing the factors responsible for this behaviour, since MWW constitutes a complex matrix, which can induce several changes in soil solution apart from those concerning surfactantstatus: publishe