Transport of dimethoate through a Mediterranean soil under flowing surfactant solutions and treated wastewater

Surfactants, which are emitted to soils mainly through wastewater disposal and also for remediation purposes, can alter pesticide sorption/desorption as well as the water flow through the soil. As a consequence, pesticide mobility may change and affect groundwater quality. Therefore, a deep insight into the coupled transport of pesticides and surfactants is necessary and helpful for contamination prevention and remediation. Dimethoate leaching was performed after flowing wastewater and surfactant solutions (Tween 80 and sodium dodecyl sulfate, SDS) through disturbed soil columns. To identify relevant parameters related to dimethoate mobility, breakthrough curves were fitted with convection dispersion (CDE) transport model. In all cases, the elution peaks showed a rapid release in the early tailing followed by a much slower release in the extended tailing with a retention factor close to 1, as corresponds to a weakly retained compound. CDE non-equilibrium parameters showed that, independently from the leaching solution employed, most of the pesticide was transported in the solution phase (convective transport). Infiltrated volume for wastewater was the highest (2× Tween and 5× SDS) for the same infiltration period, which increases the risk of early groundwater pollution. On the other hand, SDS decreased soil permeability providing a slight retention of dimethoate on soil, mainly in the lower column layer.