To estimate the treatment load of pesticides for wastewater treatment plants (WWTPs) on an urban scale, we developed a SWMM-based screening model that integrates the mass balance of pesticides in residential soil and the storm-water runoff passing through residential lawns. Furthermore, we introduce an approximate approach that simplifies the simulation using the octanol-water partition coefficients (i.e., log K-ow) of pesticides. The results indicate that the simulated transport factors (i.e., the dissipation kinetics-relevant property from the soil) of systemic pesticides (i.e., log K-ow < 2.0) are constant, whereas those of non-systemic pesticides decrease with increasing log K ow , indicating that highly lipophilic pesticides are thermodynamically favored for soil absorption. By using the approximate approach, we estimated the total mass of pesticides entering the urban sewer system and the pesticide concentrations in the influent of WWTPs for a midsize city. The results indicate that the estimated concentration of systemic pesticides in the influent is -9.2 ng L-1 and that of pesticides with log K-ow values above 3.0 is below 0.84 ng L-1. The pesticide concentrations are consistent with published field data, indicating that the approximate approach can be applied as preliminary modeling tool to recommend pretreatment values for urban WWTPs. Although the model must be further validated and refined using field data, the screening method can be used to help urban planners and engineers to manage the treatment process of pesticides in WWTPs.
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