Pesticide washoff from concrete surfaces: literature review and a new modeling approach

Use of pesticides over impervious surfaces like concrete and subsequent washoff and offsite transport significantly contribute to pesticide detection and aquatic toxicity in urban watersheds. This paper presents a comprehensive study on pesticide washoff from concrete surfaces, including reviews of reported experiments and existing models, development of a new model, and its application to controlled experimental conditions. The existing modeling approaches, mainly the exponential function and power-law function, have limitations in explaining pesticide washoff processes characterized from experimental data. Here we develop a mathematical and conceptual framework for pesticide washoff from concrete surfaces. The new modeling approach was designed to characterize pesticide buildup and washoff processes on concrete surfaces, including the time-dependence of the washoff potential after application and the dynamics in pesticide washoff during a runoff event. One benefit is the ability to integrate and quantify multiple processes that influence pesticide washoff over concrete surfaces, including product formulation, aging effects, multiple applications, and rainfall duration and intensity. The model was applied to experimental configurations in two independent studies, and satisfactorily simulated the measured temporal variations of pesticide washoff loads from concrete surfaces for the five selected pyrethroids in 15 runoff events. Results suggested that, with appropriate parameterization and modeling scenarios, the model can be used to predict washoff potentials of pesticide products from concrete surfaces, and support pesticide risk assessments in urban environmental settings.