Removal of Urban-Use Insecticides in a Large Open-Water Wetland Pond

Worsening freshwater scarcity has heightened the need for treatment technologies capable of eliminating chemical and biological contaminants to allow for the beneficial use of traditionally underutilized water resources. In urbanized arid and semiarid regions such as California, urban drainage represents an increasingly important water source for augmenting water supply. However, monitoring shows that urban streams are contaminated ubiquitously with urban-use insecticides (e.g., pyrethroids and fipronil) that have broad-spectrum toxicity. In this study, a large open-water wetland pond (OWWP), characterized by shallow water depth and the absence of permanent vegetation, was evaluated for the removal of pyrethroids and fipronil (and its biologically active degradates). Concentration-based removal and changes in the pesticide mass flux were calculated to determine the efficacy of the OWWP. Toxic units for indicator aquatic invertebrates were estimated before and after the OWWP treatment to determine reductions in potential aquatic toxicity. Contaminant concentrations in water and sediment consistently decreased as the water was moving through the OWWP. Concentration-based removals were 44.2–100% for fipronil compounds, 61.8–100% for bifenthrin, and 47.3–92.7% for cyfluthrin, and the removal was attributed to sedimentation, in situ microbial degradation, and photolysis. The mitigation of these urban-use insecticides by the OWWP was similar to that of a densely vegetated constructed wetland at the same site. Therefore, OWWPs represent a low-maintenance and effective wetland configuration for large-scale water reclamation and may be particularly useful for arid and semiarid regions with favorable meteorological conditions (e.g., intense sunshine and high temperature).