Urban Insecticides in Surface Water: Runoff Source Identification and Large-Scale Constructed Wetland Treatment
Abstract
ABSTRACT OF THE DISSERTATION
Urban Insecticides in Surface Water: Runoff Source Identification and Large-Scale Constructed Wetland Treatment
by
Zachary Michael Cryder
Doctor of Philosophy, Graduate Program in Environmental Toxicology
University of California, Riverside, June 2020
Dr. Jay Gan, Chairperson
Fipronil and pyrethroids are insecticides applied at high rates in urban environments for indoor and outdoor elimination of pests such as ants, termites, roaches, and fleas. Applied residues of fipronil and its degradation products (hereafter: fiproles) as well as pyrethroids are easily transported offsite in surface runoff and wastewater. In surface water, fiproles and pyrethroids elicit toxicity in non-target aquatic and benthic organisms. Failing to alleviate this pollution will result in ecological impacts and as-yet-unknown human health impacts following reuse of scarce water resources. This dissertation addresses the need to reduce urban insecticide contamination of surface water by investigating urban runoff sources of fiproles and examining the comparative efficacy of a full-scale vegetated constructed wetland and a unit process open water constructed wetland in treating water contaminated with fiproles and pyrethroids. If the sources of fiproles in urban surface runoff are identified, it will be possible to modify pesticide application practices to mitigate surface water contamination by these pollutants. Therefore, runoff, soil, urban dust, and concrete wipe samples were collected from fipronil-treated homes to identify the contributions of these compartments to urban runoff of fiproles. Concrete surfaces and urban dust were shown to be the dominant contributors of fiproles to surface runoff, indicating that limiting application on these matrices would substantially reduce contamination. In addition to mitigating urban insecticide pollution, it is also necessary to uncover strategies to treat contaminated water bodies. To this end, water, sediment, and plant samples from a vegetated constructed wetland were monitored for fiproles and pyrethroids. All contaminants were effectively treated by the wetland via partitioning into sediment and subsequent degradation as well as uptake by or adsorption to aquatic macrophytes. To compare the effect of constructed wetland design on removal of fiproles and pyrethroids, water and sediment samples were also collected from a unit process open water constructed wetland. Despite the absence of macrophytes, this system was still effective for contaminant removal. Overall, this research highlights the feasibility of combining mitigation and treatment strategies to attain the goal of reducing urban insecticide contamination in surface water.