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Decontamination of Malathion from Drinking Water Distribution System and Premise Plumbing Infrastructure
Citation:
Szabo, J., J. Hall, J. Goodrich, AND S. Witt. Decontamination of Malathion from Drinking Water Distribution System and Premise Plumbing Infrastructure. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-23/330, 2023.
Impact/Purpose:
This experiment focused on decontamination of a pesticide (malathion) that enters drinking water distribution pipe and home plumbing. Malathion is a registered pesticide that is used to kill insects and is widely available in commercial pesticide products. To start this experiment, a commercially available malathion product was mixed in water and injected into the WSTB pipe and the Residential Water Service Simulator (RWSS) in an adjacent building. The effectiveness of using flushing to decontaminate malathion was assessed in both systems.
Description:
This report summarizes the results of infrastructure decontamination experiments performed at the WSTB. These experiments focused on simulating contamination of drinking water distribution pipes with a commonly available insecticide formulation containing malathion. Malathion is used to control mosquitoes and a variety of insects that attack fruits, vegetables, landscaping plants, and shrubs. Large quantities of malathion containing insecticides can be purchased at a hardware store and later introduced into a water system. However, malathion is also an organophosphorus pesticide and is a surrogate for the chemical warfare agent (CWA) VX (Bartelt-Hunt et al, 2008). Thus, malathion can be used to assess CWA decontamination in water systems instead of VX, which would be prohibitively expensive to use at the full scale. To assess infrastructure decontamination, common processes used by water utilities to clean their pipes were implemented. First, a fire hydrant in the 450-ft WSTB distribution pipe was opened, and the water was flushed at approximately 50 gpm (189 L/min, velocity of 0.32 ft/sec) for 20 minutes (min). Flow was reduced to 15 gpm (57 L/min) for an additional four hours, then reduced to a 2.5 gpm (9.5 L/min) for an additional three days. Bulk water samples (BWS) and biofilm samples of the pipe interior were taken during each phase of the experiment to determine if contamination was removed from the distribution pipe. In addition, a premise plumbing system, which included a hot water heater, refrigerator, dishwasher, and washing machine, was contaminated with malathion. The system was flushed by opening taps or running the appliance.