SusChEM: GOALI: Harnessing the Antimicrobial Properties of Copper to Control Legionella in Plumbing Systems

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Proposal Number: 1706733PI Name: Marc A. Edwards The growing public health threat in drinking water from opportunistic pathogens (OPs), such as Legionella, calls for practical engineering solutions that are compatible with sustainability goals. Taking advantage of the natural disinfecting properties of copper (Cu) pipes, which are widely used in plumbing systems, is an attractive approach for control of Legionella; however, Cu is not consistently effective in practice, as it sometimes inhibits and other times stimulates Legionella growth. This research seeks to address this fundamental knowledge gap through bench, pilot, and field-scale studies to identify the water chemistries that enhance or inhibit Cu-driven disinfection of Legionella. This research is potentially transformative as it will inform practical, economical, and sustainable means of addressing a key public health threat just as trillions of dollars will be invested to upgrade antiquated water infrastructure.The overarching hypothesis for this research is that water chemistry directly and indirectly influences Cu toxicity towards Legionella. The specific objectives are to: 1) Determine the effects of Cu speciation, complexation, and precipitation in governing toxicity towards Legionella under conditions relevant to hot water building plumbing systems; 2) Explore the role of microbial communities inhabiting plumbing systems to mediate toxicity of Cu, e.g., through shielding or responding to nutrients released from corrosion reactions (e.g., H2 evolved), and confirm Objective 1 phenomena under realistic pilot-scale plumbing conditions; and 3) Conduct a field survey to validate relationships among physicochemical, Cu speciation/solubility, and microbial factors in real-world plumbing systems and illuminate drivers of Cu-enhanced versus Cu-inhibited Legionella growth. This study will be the first systematic examination of the speciation- and solubility-dependent nature of Cu toxicity towards Legionella in potable water systems, particularly within hot water that is most relevant to OP proliferation. Of particular interest is the occurrence and behavior of cuprous (Cu1+) ions. Cu1+ is probably non-toxic to Legionella and may even indirectly stimulate its growth by catalyzing deposition corrosion of less noble metal plumbing materials which will then provide H2 for autotrophic hydrogen-oxidizing bacteria. Cupric (Cu2+) ions have strong biocidal properties, but effectiveness may be limited by temperature, redox, inorganic and organic ligands, corrosion control agents, and biofilm properties. An innovative combination of tools will be used to characterize complex interdependencies among the microbial community composition, physicochemical properties, Cu speciation, and Legionella, including next-generation DNA sequencing, green-fluorescence protein modified strains, flow cytometry, scanning electron microscopy, and x-ray diffraction crystallography. Knowledge generated by this research has the potential to guide building maintenance practices to prevent the proliferation of Legionella.