Rapid Solar Photoinactivation of Influenza Virus and Phi6 in Colored Surface Water

Indirect transmission through aquatic environments is critical to interspecies transmission of influenza, but knowledge of sunlight inactivation of the virus, or any enveloped virus, in water is lacking. This study characterizes the photoinactivation of two enveloped viruses (Phi6 and influenza A virus, IAV), and a nonenveloped virus (MS2) in clear and colored surface waters using simulated sunlight. We measured light-screening corrected decay rate constants ($\hat{k}$) using infectivity assays. $\hat{k}$ values were greater, especially for IAV, in colored surface water versus clear water. $\hat{k}$ values were generally greatest for IAV, followed by Phi6, then MS2, suggesting greater susceptibility of enveloped viruses to sunlight. Most $\hat{k}$ values for IAV and Phi6 did not differ with UV irradiance variations in colored surface water, indicating dominance of indirect, photochemically produced reactive intermediate-mediated inactivation pathways. Additional experiments with Phi6 as a representative enveloped virus suggest the importance of hydroxyl radicals, indicate adsorption of NOM promotes photoinactivation, and sublethal damage of the virus may occur. For IAV, modeled time for 99% inactivation in a well-mixed 1 m deep wetland water column is 1.2 h, compared to 1.8 h in clear water. These findings, particularly those for IAV, can inform human and animal health protection strategies.