Sunlight photolysis of SARS-CoV-2 N1 gene target in the water environment: considerations for the environmental surveillance of wastewater-impacted surface waters

Wastewater surveillance of SARS-CoV-2 has been used to supplement clinical testing data for situational awareness of COVID-19 disease trends. Many surveillance programs utilize sewer networks and centralized wastewater treatment plants for sampling. However, many regions lack wastewater collection and treatment infrastructure, which presents additional considerations for wastewater surveillance, including environmental decay of the RT-qPCR gene targets used for the quantification of SARS-CoV-2. Given the role of sunlight in RNA decay, we evaluated sunlight photolysis of the N1 gene target in heat-inactivated SARS-CoV-2 with a solar simulator under laboratory conditions, in a photosensitizer-free matrix and wastewater. Insignificant photolysis was observed in the photosensitizer-free matrix. Conversely, significant decay was observed in wastewater at a shallow depth, indicating a role of indirect photolysis. Given that sunlight irradiance is affected by season, latitude, and light attenuation, first-order decay rate models were used to evaluate the effect of water depth, time of year, and latitude on decay kinetics. Decay rate constants decreased with greater depth of the water column, at high latitudes, and in the winter, and indicated that sunlight-mediated decay of the N1 target is likely to be minimal and unlikely to confound results from surveillance programs that evaluate samples collected from wastewater-impacted surface waters.