New research from Bangor University, conducted as part of the BlueAdapt project, reveals how sunlight and water type (River, Estuary or Sea) affect how long pathogenic viruses with human sewage can survive in water, providing critical insights for managing environmental and public health risks in our rivers, lakes and coastal areas. The study builds on previous findings about the behaviour of viruses in seawater at different temperatures, examining how various environmental conditions impact the degradation of common wastewater viruses, including Influenza and Norovirus.
The research team highlight that sunlight—particularly UV radiation—plays a crucial role in accelerating viral decay, significantly reducing virus concentrations within hours in sunlit conditions. “Without sunlight, virus persistence can extend from days to weeks, posing a continuous risk in shaded or deeper waters,” explained Dr Jessica Kevill from Bangor University’s School of Environmental & Natural Sciences. “When we added simulated sunlight to the mix, we saw significant reductions in viral presence within 24 to 72 hours, depending on the virus. This suggests that UV radiation can be one of the most effective natural viral inactivators, which has important implications for coastal water safety, especially after sewage spills.”
The researchers used advanced genetic methods to check not only for the presence of viral genetic material but also for the integrity of the protective shells that keep viruses infectious. These measurements provide a clearer understanding of the viruses’ potential to infect humans after being released into natural water systems.
In a previous study with Exeter University, research showed that viruses survive longer in seawater at lower temperatures, indicating that while heatwaves may slightly reduce viral risks, they do not eliminate them entirely.
This latest research, however, highlights that other environmental factors, such as salinity and sunlight, also have a major influence on viral survival. Without sunlight, viruses could survive from 14 hours to over 25 days, depending on the water type and virus. In sunlight, survival times dropped dramatically to just 2.5 hours to 2 days.
“This finding really highlights the need to assess viral infectivity in risk assessments,” Jessica added. “Relying solely on viral genome detection may overestimate the actual health risk, as it doesn’t account for whether these viral particles are still viable and capable of causing human infection. Our data suggest that viral integrity tests are critical for accurately assessing risk, especially in dynamic environments like estuaries and coastal waters.”
The implications of this research are significant: as climate change continues to exacerbate extreme weather and increase untreated wastewater discharges, water quality management must adapt. UV radiation could play a vital role in managing viral risks naturally in shallow, sunlit waters, while viral integrity testing could offer a more precise measure of viral risk across various aquatic environments.
For health and environmental agencies, these findings highlight the importance of monitoring viral integrity alongside concentration in public waters. “In the face of rising temperatures and unpredictable extreme weather, the need for advanced, accurate water monitoring has never been greater,” said Professor Will Gaze, from the University of Exeter, who collaborated with Jessica on the first study. “This research points us toward more effective measures for protecting public health.”