Climate Extremes Fuel Virus Spread in Waterways Polluted by Wastewater

The study of climate change has primarily focused on the increasing frequency and intensity of extreme weather events, which have caused significant damage, loss of life and harm to infrastructure.

Human activities, coupled with urbanisation, are leading to the widespread contamination of water bodies, and the effects of climate change are likely to worsen this issue. Rising temperatures will lead to more frequent and severe heat waves, as well as changes in rainfall patterns and cloud formations.

In the United Kingdom, climate projections indicate milder winters and wetter summers in the 21st century, along with a rise in extreme rainfall events. Heavy rainfall can overwhelm wastewater systems, causing sewage overflow into rivers, lakes, and beaches. Sewage contains human waste, dead cells, food and pharmaceutical byproducts, and various bacteria and viruses, primarily from individuals infected with harmful pathogens.

The UK’s wastewater treatment plants are generally effective at removing viruses; however, discharges into the environment still pose significant risks. Climate change is causing prolonged rainfall events, while heat waves are becoming more frequent throughout the country.

A study titled “Comparative impact of sunlight and salinity on human pathogenic virus survival in river, estuarine, and marine water microcosms,” published on 15 June 2025, in the Water Research Journal, examines how quickly viruses found in sewage, such as Adenovirus, Enterovirus, Hepatitis A, Influenza A, Norovirus GII, and Respiratory Syncytial Virus, decay in water bodies like rivers, estuaries, and marine environments, both with and without sunlight.

To investigate the impact of environmental factors on sewage-linked viruses, researchers developed methods to filter out viruses that are too damaged to cause infection and identify several that are infectious. They conducted a series of experiments simulating various short- and long-term weather events and rising temperatures to assess how these conditions affect the viruses and their potential risk to human health.

In these experiments, the researchers introduced infectious viruses into bodies of water and monitored their degradation over a period of two weeks. They exposed the samples to various water temperatures and simulated sunlight, measuring the decline of the virus at multiple intervals.

The researchers calculated the “T90 decay rates,” representing the time it takes for viral loads to decrease by 90%. They found that the type of water, whether river, estuarine, or sea, had no significant impact on the viruses’ infectivity or detectability. Instead, sunlight emerged as a critical factor in the decay of viruses across all water types.

Without sunlight, the primary factor affecting viral decay was time; viruses can take between 0.3 and 24.3 days to decrease by 90%. However, when the researchers simulated sunlight, the breakdown process accelerated significantly, with a 90% reduction occurring within 1 to 3 days for all types of viruses. T90 times ranged from 7 to 62.8 hours. The effect of salt on viral decay in water varied depending on the specific virus and the type of water.

The study recommends that individuals avoid recreational activities in waters impacted by sewage discharge for at least 2.5 days during cloudy weather and at least 24 hours after sunny days to reduce the risk of infection.

These findings highlight the critical role environmental factors, especially sunlight, play in how long viruses remain active in water. This information is crucial for enhancing sewage treatment practices and evaluating public health risks, particularly as climate change and urban development increase the frequency of sewage spills.

The results can help government authorities enhance water quality models and risk management strategies, ultimately safeguarding public health in both coastal and inland water areas.

Read the study: Comparative impact of sunlight and salinity on human pathogenic virus survival in river, estuarine, and marine water microcosms.