Climate change has already begun to alter the environment in many ways, but scientists are also vigilantly watching for the ripple effects that will spread to human health. Now, they’re raising the alarm about exposure to viruses lingering in sewage as the world gears up for more frequent storms this century.
A new study published in the journal Water Research warns of virus transmission through sewage systems, a public health risk that could grow in severity as wastewater continues to spill into lakes and rivers after storms. To better understand virus survival in water, researchers focused on environmental factors like varying weather conditions and salinity.
Viruses Starting in the Sewer
Pathogenic viruses often enter wastewater from fecal matter of infected individuals, who can shed billions of viral particles when using the toilet. These often take the form of enteric viruses, which primarily affect the gastrointestinal tract and can cause symptoms like diarrhea and nausea. This group of viruses includes adenovirus, rotavirus, and hepatitis A virus.
Although wastewater treatment plants can usually remove up to 99 percent of impurities, it is still possible for some virus-laden wastewater to be discharged into the environment. This has become a growing public health concern as more extreme rainfall events are expected to slam Earth in the coming years. As a result, sewer overflows may soon become more prevalent, spreading pathogens to bodies of water. To make matters worse, a hike in summer heatwaves in the future means more people will flock to recreational waters, compounding the chances of potential human exposure to wastewater viruses.
Read More: Intense Storms Bring 16 Billion Tons of Snow to Greenland, Restoring Ice Sheet
How Sunlight Can Vanquish Viruses
The new study aimed to examine how salinity and sunlight influence the survival of viruses in water. After introducing sewage-linked viruses to samples of river, estuary, and seawater, researchers monitored the effects of these factors on viral decay. They specifically measured T90 decay rates, which represent the time it takes for viral loads to drop by 90 percent.
The salinity experiment yielded mixed results, with viral decay mainly depending on the type of virus. Enterovirus, for example, displayed greater persistence in seawater since higher salinity enhances its thermostability. Overall, in dark conditions, most viruses survived longer in seawater compared to freshwater.
Salinity, though, did not drive viral decay nearly as much as sunlight. In temperatures as high as 30 degrees Celsius (86 degrees Fahrenheit), enteric viruses stayed infectious in seawater for up to three days. In cooler temperatures, the survival period extended to around a week. However, when viruses were exposed to sunlight, many of them did not survive as long, decaying in under 24 hours. Cloudy conditions, meanwhile, caused viruses to remain viable for around 2.5 days.
“Without sunlight, virus persistence can extend from days to weeks, posing a continuous risk in shaded or deeper waters,” said study author Jessica Kevill, an environmental virologist from Bangor University, in a statement. “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.”
Into Uncharted Waters
The researchers advise that a batch of environmental factors will influence assessments of water quality in the future. UV radiation, in particular, could help constrain viral growth in water, but scientists will also need to consider escalating temperatures, changing cloud cover, and altered salinity from sea level rise, which can reshape microbial communities in coastal environments.
In the long run, though, more efficient sewage treatment practices may be able to nip pathogen spread at the bud, an improvement that could keep those spending a day at the beach safe.
Read More: Microplastics May Contribute to Antibiotic Resistance
Article Sources
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Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine.
