Threat of sewage-borne viruses: As the world grapples with the impact of climate change and urbanisation, an overlooked yet critical public health threat is emerging: virus-laden sewage spilling into water bodies. New research reveals how the increasing frequency of extreme weather events leads to the spread of dangerous pathogens, posing severe risks to human health. Recent studies highlight that urban wastewater contains a diverse array of human pathogenic viruses, often in high concentrations, making sewage spills a major public health risk. The persistence and decay of these viruses under dynamic environmental conditions remain poorly understood, raising significant concerns about water quality management and the potential for widespread viral infections.
Modern urban wastewater systems receive vast amounts of faecal matter carrying billions of viral particles from infected individuals. Enteric viruses such as adenovirus, rotavirus, and hepatitis A are among the most common pathogens found in sewage, with the potential to cause severe gastrointestinal and respiratory diseases. While wastewater treatment plants eliminate most contaminants, the reality is stark—sewage spills and treated effluents continue to introduce harmful viruses into lakes, rivers, and oceans.
Survival of sewage-borne viruses
Extreme weather events, particularly intense rainfall, increase the likelihood of sewer overflows. This phenomenon is causing untreated wastewater to infiltrate natural water systems, increasing human exposure to infectious agents. In tandem, rising global temperatures are driving more people to seek relief in recreational waters, heightening the risk of viral transmission. The convergence of environmental and human factors creates a dangerous cocktail for public health. Scientists have observed that combined sewer overflows contribute significantly to water pollution, releasing untreated human waste, antibiotics, and pathogens into water bodies. Furthermore, studies indicate that even treated sewage effluent can still contain potentially infectious human enteric viruses, posing ongoing risks to human health.
Recent studies have investigated how viruses persist in different aquatic environments, considering factors such as temperature, salinity, and sunlight exposure. While viral decay occurs over time, the process is highly variable. Research shows that enteroviruses can remain infectious in seawater for up to 120 days, while others, like adenoviruses, exhibit remarkable resilience across freshwater and marine environments. The behaviour of viruses in aquatic environments is influenced by a complex interplay of physical, chemical, and biological factors.
Virus concentration in sewage water
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Salinity influences virus stability, with some viruses persisting longer in seawater due to enhanced thermostability. Enteroviruses, for example, display a greater ability to survive in higher salinity conditions, making coastal regions particularly vulnerable. However, the most significant environmental determinant of viral decay is sunlight exposure. Ultraviolet (UV) radiation plays a crucial role in deactivating viruses, with experimental results demonstrating a significant reduction in viral loads within 24 to 72 hours under direct sunlight.
In contrast, viruses in shaded or deeper waters can persist for weeks, posing a persistent infection risk. Researchers have observed that viral decay is accelerated under high UV radiation, but cloudy weather conditions prolong the survival period, enabling pathogens to linger in the water for days. Temperature is another factor that affects virus persistence, as some pathogens can survive for longer durations in cooler conditions, extending the risk window for human exposure.
A study published in Water Research explored the effects of environmental conditions on virus decay in different water types, including river, estuary, and marine water. The research found that, in the absence of sunlight, viruses could remain infectious for periods ranging from 0.3 to 24.3 days, depending on the virus type. Simulated sunlight significantly accelerated viral decay, with some pathogens losing viability in as little as 7 to 62.8 hours. The findings emphasise the critical role of solar radiation in viral inactivation and the necessity of incorporating sunlight exposure into water quality assessment models.
Limits of wastewater treatment
Despite advancements in wastewater treatment technologies, the removal of viruses from sewage remains an ongoing challenge. Studies indicate that up to 80% of human enteric viruses survive conventional treatment processes, continuing to be discharged into the environment. Combined Sewer Overflows (CSOs) compound this issue by releasing untreated sewage directly into water bodies during heavy rainfall events. Moreover, sewage spills have been linked to contamination of shellfish beds, increasing the risk of viral infections through seafood consumption.
Furthermore, wastewater treatment plants act as viral reservoirs, with potential risks extending beyond water contamination. Workers at these facilities face exposure to bioaerosols containing harmful pathogens, and inadequately treated wastewater used for irrigation introduces viral risks to agriculture and food systems. Research suggests that aerosolised viruses can travel significant distances, raising concerns about occupational health hazards for those handling sewage and sludge. Wastewater-based epidemiology has shown that viral loads in wastewater can serve as indicators of disease prevalence in communities, offering valuable insights into public health trends. However, this also highlights the need for improved viral monitoring and containment measures in sewage systems.
Need for urgent action
Projections for the 21st century indicate a shift toward more extreme weather patterns, with milder, wetter winters and hotter, drier summers. Increased rainfall will drive higher volumes of untreated wastewater into natural water systems, while higher temperatures could extend the lifespan of viruses in the environment. In coastal regions, sea level rise and changing salinity gradients may further influence virus persistence and dispersal.
At the same time, climate-induced changes in microbial communities may create new pathways for viral transmission. Viruses that bind to organic particles in water can persist longer, forming aggregates that protect them from environmental degradation. This aggregation, combined with altered salinity profiles in estuaries, can influence the movement and viability of pathogenic viruses, increasing the difficulty of predicting and mitigating outbreaks. The long-term implications of these dynamics remain poorly understood, necessitating further research to refine risk assessment models. Scientists highlight that the interplay of viral persistence and environmental changes calls for a re-evaluation of current water safety standards and monitoring protocols.
Given the growing evidence of sewage-related viral threats, policymakers must act decisively to strengthen wastewater management systems. Upgrading wastewater treatment plants with advanced disinfection technologies, such as UV irradiation and membrane filtration, is essential to reducing viral contamination. Research has demonstrated that enhanced filtration and UV-based disinfection significantly reduce viral loads, making them critical additions to wastewater treatment strategies. Expanding wastewater-based epidemiology programs can provide early warnings for viral outbreaks, aiding public health preparedness and response. Strengthening regulatory frameworks is necessary to enforce stricter guidelines for wastewater treatment and CSO management, particularly in flood-prone urban areas.
Public awareness and behavioural change also play a crucial role in mitigating risks associated with sewage contamination. Educating communities about the dangers of waterborne viruses and promoting better sanitation practices can help reduce exposure. Additionally, integrating climate projections into water quality models can enhance our ability to predict viral persistence and improve environmental risk assessments. Researchers stress that incorporating real-time viral detection methods into wastewater monitoring can help identify potential outbreaks before they escalate into widespread public health crises.
The intersection of climate change, urbanisation, and inadequate wastewater management is creating an unprecedented challenge in public health. Without urgent action, exposure to sewage-borne viruses will become a growing threat to global health security. Policymakers, researchers, and communities must collaborate to ensure that water systems are resilient in the face of evolving environmental pressures. A comprehensive approach that integrates advanced wastewater treatment, enhanced monitoring systems, and climate-responsive public health policies is the only way forward. The health of future generations depends on the choices we make today.