US, WASHINGTON (ORDO NEWS) — Scientists from Poland and the UK have studied how dangerous it can be to get sewage into natural freshwater bodies, such as rivers and lakes. According to researchers, whose work has so far been published on the medRxiv preprint portal , contamination of freshwater systems with pathogenic microorganisms can have serious consequences, including for the environment and the second wave of Covid-19.
Coronaviruses are known to survive in water (and cold water is better than hot water for them), and viral particles in the sewers correlate with the prevalence of infection in the population. There are many possible ways to contaminate the water we drink or use for cooking: for example, spills and leaks from sewer pipes, failure of wastewater treatment systems; lack of infrastructure in poor regions of the world and so on.
“Viral pathogens that can be transmitted through water and carry a health risk, as defined by WHO, include adenovirus, astrovirus, hepatitis A and E, rotavirus, norovirus and other enteroviruses. The survival of a large family of coronaviruses in water supply systems has already been established, viral loads in untreated wastewater and their relation to the infection rates of the population have been identified. Together, this indicates that SARS-CoV-2 coronavirus can survive in water, and viral loads in untreated wastewater are probably high in countries most susceptible to infection, therefore, water contaminated with effluents is a potential fecal -oral way of transmission,” the scientists write.
An in vitro study showed that SARS-CoV-2 can remain viable for 25 days. In addition, the authors assessed the risks that residents of many countries might face as a result of wastewater leakage into fresh water bodies. The relative risk (Eng. Relative risk (RR)) associated with this depended on the degree of domestic water use, as well as the weather, terrain and topography of the area. Thus, countries with high water consumption and high dilution of wastewater entering water bodies, such as Canada and Norway, had the lowest RR. The highest rates were in countries such as Germany, the United Kingdom, Spain and Morocco, where water consumption was low or medium, but the dilution was similar.
The authors determined the upper and lower limits for the concentration of SARS-CoV-2 in the first 24 hours after the spill of wastewater. They also noted that in countries with high RR, if the water was colder and the incidence was high, the rates of the viable virus were greater. When calculating the scientists proceeded from the assumption that infection requires 100 virus particles per 100 milliliters of water. Thus, it turned out that a resident of any country where RR is highest, after drinking 100 milliliters of contaminated water within 24 hours, will receive about 470 virus particles and, most likely, will become infected.
This is equivalent to one or two sips of water. Meanwhile, if you are directly in the river or lake for 45 minutes, you can swallow three times more – about 280 milliliters. In addition, animals that feed on grass or shrubs growing in areas contaminated with such water may be at risk.
The fact that coronavirus can survive and spread through water bodies can affect the supply of drinking water to countries that are primarily dependent on rivers or reservoirs, as well as residents of regions with poor sanitary conditions. The best ways to provide people with safe drinking water are filtration, chlorination or ultraviolet disinfection. However, the applied doses of chlorine or ultraviolet radiation often vary from one region to another and may not meet the minimum limits necessary to reduce viral load.
“Natural bodies of water can serve as reservoirs and distribution routes for SARS-CoV-2. In many countries, they pose a real threat to health, so if leaks from sewers have recently occurred, then the contact of people and animals with river and lake waters should be minimized. We also recommend that regional or nationwide approaches to drinking water treatment be reviewed to reduce the chances of SARS-CoV-2 surviving in water systems. Boiling drinking water will deactivate the virus. At the same time, fresh food products that become contaminated (for example, when washing or processing) can remain contagious for up to 25 days,” the experts explained.
In addition, scientists talked about the survival of coronavirus in seawater. According to them, its stability at different pH values and salt concentrations in cold water may mean that it is able to “live” both in fresh water bodies and in the seas and oceans. Although human-to-human transmission is recognized as the primary pathway, SARS-CoV-2 can accumulate in acceptors, such as mollusks.
“In addition, ACE2 receptors in many cetacean species are very similar to their human counterpart, so they may be vulnerable to SARS-CoV-2. Of particular concern are whales, as large volumes of water constantly pass through their throats, ”the scientists concluded.
The Rospotrebnadzor managed to criticize this study. “There is no scientific evidence that Covid-19 is able to spread due to the use of water. It should be borne in mind that in open reservoirs there is high insolation, which is detrimental to coronavirus. Coronavirus is transmitted from person to person mainly by airborne droplets. As for open water bodies, there is a chance to get a bacterial or parasitic infection, but not a coronavirus infection, ” said Mikhail Lebedev, an employee of the Center for Molecular Diagnostics CMD of the Central Research Institute of Epidemiology of Rospotrebnadzor.
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