When human sewage gets into our water systems, it can have disastrous effects on health. The 1955-1956 outbreak of hepatitis in New Delhi due to contamination of the Jumna River was one of the first instances which led scientists to link human health with sewage contaminated water (Bosch, 1998). Since then, research has found over 150 virus species which can cause illnesses such as hepatitis, gastroenteritis, meningitis, fever, conjunctivitis and rashes (Bosch, 1998; Farkas et al., 2020) – in Rio de Janeiro’s coastal waters, 96% of samples contained at least one type of virus (Staggemeier et al., 2017).
“Fecal pollution of recreational waters remains a significant public health issue, especially in developing countries.” – Staggemeier et al. 2017
These viruses enter the water systems through the discharge of sewage-contaminated water, surface runoff, waste from slaughterhouses and industrial activities (Staggemeier et al., 2017). Viruses are present in high concentrations in sewage, as a person suffering from gastroenteritis can excrete 105-1011 virus particles per gram of stool (Bosch, 1998). This can quickly spread viruses when we are exposed to this contaminated water, through drinking or swimming in it, eating foods which have been fertilised with it or most notably through eating shellfish, which concentrate viruses and bacteria in their flesh (Bosch, 1998).
The survival time of a virus is extremely important in determining the danger it poses – the longer it can survive outside a host (a sick person), the more likely it is that someone else will become exposed to it (Rzezutka & Cook, 2004). A fascinating study by Rzezutka and Cook (2004) looked at the virus particles in a variety of situations, finding that their survival is most affected by heat, pH and moisture. When looking at foods which had been fertilised with contaminated water, they found that uncovered vegetables had lower virus present on their skins than covered; viruses survived for longer on tomatoes and spinach than cabbage because of their smoother skin; and pasteurised milk could contain poliovirus particles for 90 days when stored at 4 degrees C (Rzezutka & Cook, 2004).
“Once on foodstuffs such as vegetables, viruses may persist under normal storage conditions over the times usual between purchase and consumption.” – Rzezutka & Cook, 2004
Though this information is alarming, new technologies in water treatment processing could hold the answer to reducing contamination. UV disinfection is used widely to inactivate microorganisms before water is released from the treatment plant (Qui et al., 2018). It works by damaging the DNA of the virus, which prevents particles replicating and spreading, which not only reduces the presence of the virus in the water initially, but also prevents recovery of the virus on the surface. UV disinfection also has benefits as no chemicals need to be added to the water, as is done with chlorination (adding chlorine) (Qui et al., 2018).
But contaminated waste is proving to be surprisingly useful – scientists around the world are finding coronavirus particles in sewage, which could be used to estimate infection rate in a community, or even predict the number of people suffering from it (Fegan, 2020, Mandal, 2020). Though this is done through making estimates, it could provide useful in assessing the infection rates of an area where other techniques such as testing and tracing are proving less successful.
References
Bosch, A. (1998) Human enteric viruses in the water environment: a minireview. Int Microbiol, 1(3), pp.191-6
Farkas, K., Mannion, F., Hillary, L.S., Malham, S.K. & Walker, D.I. (2020) Emerging technologies for the rapid detection of enteric viruses in the aquatic environment. Current Opinion in Environmental Science & Health, 16, pp.1-6
Fegan, C. (2020) Rising levels of virus in sewage could be early warning of surge [online] Available at: https://www.independent.ie/world-news/coronavirus/rising-levels-of-virus-in-sewage-could-be-early-warning-of-surge-39571218.html (Accessed: 15/10/2020)
Mandal, A. (2020) Wastewater analysis predicts COVID-19 spread [online] Available at: https://www.news-medical.net/news/20200922/Wastewater-analysis-predicts-COVID-19-spread.aspx (Accessed: 15/10/2020)
Qiu, Y., Li, Q., Lee, B.E., Ruecker, N.J., Neumann, N.F., Ashbolt, N.J. & Pang, X. (2018) UV inactivation of human infectious viruses at two full-scale wastewater treatment plants in Canada. Water research, 147, pp.73-81
Rzeżutka, A. & Cook, N. (2004) Survival of human enteric viruses in the environment and food. FEMS microbiology reviews, 28(4), pp.441-453
Staggemeier, R., Heck, T.M., Demoliner, M., Ritzel, R.G., Röhnelt, N.M., Girardi, V., Venker, C.A. & Spilki, F.R. (2017) Enteric viruses and adenovirus diversity in waters from 2016 Olympic venues. Science of the Total Environment, 586, pp.304-312
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Another interesting blog. Very informative as usual.
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