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Dr Catherine Conlon Sewage in our waterways has huge health and environmental consequences

The public health doctor looks at the latest EPA wastewater treatment report and the damage that sewage-infected water can cause to our health and environment.

AS THE GLOBAL population increases, so also, inevitably, does the volume of global sewage. Added to that, the growth in global wealth means that wastewater, including sewage, contains increasing amounts of dangerous chemicals, toxic substances and the debris associated with modern consumer lifestyles.

Globally, the UN reported in 2023 that at least 1.7 billion people in 2022 were using a drinking water source that was contaminated with faeces. Microbial contamination of drinking water as a result of contamination with faeces poses the greatest risk to drinking water safety. Microbial contaminated drinking water transmits diseases such as diarrhoea, cholera, dysentery, typhoid and polio and is estimated to cause over half a million (505,000) diarrhoeal deaths each year.

In 2022, about three quarters (73%) of the global population of six billion people were reported by the UN to have access to a safely managed drinking water service, located on premises, available when needed and free from contamination.

No awards here

While the EPA’s drinking water reports show that the quality of water in regulated water supplies is high, a new report from the EPA Urban Wastewater Treatment in 2022 warns that wastewater continues to harm the quality of many of Ireland’s rivers, estuaries, lakes and coastal waters with half a billion litres of wastewater that have not been adequately filtered or disinfected, discharged every single day.

Launching the report, Dr Tom Ryan, EPA Director said:

While it is encouraging to see continued progress in stopping the unacceptable practice of discharging raw sewage into our environment, waste water remains a significant pressure on Ireland’s water ways and is adversely impacting water quality.

The EPA reports states that 30 years after Ireland was required to bring provisions into force to comply with EU treatment standards to protect the environment, less than half (45%) of wastewater is treated to these standards. The completion of the upgrade to Ireland’s largest treatment plant at Ringsend will improve the situation significantly, but Ringsend is not the only problem.

The report highlights 26 towns and villages that are not connected to any wastewater treatment plan so that the raw sewage of 54,000 people enters waterways completely untreated.

Dublin, Cork and Limerick are highlighted among 15 cities and towns where wastewater treatment cannot handle the workload placed on them and needs upgrading, expansion or replacement.

What are the risks to health from sewage overflow?

An ECDC report (2021) on risks of infectious disease from untreated sewage lists the risk of infection from gastrointestinal pathogens such as E.coli, norovirus, rotavirus, Cryptosporidium, Giardia, Campylobacter, different Salmonella enterica serotypes, Shigella and hepatitis A. Other diseases such as leptospirosis and tetanus may also occur.

Norovirus produces a clinical condition characterised by pronounced vomiting and mild diarrhoea. Between 1% and 5% of the population will develop norovirus gastroenteritis each year. The human gastrointestinal tract provides a reservoir for this RNA virus that is the commonest cause of infectious intestinal disease. It can be spread by person- to- person contact but can also be food as well as water borne. Because it is highly infectious it has a high outbreak potential whether transmitted person-to person or through food or water. The incubation period for symptoms is short – usually between 24 and 48 hours.

E.coli are bacteria that form part of the normal flora of the lower gastrointestinal tract of vertebrates. Verotoxigenic E.coli (VTECs) were first identified as human pathogens four decades ago in 1982 and since then have evolved and spread to become one of the most serious infectious intestinal diseases in Europe and North America. Ireland has one of the highest VTEC notification levels in the EU. 

VTEC produces a potentially serious, highly infectious diarrhoeal and systemic illness. In about a tenth of cases, it causes a condition called haemolytic uraemic syndrome (HUS), which is the commonest cause of acute renal failure in young children. VTECs are transmitted through ingestion of food or water contaminated with infected faeces as well as by direct contact with an infected animal.

Cryptosporidiosis is a protozoal parasite. Symptoms generally begin a week after swallowing the bug but can start after a couple of days. The most common symptom is watery diarrhoea but this can be accompanied by vomiting, fever and stomach cramps. Symptoms usually last between one and two weeks. While it is a mild disease in healthy people, it can be worse in small children and elderly people and can be very serious for people who are immunocompromised.

The HSE recently reported increased levels of cryptosporidiosis in travellers coming home from some parts of Spain, particularly Salou in Catalonia. The symptoms may go in cycles in which you may seem to get better for a few days, then feel worse again before the illness ends.

Giardiasis is a parasitic infection of the upper small bowel that occurs across the world. It is a common cause of traveller’s diarrhoea and probably the most important cause of parasitic gastroenteritis in the developed world. Giardia lamblia is the causative parasite.

Humans are the primary reservoir but they are also found in beavers, dogs, cats, chickens and rats. Transmission involves ingestion of Giardia cysts, most frequently associated with consumption of contaminated water or contact with recreational water. Giardia cysts are quite resistant to chlorination, making water filtration a crucial element of effective water treatment to prevent giardiasis.

Typically giardiasis presents with abdominal pain, flatulence, foul smelling greasy stools and bloating nausea. It can be treated with antibiotics. Hepatitis A is another nasty bacterial infection that can result from contact with sewage in open water. Cases are less common in Ireland, but do occur. It produces an acute infection of the liver and is important because it can cause severe and prolonged disease and has a high outbreak potential if transmitted through water.

Leptospirosis can make its way into sewage through infected urine from rats. People who swim or use water for other recreational purposes such as rowing or canoeing can be at risk. This is why the annual Liffey or Lee swim does pose a risk to swimmers- particularly if they are swimming with open wounds that are not covered.

Illness is usually a mild flu-like illness with persistent or severe headaches. A minority develop a more severe illness (Weil’s Disease) with liver and kidney failure that can be fatal in a small proportion of cases.

Impacts of sewage on nature

Sewage can also have deadly effects on nature in terms of animals and plants living in waterways. Algal blooms are encouraged by the presence of sewage and can lead to the deaths of many other species, according to a report from the UK Natural History Museum (2021).

Dr Anne Jungblut, Principal Researcher in algae, fungi and plants at the Museum, said algal blooms are a big problem.

A large amount of algae has an impact on the rest of the ecosystem, such as blocking out the light that plants need for photosynthesis. When these plants, and the algae itself start to die they are eaten by a lot of bacteria which reduces oxygen in the water, killing fish and other organisms.

Freshwater insects are badly affected by a lack of oxygen.

Entomologist at the Museum, Steve Brooks agrees.

Insects are like a canary in a coal mine, providing an early warning system that something isn’t right.

Fish depend on these insects for their survival. While fish can swim away from sewage, they can’t survive if their prey has disappeared.

It will take a multi-billion euro investment to bring all waste-water treatment systems up to the standard needed to protect our environment and also provide for future needs. In the midst of a climate crisis with increasing rain intensity aggravating an already severely overstretched system – the EPA advises that resources are prioritised where they are needed most and will bring the greatest benefits.

Dr Catherine Conlon is a public health doctor in Cork and former director of human health and nutrition, safefood. 

*** Last week, Noteworthy, the investigative platform of The Journalreported that there are almost 40 locations around Ireland where raw or poorly-treated sewage is discharged directly into the environment, in many cases negatively affecting bathing water quality.

Investigative reporter Alice Chambers found that bathing restrictions have almost tripled in the last decade and this summer saw over half of bathing waters affected. Contamination from wastewater treatment plants was the top reason for swimming bans in 2022 and 2023.

The beaches with the highest number of days of bans were Sandymount and Dollymount Strand, right beside the Ringsend Wastewater Treatment Plant which fails to meet EU treatment standards. The full investigation by Noteworthy can be read here.

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Dr Catherine Conlon
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