What is microbial water pollution in an urban context?
Microbes are microscopic organisms that are ubiquitous in our environment. They are in us, on us and all around us, and can be beneficial or harmful. Various members of the vast array of microbiological organisms play their part in keeping nature in balance. For instance, some microbes are essential to break down food during digestion in humans and animals so that the nutrients can be released and absorbed by the body. These are the normal microbial flora of the digestive tract. Microbes are useful in ecosystems too: they assist with the breakdown of plant material so that the nutrients can be released back into the soil.
Microbes can also cause harm — particularly through their role in causing disease. When a microbiological organism can cause disease in humans or animals, it is referred to as a pathogen. Pathogenic organisms are normal components of all ecosystems, but contamination by faecal matter poses the single biggest health risk to most people, particularly those living in poorly serviced urban areas.
All of these can be carried by untreated or poorly treated sewage leaking or spilling from poor infrastructure, or passing through poorly functioning wastewater treatment works, before being released into rivers or the ocean. Poorly constructed or maintained landfill sites can also release pathogens into the environment. Disease-causing microorganisms released into the environment inevitably spread to plants, wildlife or human beings. Much of this spread happens via waterborne routes. Microorganisms such as intense algal blooms can also reduce the amount of oxygen in lakes or streams, and causing harm to animal and plant life.
Worldwide, microbial contamination of water is an ever-present problem. Environmental contamination by human and animal pathogens can be transmitted via polluted water to soil. Fresh produce irrigated by contaminated water can infect people, and contribute to person-to-person transmission once someone has been infected. These multiple pathways of transmission and infection make the identification of the original source of the pathogen difficult, especially since the vast majority of infections do not produce symptoms immediately. People are not always aware of all the contacts and exposures that they have had during the previous few days. A source of contamination may only be identified after a number of people acquired the infection. Thus control of waterborne infections depends heavily on the availability of properly designed and maintained systems to dispose of urban waste.
Microbial pathogens found in wastewater
The most common human microbial pathogens found in wastewater are enteric in origin (relating to or occurring in the intestines). Enteric pathogens enter the environment in the faeces from the hosts — either animal or human — and flow into water either directly through defecation into water, contamination with sewage leaking directly into the water source or through run-off from soil and other land surfaces.
The types of enteric pathogens that can be found in water include viruses, bacteria, protozoa and helminths. Viruses do not replicate in the environment (outside their hosts) but can survive under certain conditions, until they are ingested by a host. Survival and multiplication or regrowth of bacteria in contaminated water depends mainly on the type of organism, the chemical and biological environmental conditions, the presence of competing microorganisms and the available nutrients. Thus, what may under one set of circumstances be a ‘safe’ concentration of pathogens can change into a risk when the circumstances change.
Pathogens released into water from skin or hair, wounds, pustules, urine, mucus, saliva and sputum and blood can also be transmitted. Infections are generally contracted by drinking contaminated water, recreational exposure to contaminated water, inhaling contaminated aerosols, ingesting seafood from contaminated water, or consuming raw food irrigated by contaminated water or organisms transmitted in the process of preparing food. The most common symptom of waterborne disease is diarrhoea. Diarrhoea is a symptom accompanying many diseases or other health conditions and is a health hazard in its own right.
Most of the diseases and deaths associated with water-related diseases — particularly in poorer parts of the urban space — infect people through:
- Ingestion of pathogens in water polluted by human or animal waste (faeces). Diseases in this category include for example cholera (Vibrio cholerae), shigellosis (dysentery caused mainly by Shigella spp. or Entamoeba histolytica), typhoid (Samonella typhi), paratyphoid (Samonella paratyphi), diarrhoea (mainly Escherichia coli or viruses such as rotavirus or norovirus), or hepatitis (Hepatitis A, E).
- Diseases associated with the lack of water to maintain personal hygiene, cleaning of clothes and cooking utensils, etc. or with contaminated water as the only water source available to the community. Diseases in this category include diarrhoea from various causes; skin and eye infections; scabies, etc.
- Diseases associated with ingestion or penetration of the skin by infections acquired from snails, fish or other aquatic animals. These diseases include schistosomiasis and diseases that are called ‘neglected tropical diseases’. As the name implies, they occur mainly in tropical and subtropical climates.
- Diseases that are transmitted by insects that breed in water (particularly in stagnant or contaminated water). Such diseases include malaria, dengue and yellow fever. These diseases are also climate-related: they occur mainly in tropical and subtropical climates.
The diseases listed under the last two bullet points do not occur in the City of Cape Town, but are given here for the sake of completeness as some of these diseases do occur in other parts of South Africa.
Challenges in handling urban waste streams
Urban wastewater streams can be divided by source into stormwater, sewage, domestic greywater and industrial wastewater. Each one of these sources of wastewater will contain a range of pathogens. This range depends on a large number of factors, which include:
- the range of pathogens found in the inhabitants of the area (wastewater reflects the disease profile of the area),
- average household composition,
- housing infrastructure (particularly the sanitation arrangements),
- the health status of the inhabitants,
- the lifestyles and products used and
- the willingness to adhere to safe household hygiene.
After wastewater leaves individual properties it enters the municipal sewage system. There is ample evidence that such systems in almost all South African towns and cities are in a dilapidated state due to years of poor maintenance, underfunding and lack of skilled supervision. Leaks and spills of sewage due to broken or blocked systems are a common sight in many streets.
Piped sewage systems should deliver the wastewater to a proper wastewater treatment works, where the water is treated to reduce microbes to safe levels. The most recent information regarding the state of wastewater treatment works in South Africa was published in 2013, when it was found that less than 10% of the 824 formal wastewater treatment works were delivering treated effluent of an acceptable standard into the environment. Most wastewater treatment works receive more wastewater than they are designed to treat, and many are poorly maintained and underfunded. All these spills and poorly treated effluent eventually make their way into the ocean.
Apart from the poorly functioning sewage systems, a large part of the City of Cape Town does not have any formal wastewater treatment facility at all. The sewage is subjected to superficial pre-treatment and then released directly into the ocean via marine sewage outfall pipes. Nearly 50 million litres of raw sewage is released into the ocean in this way every day. Read more about marine outfalls here.
“Every sewage treatment works is built close to a river because the effluent – which is meant to be clean – is returned to nature. That, by definition, is how they work all over the world. But, what is happening in many of these treatment works is that the poorly treated, contaminated effluent is being pumped into the rivers”
Jo Barnes, epidemiologist
Algal Blooms and risks
When high levels of microbial pollution exists in water, phytoplankton or blue-green algae grow quickly, feeding on the nutrients from the pollution. Blue-green algae are cyanobacteria, a type of bacteria with attributes of both bacteria and algae. These cyanobacteria can be found in almost all water systems such as dams, rivers and oceans, and can appear individually or in groups.
In the right conditions, blue-green algae can grow rapidly and form visible blooms, or scums. Blooms are usually somewhere between dark green and yellowish brown, and can turn the surrounding water green. These blooms occur when there are large amounts of nutrients to support the development of huge numbers of the algae. This occurs in waters that are contaminated with untreated or poorly treated human sewage, animal manure or fertiliser runoff. It is referred to as eutrophication, or more accurately hypertrophication. This is the ecosystem response to the addition of artificial or natural substances, such as nitrates and phosphates, through fertilisers or sewage to an aquatic system.
Blooms generally occur during summer and autumn, when nutrient levels are high, temperatures are warm, and the water is relatively still. Weather conditions, nutrient levels and water flow will affect how long a bloom lasts. These blooms often surround the Cape Peninsula and are visible from space, due to their extent.
Satellite imagery indicating high chlorophyll values (in red) in False Bay around Cape Town. (Silvia Inés Romero, SHN-UBA-UNDEF Argentina)
Satellite Images of phytoplankton / algal bloom in False Bay in 2018 (Silvia Inés Romero, SHN-UBA-UNDEF Argentina)
Water affected by blue-green algae may not be suitable for drinking, recreation or agricultural use. Human contact with these blooms can cause illness such as hay fever-like symptoms, skin rashes, eye irritations, vomiting, gastroenteritis, diarrhoea, fever and pains in muscles and joints. Effects of algal blooms on water bodies can include hypoxia (the depletion of oxygen in the water), which when severe, will cause die-off of specific fish and other animal populations.
Some species of blue-green algae produce harmful toxins which can have serious health effects, when eaten, inhaled or skin contact is made. Ingesting toxins by eating contaminated species can also cause gastroenteritis symptoms, such as vomiting, diarrhoea, fever and headaches. Toxins can also have a damaging effect on the liver and the nervous system. In extreme cases death can result.
Avoid contact with algae-affected water and organisms, particularly in areas with visible scums or discoloured water. Follow the advice on any nearby signs and keep out of the water until authorities advise that the risk has passed.
If you come into contact with contaminated water, you should remove any affected clothing and wash yourself thoroughly with clean water. Always wash any contaminated clothes thoroughly with clean water before wearing it again. Affected wetsuits should be rinsed in fresh water to remove any trace of algae. If you feel sick, see a doctor.