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E. coli

Protozoa

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E. coli

E. coli is a very common type of bacteria that is found within the intestinal tract of warm-blooded animals (e.g. humans, birds, dogs, cattle). It is found within water and soil environments and its presence indicates that there is a fecal input to the environment it was found, whether it originated from humans or other animals in the area.

Since E. coli is a living organism, it requires ideal environmental conditions to survive, relating to temperature, acidity, and having an abundance of energy available. Within the intestine, E. coli populations will thrive, however, once transported into a different environment (e.g. soil, lake, stream) the survivability of E. coli drops and can have a half life of 3 days in soil environments. However, this still provides enough time to be transported between different environments. E. coli is more easily transported during rainy conditions when there is more connectivity between different environments (e.g. streams, fields, roadways) due to runoff and increased groundwater flow. As an example, animal remains from birds, dogs, or cattle in a field or parking lot can be transported by runoff from rainwater directly into neighbouring streams and lakes, which in turn directly transports E. coli constituents.

When E. coli is ingested in excessive amounts by humans it can cause diseases such as Salmonellosis, cholera, or typhoid fever, which each have stomach related symptoms: vomiting, diarrhea, cramps. In fact, E. coli is commonly ingested (through orifices in face and body) in high concentrations when people swim in lakes or beaches shortly after a large rainfall. This is because after it rains, many streams, agricultural drains, groundwater flows, and runoff flows all contain elevated concentrations of E. coli which flow directly into beach and lake areas. This is why signs like these:

are occasionally seen on beachfronts to warn people about swimming.

Protozoa

Protozoa are single celled organisms that can be found in nearly all environments/habitats, including on or inside most humans. There are multiple species of protozoa that exist, with some being commensal (not considered harmful) and others being pathogenic and causing diseases to humans and animal species.

Protozoan diseases to humans are more concerning in developing countries due to poor water quality and potentially infected foods, while in developed countries there is more concern regarding infections from bacteria and viruses. Disease symptoms from protozoa can range from mild to life threatening, with predominant symptoms being gastrointestinal, such as diarrhea or contracting diseases such as dysentery.

Two well-known disease-causing protozoa are Giardia and cryptosporidium, which are also found to be highly persistent in the environment. In the early life cycle stage of protozoa, a cyst/ oocyst is present, which is a highly resistant cell with a strong outer protective wall that allows the protozoa to survive for up to months in different environments prior to being transferred to other hosts/animals. This makes protozoa challenging to kill when purifying and treating wastewater. Typically, many disease-causing microorganisms are killed with chlorine when purifying water, however, some forms of protozoa must alternatively be filtered out due to their resistant cellular structure.

To outline the strong survivability of some protozoa, it was found in a study that Giardia could survive for up to 77 days in water at a temperature of 8 °C but only 4 days at 37 °C. This additionally outlines the importance of temperature on the survivability of microorganisms, with colder temperatures allowing longer survival times.

Viruses

Viruses are small parasites that can only replicate within a host and have a surrounding protective protein coat. It is unknown whether viruses can be classified as living or non-living based on biological classifications of what is considered a living organism, and additionally do not require food for survival. Viruses are sourced from animals or individuals that have been infected, in which you can become infected with a virus by consumption of contaminated food, water, or transmission by another infected individual (e.g. particle droplets from breath). Viruses can also be transported into the environment by fecal matter, however, it is important to note that viruses are only present and can only be transmitted by infected individuals. Additionally, viruses can be pathogenic (cause diseases and associated symptoms) or non pathogenic. In fact, there are around 160 viruses that are pathogenic within humans.

Due to virus’ small size and their protective outer protein coat, they are easily transported in soil and water environments and are highly persistent. Many bacteria and protozoa are contained in soil environments due to a process called “straining” which is the blockage of transport pathways through soil due to small suspended particles or organic material. This reduces the amount of bacteria that is released to larger environmental systems such as streams or lakes and helps maintain harmful bacterial levels within water. However, viruses are small enough that the straining process is not as effective and they can be more easily transported through soils. This is important to know since viruses can be indirectly transported to drinking water wells or recreational bodies of water by groundwater.

As an example, in a research study by Mia Catherine Mattioli in 2021 in Pennsylvania, U.S. there was an outbreak of a virus called norovirus at a campground. The cause of this virus outbreak was due to a storage container for wastewater in a septic tank that was leaking. The wastewater constituents that leaked from the container were transported down into the underlying soil and rock directly into a nearby drinking water well. This is outlined in the image below:

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