Biological Factors: Impacting Water Pollution Severity

Water pollution is the contamination of water by harmful substances, which can have devastating effects on both human health and the environment. These substances, which include bacteria, viruses, fertilisers, pesticides, and plastics, can cause illness and even death in humans and aquatic organisms. One of the main biological causes of water pollution is eutrophication, which occurs when large quantities of nutrients are introduced into a body of water, leading to a depletion of dissolved oxygen and the death of aquatic life. Additionally, biological organisms such as algae can create nuisances in water supplies, affecting the palatability of the water. Water pollution is predominantly caused by human activity, with agricultural, industrial, and livestock farming practices being major contributors.

Algae and water supply

Algae are a natural feature of aquatic environments. While most algae are harmless, some types of cyanobacteria can be harmful. Cyanobacteria are photosynthetic bacteria that live in water and produce oxygen. They are often green or blue-green, but can also be white, brown, blue, yellow-brown, or red. Cyanobacteria can reproduce quickly in favourable conditions, such as still or slow-flowing water with sufficient nutrients, especially nitrogen and phosphorus.

When cyanobacteria increase to excessive levels, they form visible 'blooms' that can lead to poor water quality and potential toxicity. These blooms can occur in freshwater, marine water, and brackish water. They can look like foam, scum, mats, or paint on the water's surface, and they may change the colour of the water. Some blooms may not be visible.

Cyanobacterial blooms can have detrimental effects on water quality and human, animal, and environmental health. Some cyanobacteria species produce toxins that can accumulate in shellfish, crustaceans, and the internal organs of fish, posing risks to those who consume them. These toxins can cause serious illnesses, including gastroenteritis, which can induce vomiting, diarrhoea, fevers, and headaches. In severe cases, cyanotoxins can damage the liver and nervous system, and there have been human deaths associated with exposure to algal toxins.

Additionally, decaying algae can deplete dissolved oxygen levels in the water, severely degrading aquatic ecosystems and leading to the death of aquatic organisms and a decline in biodiversity. This process, known as eutrophication, occurs when there is an excess of nutrients in a water body, causing rapid growth of aquatic plant and bacterial life. Eutrophication can be detrimental to water supplies, recreational activities, and water-dependent industries.

To prevent and manage cyanobacterial blooms, it is crucial to minimise the nutrient load entering waterways. This can be achieved through appropriate treatment and disposal of stormwater, agricultural effluent, and sewage. Regular water sampling and monitoring are essential to detect potentially harmful blooms and ensure safe drinking water supplies.

Sewage and wastewater

Wastewater contains a range of harmful substances, including metals, solvents, toxic sludge, and stormwater runoff, which carries road salts, oil, grease, chemicals, and debris. When released into water bodies, these substances can have detrimental effects on both human health and the environment.

Untreated human sewage, for example, is rife with infectious diseases such as salmonella, hepatitis, dysentery, and cryptosporidium. Studies have linked water pollution to various illnesses, including gastroenteritis, ear infections, and waterborne illnesses that can cause severe health issues and even death.

The impact of sewage pollution extends beyond human health. It also threatens biodiversity and ecosystem health. Untreated and poorly treated sewage increase the concentrations of nutrients, pathogens, endocrine disruptors, heavy metals, and pharmaceuticals in natural ecosystems. This elevated level of pollutants can lead to eutrophication, creating ""dead zones" in water bodies where aquatic life cannot survive due to depleted oxygen levels.

The consequences of sewage and wastewater pollution are far-reaching, and addressing this issue is crucial for ensuring clean water, protecting ecosystems, and safeguarding public health.

Eutrophication

The algal blooms caused by eutrophication can block sunlight from reaching photosynthetic marine plants, disrupting their growth. Additionally, the blooms can deplete the oxygen in the water, leading to the death of aquatic organisms such as fish, which rely on oxygen to survive. This phenomenon is known as hypoxia or anoxia, creating "dead zones" in the water. Eutrophication has been linked to the destruction of economically important fisheries and the degradation of water quality, with toxic algal blooms posing risks to both aquatic life and humans.

The introduction of excessive nutrients into water bodies can also alter the structure of aquatic communities. For example, small-bodied zooplankton tend to dominate during cyanobacterial blooms, which are associated with high nutrient concentrations. Eutrophication can further impact the growth and success of predators that rely on light to catch prey, as well as impair the chemosensory abilities of organisms that depend on chemical cues for survival.

The economic impacts of eutrophication are significant, particularly in regions where commercial shellfisheries are prevalent. For instance, eutrophication has cost shellfisheries in Long Island Sound millions of dollars annually since 1985, and it is estimated that without intervention, the Sound could lose all its seagrass beds by 2030. Additionally, the reduction in fish catch due to eutrophication can lead to smaller harvests and more expensive seafood.

To mitigate the effects of eutrophication, various strategies have been employed, including nutrient diversion, altering nutrient ratios, physical mixing of water, and the use of algaecides. However, these approaches have often proven ineffective or impractical, especially for large and complex ecosystems. Biomanipulation, which involves altering the food web to restore ecosystem health, has been suggested as an alternative approach. Nevertheless, addressing eutrophication remains a complex issue that requires collective efforts from scientists, policymakers, and citizens to reduce nutrient inputs and develop long-term management techniques.

Oil spills

In addition to the environmental and wildlife impacts, oil spills can also have significant economic and social consequences. They can disrupt professional and recreational activities, decrease property values in affected areas, and have a negative aesthetic impact on marine and beach environments. The overall economic impact on the community can be substantial, and the clean-up costs of oil spills can be significant.

The transportation and storage of oil are subject to leakage, which can have devastating effects on water resources. Oil spills from tankers can be particularly severe due to the large quantity of oil released in a single location. To prevent and mitigate the impacts of oil spills, regulations such as the Oil Pollution Act have been implemented, requiring oil storage facilities to prepare "Facility Response Plans" and companies to have detailed clean-up and containment plans in place.

Pathogens

To prevent and treat waterborne diseases caused by pathogens, it is essential to sanitise drinking water with chlorine-based compounds or by boiling. In emergency situations, boiling water for at least one minute is sufficient to kill most disease-causing pathogens. Alternatively, household bleach can be used for disinfection, but it is important to follow instructions and use the correct type and amount to ensure effectiveness.

The transmission of pathogens can occur through various faecal-oral routes, including fingers, flies and other insects, fields (agriculture), food, and fluids. The relative importance of these pathogens in causing illnesses depends on their persistence in the environment, minimal infective dose, ability to induce human immunity, and latency periods.

Overall, pathogens are a significant concern in water pollution, and proper sanitation practices are crucial to prevent the spread of waterborne diseases.

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