Water Contaminants: Understanding Common Pollutants And Their Sources

Water pollution is a pressing issue that poses a significant threat to both human health and the environment. It occurs when harmful substances contaminate water bodies, degrading water quality and making it unsafe for human use and aquatic life. Water pollution can be caused by a wide range of substances, including toxic waste, petroleum, chemicals, heavy metals, pesticides, plastics, and disease-causing microorganisms. These pollutants can originate from various sources, such as industrial activities, agricultural runoff, sewage discharges, and urban stormwater runoff. The accumulation of these pollutants in water sources can lead to the degradation of aquatic ecosystems, the spread of water-borne diseases, and a negative impact on the surrounding environment. Understanding the various water pollutants and their sources is crucial for developing effective strategies to mitigate water pollution and ensure the availability of clean and safe water for current and future generations.

Industrial and Sewage Waste

Industrial wastewater often contains a mix of toxic substances, including heavy metals such as lead, mercury, cadmium, copper, and selenium, which are used in manufacturing, mining, and car production. Petroleum products, such as fuel and lubricating oils, are also common in industrial wastewater, especially from the plastic manufacturing industry. Hazardous wastes, which are highly flammable and corrosive, are another type of pollutant found in industrial wastewater, mainly from construction, demolition, manufacturing, and waste treatment processes.

The chemical industry faces significant challenges in treating its wastewater due to the presence of conventional pollutants like oil, grease, and suspended solids, as well as more harmful substances such as ammonia, chromium, phenols, sulfides, and cyanide. The production of pharmaceuticals and chemicals can result in wastewater contaminated with active pharmaceutical ingredients, especially during the cleaning of production facilities.

Sewage wastewater, also known as domestic sewage, carries used water from households. While it is mostly water (more than 99.9% by weight), the remaining impurities can pose significant challenges for disposal. These impurities include putrescible organic materials, plant nutrients, and disease-causing microbes. Sewage discharges can also lead to excessive amounts of nitrates and phosphates in lakes, causing rapid algae growth and eutrophication, which accelerates the natural aging of lakes.

Inadequate sewage treatment systems can release untreated wastewater, contributing to water pollution. According to the United Nations, more than 80% of the world's wastewater flows back into the environment without proper treatment. This untreated wastewater contains harmful pathogens, such as bacteria and viruses, as well as heavy metals and toxic chemicals, posing risks to both human health and the environment.

Agricultural Activities

Agriculture is a major cause of water pollution, accounting for 70% of water withdrawals worldwide. Farms discharge large quantities of agrochemicals, organic matter, drug residues, sediments, and saline drainage into water bodies. The use of pesticides and fertilizers in agriculture can contaminate both groundwater and surface water. Organic livestock waste, antibiotics, silage effluents, and processing wastes from plantation crops are also sources of pollution.

One of the main ways that agricultural activities pollute water is through runoff. Agricultural runoff is the leading cause of water quality impacts on rivers and streams, the third leading source for lakes, and the second-largest source of impairments to wetlands. Soil erosion, nutrient loss, bacteria from livestock manure, and pesticides are primary stressors on water quality. Rainfall and snowmelt can transport these pollutants to surface waters, and they can also be carried by irrigation return flows and infiltration.

Excessive sedimentation from erosion can overwhelm aquatic ecosystems, smother breeding areas, and degrade coastal and marine ecosystems, including coral reefs. Increased levels of nitrogen and phosphorus from fertilizer and manure can stimulate algal blooms in lakes and rivers, leading to hypoxic conditions that are harmful to aquatic life. Algae can also affect the recreational use of local streams, downstream reservoirs, and estuaries.

Another emerging class of agricultural pollutants is veterinary medicines (antibiotics, vaccines, and growth promoters). These move from farms through water to ecosystems and drinking water sources. The increased use of antibiotics and antifouling agents in aquaculture can contribute to polluting downstream ecosystems.

Oil Spills

Sources of Oil Spills

The transportation and transfer of oil increase the risk of oil spills. Oil is often transported between ocean tankers, pipelines, trains, and trucks, and as the number of transfers increases, so does the risk of spilling. The use of supertankers to transport oil has been a significant contributor to oil spills, with intensified petroleum exploration and production on continental shelves leading to more frequent spills. Oil spills can also occur during drilling and pumping operations, with oil companies transporting crude oil by pipes, ships, trucks, or trains to refineries.

Effects of Oil Spills

Cleanup and Restoration

Cleanup activities can never entirely remove the spilled oil, and it is crucial to ensure that the chosen cleanup methods do not cause additional harm. After the Exxon Valdez oil spill in 1989, it was discovered that high-pressure, hot-water hoses used for cleanup caused more damage than the oil alone. The Oil Pollution Act of 1990 established that those responsible for oil spills are liable for paying for cleanup and restoration. Federal, state, and tribal agencies work together with the responsible party to select restoration projects with input from the public.

Microorganisms

Water pollution occurs when harmful substances contaminate a body of water, degrading water quality and rendering it toxic to humans or the environment. One such harmful substance is microorganisms, which can cause microbial pollution of water. This type of pollution is a significant issue, as many people lack access to clean and healthy drinking water and die as a result of waterborne bacterial infections.

Microbial water pollution is mainly caused by pathogenic microorganisms, which include pathogenic bacteria, viruses, parasites, and protists. These microorganisms can originate from various sources, such as failing septic systems, wastewater treatment plant releases, livestock, and stormwater runoff. Fecal contamination, indicated by the presence of fecal coliform bacteria, is a significant concern in water quality assessment. Escherichia coli (E. coli) is a specific type of coliform bacteria that signifies fecal contamination. Other fecal indicators used are fecal streptococci and Clostridium perfringens.

Waterborne bacterial infections can have severe health consequences, including cholera, typhoid fever, and bacillary dysentery, and diarrhea, which can be fatal if untreated. The presence of pathogenic microorganisms in drinking water poses a significant risk to human health, and the disinfection of water supplies is crucial to prevent the spread of these microorganisms. Various disinfection methods are employed, such as chemical, physical, and advanced oxidation processes, each with its own advantages and limitations. For example, chlorine, chloramine, or chlorine oxide are commonly used due to their low cost and ease of implementation, but excessive use can cause an unpleasant taste and irritate mucous membranes.

Additionally, ultraviolet (UV) water treatment is a physical disinfection method that uses germicidal UV light to kill microorganisms by damaging their genetic components. While UV light has the advantage of inactivating many pathogenic microbes without affecting minerals in the water, it is not suitable for water with high turbidity or high levels of dissolved and suspended solids. Distillation is another common technique, involving heating contaminated water to its boiling point to produce steam, but it may not be effective against all microorganisms.

Overall, the presence of pathogenic microorganisms in water supplies poses a significant threat to human health, and the effective treatment of drinking water is essential to prevent the spread of waterborne diseases and ensure access to clean and safe drinking water worldwide.

Chemical Contamination

Water pollution is a widespread problem that jeopardises human health. Chemical contamination is one of the main ways in which water sources become polluted. Chemical contaminants can be either naturally occurring or man-made. Man-made chemical contaminants include disinfection byproducts, solvents, pesticides, and pharmaceuticals.

Natural sources of chemical contamination include rocks and soil, which can contain chemicals such as arsenic and radon that dissolve into water. Human and animal waste is another source of chemical contamination, as up to 90% of oral drugs pass through the body and end up in the water supply. Personal care products such as soaps, cosmetics, and fragrances can also contaminate water.

Agricultural practices contribute significantly to water pollution. Fertilisers, pesticides, and other chemicals applied to land can contaminate nearby water sources. In the United States, agricultural pollution is the leading cause of contamination in rivers and streams. Industrial effluents and sewage are other major sources of chemical contamination, discharging organic and inorganic pollutants into water bodies.

Inorganic pollutants, such as heavy metals, are particularly harmful as they are non-biodegradable and pose threats to aquatic life and public health. Examples of inorganic pollutants include arsenic, lead, chromium, cadmium, and mercury. Mercury, for instance, is a toxic metal that does not break down into less harmful substances and can evaporate and become airborne.

Water treatment plants play a crucial role in mitigating chemical contamination. However, even treated wastewater can contain emerging organic waste pollutants (EOWPs) that disrupt aquatic ecosystems. Additionally, transboundary pollution occurs when contaminated water from one country spills into the waters of another, either through disasters like oil spills or the gradual spread of industrial, agricultural, or municipal discharge.

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