Meghan Hodges
Water pollution is the release of substances into bodies of water, making it unsafe for human use and disrupting aquatic ecosystems. Water pollution can be caused by a wide range of contaminants, including toxic waste, petroleum, pesticides, heavy metals, agricultural and industrial chemicals, hydrocarbon fuels, radioactive materials, sewage, pharmaceutical drugs, and biological agents such as bacteria, parasites, and viruses. These contaminants can enter water sources through various human activities, such as industrial processes, agriculture, and improper waste disposal, ultimately rendering the water unsafe for drinking, cooking, cleaning, and other activities.
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What You'll Learn
Microplastics and other plastics
Microplastics are minuscule plastic fragments that are smaller than 0.04 inches or 5mm in size. They can be found in products like cosmetics, biomedical products, toothpaste, and lotions, where they are intentionally manufactured in small sizes. They can also be secondary microplastics, which are plastic particles that break down from larger plastic materials, such as food wrapping, tires, and synthetic textiles.
The presence of microplastics in water, especially natural freshwater systems, has become a significant environmental concern. A 2022 study found that microplastics accumulate within freshwater systems, particularly at the source of rivers or streams, where the slow water flow favours the piling up of microplastics. This has detrimental effects on aquatic life, with 55% of marine organisms facing entanglement and 31% facing health issues due to ingestion of microplastics.
The sources of microplastics in water are diverse. They can come from decomposing plastic bottles and bags, as well as being intentionally manufactured into certain products. A significant amount of microplastics also comes from rivers, with fibers composing an average of 71% of the total number of microplastic particles found in river water samples. Urban watersheds, in particular, are associated with high concentrations of microplastics, including plastic fragments, films, and foams.
The impact of microplastics on human health is still being researched, but it is known that they can enter the human diet through the food chain. A study by Loyola University Chicago biologists found that 85% of fish sampled from rivers in Michigan and Wisconsin had microplastics in their digestive tracts. Additionally, the contaminants that accumulate on plastic particles, such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and trace metals, can further pose health risks.
To address the issue of microplastics in water, individuals can play a key role by reducing, recycling, and reusing plastic products. Supporting products made with bio-based and biodegradable plastics and packaged in sustainable materials is also crucial. However, significant change will require big companies and the food packaging industry to adopt more sustainable practices and switch to alternative packaging.
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Agricultural and industrial chemicals
Agriculture is the world's largest consumer of freshwater resources, with farming and livestock production using about 70% of the earth's surface water supplies. It is also a serious water polluter. Globally, agriculture is the leading cause of water degradation. In the United States, agricultural pollution is the top source of contamination in rivers and streams, the second-biggest source in wetlands, and the third main source in lakes. It is also a major contributor to contamination in estuaries and groundwater.
Agricultural activities release four categories of water pollutants: nutrients, pathogens, pesticides, and silts. Animal waste and chemical fertilizers are applied to the soil to provide the nitrogen, phosphorus, and trace elements necessary for crop growth. When applied, these fertilizers are either taken up by crops, remain in the soil, or enter aquatic environments. Nitrogen (N) compounds can accumulate in the soil crust and vadose zone for years. N, in the presence of oxygen, is transformed into nitrite (NO2-) or nitrate (NO3-). The fundamental paths of the N cycle include nitrogen fixation, nitrification, denitrification, ammonification, volatilization, and atmospheric deposition.
Non-point source water pollution, also known as "diffuse" source pollution, arises from a broad group of human activities where the pollutants have no obvious point of entry into receiving watercourses. In contrast, point source pollution represents activities where wastewater is routed directly into receiving water bodies, such as through discharge pipes, and can be more easily measured and controlled. Non-point source pollution is much more difficult to identify, measure, and control.
Industrial effluents can be classified according to the dominant nature of the pollution, and they may be characterized by a high concentration of organic or inorganic compounds. Industries that generate wastewater include refineries, mining, tanneries, pharmaceuticals, pulp mills, and sugar production/distilleries. The food and agriculture industries generate wastewater with high biochemical oxygen demand (BOD), estimated at 0.6–20 m3 wastewater/ton of product. The distillery industry generates ~15 L of wastewater per liter of alcohol with a BOD level of about 90,000 mg/L.
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Radioactive materials
The presence of radionuclides in water sources can have detrimental effects on human health. When ingested through contaminated water or food prepared with contaminated water, radionuclides can accumulate in the body and lead to various health issues. For example, radioactive iodine-131, a common fission product, can impair or destroy the thyroid gland if inhaled or ingested in large quantities. The degree of hazard posed by radionuclide contamination depends on several factors, including the concentration of the contaminants, the energy and type of radiation emitted, and the proximity of the contamination to the body's organs.
To address the issue of radionuclide contamination in water, public drinking water systems play a crucial role. These systems regularly test and filter out radionuclides to ensure that the water supplied to the public meets all federal, state, and local drinking water standards. The United States Environmental Protection Agency (EPA) sets Maximum Contaminant Levels (MCLs) for radionuclides in public drinking water under the Safe Drinking Water Act. Additionally, public drinking water suppliers identify the paths that water travels to reach the drinking water system, prepare for emergencies, and participate in voluntary programs to prevent water sources from becoming contaminated.
It is important to note that not all radioactive materials are considered contamination. When radioactive materials are contained within sealed and designated containers, they are not referred to as contamination. However, when these materials are released into the environment or come into contact with humans, they pose a significant risk and are then classified as contamination. The containment of radioactive materials is a primary method for preventing contamination and mitigating its impact on the environment and human health.
Radioactive waste, a specific type of radioactive material, poses unique challenges due to its persistence in the environment for thousands of years. The cleanup and disposal of radioactive waste can be extremely costly and time-consuming. For example, the decommissioned Hanford nuclear weapons production site in Washington is expected to cost over $100 billion to clean up, with efforts extending through 2060. Properly addressing radioactive waste and contamination is crucial to protect groundwater, surface water, and marine resources from irreversible damage.
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Sewage and other waste
The decomposition of organic matter in sewage by bacteria and other microorganisms depletes the dissolved oxygen content of the water, creating "dead zones" where aquatic life cannot survive due to the lack of oxygen. Sewage can also promote the growth of algae, including toxic green algae, which can eventually lead to eutrophic zones. These harmful algal blooms, known as "red tides," often poison or kill wildlife and humans who consume contaminated seafood.
In addition to sewage, other waste products contribute to water pollution. Agricultural waste, including fertilizers, pesticides, and animal waste, washes into waterways during rainfall, introducing nutrients and pathogens. Industrial waste discharges also release toxins and chemicals into water sources, including nitrogen, bleach, salts, pesticides, metals, and toxins produced by bacteria. Municipal waste contributes to nutrient pollution, particularly nitrates and phosphates, which are common in farm waste and fertilizer runoff.
Radioactive waste is another form of pollution, generated by uranium mining, nuclear power plants, military weapons, and research or medical activities. This waste can persist in the environment for thousands of years, threatening groundwater, surface water, and marine resources. The presence of radioactive contaminants in water can result from both leaching from natural deposits and human activities such as milling, nuclear processes, and agricultural practices.
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Pesticides and fertilisers
Pesticides are materials used to control, prevent, kill, reduce, or repel pests. They can be made from natural ingredients or synthetic chemicals. All pesticides are toxic to some degree, and their overuse or misuse can harm the environment and human health. Pesticides can enter water sources through improper disposal, runoff, or leaching from soil. Their presence in water can be deadly to aquatic organisms, including tiny creatures known as aquatic invertebrates, which many larger organisms rely on for survival.
Fertilizers, on the other hand, are substances that provide nutrients to support plant growth. While they are essential for agriculture, they can also contribute to water pollution. When excess fertilizers are used in crop production, the remaining nutrients, particularly nitrogen and phosphorus, can be washed off the soil during irrigation or rainfall, eventually polluting water resources.
The solubility of pesticides in water is a critical factor in determining their potential for water pollution. Many pesticides are designed to be water-soluble to facilitate their application and absorption by the target organism. However, this solubility increases the risk of leaching into water sources. Residual herbicides, which are designed to bind to the soil structure, generally have lower solubility, but their persistence in the soil can lead to other issues.
The half-life of a pesticide, or how long it takes for it to break down, is another important consideration. More stable pesticides have longer half-lives and persist in the environment for extended periods, increasing the likelihood of water contamination. Additionally, factors such as soil temperature and microbial activity influence the breakdown rate of pesticides in the soil.
To prevent pesticides and fertilizers from contaminating water sources, proper application and disposal practices are crucial. Applying these substances under calm weather conditions, with wind speeds below 10 mph and no rain or snow in the forecast, can minimize their movement into waterways.
The impact of pesticides and fertilizers on water quality is a global concern, with over 4,000,000 tons of pesticides used annually worldwide. Their presence in water can have detrimental effects on aquatic ecosystems and human health, especially for young children. Biodegradable and biocompatible pesticides have been introduced to mitigate the negative impacts of synthetic pesticides, but the issue of water pollution from these substances remains a significant challenge.
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Frequently asked questions
Contaminated water is caused by the release of substances into bodies of water that make it unsafe for human use and disrupt aquatic ecosystems. There are four types of contaminants: physical, chemical, biological, and radiological. Here are some examples of each:
- Physical: Suspended sediment or organic material.
- Chemical: Nitrogen, bleach, salts, pesticides, metals, toxins produced by bacteria, and human or animal drugs.
- Biological: Bacteria, viruses, protozoa, parasites, and other microorganisms.
- Radiological: Radioactive waste from uranium mining, nuclear power plants, and military weapons.
There are many sources of contaminated water, including agricultural and industrial activities, sewage, and oil spills. For example, fertilizers, pesticides, and animal waste from farms can wash into waterways during rain, while oil spills can release large amounts of petroleum into the ocean. Sewage can also promote the growth of harmful algae, creating "dead zones" where aquatic life cannot survive due to a lack of oxygen.
Humans can be exposed to water contaminants through drinking, bathing, or even consuming food prepared with contaminated water. These contaminants can pose health risks by causing diseases, acting as poisons or carcinogens, or impacting specific organs like the kidneys. For example, arsenic, a common contaminant in groundwater, can be toxic and has been linked to health issues in over 140 million people across 50 countries, according to the World Health Organization (WHO).
