Greta Jimenez
Groundwater contamination is a critical issue that threatens the health and well-being of millions worldwide. The two primary sources of groundwater pollutants are natural processes and human activities, encompassing industrial, agricultural, and municipal sources. Natural contamination includes arsenic, radon, boron, and fluoride, while human-induced pollutants range from leaking fuel tanks and toxic chemical spills to pesticides, fertilizers, and waste leached from landfills. Understanding and addressing these diverse sources of groundwater pollution are essential to safeguard this precious and vital resource.
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What You'll Learn
Natural vs. human-induced pollutants
Groundwater pollution can occur as a result of both natural processes and human activities. Even though groundwater often appears clear and clean because the ground naturally filters out particulate matter, it can still contain natural and human-induced chemicals.
Natural Pollutants
Natural processes can contaminate groundwater with high concentrations of arsenic, which is recognised by the World Health Organization (WHO) as one of the most serious inorganic contaminants in drinking water worldwide. Arsenic is a semi-metallic element that occurs naturally in some soils and rock formations, and can enter the environment through natural processes such as weathering. In Asia, particularly in China, India and Bangladesh, severe contamination of groundwater by naturally occurring arsenic is a significant issue, affecting millions of people.
In addition to arsenic, other natural contaminants that can be found in groundwater include radon, boron, nitrate, fluoride and uranium. These substances can occur naturally in the soil, rocks and water, and can be released into the environment through natural processes such as microbial activity and weathering. For example, in California, nitrate is a common groundwater contaminant that leaches into the soil and water supply from various sources, including irrigation water containing fertilizers, septic systems, and natural conditions.
Human-Induced Pollutants
Human activities can also significantly contribute to groundwater pollution. Industrial activities, such as the use of solvents, gasoline, hydrocarbons, paint, and the release of industrial waste, can introduce toxic chemicals and heavy metals into groundwater systems. Agricultural practices, including the use of pesticides, herbicides, and fertilizers, can also lead to groundwater contamination. These pollutants can be carried by rainwater into groundwater systems, or can leach into the soil and water supply, posing risks to human health and the environment.
In addition to industrial and agricultural sources, urban activities such as leaking fuel tanks, sewage systems, and chemical spills can also contribute to groundwater pollution. Human activities, such as land use, well drilling, and pumping rates, can further impact the quality of water in supply wells, particularly when associated with naturally-occurring trace elements in aquifers.
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Arsenic contamination
Inorganic arsenic is the most common form found in soil and water. It can exist in two oxidation states: arsenic AsIII (arsenite) and arsenic AsV (arsenate). Arsenic is highly toxic to humans, with ingestion of just 100 milligrams typically resulting in severe poisoning. Prolonged exposure to inorganic arsenic in drinking water can cause arsenicosis, a debilitating disease characterised by skin lesions and pigmentation. Arsenic poisoning can also lead to potentially fatal diseases, including skin and internal cancers.
According to the World Health Organization (WHO), arsenic is one of the most serious inorganic contaminants in drinking water worldwide. Arsenic contamination is particularly prevalent in Asia, including China, India, and Bangladesh. In Bangladesh, arsenic contamination of groundwater has been a long-standing issue, with millions of people exposed to unsafe drinking water. UNICEF and the World Bank advocated the use of tube wells to access deeper groundwater, but this led to one of the largest mass poisonings as the water was contaminated with arsenic.
The International Atomic Energy Agency (IAEA) has collaborated with the Bangladesh Atomic Energy Commission to address arsenic contamination using nuclear techniques. By analysing the age and movement of groundwater, they have helped predict safe water sources. Arsenic removal filters (ARF) are also available, but they are often costly and require maintenance, which can be challenging in developing regions.
In the United States, arsenic contamination has been reported in various states, including California, where more than 800 drinking water wells exceeded federal standards for arsenic levels in 2021. The USGS actively monitors drinking water supplies for arsenic contamination and works with other organisations to study and address this issue.
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Agricultural pollution
Agriculture is a major source of groundwater pollution. Farms discharge agrochemicals, organic matter, drug residues, sediments, and saline drainage into water bodies. These agricultural activities have altered the natural flow of water, and agricultural chemicals enter streams and aquifers.
Agricultural contaminants can impair the quality of surface water and groundwater. Fertilizers and pesticides don't remain stationary on the landscape where they are applied; instead, runoff and infiltration transport these contaminants into local streams, rivers, and groundwater. When land is converted to agricultural use, it is modified to be optimized for agricultural production, which often has unintended environmental impacts on receiving waters and their ecosystems, including changes in water quality and quantity.
In the US, agriculture is the main source of pollution in rivers and streams, the second main source in wetlands, and the third in lakes. In China, agriculture is responsible for a large share of surface-water pollution and is responsible almost exclusively for groundwater pollution by nitrogen. In the European Union, 38% of water bodies are under pressure from agricultural pollution.
A new class of agricultural pollutants has emerged in the form of veterinary medicines (antibiotics, vaccines, and growth promoters), which move from farms through water to ecosystems and drinking water sources. In addition, fish excreta and uneaten feeds from fed aquaculture diminish water quality. The increased production has combined with the greater use of antibiotics, fungicides, and anti-fouling agents, which may contribute to polluting downstream ecosystems.
Nitrate from agriculture is now the most common chemical contaminant in the world's groundwater aquifers. High levels of nitrates in water can cause "blue baby syndrome", a potentially fatal illness in infants.
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Industrial pollution
One of the primary sources of industrial groundwater pollution is waste disposal. Industries often generate large quantities of waste, including solid, liquid, and chemical waste. Improper disposal methods, such as dumping waste into pits or landfills, can lead to the leaching of pollutants into the soil and, subsequently, into the groundwater. This was a common practice before the enactment of environmental regulations in the 1970s. Even decades later, the remnants of these practices continue to contaminate groundwater, as evidenced by the sulfuric acid industry waste in Argentina, which still affects the Río de la Plata coastal plain.
Industrial activities that use or produce toxic chemicals, such as solvents, gasoline, hydrocarbons, paints, and heavy metals, pose a significant risk to groundwater sources. Spills, leaks, and improper waste management practices can allow these chemicals to infiltrate the soil and reach underlying aquifers. For example, gasoline spills and leaks from underground storage tanks can quickly contaminate karst aquifers, as seen in the case of Barton Springs.
Another critical aspect of industrial pollution is the discharge of industrial waste into water bodies. This can include both surface water and groundwater sources. Industries may release untreated or partially treated wastewater, containing various contaminants, directly into rivers, lakes, or other water bodies, which then flow into and contaminate groundwater reserves. This was observed in the Río de la Plata coastal plain in Argentina, where industrial activities led to chemical modifications in both surface water and groundwater.
Furthermore, certain industries, such as refineries and petrochemical plants, can contribute to groundwater pollution through their routine operations. The presence of these industries can alter the natural composition of the surrounding soil and water. For instance, the development of a petrochemical pole and refineries in the early 1920s in Argentina led to environmental changes and heavily contaminated soils, impacting both surface water and groundwater.
The impact of industrial pollution on groundwater is not limited to the immediate vicinity of the pollution source. Contaminants can migrate over time, affecting distant water sources. This was observed in Hinkley, California, where groundwater was contaminated with hexavalent chromium, resulting in a legal case and a multimillion-dollar settlement in 1996, as dramatized in the film "Erin Brockovich."
To address the issue of industrial groundwater pollution, it is essential to implement stringent regulations and monitoring practices. Governments and regulatory bodies must enforce proper waste management practices, ensure the safe disposal of hazardous substances, and hold industries accountable for any environmental damage they cause. Additionally, the development of alternative technologies and treatment methods, such as portable water purification devices or "point-of-use" (POU) water treatment systems, can help mitigate the impact of industrial pollution on groundwater sources.
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Treatment and removal methods
Groundwater pollution can be caused by untreated waste discharge, leaking sewers, and the spreading of wastewater or sewage sludge in agriculture, which can lead to diseases like skin lesions, bloody diarrhoea, and dermatitis. It can also be caused by industrial discharges, urban activities, agriculture, groundwater pumpage, and the disposal of waste.
Groundwater remediation is the process of treating polluted groundwater by removing or converting contaminants into harmless products. This process aims to make groundwater safe for human use and to minimise the negative impact of contaminants on the environment. There are two types of groundwater remediation: in situ (on-site) and ex situ (off-site). In situ remediation involves cleaning the water where it is situated, while ex situ remediation involves excavating and removing contaminated water off-site.
The specific treatment approach depends on the type of site, such as an industrial site or brownfield, and may require various tests and cleaning phases. After each phase, the groundwater is sampled and tested against regulatory standards. If the data exceeds the required standards, additional rounds of testing and treatment may be necessary, and projects can take years to complete.
Various technologies and methods are employed to remediate contaminated groundwater, including biological, chemical, and physical treatment processes. For instance, portable water purification devices or "point-of-use" (POU) water treatment systems can be used to remove certain forms of groundwater pollution, such as fecal pollution, pathogens, chlorine, heavy metals, and odours. Specific technologies like arsenic removal filters (ARF) can also be utilised. Other techniques include boiling, filtration, activated charcoal absorption, chemical disinfection, ultraviolet purification, and solar distillation.
To address pollution and protect water sources effectively, it is crucial to identify the source of contamination (point source or non-point source) and the impacted water body (groundwater, surface water, or ocean water). Point source pollution originates from a single source, such as wastewater discharge from manufacturers or leaking septic systems, while non-point source pollution comes from diffuse sources. Regulations, such as the Clean Water Act, play a vital role in holding polluters accountable and establishing standards for allowable discharges into water bodies.
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Frequently asked questions
There are various types of groundwater pollutants, but two of the most common are natural and human-induced chemicals. Natural pollutants include arsenic, radon, boron, and fluoride. Human-induced pollutants include pesticides, herbicides, fertilizers, industrial waste, and sewage.
Arsenic can occur naturally in groundwater, especially in Asia, including China, India, and Bangladesh. Arsenic can also be released into groundwater through microbial activity and the use of wood preservatives, agricultural chemicals, herbicides, and pesticides.
Agriculture is a major contributor to groundwater pollution through the use of fertilizers, pesticides, and animal waste. When it rains, these contaminants wash into waterways, leading to nutrient pollution and algal blooms that are harmful to people and wildlife.
Consuming polluted groundwater can have severe health impacts, including gastrointestinal illness, cholera, typhoid, amoebiasis, giardiasis, and E. coli. Arsenic poisoning, for example, can result from ingesting just 100 milligrams of arsenic, leading to severe poisoning.
