Water And Soil Pollution: Sources And Their Impacts

Water and soil pollution are pressing issues that have detrimental effects on human health and the environment. Water, a universal solvent, readily dissolves and mixes with toxic substances, making it vulnerable to pollution. Sources of water pollution include toxic green algae, sewage treatment plants, industrial waste, agricultural runoff, and marine debris. Soil, a vital component for human health and ecosystems, is threatened by pollutants such as heavy metals, pesticides, fertilizers, and plastic particles. These contaminants originate from human activities like mining, agriculture, and industrial processes, ultimately impacting soil quality and human well-being. Understanding and addressing these sources of pollution are crucial steps towards mitigating their harmful effects.

Industrial and agricultural waste

Industrial waste is defined as waste generated by manufacturing or industrial processes. This includes cafeteria garbage, dirt and gravel, masonry and concrete, scrap metals, trash, oil, solvents, chemicals, weed grass and trees, wood and scrap lumber, and similar wastes. Industrial solid waste can be solid, liquid, or gases held in containers, and it is divided into hazardous and non-hazardable waste. The main types of industrial waste that cause water pollution include petroleum products, heavy metals, hazardous wastes, and sediments. Petroleum products are used as fuel or lubricating oil and are produced during the manufacture of plastics. Heavy metals, such as copper, lead, and selenium, come mainly from the manufacturing of cars, mines, or exhaust air systems. Hazardous wastes are highly flammable and corrosive and come from construction, demolition, manufacturing, trade, and waste treatment processes. Finally, sediments occur when non-degradable toxins accumulate in aquatic sediments for years due to the discharge of polluted industrial wastewater and slowly enter the groundwater.

The discharge of residual pollution from industrial waste into public waters has serious consequences. Many of the hazardous substances from industry are difficult to biodegrade and, therefore, accumulate in water sediments. This has resulted in fish, crustaceans, and other creatures becoming ill and dying, thus reducing biodiversity. The polluted water from rivers and the contaminants from the water sediments can enter the groundwater and, consequently, drinking water. For example, chlorobenzene, a carcinogenic hazardous substance, is used as a solvent in the textile industry and is produced as an intermediate product in the manufacture of insecticides, dyes, pharmaceuticals, and fragrances.

In addition to water pollution, industrial waste also contributes to soil pollution. Nanomaterials and microplastics, which are by-products of industrial activities, are now a significant component of household air pollution from synthetic carpets and clothing. These particles can enter the human body through the air in the form of particulates or dust and can also contaminate drinking water.

Agricultural waste also significantly impacts water quality. Agriculture accounts for 70% of water withdrawals worldwide and is a leading cause of water quality impacts to rivers and streams, the third leading source for lakes, and the second-largest source of impairments to wetlands. Agricultural runoff, including pesticides, fertilizers, and animal manure, can enter groundwater, depending on local land use and geologic conditions. 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. Bacteria and nutrients from livestock and poultry manure can contaminate drinking water supplies and affect beach and shellfish bed closures.

In addition, 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. Fish excreta and uneaten feeds from fed aquaculture also diminish water quality, and the increased use of antibiotics and anti-fouling agents may contribute to polluting downstream ecosystems. To mitigate these issues, buffer strips, integrated farming, and soil and water conservation practices can be adopted.

Microplastics and nanoplastics

The small size of microplastics and nanoplastics allows them to act as vectors for other pollutants, especially heavy metals and hydrophobic organic chemicals (HOCs), which may enhance their overall toxicity. In marine and coastal environments, microplastics can adsorb varying amounts of heavy metals and organic pollutants depending on their hydrophobicity. As they degrade further into nanoplastics and come into contact with various biomolecules, a biomolecule corona can form, altering their persistence, bioavailability, and ecotoxicity.

The impact of microplastics and nanoplastics on human health is a growing concern. These plastic particles can enter the human body through the ingestion of contaminated food and water supplies, as well as the inhalation of airborne plastic particles originating from synthetic textiles and polluted outdoor air. While the skin membrane is too fine for microplastic particles to pass through, nanoplastics may be able to penetrate through wounds and weakened skin barriers. Recent studies have confirmed the presence of plastic particles in human stool samples, indicating that ingestion is the primary route of human exposure to these pollutants.

The prevalence of microplastics and nanoplastics in the environment is a result of their widespread use and disposal. Most plastics end up in landfills, oceans, and other waterways after being discarded by consumers. The breakdown of plastics into micro and nano-sizes has raised concerns about their toxicity to the environment and humans. However, research on the impact of nanoplastics on human health, particularly at the subcellular and molecular levels, is still limited.

To address the issue of microplastic and nanoplastic pollution, there is a need for source identification, pathway assessment, and mapping of accumulation zones. This information will guide the development of policies and actions to reduce or mitigate plastic releases. Additionally, more research is required to understand the sources, pathways, toxicity, and ecological consequences of these pollutants, especially in complex environments and possible accumulation zones.

Sewage and wastewater treatment

Domestic sewage, which makes up the majority of wastewater, contains dissolved and suspended impurities, including putrescible organic materials, plant nutrients, and disease-causing microbes. These impurities can include pathogens, phosphorus, nitrogen, and heavy metals, which are harmful to the environment and human health. According to the United Nations, more than 80% of the world's wastewater is released back into the environment without proper treatment, contributing to water pollution. In the US alone, sewage treatment systems release over 850 billion gallons of untreated wastewater annually.

Industrial wastewater is another major contributor to pollution. It contains specific chemical compounds, depending on the industrial process, such as manufacturing or chemical operations. These chemicals can include solvents, toxic sludge, and heavy metals, which have detrimental effects on aquatic ecosystems and human health.

Wastewater treatment plants aim to remove these pollutants before releasing the treated water into local water bodies. However, the effectiveness of these treatments varies, and some plants struggle to keep up with the demand, leading to the release of untreated or partially treated wastewater.

The improper management of septic systems, used by approximately 20% of US homes, can also lead to elevated nitrogen and phosphorus levels in local water bodies or groundwater, contributing to nutrient pollution.

The release of untreated or partially treated wastewater has significant consequences. For example, water pollution can cause harmful algal blooms, reducing oxygen levels in the water and creating "dead zones" devoid of life. Additionally, sewage-laden coastal waters have been linked to health issues in humans, including skin rashes, respiratory infections, and hepatitis.

Fertiliser and pesticide runoff

Fertilisers and pesticides are essential for maintaining crop yields. However, they can have detrimental effects on the environment when not managed properly. Fertiliser and pesticide runoff is a major environmental concern as it introduces harmful substances into natural water systems, impacting aquatic ecosystems and human health.

To prevent fertiliser runoff, it is recommended to keep fertilisers away from water sources. This can be done by maintaining a distance of at least 20 feet between fertilised areas and nearby water sources. Additionally, farmers can adopt nutrient management techniques by applying the right amount of fertiliser at the right time of year, with the appropriate method and placement. Implementing conservation tillage can also help by reducing the frequency and intensity of tilling, which improves soil health and reduces erosion and runoff.

By managing fertiliser and pesticide application and adopting conservation practices, the environmental impact of runoff can be minimised, protecting both ecosystems and human health.

Deforestation and erosion

Trees also act as a natural barrier, protecting the soil beneath from erosion. With deforestation, the absence of trees leaves the soil vulnerable to erosion by wind and rain. Erosion not only results in the loss of fertile topsoil, essential for agriculture, but also leads to increased sedimentation in rivers and streams. This sedimentation clogs waterways, disrupting aquatic ecosystems and reducing fish populations. Additionally, eroded soil, along with pesticides and fertilizers from agricultural fields, washes into freshwater habitats, causing pollution and further damaging these ecosystems.

The conversion of forests into crop fields or pasture land is a significant driver of deforestation. Agricultural practices, such as overgrazing, improper land management, and the use of pesticides and chemicals, can further accelerate soil erosion. Overgrazing reduces ground cover, exposing the soil to wind and water erosion. The excessive use of pesticides and chemicals can alter soil composition, disrupt the balance of microorganisms, and promote the growth of harmful bacteria.

Infrastructure development, including the construction of roads, railways, power lines, and dams, is another leading cause of deforestation. Poorly planned infrastructure projects can fragment and destroy forest habitats, interrupt wildlife migration routes, and contribute to soil erosion and pollution. Linear infrastructure, such as roads and railways, can increase deforestation rates in nearby areas, as seen in the Brazilian Amazon, where 95% of deforestation occurs within close proximity to roads.

The impacts of deforestation and erosion extend beyond environmental degradation. Soil erosion reduces land productivity for agriculture, creates new deserts, and alters water flow patterns. The loss of fertile soil due to erosion also leads to the release of pollutants, such as pesticides and fertilizers, into water bodies, further degrading water quality. Additionally, the expansion of cropland areas to compensate for the loss of arable land can drive further deforestation, perpetuating a cycle of environmental degradation.

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