Brian Barton
Soil pollution is defined as the presence of toxic chemicals in the soil, in concentrations that pose a risk to human health and the ecosystem. These chemicals enter the soil through human activities and natural processes. Human activities that contribute to soil pollution include the use of pesticides, herbicides, and fertilizers in agriculture, industrial waste, and urban waste. Natural processes that lead to soil pollution include the accumulation of toxic chemicals through atmospheric deposition and precipitation. The contaminants in polluted soil can have severe health implications for humans, plants, and animals.
| Characteristics | Values |
|---|---|
| Chemicals | Pesticides, petroleum hydrocarbons, solvents, lead, heavy metals, polynuclear aromatic hydrocarbons (PAHs), herbicides, ammonia, naphthalene, mercury, nitrates, and radioactive substances |
| Causes | Industrial activity, agricultural chemicals, improper disposal of waste, urbanisation, and natural processes |
| Effects | Soil degradation, reduced crop yields, health risks to humans, animals, and plants, water contamination, and ecological damage |
| Treatment | Soil washing, chemical oxidation, thermal treatment, excavation, and aeration |
| Prevention | Soil testing, proper waste disposal, safe industrial practices, and responsible agricultural chemical use |
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What You'll Learn
Pesticides and herbicides
Pesticides are often used as a quick, easy, and inexpensive solution for controlling weeds and insect pests in urban landscapes and agriculture. However, this comes at a significant cost to the environment. Pesticides have contaminated almost every part of our natural world, from the soil and air to surface and groundwater. They are designed to kill insects and weeds, but they can also be toxic to many other organisms, including birds, fish, beneficial insects, and non-target plants. Insecticides are generally the most acutely toxic class of pesticides, but herbicides can also pose risks to non-target organisms.
The overuse and misuse of pesticides can degrade the soil and harm the community of organisms living in it. Some pesticides are more toxic to soil organisms than others, and certain pesticides may persist in the soil for longer periods, lingering for years or decades after application and continuing to harm soil health. Soil organisms encounter a toxic cocktail of chemicals, as farmers typically use multiple pesticides simultaneously. Pesticides in the soil may be taken up by plant roots and moved to other plant tissues, including fruit. They are also more likely to leach through sandy or coarse-grained soils and contaminate groundwater.
A 2021 peer-reviewed study found that pesticides kill or harm soil invertebrates in 71% of cases reviewed. Negative effects were observed across all studied pesticide classes, including organophosphate, neonicotinoid, pyrethroid, and carbamate insecticides, as well as amide/anilide herbicides and benzimidazole and inorganic fungicides. Pesticides can directly kill soil invertebrates, reduce their reproduction and growth, and impact their cellular function and overall species diversity.
Herbicides, while often considered less harmful, can also cause significant environmental damage. For example, the herbicide 2,4-D was the most commonly found pesticide in a study of 13 streams, detected in 92% of samples. It caused physiological stress responses in sockeye salmon and reduced the food-gathering abilities of rainbow trout. Glyphosate or glyphosate-containing products can cause erratic swimming and labored breathing in fish, increasing their chances of being eaten by predators.
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Industrial waste
Mining activities, for example, can release trace elements such as arsenic, cadmium, cobalt, copper, lead, mercury, and nickel into the environment. The extraction of precious metals can also generate chemically enriched waste, including cyanide solutions. In addition, the use of chemicals in mining and metal processing can further contaminate the soil.
The manufacturing industry, particularly the textile industry, has been known to release untreated effluents containing toxic chemicals such as PFAS (polyfluoroalkyl substances) and dyestuffs, which can pollute soil when spilled or used for irrigation. Leather manufacturing and tanneries produce wastewater containing chlorinated phenols, PCBs, pesticides, and other organic chemicals that are responsible for significant soil pollution.
Energy production, including petroleum refining and fuel combustion, can also contribute to soil pollution. Petroleum spills can contaminate soil with toxic hydrocarbons, and fuel combustion can release mercury and other heavy metal compounds that accumulate in plants and animals, potentially impacting human health through the food chain.
Construction and transportation industries also play a role in soil pollution. Construction sites can generate waste rock deposits and smelting operations, while transportation can lead to petroleum or diesel spills from fuel transportation pipes.
The impact of industrial waste on soil pollution can be long-term, with some organic pollutants, such as persistent organic pollutants (POPs), resisting environmental degradation and accumulating in soils. This can have detrimental effects on plant growth, the food chain, and human health, as contaminants can enter the human body through direct contact, inhalation, or consumption of contaminated plants and animals.
To combat soil pollution from industrial waste, proper waste management practices, such as hazardous waste walk-through programs and improved disposal methods, are essential. By taking environmental responsibility and adopting sustainable practices, industries can help create a safer and more sustainable future.
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Urban waste
- Wastewater and Sewage Contamination: Leakages from wastewater systems introduce various contaminants into the soil, including faecal bacteria, which can eventually reach groundwater. Sewage produced in urbanized areas, if not properly disposed of, can contaminate soil with carcinogenic substances.
- Industrial and Electronic Waste: Industrial activities generate toxic wastes that, when improperly managed or disposed of, contribute to soil pollution. This includes electronic waste (e-waste), which contains hazardous substances like brominated flame retardants (BFRs) found in urban soils near waste and industrial sites.
- Atmospheric Deposition: Urban soil pollution can also result from atmospheric deposition of emissions from industrial and artisanal activities, municipal solid waste incineration, and mining activities in surrounding areas. These emissions contain pollutants that settle onto the soil.
- Transport and Emissions: Transport and emissions from vehicles contribute to soil pollution in urban areas. This includes the release of polycyclic aromatic hydrocarbons (PAHs) from vehicle emissions, leading to soil contamination. Additionally, the use of lead-based paints in the past has resulted in lead contamination in urban soils.
- Solid Waste Management: Poor waste management practices, such as open and unsanitary landfills, contribute to soil contamination. Recycling, waste reduction, and proper treatment of special wastes (e.g., electronics, plastics) are crucial in mitigating soil pollution associated with urban solid waste.
- Domestic and Commercial Waste: Urban areas generate significant amounts of domestic and commercial waste, which can include hazardous substances. Proper segregation and disposal of this waste are essential to preventing soil pollution.
Soil pollution from urban waste has far-reaching consequences, impacting plants, animals, and humans. It can lead to the degradation of essential soil nutrients, affecting plant growth and the entire food chain. Humans, especially children, are susceptible to health risks associated with contaminated soil, including skin irritation, chronic conditions like cancer, and developmental disorders. Therefore, effective waste management and pollution control measures are crucial to mitigating the impact of urban waste on soil pollution.
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Volatile organic compounds
Soils may act as sources or sinks of VOCs. In soils, VOCs are mainly produced by plants and microorganisms. VOCs emitted by plant roots or seedlings have been identified, and their functions have been proposed. Interactions between plants and microbes mediated by VOCs, as well as plant VOC production, measurement, and VOC influences on plants, have been discussed in several reviews.
VOCs can have a detrimental impact on the physical, chemical, and biological properties of soil. They can alter soil structure, reducing its porosity and impairing water infiltration and retention capabilities. This can lead to the degradation of essential soil nutrients, which can then impact plant growth and the entire food chain.
The effect of water on VOCs varies; polar compounds are more strongly retained than aromatic and aliphatic molecules. Soil moisture, temperature, and the presence of plant roots can influence VOC exchange rates. Increases in soil temperature and decreases in soil water availability might enhance soil VOC emissions.
Reduced microbial diversity in soil has been found to increase VOC emissions, while the number of different VOCs emitted decreases. Proteobacteria, Bacteroidetes, and fungi phyla were positively correlated with VOC emissions, while other prokaryotic phyla were negatively correlated or slightly positively correlated.
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Heavy metals
Some of the heavy metals that have been found at higher levels in contaminated soil include Copper (Cu), Lead (Pb), Zinc (Zn), Nickel (Ni), Cadmium (Cd), Chromium (Cr), Iron (Fe), Manganese (Mn), and Arsenic (As). While some heavy metals, such as Co, Cu, Fe, Mn, Mo, Ni, V, and Zn, are required in trace amounts by organisms, excessive amounts can be harmful. Pb, Cd, Hg, and As, on the other hand, are considered the "main threats" as they have no beneficial effect on organisms and are highly toxic.
The presence of heavy metals in soil can have detrimental effects on plant growth and performance. Studies have shown that even low concentrations of Pb, Cd, Hg, and As can lead to significant reductions in plant height, shoot and root growth, and panicle formation. This, in turn, can impact food security and the entire food chain. Additionally, heavy metals can interfere with the activity of microorganisms and earthworms in the soil, further disrupting the natural balance.
To address heavy metal pollution in soil, various remediation techniques have been developed, including physical, chemical, and biological methods. Biological methods, such as bioremediation and phytoremediation, are often preferred as they are more environmentally friendly and encourage the reestablishment of plants on treated soils. Phytoremediation, for example, uses vegetation and associated microbiota to remove, contain, or render heavy metals harmless. However, the success of phytoremediation depends on factors such as growing conditions, plant tolerance to pollutants, and the specific metal hyperaccumulators used.
Overall, the presence of heavy metals in soil is a significant environmental concern that requires effective solutions to mitigate their impacts on human health, ecosystems, and the food chain. Preventing the contamination of soil by heavy metals should be a priority for humans and the environment alike.
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Frequently asked questions
Soil pollution is caused by the presence of toxic chemicals, known as soil pollutants, in high enough concentrations to pose a risk to human health and/or the ecosystem. These chemicals include pesticides, fertilizers, herbicides, heavy metals, petroleum hydrocarbons, and volatile organic compounds (VOCs).
Pesticides are substances used to kill pests, such as insects and weeds. They are synthetic toxic chemicals that can accumulate in the soil due to their non-biodegradable nature, leading to ecological repercussions and health risks for humans and other organisms.
Heavy metals such as lead, arsenic, cadmium, and manganese can contaminate soil through industrial activities, vehicle emissions, tire wear, and proximity to roadways or industrial areas. These metals pose significant health risks, including reduced IQ, cancer, and various other negative health effects.
VOCs are organic chemical compounds that evaporate easily at room temperature. They are commonly found in petroleum fuels, paint thinners, and dry cleaning agents. When soil becomes contaminated with VOCs, its physical, chemical, and biological properties can be altered, impacting soil structure and water infiltration capabilities.
