Brian Barton
Soil pollution is a growing threat to global health, causing an estimated 9 million premature deaths in 2015 alone. It is caused by the presence of xenobiotic (human-made) chemicals or other alterations in the natural soil environment. While some pollutants are naturally accumulated in soil, such as perchlorates in arid ecosystems, almost all cases of soil pollution are anthropogenic in nature. The most common types of pollutants include heavy metals, toxic organic chemicals, pesticides, biological pathogens, and plastic waste. These pollutants can have adverse effects on human and ecosystem health, causing various health issues such as headaches, nausea, fatigue, skin rashes, and eye irritation, and more severe conditions like cancer. Soil pollution also affects plant life, reducing crop yields and threatening soil functions. The remediation of polluted soils is essential to minimize the impact on human health and the environment.
| Characteristics | Values |
|---|---|
| Causes | Natural processes, anthropogenic (man-made) causes |
| Man-made causes | Industrial waste, agricultural pesticides, improper disposal of waste, industrial activities, munitions, manufacturing |
| Natural causes | Atmospheric deposition, transportation of pollutants with precipitation water, accumulation of toxic chemicals, arid environments |
| Pollutants | Heavy metals (lead, mercury, cadmium, chromium), petroleum hydrocarbons, solvents, pesticides, polynuclear aromatic hydrocarbons (PAHs), dioxins, benzene, methylbenzene, herbicides, insecticides, fungicides, inorganic arsenic, radionuclides, biological pathogens, plastic waste |
| Effects | Soil degradation, health risks (cancer, congenital disorders, cardiovascular issues, CNS depression, organ damage), reduced crop yields, soil erosion, decreased nutrient availability, increased soil salinity, groundwater contamination, bioaccumulation in plants and animals |
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What You'll Learn
- Industrial waste, e.g. pesticides, incineration of waste, and petroleum hydrocarbon waste
- Agricultural chemicals, e.g. pesticides, herbicides, insecticides, and fungicides
- Heavy metals, e.g. lead, mercury, chromium, arsenic, cadmium, and aluminium
- Xenobiotics, i.e. human-made substances not found in nature, e.g. PAHs, dioxins, and benzene
- Natural processes, e.g. atmospheric deposition, precipitation, and arid environments
Industrial waste, e.g. pesticides, incineration of waste, and petroleum hydrocarbon waste
Industrial waste is a major contributor to soil pollution, with a range of harmful chemicals and compounds being released into the soil. This includes pesticides, incineration waste, and petroleum hydrocarbon waste.
Pesticides are widely used in agriculture to control pests and weeds, but their excessive use and improper disposal can lead to soil pollution. When pesticides are applied to crops, they can be washed off by rainfall or irrigation, ending up in the soil. Leaking pipes, spills, damaged containers, waste dumps, and underground storage tanks can also lead to accidental pesticide release. The disposal of obsolete pesticide stocks and contaminated soil is challenging, with incineration being costly and impractical for small waste generators. The persistence of pesticides in the environment due to their long half-lives poses risks to humans and the environment, including water and soil pollution.
Incineration of waste is another source of soil pollution. Dioxins, for example, are produced during the incineration process and can contaminate the soil. Open burning of plastics, in particular, releases polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, which are persistent organic pollutants (POPs) regulated by the Stockholm Convention.
The petroleum industry generates numerous hydrocarbon waste products, such as benzene and methylbenzene, which are known carcinogens. Spills and leaks during transportation can contaminate soils with these hydrocarbons, leading to soil pollution. Additionally, activities related to metal casting factories and underground mining can result in the dispersion of metallic contaminants and heavy metals into nearby soils, further exacerbating the issue.
Soil acts as a natural sink for contaminants, accumulating and sometimes concentrating pollutants from various sources. These pollutants can have detrimental effects on plant life, increasing soil salinity and reducing nutrient availability, making it challenging for plants to thrive. When plants are grown in polluted soil, they can accumulate high concentrations of soil pollutants through bioaccumulation, passing these pollutants up the food chain when consumed by herbivores.
The impact of soil pollution on human health cannot be understated. Soil pollutants like petroleum hydrocarbons and industrial solvents have been linked to congenital disorders. Additionally, children are especially vulnerable to pollutants like lead, which can cause central nervous system depression and damage to vital organs. Soil pollution can also lead to an increased risk of developing cancer and cardiovascular diseases.
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Agricultural chemicals, e.g. pesticides, herbicides, insecticides, and fungicides
Agricultural chemicals are a major cause of soil pollution. Pesticides, herbicides, insecticides, and fungicides are all designed to kill or control unwanted organisms, but they can also have unintended consequences for the environment and human health.
Pesticides are a broad category of substances used to kill pests. This includes insecticides, which target insects, fungicides, which target fungi, herbicides, which target weeds and other unwanted plants, and rodenticides, which target rodents. Pesticides can be organic or inorganic, with inorganic pesticides including copper sulfate, ferrous sulfate, copper, lime, and sulfur. Many pesticides are synthetic chemical compounds, such as organochlorine insecticides, which were widely used to control diseases like malaria and typhus but have since been banned or restricted due to their harmful effects on non-target organisms and the environment. Other types of pesticides include organophosphates, carbamates, and pyrethroids.
The use of pesticides in agriculture can result in soil pollution through various pathways. Pesticides can reach the soil after being sprayed on foliage and then washed off by rainfall or irrigation, or they can be released from treated seeds or applied directly to the soil. Accidental releases can also occur due to leaking pipes, spills, damaged containers, waste dumps, or underground storage tanks. The improper disposal of unwanted or outdated pesticides and their packaging can further contribute to soil pollution.
Once in the soil, pesticides can exhibit different behaviors depending on their chemical properties. Some pesticides, such as organochlorine DDT, endosulfan, endrin, heptachlor, and lindane, are hydrophobic, persistent, and bioaccumulable, meaning they strongly bind to soil particles and have long half-lives. This can lead to the accumulation of toxic residues in the soil, which can then be taken up by plants through a process called bioaccumulation. Other pesticides, such as carbamates, fungicides, and some organophosphorus insecticides, are not persistent in the soil but can leach into different environmental media, including water, posing risks to drinking water supplies and the food chain.
The use of agricultural chemicals has raised concerns due to their potential impacts on human health and the environment. Pesticides can be toxic not only to target pests but also to non-target organisms, including birds, fish, beneficial insects, and plants. They can contaminate the air, water, soil, and crops, leading to environmental pollution and food contamination. Additionally, the rampant use of these chemicals can have unintended consequences, as illustrated by the controversy surrounding their use and abuse. Furthermore, climate change-related factors are leading to increased pesticide usage, exacerbating the problem of pesticide pollution.
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Heavy metals, e.g. lead, mercury, chromium, arsenic, cadmium, and aluminium
Heavy metals are naturally occurring elements with a high atomic weight and a density of at least five times that of water. They have a wide range of industrial, domestic, agricultural, medical, and technological applications, leading to their presence in the environment. Heavy metals are toxic to humans and the environment, and their presence in soil can cause soil pollution.
Some of the most common heavy metals that induce human poisoning include mercury, lead, chromium, cadmium, and arsenic. These metals are known as carcinogens and can cause multiple organ damage, even at lower levels of exposure. They are also considered systemic toxicants, which means they can induce multiple organ damage even at lower levels of exposure. For example, lead can cause depression of the central nervous system and damage vital organs such as the kidneys and liver. Children are especially vulnerable to lead poisoning, which can also increase their risk of developing cancer.
Heavy metals can enter the soil through various sources, including mining activities, agricultural activities, electronic waste, and medical waste. They can also enter the soil through industrial waste, such as the improper disposal of waste and the discharge of industrial waste into soils. Once in the soil, heavy metals can accumulate to toxic levels, particularly in agricultural soils, adversely affecting crop health and productivity. The toxicity of heavy metals on crops depends on several factors, including crop type, growth conditions, and the developmental stage of the crop. Heavy metals can disrupt the normal structure and function of cellular components and impede various metabolic and developmental processes in plants.
Soil acts as a natural sink for contaminants, accumulating and sometimes concentrating them. When the amounts of contaminants exceed natural levels, pollution is generated. Heavy metal pollution in soil can have several negative effects on the environment and human health. It is important to test soil for heavy metals, especially if children will be playing in the area or if edible plants are being grown.
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Xenobiotics, i.e. human-made substances not found in nature, e.g. PAHs, dioxins, and benzene
Xenobiotics are human-made substances that are not found in nature. The term 'xenobiotic' is derived from the Greek words 'xenos' (foreigner) and 'bios' (life). These compounds are usually introduced for domestic, agricultural, and industrial purposes. Xenobiotics can have toxic, mutagenic, or teratogenic effects on humans and the environment. They are often present in wastewater treatment plants, affecting both humans and animals.
Xenobiotics include pharmaceuticals, pesticides, pollutants, carcinogens, volatile petrochemicals, food additives, and more. For example, the manufacture of pesticides and the incineration of waste produce dioxins, which are xenobiotics. Dioxins are subject to the Stockholm Convention, which aims to control and eliminate persistent organic pollutants (POPs). These pollutants accumulate through the food chain and are toxic to humans and wildlife.
Polycyclic Aromatic Hydrocarbons (PAHs) are another group of xenobiotics. PAHs are organic compounds released by the petroleum industry and are responsible for pollution in aquatic habitats. They are also found in coal refineries, phenol manufacturing, and as a result of crude oil spills. PAHs are a group of different organic compounds, including naphthalene, phenol, phenanthrene, anthracene, biphenyl, and pyrene.
Benzene is a known carcinogen and a xenobiotic. It is one of the many petroleum hydrocarbon waste products created by the petroleum industry. These waste products are known to have negative effects on human health, including congenital disorders and an increased risk of developing cancer.
While natural processes can lead to soil pollution in rare cases, man-made contaminants are the primary cause of soil pollution. Xenobiotics, as human-made substances, contribute significantly to soil pollution. They can enter the soil through industrial waste, agricultural activities, and improper waste disposal. The presence of xenobiotics in the soil can have detrimental effects on plants, animals, and humans.
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Natural processes, e.g. atmospheric deposition, precipitation, and arid environments
Soil pollution is the presence of toxic chemicals (pollutants or contaminants) in soil, in high enough concentrations to pose a risk to human health and/or the ecosystem. While most cases of soil pollution are anthropogenic in nature, there are some rare natural processes that can lead to soil pollution.
One such process is atmospheric deposition, where pollutants are naturally accumulated in soils due to the differential deposition of soil by the atmosphere. This can occur through wind activity or other types of soil disturbances, and from surface water bodies and shallow groundwater flowing through the soil. An example of atmospheric deposition is the long-range transport of dust from Africa to North America, leading to elevated levels of Hg, Se, and Pb in North American soil.
Another natural process that can lead to soil pollution is precipitation, where pollutants are transported with precipitation water and deposited onto the soil. This can occur through rainfall or irrigation, as seen in the case of pesticides being washed off treated foliage and ending up in the soil.
In rare cases, arid environments can also contribute to soil pollution. For example, the accumulation of compounds containing the perchlorate anion (ClO4–) has been observed in some dry, arid ecosystems. Perchlorates can be naturally produced in soils containing chlorine and certain metals during a thunderstorm. An example is the accumulation of higher levels of perchlorate in the soil from the Atacama Desert in Chile, which is attributed to natural processes in arid environments.
It is important to note that while these natural processes can lead to soil pollution, the contamination threshold is only crossed when the amounts of soil contaminants exceed their natural levels. Below these levels, the presence of contaminants in soil is considered normal and does not constitute soil pollution. Additionally, soil acts as a natural sink for contaminants, accumulating and sometimes concentrating them.
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