Soil Pollution: Understanding The Contaminants In Our Soil

Soil is foundational to human health, supporting diverse ecosystems and critical ecological services such as pollination, water retention, and carbon capture. However, soil pollution, caused by both natural and anthropogenic factors, poses a significant threat to soil health and, consequently, human health. Soil pollution refers to the contamination of soil by toxic substances, including heavy metals, pesticides, and radioactive materials, which can have detrimental effects on human and ecosystem well-being. With soil pollution contributing to approximately 500,000 premature deaths globally each year, understanding and addressing this issue is crucial for safeguarding the environment and human populations.

Natural vs. anthropogenic causes of soil pollution

Soil is foundational to human health and survival. It is essential for growing crops, providing food, and sustaining populations. However, soil pollution poses a significant threat to soil health and, consequently, to human health. Soil pollution arises from various sources, primarily due to human activities, but natural causes also contribute to soil pollution.

Natural Causes of Soil Pollution

Natural processes can influence the toxicity and contamination levels of human-released chemicals in the soil. Natural disasters, such as floods, tsunamis, and storm surges, can also lead to soil pollution. Additionally, natural accumulation of chemicals can, in rare cases, result in soil pollution.

Anthropogenic Causes of Soil Pollution

Anthropogenic or man-made causes of soil pollution are the primary contributors to soil contamination. These include:

• Industrial activities: Waste materials from industries can linger on the soil surface, making it unsuitable for plant growth. Accidental spills and leaks during storage, transport, or use of chemicals can also occur.
• Agricultural activities: The overuse of chemical fertilisers, pesticides, and herbicides contaminates the soil. These chemicals seep into the ground, reducing soil fertility and making it more susceptible to erosion. Plants absorb these pesticides, and when they decompose, they contribute to soil pollution.
• Waste disposal: Improper disposal of waste, including municipal, nuclear, and mining waste, leads to soil pollution. This includes urban waste, such as garbage, rubbish, dried sludge, and sewage, which can contain toxic substances.
• Construction sites: Construction activities can release various chemical substances, such as asbestos and fine particulate matter, which can easily spread through the air and contaminate the soil.
• Mining activities: Mining processes can disturb the soil and release toxic materials, including heavy metals.
• Vehicle exhaust: Lead released from automobile exhaust can settle on roadsides and contaminate the soil.
• Deforestation: Clearing forests can lead to soil erosion and the release of sequestered pollutants, contributing to airborne dust and further soil pollution.

Health hazards of soil pollution

Soil pollution is a serious environmental concern due to the health hazards it poses. Soil may be polluted by heavy metals, organic chemicals such as pesticides, biological pathogens, and micro/nanoplastic particles. The presence of heavy metals such as lead and mercury in high concentrations can make soil highly toxic to humans. Polycyclic aromatic hydrocarbons (PAHs) are organic compounds that have been linked to several forms of cancer and cardiovascular disease in humans. Soil pollution due to PAHs can come from vehicle emissions, cigarette smoke, and the extraction of shale oil.

The improper disposal of toxic industrial/chemical waste is another cause of soil pollution. This includes the use of toxic pesticides, which can contaminate soil and result in food crop contamination and disease. The health effects of contaminated crops include colorectal cancer, bladder and breast cancer, thyroid disease, methemoglobinaemia, and neural tube defects. Soil pollution can also occur due to nuclear waste, e-waste, and coal ash.

Airborne soil contamination is another less acknowledged cause of health hazards. Cultivation for agricultural production and wind erosion from unpaved roads and worksites can release soil into the atmosphere as dust. This airborne dust can cause irritation of the respiratory tract and increase the risk of pulmonary diseases such as pneumonia, chronic obstructive bronchitis, and lung cancer. The dust may also carry pathogens, harmful gases, organic chemicals, heavy metals, and radioactive materials, which can cause severe adverse health effects.

Soil pollution reduces the soil's ability to yield food and supports ecosystems and critical ecological services such as pollination. It also impacts the water supply by causing water pollution when soil pollutants wash into rivers. Soil health is connected to human health, and pollution poses a significant threat to both.

Soil pollution and food security

Soil pollution is a pressing issue that poses a significant threat to human health and food security. It refers to the contamination of soil with abnormally high concentrations of toxic substances, which can have detrimental effects on the ecosystem and human well-being. The pollution of air, water, and soil is responsible for a substantial number of deaths each year, with cardiovascular disease being the most prevalent pollution-related disease.

Soil, whether polluted or not, naturally contains a range of compounds, including metals, inorganic ions, salts, and organic compounds. However, soil pollution occurs when the amounts of these compounds exceed natural levels. This can happen due to anthropogenic (man-made) causes, such as improper waste disposal, industrial activities, agricultural pesticides, and urban waste, or natural causes, like the accumulation of certain compounds in arid ecosystems.

The primary pollutants of soil are biological agents and human activities. Agricultural practices, such as the excessive and improper use of pesticides, herbicides, and fertilizers, can contaminate crops and soil, impacting their health and composition. This, in turn, affects the ability of plants to absorb nutrients, leading to diminished nutrient uptake by crops and exacerbating micronutrient deficiencies in the food chain. For example, heavy metal pollution from lead and cadmium in the soil can inhibit the absorption of essential minerals by plant roots, resulting in lower concentrations of vital micronutrients in fruits and vegetables.

Additionally, industrial activities and urban waste contribute to soil pollution. Improper disposal of toxic industrial and chemical waste, such as nuclear waste, e-waste, and coal ash, can severely contaminate the soil. Urban waste, including garbage, sewage, and sludge, can also contain carcinogenic substances. Furthermore, radioactive substances like radium, thorium, and uranium can infiltrate the soil, creating toxic effects and posing risks to human health.

The impact of soil pollution on food security is concerning. Healthy soil is essential for producing safe and nutritious food, supporting diverse ecosystems, and providing critical ecological services like pollination and water regulation. Soil pollution reduces the soil's ability to yield food, leading to crop contamination and disease. Implementing sustainable agricultural practices, such as organic farming and soil remediation techniques, is crucial to reducing soil pollution and enhancing soil fertility, thereby improving food security.

Addressing soil pollution requires a multi-faceted approach, including the adoption of sustainable practices and the remediation of contaminated soils. By mitigating soil pollution, we can enhance food security, protect human health, and ensure the long-term viability of our food systems.

Soil remediation techniques

In-Situ Soil Remediation

In-situ remediation involves treating the contaminated soil in place, without removing it from the site. This method includes various technologies such as:

• In Situ Chemical Oxidation (ISCO): This process uses reduction/oxidation (redox) reactions to convert hazardous compounds into non-hazardous or less toxic, more stable compounds.
• In Situ Chemical Reduction: This technique involves placing a reductant or reductant-generating material in the subsurface to degrade toxic organic compounds into potentially non-toxic or less toxic compounds.
• In Situ Thermal Treatment: This method applies heat to polluted soil to destroy or volatilize organic chemicals, which can then be extracted through collection wells for further treatment.
• Air Sparging: Air or oxygen is injected through a contaminated aquifer to remove volatile and semi-volatile organic contaminants by volatilization.
• Activated Carbon (AC)-Based Technology: AC-based amendments are used for in situ remediation of soil and groundwater, removing contaminants through adsorption and degradation.

Ex-Situ Soil Remediation

Ex-situ remediation involves removing the contaminated soil from the site and treating it elsewhere. Examples of ex-situ techniques include:

• Horizontal Remediation Wells (HRWs): These are installed below ground, offering an alternative to conventional vertical wells, especially when access to soil and groundwater contamination is obstructed by surface barriers.
• Solvent Extraction: An organic solvent is used to separate organic and metal contaminants from the soil, followed by a separation process to remove the contaminants.
• Ex Situ Thermal Treatment: This method involves the destruction or removal of contaminants through exposure to high temperatures in treatment cells or combustion chambers.
• Bioreactor Landfills: These use liquid and air to enhance microbial processes, rapidly transforming, degrading, and stabilising organic waste.

Combined Remedies

In some cases, a combination of in-situ and ex-situ techniques may be necessary to effectively clean up a contaminated site. Treatment trains are planned series of actions that address the problem using multiple technologies. For example, electrokinetics can be used to mobilise charged species in the soil, while evapotranspiration covers help manage water precipitation on landfills to contain waste.

Bioremediation

Bioremediation uses microorganisms to degrade organic contaminants in soil, groundwater, sludge, and solids. The microorganisms break down the contaminants by using them as an energy source or cometabolising them with another energy source. While bioremediation can be a lengthy process, it is often more cost-effective than other techniques.

Soil Amendments

Soil amendments, such as Blastox 215®, can be added directly to contaminated soil to stabilise and encapsulate heavy metals, rendering them non-hazardous. These amendments reduce the mobility and availability of contaminants in the soil.

Soil pollution in China

Soil pollution, defined as the contamination of soil with toxic substances at higher-than-normal concentrations, is a significant environmental issue in China. It poses risks to human health, the environment, and agricultural productivity. China's rapid industrialisation, extensive agricultural practices, and inadequate waste management have led to soil degradation and the presence of harmful substances.

One prominent example of soil pollution in China is the widespread contamination by heavy metals, including cadmium, arsenic, and lead. This is primarily due to industrial activities and the improper disposal of waste. Hunan Province, known for its nonferrous metal mining, has experienced serious environmental and health issues due to elevated levels of cadmium in the soil. This has contaminated local food sources, particularly rice, raising food safety concerns and impacting millions of residents.

The extensive use of chemical fertilisers and pesticides in agriculture has also significantly contributed to soil pollution in China. This has led to reduced soil fertility and decreased agricultural productivity. Contamination of the food chain poses risks to human health, and water pollution occurs through the leaching of contaminants. Soil pollution in China has far-reaching consequences, underscoring the urgent need to address this issue effectively.

To tackle soil pollution, China has recognised it as a key national priority and is investing significant funds in soil remediation. The country has also developed its own Soil Environmental Quality Standards (SEQS) to define and address pollution problems. Additionally, China is exploring the polluter-pays principle when implementing regulations under its new soil pollution control law. However, enforcement challenges exist, as it can be difficult to identify the responsible parties for pollution.

Frequently asked questions