What are the pollutants that contaminate soil
There are multiple sources of soil pollution. Some of the most dangerous soil pollutants are xenobiotics—substances not naturally found in nature, synthesized by humans. The term “xenobiotic” has Greek roots—”Xenos” (foreign) and “Bios” (life). Many xenobiotics are known to be carcinogenic. Below is an illustration detailing the main soil pollutants.
Different types of pollutants:
Heavy metals
The presence of heavy metals (such as lead and mercury in abnormally high concentrations) in soils can make them highly toxic to humans.
Toxic metals that cause soil pollution
These metals can come from various sources, such as mining activities, agricultural activities, electronic waste (e-waste), and medical waste.
Polycyclic aromatic hydrocarbons (PAHs)
Polycyclic aromatic hydrocarbons (often abbreviated as PAHs) are organic compounds that:
- Contain only carbon and hydrogen atoms.
- Have more than one aromatic ring in their chemical structure.
Common examples of PAHs include naphthalene, anthracene, and phenalene. Exposure to PAHs has been linked to several types of cancer. These organic compounds can also cause cardiovascular diseases in humans.
Soil pollution due to PAHs can be caused by coke (coal) processing, vehicle emissions, cigarette smoke, and oil shale extraction.
Industrial waste
Some common soil pollutants that may come from industrial waste include:
- Chlorinated industrial solvents
- Dioxins produced in the manufacture of pesticides and waste incineration
- Plasticizers/dispersants
- Polychlorinated biphenyls (PCBs)
The petroleum industry generates many petroleum hydrocarbon wastes. Some of these wastes, such as benzene and methylbenzene, are known to be carcinogenic.
Pesticides
Pesticides are substances (or mixtures of substances) used to kill or inhibit the development of pests. Common types of pesticides used in agriculture include:
- Herbicides – used to kill/control weeds and other unwanted plants.
- Insecticides – used to kill insects.
- Fungicides – used to kill parasitic fungi or inhibit their growth.
However, the unintended spread of pesticides into the environment (commonly known as “pesticide drift”) raises a series of environmental issues, such as water and soil pollution.
Herbicides
- Triazines – a class of organic compounds with a ring consisting of three carbon and three nitrogen atoms. They are frequently used in agriculture as herbicides, the most well-known being atrazine.
- Carbamates – esters of carbamic acid, mainly used as insecticides. These compounds act by inhibiting an essential enzyme in the nervous system of insects.
- Amides – derivatives of carboxylic acids where the –OH group of the acid is replaced with an –NH₂ group. Amides have various applications, from medicine to the production of plastics.
- Phenoxyalkanoic acids – derivatives of carboxylic acids with a structure that includes an aromatic ring (phenol) attached to an alkyl chain. They are used as systemic herbicides, such as 2,4-D, which controls weeds.
- Aliphatic acids – organic acids containing non-aromatic carbon chains. The most well-known aliphatic acid is acetic acid (vinegar). They are essential in organic chemistry and have multiple industrial uses.
Insecticides
- Organophosphates – a class of chemical compounds containing phosphorus, frequently used as insecticides. They act by inhibiting acetylcholinesterase, an enzyme essential for the functioning of the insect nervous system, but they can also be toxic to humans.
- Chlorinated hydrocarbons – organic compounds containing carbon and hydrogen atoms with attached chlorine atoms. They are used as pesticides (e.g., DDT) or in industry, but they persist in the environment and can have negative effects on health and ecosystems.
- Arsenic-containing compounds – these compounds, which include arsenic in their chemical structure, were used in the past as pesticides and herbicides, but many are highly toxic to humans and the environment. For this reason, their use is strictly regulated or banned.
- Pyrethrum – a natural insecticide extracted from chrysanthemum flowers. It is relatively safe for humans and animals and has a quick effect on insects by blocking nervous system functions. It is often used as a less toxic alternative to other pesticides.
Fungicides
- Mercury-containing compounds – these include substances with mercury in their structure, such as methyl mercury or mercury chloride. They were previously used in agriculture, medicine, and industry, but due to their high toxicity and devastating effects on human health and the environment, their use is now strictly regulated or banned.
- Thiocarbamates – derivatives of carbamates, containing a sulfur atom in their structure. Thiocarbamates are primarily used as herbicides and fungicides, effective in combating weeds and plant diseases.
- Copper sulfate – an inorganic chemical substance widely used as a fungicide and algicide. It is effective in controlling plant diseases caused by fungi and is also used to combat algae in bodies of water. Although relatively effective, excessive exposure to copper can be toxic to the environment and aquatic organisms.
These chemical substances pose several health risks to humans. Examples of health hazards related to pesticides include central nervous system disorders, immune system diseases, cancer, and congenital disabilities.
Effects of soil pollution on plants and animals
Soil pollution has devastating effects on its health and fertility, and one of the most severe consequences is the reduction of essential nutrients available for plants. This phenomenon leads to a series of issues affecting plants, ecosystems, and agriculture. Polluted soils can no longer provide necessary nutrients, such as nitrogen, phosphorus, and potassium. Without these nutrients, plants cannot perform photosynthesis and other essential metabolic processes, slowing their growth and making them more vulnerable to diseases and pests.
Plants grown in polluted soils can accumulate high concentrations of pollutants through a process known as bioaccumulation. When these plants are consumed by herbivores, all accumulated pollutants move up the food chain. This can lead to the loss/extinction of many desirable animal species. These pollutants may also eventually reach the top of the food chain and manifest as diseases in humans.
Effects of pollution on human beings
Humans can be affected by soil pollution through the inhalation of gases released by soils that move upward or by inhaling matter disturbed and carried by wind due to various human activities on the soil. Soil pollution can cause a variety of health issues, starting with headaches, nausea, fatigue, skin rashes, eye irritation, and potentially leading to more severe conditions, such as neuromuscular blockage, kidney and liver diseases, and various forms of cancer.
Effects of pollution on the ecosystem
Since volatile contaminants in soil can be carried into the atmosphere by wind or seep into groundwater reserves, soil pollution can directly contribute to air and water pollution.
It can also contribute to acid rain (through the release of large amounts of ammonia into the atmosphere). Acidic soils are inhospitable to many microorganisms that improve soil texture and help break down organic matter. Thus, the negative effects of soil pollution also impact soil quality and texture.
Crop yields are heavily affected by this form of pollution. In China, over 12 million tons of grain (worth approximately $2.6 billion) are considered unfit for human consumption due to heavy metal contamination (according to studies by China Dialogue).
These outcomes are the result of uncontrolled industrial, agricultural, and urban activities that introduce toxic chemicals and heavy metals into the soil. The negative impact of soil pollution on the food chain and groundwater sources highlights the need for immediate and effective soil pollution reduction measures to address this issue.