Also know as “invisible pollution,” soil pollution occurs when the presence of toxic substances in the soil reach high enough concentrations to pose a threat to human health and/or the ecosystem. It’s called invisible pollution because its effects aren’t as easily observable as other forms of pollution such as air and water. All soils, polluted or not, include an assortment of inorganic and organic substances that are naturally present. When the quantities of soil contaminants exceed natural levels, pollution is created. Various contaminants can enter the soil from the air, through wind and rain, as well as rivers, streams, and underground water sources.
Most common types of soil contaminants
- Lead (Pb): lead paint, mining, foundry activities, vehicle exhaust, construction activities, agricultural activities
- Mercury (Hg): mining, coal burning, alkali and metal processing, medical waste
- Arsenic (As): mining, coal-fired power plants, lumber facilities, electronics industry, foundry activities, agricultural activities
- Copper (Cu): mining, foundry activities, construction activities
- Zinc (Zn): mining, foundry activities, construction activities
- Nickel (Ni): mining, foundry activities, construction activities
- Polyaromatic Hydrocarbons (PAHs): coal burning, vehicle emissions, smoke (particles accumulate in the air and settle in the ground)
- Herbicides/Insecticides: gardening, agricultural activities
Main Causes of Soil Pollution
1. Industrial Activity
In the last century, mining, foundry, and manufacturing have increased exponentially, causing industrial activities to become the greatest source of soil pollution. In today’s technologically based world, most businesses rely on the extraction of minerals. No matter what’s being extracted, the byproducts contain pollutants that are rarely disposed of properly which makes soils unsuitable for use.
2. Agricultural Activities
Fertilizers and pesticides are filled with chemicals that aren’t produced in nature and can’t be broken down by it either. Because of this, they stay in the ground and gradually decrease the fertility of soil. Some compounds damage the entire makeup of soil and make it more susceptible to erosion.
3. Waste Disposal
While industrial waste causes the most pollution, another method we’re adding to it is through human waste. Our bodies are filled with toxins that leak into the ground as our waste decomposes. Even though it moves through the sewer system, it eventually ends up in a landfill. There’s also a massive sum that’s dumped into landfills in the shape of diapers.
4. Oil Spills
Oil spills can occur during storage and transportation or through leaks in machinery such as cars. You can easily see oil on the ground at the majority of gas stations, in driveways, or where cars are commonly parked. After working on cars or other machinery, mechanics also end up washing the oil off their bodies and down the drain. The compounds within oil destroys the quality of soil, making it unsuitable for growth, and water unsuitable for drinking.
5. Acid Rain
Acid rain forms when pollutants in the air from fuel burning emissions mixes with rain. As it gets absorbed by the ground, the acid rain can dissolve away a number of the critical nutrients found in soil and adjust its structure.
6. Leaking Sewers, Underground Tanks, and Underground Pipelines
Underground sewer systems, pipes, and tanks can leak if they crack due to rusting or the natural adjustments of the earth. When this occurs, toxic compounds are released into the surrounding soils resulting in its pollution. Leaking sewers can also release harmful disinfectants such as trihalomethanes that destroy beneficial bacteria in the soil.
7. Construction Activities
In virtually every metropolitan area, wastes and other hazardous building materials used at construction sites can pollute the soil. With a growing population, development of more and more areas is at an all time high.
Effects of Soil Pollution
1. Changes in Soil Structure
As toxicity rises, fungi and bacteria that bind soil start to decrease, which causes soil erosion issues. Some chemicals can cause the death of organisms such as earthworms and may result in unfavorable changes in soil structure. Beyond that, it might also force different predators to seek food in other areas, disrupting the balance of the food chain.
2. Decreased Soil Fertility
The harmful chemicals within soil may destroy many beneficial nutrients and so, reduce the yield from potential crops. Anything that is harvested may lack quality nutrients and could contain toxic substances that cause significant health problems in people that consume them. As fertility declines, land becomes unsuitable for agriculture and for any local vegetation to survive. Long term soil pollution can even lead to widespread famines if the plants are unable to grow in it.
3. Effect on Human Health
Soil pollution can cause disease in humans and animals through bioaccumulation. Bioaccumulation occurs when plants grown in polluted soils absorb toxins, and in turn deliver them to the creatures that eat them. Toxic amounts of heavy metals in the body can damage organs such as the kidney and liver and cause neuromuscular blockages triggering headaches, fatigue, and nausea, among other ailments. In fact, many common soil pollutants are carcinogenic and those exposed to them are far more likely to develop cancer than those who aren’t.
4. Toxic Air
Soil pollution also contributes to air pollution by releasing volatile compounds into the atmosphere, and the more it contains, the more it releases. The emission of toxic and foul gases from landfills pollutes the environment and causes serious health effects for some people. And because of deforestation and constant development, enough plants cannot grow to remove harmful other compounds from the atmosphere. In turn, this causes a greater greenhouse effect and contributes further to global warming.
5. Effects on the Economy
In addition to creating health problems, soil pollution also causes economic issues. According to a scientific sampling, 100,000 square kilometers of China’s agricultural land has been severely polluted and an estimated 12 million tons of grain are contaminated every year, which equates to a loss of $2.5 billion.
Reversing Soil Pollution
Hyperaccumulators are plants that absorb and store extremely high concentrations of metals from soil and are capable of growing in soils too toxic for other plants. This makes hyperaccumulators a perfect option for cleaning contaminated soils through a process called phytoremediation.
Phytoremediation is the direct use of living green plants for removal, degradation, or containment of pollutants in soils, sludges, sediments, surface water
There are over 500 known species of hyperaccumulating plants and interest in them is growing because of their ability to extract metals from contaminated sites.
List of Hyperaccumulating Plants
- Aluminum (Al): Highland Bent Grass, Barley, Hydrangea, Native Lassiandra, Hairy Goldenrod, Horse Bean
- Silver (Ag): Rapeseed Plant, Osiers, European Pine, Indian Mustard
- Arsenic (As): Common Bent Grass, Colonial Bent Grass, Ink Stain Bolete, Ladder Brake Fern, Violet Crown Cup
- Chromium (Cr): Duckweed Fern, Smooth Water Hyssop, Indian Mustard, Rapeseed Plant, Tape Grass, Water Hyacinth, Sunflower, Alfalfa, Alpine Pennycress
- Copper (Cu): Pacific Mosquito Fern, Brahmi, Indian Mustard, Water Hyacinth, Copper Flower, Sunflower, Duckweed, Alpine Pennycress
- Manganese (Mn): Highland Bent Grass, Pacific Mosquito Fern, Indian Mustard, Sunflower, Koshiabura
- Mercury (Hg): Brahmi, Rapeseed Plant, Water Hyacinth, Osiers
- Molybdenum (Mo): Alpine Pennycress
- Naphthalene: Tall Fescue, Pink Clover
- Lead (Pb): Highland Bent Grass, Ragweed, Pacific Mosquito Fern, Smooth Water Hyssop, Indian Mustard, Rapeseed Plant, Water Hyacinth, Morning Glory, Duckweed, Alpine Pennycress, Common Wheat
- Selenium (Se): Muskgrass, Ragweed, Osiers
- Zinc (Zn): Highland Bent Grass, Indian Mustard, Rapeseed Plant, Sunflower, Water Hyacinth, Bladder Campion, Alpine Pennycress
Through phytoremediation, hyperaccumulating plants generate another field of interest called phytomining. Phytomining is the process by which target metals are extracted from hyperaccumulating plants, and can be done in various ways. The most effective way, however, is to burn the plant material in a furnace and recover the metals from the ashes. Some results yielded 100mg of nickel from 500mg of plant ash. According to a 2009 study, a hectare of the plant Brassica Juncea, or Brown Mustard, could return a profit of approximately $26,000.
While the latest discoveries have yet to provide a sustainable and scalable method, interest in the subject is growing because of the pressures on mining companies to operate in a sustainable way.