Soil contamination facts for kids

Soil contamination, also known as soil pollution or land pollution, happens when harmful substances are found in the soil. These substances are often chemicals made by humans, or they can be natural substances that are present in amounts that are too high. Soil pollution is a type of land degradation, which means the soil becomes less healthy and useful.

This pollution usually comes from factories, farms using too many chemicals, or from throwing away trash incorrectly. Common pollutants include chemicals from oil, special types of hydrocarbons, solvents, pesticides, lead, and other heavy metals. The more industry and chemicals a place has, the more likely its soil is to be polluted. People worry about soil pollution because it can harm our health. You can get sick from touching polluted soil, breathing in its fumes, or if the chemicals get into our drinking water. Cleaning up polluted soil is a big, expensive job that needs experts in many different fields.

In places like North America and Western Europe, people know a lot about polluted land. Many countries there have laws to find and clean up these areas. However, developing countries often have fewer rules, even though some have a lot of industry.

What Causes Soil Pollution?

Soil pollution can happen in many ways. Here are some of the main causes:

• Tiny plastic pieces: Called Microplastics, these can get into the soil from broken-down plastic waste.
• Oil spills: When oil leaks from pipes or tanks, it soaks into the ground.
• Mining and heavy industries: These activities can release harmful chemicals into the soil.
• Accidental spills: Sometimes, chemicals spill by mistake during different activities.
• Leaking tanks: Underground storage tanks and their pipes can rust and leak their contents.
• Acid rain: Rain that has become acidic from air pollution can make soil unhealthy.
• Intensive farming: Growing too many crops on the same land can make the soil less healthy.
• Farm chemicals: Things like pesticides (to kill pests), herbicides (to kill weeds), and fertilizers can pollute the soil if used too much.
• Chemicals from oil: These are called petrochemicals.
• Industrial accidents: Factories can have accidents that release pollutants.
• Road debris: Bits of tires, oil, and other materials from roads can pollute the soil nearby.
• Building work: Construction can disturb soil and release contaminants.
• Old paint: Lead-based paints on the outside of buildings can flake off and get into the soil.
• Polluted water: Dirty water from the surface can drain into the soil.
• War materials: Old ammunition, chemical weapons, and other war agents can contaminate land for a long time.
• Waste disposal: How we get rid of trash is a big cause of soil pollution:
  • Dumping oil and fuel.
  • Nuclear wastes, which are very dangerous.
  • Factories directly dumping waste into the soil.
  • Releasing sewage (wastewater) without proper treatment.
  • Landfills and illegal dumping sites.
  • Fly ash from burning coal.
  • Electronic waste (e-waste) like old phones and computers.
• Natural rocks: Some rocks naturally contain high amounts of toxic elements, which can contaminate the soil.
• Vehicle pollution: Lead from old car exhaust, and cadmium and zinc from tire wear, can get into the soil.
• Air pollution: Strong air pollutants from burning fossil fuels can fall onto the soil and contaminate it.

The most common chemicals found in polluted soil are oil-related chemicals, solvents, pesticides, lead, and other heavy metals. Any activity that harms the soil in other ways, like causing erosion or making it too compact, can also make pollution worse and harder to clean up.

E-waste processing in Agbogbloshie, Ghana. Improper disposal of manufactured goods and industrial wastes, often means that communities in the global south have to process goods. Especially without proper protections, heavy metals and other contaminates can seep into the soil, and create water pollution and air pollution.

Before the 1960s, a lot of pollution came from coal ash, which was used for heating homes and in factories. Coal naturally contains lead, zinc, and other heavy metals. When coal burns, these metals become concentrated in the ash. This ash can contain enough lead to be considered a dangerous waste. Coal ash also often contains harmful chemicals called PAHs (polynuclear aromatic hydrocarbons), which are known to cause cancer. You might recognize coal ash or slag in soil as off-white grains, gray soil, or bubbly, pebble-sized pieces.

Treated sewage sludge, also called biosolids, is sometimes used as a fertilizer. However, it can contain more contaminants like germs, pesticides, and heavy metals than other fertilizers. In the European Union, treated sewage sludge is allowed to be sprayed on land because it's rich in nitrogen and phosphate, which are good for farming. But experts say we need to control this to prevent harmful germs from getting into water and to stop heavy metals from building up in the topsoil.

Pesticides and Herbicides

A pesticide is a substance used to kill pests. Pests can be insects, weeds, or other organisms that harm crops or spread diseases. While pesticides can be helpful, they can also be toxic to humans and other living things.

Herbicides are a type of pesticide used to kill weeds, especially on roads and railways. Most herbicides break down naturally in the soil. However, some older types of herbicides contained a very toxic impurity called dioxin, which could be deadly even in small amounts. Another herbicide, Paraquat, is very toxic but breaks down quickly in the soil and doesn't harm soil animals.

Insecticides are used to protect crops from insects. In tropical areas, a lot of food is lost to insects during storage. Early insecticides used in the 1800s were inorganic, like compounds of arsenic. Nicotine has also been used as an insecticide since 1690.

Today, there are two main groups of human-made insecticides:

1. Organochlorines: This group includes chemicals like DDT, Aldrin, Dieldrin, and BHC. They are cheap to make, powerful, and stay in the environment for a long time. DDT was used a lot from the 1930s, but its use dropped when people realized it was harming the environment. It was found all over the world, even in the snow in Antarctica. DDT doesn't dissolve well in water but dissolves easily in blood. It affects the nervous system and can make bird eggshells thin and break easily, which led to a decline in birds of prey like ospreys and peregrine falcons in the 1950s. These birds are now recovering. DDT can also build up in the food chain, meaning animals higher up the chain get more of it. While levels in human food were generally low, DDT was banned in the UK and the United States to stop it from building up further. However, US companies continued to sell DDT to developing countries that couldn't afford safer, more expensive alternatives.

1. Organophosphates: Examples include parathion, methyl parathion, and Malathion. Parathion is very toxic, but Malathion is generally considered safer because it's less toxic and breaks down quickly in the body. This group of insecticides works by disrupting nerve signals, leading to uncontrolled muscle movements.

Agents of War

When weapons are disposed of, or when they are made quickly during wartime, they can contaminate soil for many years. For example, mustard gas stored during World War II has polluted some areas for up to 50 years. Also, the testing of Anthrax as a biological weapon contaminated an entire island called Gruinard Island.

How Soil Pollution Affects People

How People Are Exposed

Polluted soil can directly affect human health if you touch it or breathe in its fumes. A bigger danger is when soil pollution seeps into underground water sources (aquifers) that people use for drinking. This can happen even far away from where the pollution started. Toxic metals can also move up the food chain if plants grow in contaminated soil and are then eaten by animals or humans. This can lead to diseases caused by pollution.

Most exposure to soil pollution happens by accident. You can be exposed by:

• Eating dust or soil directly.
• Eating food or vegetables grown in polluted soil, or food that has touched contaminants.
• Your skin touching dusty or dirty soil.
• Breathing in fumes from the soil.
• Breathing in dust clouds when working in soil or in windy places.

Some studies suggest that about 90% of exposure happens through eating contaminated food.

What Are the Consequences?

The health problems from soil pollution depend on the type of pollutant, how you're exposed, and how vulnerable you are. Researchers believe that pesticides and heavy metals in soil can harm heart health, causing inflammation and affecting the body's internal clock.

Long-term exposure to chemicals like chromium, lead, other metals, oil products, solvents, and many pesticides can cause cancer, congenital disorders (problems present at birth), or other long-term health issues. Even natural substances, like high levels of nitrate and ammonia from animal waste on farms, can become health hazards in soil and groundwater if they are too concentrated.

Long-term exposure to enough benzene can increase the risk of leukemia. Mercury and cyclodienes are known to cause kidney damage and some irreversible diseases. PCBs and cyclodienes are linked to liver problems. Organophosphates and carbonates can disrupt nerve signals, leading to muscle problems. Many chlorinated solvents can cause liver and kidney changes, and affect the central nervous system. There are also many other health effects like headaches, nausea, tiredness, eye irritation, and skin rashes. At high enough levels, many soil pollutants can even cause death through direct contact, breathing in fumes, or drinking contaminated groundwater.

The Scottish Government has asked the Institute of Occupational Medicine to review how to assess health risks from contaminated land. The goal is to help Scottish local authorities figure out if sites pose a significant risk to human health.

How Soil Pollution Affects Nature

This area is contaminated with stagnant water and refuse making the environment unhygienic

Soil pollutants can have very bad effects on ecosystems. Even small amounts of dangerous chemicals can drastically change the soil's chemistry. These changes can affect how tiny organisms and insects in the soil live and grow. This can lead to the disappearance of some parts of the food chain, which then affects animals that eat them. For example, it's well known that DDT builds up in the food chain, making bird eggshells weak and leading to more chick deaths, which can cause species to disappear.

Agricultural lands with soil contamination also suffer. Pollutants often change how plants grow, leading to smaller crop yields. This also harms soil conservation, because weak crops can't protect the soil from erosion. Some of these chemical pollutants stay in the soil for a very long time, and sometimes, new harmful chemicals are formed as the original ones break down.

How Contaminants Affect Soil Functions

Heavy metals and other soil pollutants can harm the activity, types, and numbers of tiny organisms in the soil. This threatens important soil functions like the natural cycling of carbon and nitrogen. However, over time, soil pollutants can become less harmful, and organisms and ecosystems can adapt. Soil properties like pH (how acidic or basic it is), how much organic matter it contains, and its texture are very important. They change how pollutants move, how available they are to living things, and how toxic they are. The same amount of a pollutant might be toxic in one type of soil but harmless in another. This shows why it's important to assess risks based on the specific soil.

How to Clean Up Polluted Soil

Cleaning up or environmental remediation is done by environmental scientists. They measure chemicals in the soil and use computer models to understand how chemicals move and where they end up. Many methods have been developed to clean up soil and sediments polluted by oil. Here are some main strategies:

• Digging it up: Excavate the polluted soil and take it to a special disposal site far from people or sensitive natural areas. This is also done for polluted mud in bays.
• Aeration: Letting air get into the soil at the polluted site. This can sometimes create air pollution as chemicals evaporate.
• Heating the soil: Using heat to warm the soil enough to turn the chemical pollutants into vapor, which can then be removed.
• Bioremediation: Using tiny microbes to break down certain organic chemicals. This can involve adding nutrients to help existing microbes or adding new microbes to the soil.
• Extracting liquids or vapors: Using special machines to pull out polluted groundwater or soil vapor, and then removing the contaminants from what's extracted.
• Containing the pollution: Covering the polluted soil with a cap or paving over it to prevent contact.
• Phytoremediation: Using plants, like willow trees, to absorb heavy metals from the soil.
• Mycoremediation: Using fungi to break down pollutants and collect heavy metals.
• Microbubbles: Using self-collapsing air microbubbles to clean oil-contaminated sediments.
• Surfactant leaching: Using special liquids to wash contaminants out of the soil.
• Solar evaporation: Using sunlight to evaporate water from moist soil, leaving heavy metal ions behind.

Soil Pollution Around the World

Different countries have their own standards for how much of a certain pollutant is acceptable in soil. Examples include guidelines from the United States EPA and Australia.

China

China's huge growth since the 1970s has led to a lot of soil pollution. The Ministry of Ecology and Environment sees this as a threat to the environment, food safety, and farming. According to one study, about 100,000 square kilometers of China's farmland are polluted. Another 21,670 square kilometers are irrigated with polluted water, and 1,300 square kilometers are covered or destroyed by solid waste. In total, this is about one-tenth of China's farmable land, mostly in developed areas. It's estimated that 12 million tons of grain are contaminated by heavy metals each year, causing huge financial losses. A recent survey showed that 19% of agricultural soils are polluted with heavy metals, and the levels of these metals have increased a lot.

European Union

In the European Union, there are over 2.5 million potentially polluted sites, and about 342,000 identified polluted sites. Most soil pollution (38%) comes from city and industrial waste, followed by the industrial and commercial sectors (34%). Oil and heavy metals are the main pollutants, making up about 60% of soil contamination. Managing these polluted sites is estimated to cost around 6 billion Euros each year.

United Kingdom

In the United Kingdom, general guidelines for soil pollution are called Soil Guideline Values (SGVs), published by the Department for Environment, Food and Rural Affairs (DEFRA) and the Environment Agency. These values help determine the minimum acceptable level of a substance. If levels are above this, there's a significant risk to human health. These values are calculated using a special model called CLEA UK.

The CLEA model helps assess risks to human health from contaminated land, as required by law. SGVs have been created for many contaminants and for three different land uses:

• Homes (with and without plants growing)
• Allotments (small plots of land for growing food)
• Commercial/industrial areas

These SGVs are used to assess long-term risks to human health. They don't apply to workers on construction sites or other things like groundwater, buildings, plants, or other ecosystems. They also don't apply to sites completely covered by hard surfaces, as there's no direct way for people to be exposed to the soil.

Canada

As of February 2021, Canada has over 2,500 contaminated sites. One well-known polluted site is near a nickel-copper smelting factory in Sudbury, Ontario. A study there found very high levels of nickel and copper in the soil close to the factory. Other metals like iron, cobalt, and silver were also found. Plants around the factory also showed signs of contamination, containing nickel, copper, and aluminum.

India

In March 2009, there were reports about uranium poisoning in Punjab, India. People thought it was caused by ash ponds from power stations, leading to severe birth defects in children. News reports claimed uranium levels were more than 60 times the safe limit. In 2012, the Indian government confirmed that groundwater in the Malwa region of Punjab had uranium levels 50% above the World Health Organization (WHO) limits in some places. However, scientific studies found that the source was not from fly ash or power plants, and the levels were not 60 times the WHO limit. The highest levels found were still lower than natural uranium levels in drinking water in other places, like Finland. Research is ongoing to find the natural or other sources of the uranium.

See also

In Spanish: Contaminación del suelo para niños