Land pollution
by Chris Woodford. Last updated: July 9, 2021.
What's beneath your feet? Maybe a wooden floor or a stone one... and, beneath that? Brick foundations, water pipes,
power cables... and who knows what else. Keep going down and you'll
come to soil, rocks, and the raw stuff of Earth. We imagine these
basic foundations of our planet to be a kind of pristine, internal
wilderness—but often that's far from the case. While we can see many
of the changes we've made to the world, some of our impacts are
virtually invisible, and land pollution is a good example. You
might see factory smoke rising through the air or oil slicks drifting
over the ocean, but you can't easily see the poisons that seep from
underground mines, the garbage we tip into landfills by the
truckload, or the way the very soil that feeds us is turning slowing
to dust. Land pollution, in short, is a much bigger and more subtle problem than it
might appear. How does it occur and what can we do about it? Let's
take a closer look!
Photo: Mining is a major cause of land pollution.
It's easy to point the finger at mine operators, but we all rely on fuels, metals, and other minerals
that come from the ground, so we're all partly responsible for the damage that mining does.
Photo by Carol M. Highsmith, courtesy of Gates Frontiers Fund Wyoming Collection within the Carol M. Highsmith Archive,
Library of Congress, Prints and Photographs Division.
What is land pollution?
If you've read our articles on water pollution and
air pollution, you'll know that pollution can be defined generally
along these lines: it's the introduction into the environment of
substances that don't normally belong there, which, in great enough
concentrations, can have harmful effects on plants, animals, and humans.
We can define land pollution either narrowly or broadly. Narrowly
defined, it's another term for soil contamination (for example, by
factory chemicals or sewage and other wastewater). In this article,
we'll define it more widely to include garbage and industrial waste,
agricultural pesticides and fertilizers, impacts from mining and
other forms of industry, the unwanted consequences of urbanization, and the systematic
destruction of soil through over-intensive agriculture; we'll take
land pollution to mean any kind of long-term land damage, destruction,
degradation, or loss.
Causes of land pollution
There are many different ways of permanently changing the land, from soil contamination (poisoning by chemicals or
waste) to general urbanization (the systematic creation of cities and
other human settlements from greenfield, virgin land). Some,
such as huge landfills or quarries, are very obvious; others, such as
atmospheric deposition (where land becomes contaminated when air
pollution falls onto it) are much less apparent. Let's consider the
main causes and types of land pollution in turn.
Waste disposal
Humans produce vast quantities of waste—in
factories and offices, in our homes and schools, and in such unlikely
places as hospitals. Even the most sophisticated waste processing
plants, which use plasma torches (electrically controlled "flames" at
temperatures of thousands of degrees) to turn waste into gas, produce
solid waste products that have to be disposed of somehow. There's
simply no getting away from waste: our ultimate fate as humans is to die and
become waste products that have to be burned or buried!
Chart: Global waste disposal: Although most of the waste we produce is relatively harmless and easy to dispose of, some is dangerous or toxic and extremely difficult to get rid of without automatically contaminating land. As this chart shows, 69% of global waste (gray slices) involves direct land contamination. A further 11% (black slice) results in potential indirect contamination—when incinerator ash returns to the land. Only 18% of waste disposal, involving composting or recycling, is "green" (green slices).
[16]
Waste disposal didn't always mean land pollution.
Before the 20th century, most of the materials people used were
completely natural (produced from either plants, animals, or minerals
found in the Earth) so, when they were disposed of, the waste
products they generated were natural and harmless too: mostly organic
(carbon-based) materials that would simply biodegrade (break down
eventually into soil-like compost). There was really nothing we
could put into the Earth that was more harmful than anything we'd taken
from it in the first place. But during the 20th century, the
development of plastics (polymers generally made in chemical plants
from petroleum and other chemicals), composites (made by combining
two or more other materials), and other synthetic (human-created)
materials has produced a new generation of unnatural materials that
the natural environment has no idea how to break down. It can take
500 years for a plastic bottle to biodegrade, for example. And while
it's easy enough to recycle simple things such as cardboard boxes or
steel cans, it's much harder to do the same thing with computer
circuit boards made from dozens of different
electronic components,
themselves made from countless metals and other chemicals, all
tightly bonded together and almost impossible to dismantle.
Nothing illustrates the problem of waste disposal
more clearly than radioactive waste. When scientists discovered how
to create energy by splitting atoms in
nuclear power plants, they
also created the world's hardest waste disposal problem. Nuclear
plants produce toxic waste that can remain dangerously radioactive
for thousands of years and, what's worse, will contaminate anything
or anyone that comes into contact with it. Nuclear plants that have
suffered catastrophic accidents
(including the Chernobyl plant in the Ukraine, which exploded in 1986, and the
Fukushima plant in Japan, which was damaged by an earthquake in 2011) are generally sealed with
concrete and abandoned indefinitely. Not surprisingly, local
communities object vociferously to having nuclear waste stored
anywhere near them.
Mining
Photo: The world's biggest copper mine,
Escondida Mine in Chile, produces roughly 5.5 percent of global copper each year; you can see the scar it's left on the landscape in this satellite photo. But we all use copper (it's in the computer you're using right now) so is this actual "land pollution" or just very necessary land use? Photo by NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team courtesy of
NASA Goddard Space Flight Center (NASA-GSFC).
Although there are many responsible mining
companies, and environmental laws now tightly restrict mining in some
countries, mines remain among the most obvious scars on (and under)
the landscape. Surface mining (sometimes called quarrying or opencast
mining) requires the removal of topsoil (the fertile layer of soil
and organic matter that is particularly valuable for
agriculture) to get at the valuable rocks below. Even if the
destruction of topsoil is the worst that happens, it can turn a
productive landscape into a barren one, which is a kind of pollution.
You might think a mine would only remove things from the land,
causing little or no pollution, but mining isn't so simple. Most
metals, for example, occur in rocky mixtures called ores, from which
the valuable elements have to be extracted by chemical, electrical,
or other processes. That leaves behind waste products and the
chemicals used to process them, which historically were simply dumped
back on the land. Since all the waste was left in one place, the
concentration of pollution often became dangerously high. When mines
were completely worked out, all that was left behind was contaminated
land that couldn't be used for any other purpose. Often old mines
have been used as landfills, adding the insult of an inverted garbage
mountain to the injury of the original damage. But at least it saved
damaging more land elsewhere.
Urbanization
Humans have been making permanent settlements for
at least 10,000 years and, short of some major accident or natural
disaster, most of the cities and towns we've created, and the
infrastructure that keeps them running, will remain with us for
thousands more years into the future. Not many of us would
automatically classify cities and other human settlements as "land
pollution"; people obviously need to live and work somewhere. Even
so, urbanization marks a hugely important change to the landscape
that can cause land pollution in a variety of subtle and
not-so-subtle ways.
Chart: Urbanization goes hand-in-hand with other changes in land use, such as deforestation. In 2018, the world had about 96 percent as much forested area as it had in 1990—a huge loss of forest in total. This chart shows 15 example countries that have either gained forest (green) or lost it (orange), with the world total shown in the middle (yellow). For each country, the bar shows the percentage of forest area in 2018 compared to 1990, so 100 percent would be no change. Drawn by explainthatstuff.com in 2021 using the latest available data from
UN Food and Agriculture Organization/World Bank, published under a Creative Commons BY-4.0 license.
With over 7.8 billion people on the planet, it
might come as a surprise to find that humans have urbanized only
about 3 percent of Earth's total land surface [1], though
about 30–40 percent of the total land area has been transformed if we include
agriculture [2]. Our impact on the planet extends much further than
urbanization might suggest. Way back in 1996, Herbert Girardet
estimated that London, England has an
ecological footprint
(area of land needed to support it) some 125 times bigger than the
city itself [3].
Add up that effect for every major city in the world and
you get an idea of how big an impact urbanization has had.
Today's figures are staggering. According to the Global Footprint Network, the ecological footprint
of most countries (what they use) hugely exceeds their biocapacity
(what they can produce): in the United States, the ecological footprint
per person is 2.4 times bigger than the biocapacity; in Germany it's 3.1 times
bigger; in China, 4.1 times bigger; and in India, 3.0 times bigger
[15].
One of the problems of urbanization is that, by
concentrating people, it concentrates their waste products at the
same time. So, for example, crudely disposing of sewage from a big
city automatically creates water or land pollution, where the same
number of people and the same volume of sewage might not create a
problem if it were created in 10 smaller cities or 100 small towns.
Concentration is always a key factor when we talk about pollution.
Having said that, it's important to remember that urbanization, when
it works, can also help people to live very efficiently. Thus,
New York has the lowest ecological footprint of any state in the USA, largely because people there have smaller homes and make
greater use of public transportation [4].
Photo: Greenfield to brownfield: This once-green field will soon be a large housing estate. People need homes to live in, but they also need green spaces—and agricultural land to feed them.
Agricultural chemicals
Those of us who are lucky enough to live in rich
countries take our basic survival for granted: aside from trips to
the grocery store, we don't worry about where our food comes from or
how it gets to us. The reality is that seven billion hungry people
consume a vast amount of food. Feeding the world on such a scale is
only possible because agriculture now works in an industrial way, with
giant machines such as tractors and
combine harvesters doing the work
that hundreds of people would have done in the past, and chemicals
such as fertilizers and pesticides (herbicides that kill weeds and
insecticides that kill bugs) increasing the amount of food that can
be grown on each piece of land. Unfortunately, most pesticides are by
definition poisons, and many remain in the soil or accumulate there
for years. One infamous and now widely banned pesticide,
DDT, is
not ordinarily biodegradable so it has remained in the environment
ever since it was first used in the mid-20th century and even spread
to such places as Antarctica [5]. DDT is just one of many
organic (carbon-based) chemicals that remain in the environment
for years or decades, known as persistent organic pollutants.
Atmospheric deposition
Air pollution doesn't remain air pollution
forever. Ideally it disperses, so the concentration of problematic
chemicals becomes so low that it no longer constitutes pollution.
Sometimes, though, it falls back to the ground and becomes either
water pollution (if it enters the oceans, rivers, and lakes) or land
pollution. Pollution created ("deposited") in water or land from
existing pollution in the air (atmosphere) is known as atmospheric
deposition. Land can become polluted by deposition in some very
unexpected ways. For example, a corridor of land either side of a
highway or freeway becomes systematically polluted over time with all
kinds of harmful byproducts of road travel—everything from fuel
spills and brake linings to dust worn from the pavement
and heavy metal deposits (such as lead) washed from the engines. These chemicals accumulate in the soil where they can undergo reactions with one another and form
substances that are even more toxic [6].
Two important things are worth noting about
atmospheric deposition. First, it means no land on Earth—not even
the most isolated island—can be considered completely safe from
pollution: even if it's hundreds or thousand miles from the nearest
factory or human settlement, even if no human has ever lived there,
it could still be polluted from the air. Second, if you're doing
something that causes pollution (maybe spreading weedkiller on your
garden or perhaps running a factory where ash is discharged
from a smokestack), the effects are not necessarily going to be
confined to the place where the pollution is first produced. It's
important to remember that pollution knows no boundaries.
Soil erosion
Photo: Soil erosion turns fields into deserts. Photo by Jack Dykinga courtesy of
US Department of Agriculture/Agricultural Research Service (USDA/ARS).
If you define "land pollution" as irreversible
damage to the land, you have to include soil erosion as a type of pollution too. Many people think soil is soil, always there, never changing,
ever ready to grow whatever crops we choose to bury in it. In
reality, soil is a much more complex growing habitat that
remains productive only when it is cared for and nurtured. Too much
wind or water, destruction of soil structure by excessive plowing,
excessive nutrients, overgrazing, and overproduction of crops erode
soil, damaging its structure and drastically reducing its
productivity until it's little more than dust. At its worst, soil
erosion becomes desertification:
once-productive agricultural areas become barren, useless
deserts. How serious is the problem? In 2001, former UN Secretary General Kofi Annan
warned the world that: "Drought and desertification threaten the livelihood of over 1 billion people in more than 110 countries around the world." [7].
Deforestation doesn't only harm the place where the trees are cut down.
A 2013 study by Princeton University researchers found that if the
Amazon rainforest were completely destroyed, it would have a dramatic
effect on the atmosphere, which would carry across to places like the
United States, causing drought and potentially desertification there
as well [8].
Unfortunately, because soil erosion has so far affected
developing countries more than the developed world, it's a problem
that receives relatively little attention. Accelerating climate
change will soon alter that. In a future of hotter weather and more
intense storms, it will become increasingly difficult to maintain
soil in a fertile and productive state, while heavy rainstorms and
flash floods will wash away topsoil more readily. Meanwhile,
agriculture may become impossible in coastal areas inundated by
saltwater carried in by rising sea levels. We might think of global
warming as an example of air pollution (because it's caused mostly by
humans releasing gases such as carbon dioxide into the atmosphere).
But if it leads to dramatic sea-level rise and coastal erosion, you
could argue that it will become an example of land pollution as well.
Effects of land pollution
With luck and the right atmospheric conditions,
air and water pollution disperse and disappear. What makes land
pollution such a problem is that land is static, so land pollution
stays exactly where it is until and unless someone cleans it up. Land
that's polluted stays polluted; land that's urbanized almost
invariably stays urbanized. As we've already see, plastics take
hundreds of years to disappear while radiation can contaminate land
for ten times longer. That means landfill sites and radioactive waste
dumps remain that way pretty much indefinitely.
The simplest effect of land pollution is that it
takes land out of circulation. The more land we use up, the less we
have remaining. That might not sound a problem where there's plenty
of land in rural areas, but it's certainly a concern where productive
agricultural land is concerned, especially as the world's population
continues to increase. The biggest problem comes when contaminated
land is returned to use, either as building or agricultural land.
Houses might be built on brownfield (former industrial) sites
that haven't been cleaned up properly, putting future owners and
their families at risk. Or people might get their water from rivers
supplied by groundwater contaminated by landfill sites, mine
workings, or otherwise polluted land some distance away. Illnesses
such as cancer develop over years or decades for a variety of reasons
and it's extremely difficult to prove that they've been caused by
something like local environmental pollution, especially when people
move homes during their lifetime. No-one knows how much land is
contaminated, how contamination varies from one place to another, or
how land contaminants react with one another once they enter
watercourses and become water pollution. So the scale of the problem
and its ultimate effects are impossible to determine.
However, we do know what effect individual
pollutants have. We know, for example, that lead is a toxic heavy
metal that has all kinds of unpleasant effects on human health; it's
been implicated in developmental deficits (such as reductions in
intelligence) in children [9].
We know that some chemicals are carcinogenic (cancer-causing) [10] while others
cause congenital defects such as heart disease [11].
At the very least, it seems prudent not
to introduce dangerous chemicals, such as persistent organic pollutants, into the environment where they may
mat harm people's health for many years into the future.
Solutions
“When you choose what to eat, what to wear or what to drive, think about how your choice impacts the land—for better or for worse.”
Monique Barbut, Executive Secretary, UNCCD, 2018.
Why does land pollution matter? Although Earth might seem a pretty big place, only about a
third of its surface is covered in land, and there are now over seven
billion people trying to survive here. Most of our energy (around 83
percent worldwide [12]) still comes from fossil fuels buried under the ground and,
since we haven't yet figured out how to mine in space, so do all our
minerals. Much of our food is grown on the surface of the planet; the
water we need comes from the planet's surface too or from rocks
buried just underground. In short, our lives are as intimately tied
to the surface of Earth as the plants that grow from the ground.
Anything that degrades, damages, or destroys the land ultimately has
an impact on human life and may threaten our very ability to survive.
That's why we need solutions to the problem.
What kind of solutions? Ideally, we'd look at
every aspect of land pollution in turn and try to find a way of
either stopping it or reducing it. With problems like waste disposal,
solutions are relatively simple. We know that recycling that can
dramatically reduce the need for sending waste to landfills; it also
reduces the need for incineration, which can produce "fly ash"
(toxic airborne dust) that blows may miles until it falls back to
land or water. We'll always need mines but, again, recycling of old
materials can reduce our need for new ones. In some countries, it's
now commonplace to require mine operators to clean-up mines and
restore the landscape after they've finished working them; sometimes
mine owners even have to file financial bonds to ensure they have the
money in place to do this. Greater interest in
organic food and farming might,
one day, lead to a reduction in the use of harmful agricultural
chemicals, but that's unlikely to happen anytime soon. Even so,
public concerns about food and chemical safety have led to the
withdrawal of the more harmful pesticides—in some countries, at
least. Meanwhile, international efforts, such as the
United Nations Convention to Combat Desertification (UNCCD), are helping to focus attention on major problems like soil erosion.
Ideally, we don't just need to stop polluting
land: we also need to clean up the many contaminated sites that
already exist. Many former nuclear sites have already been cleaned up
as much as possible; in the UK, for example, the Nuclear
Decommissioning Authority is currently spending around £117 billion ($146,000 million)
to clean up 17 former nuclear sites—and the figure keeps on rising [13]. In the United States, a program called the Superfund has been decontaminating hundreds of polluted sites since 1980. Where sites can't be completely restored, it's possible
to "recycle" them and benefit the environment in other ways; for example,
a number of contaminated sites and former mines in the United States have now become wind farms or sites for large areas of solar panels [14].
New technologies will almost certainly make
it easier to "recycle" polluted land in future. For example, the
relatively new form of waste disposal called plasma gasification
makes it possible to "mine" former landfills, converting the old
waste into an energy-rich gas and a relatively safe solid waste that
can be used as a building material. Bioremediation is another
very promising land-cleaning technology, in which microbes of
various kinds eat and digest waste and turn it into safer
end-products; phytoremediation is a similar concept but
involves using plants, such as willow trees, to pull contaminants
from the soil.
All these things offer hope for a better future—a future where we value the environment more,
damage the land less—and realize, finally, that Earth itself is a limited and precious resource.
Photo: Bioremediation. Thankfully, microorganisms don't mind tackling the kind of waste we'd prefer to dump and ignore. Here, scientists at Oak Ridge National Laboratory in Tennessee are testing
whether soils contaminated with toxic chemicals such as PCBs (polychlorinated biphenyls) can be
cleaned up by bacteria. Photo courtesy of US
Department of Energy.
