Our Small World

Pollution Without Boundaries

  • Print

Acid rain eating away at forests, chemicals from far away collecting in Arctic animals, changes in the chemistry of seawater, a mysterious virus from overseas—they’re distress calls from a planet where pollution is an increasingly global problem.

Watching America’s spacious skies turn smoggy and dirty, lawmakers in the mid to late 20th century decided something had to be done. Since 1963, they’ve passed various laws requiring factories and power plants to clean up what comes out of their smokestacks. These laws are known jointly as the Clean Air Act.

The laws are working. Scrubbers, or filters, on smokestacks keep many harmful chemicals from entering the air. In the 1980s, for example, the U.S. pumped 16 million tons of sulfur dioxide into the air. By 2000, that number had dropped to 11 million tons.

The United States is still far from perfect in terms of air pollution. But the nation has taken actions to improve the situation.

Picture yourself in a large, locked room. Now imagine that someone at the other end is setting off smoke bombs. At first, you might barely see or smell the smoke. Sooner or later, though, it will make its way toward you. Since the room is locked, you have no way to escape.

click to enlarge image
Pink arrows show the
path of pollution wafting
from China to the Pacific.

Source: NASA Earth

That’s basically the situation we’re all in when it comes to polluting our planet. Earth is large, yes, but it’s not infinite. Moreover, it’s a closed system. Whatever we pump into our air or water stays with us. More and more often, that’s causing global problems. Pollution from one place can make trouble hundreds or even thousands of miles away. This is called transboundary pollution.

It’s tempting, when reading about an environmental issue in some distant state or foreign land, to think, “Well, that’s not my problem.” In an increasingly globalized world, however, that thought rings less and less true. It’s growing ever clearer that problems in one place can affect distant environments and people. Here are just a few examples of what’s happening.


Some years ago, Canadians noticed that many of their forests were dying. Something was hurting the trees, but what? The answer lay to the south—power plants in the United States. To generate energy, the plants burned fossil fuels. That released nitrogen and sulfur into the air. These chemicals combined with water vapor in clouds to form acid rain. Something similar—acid rain hurting faraway forests—occurs all over the world.


The power plants that provide electricity for the buildings in this image also release chemicals that produce acid rain.
Source: Environmental Protection Agency


Acid rain is not pure acid, of course. But it’s far more acidic than ordinary rain. The acid causes damage wherever the rain falls. Trees start to die. Lake water turns acidic, harming the plants and animals that live in them. Stone buildings suffer erosion. All because of pollutants that might have been released in other nations.

click to enlarge image
Bioaccumulation basics: Tiny creatures eat or absorb pollutants. Small fish eat the tiny creatures. Larger fish eat the small fish. Seals and whales eat the larger fish. Polar bears eat the seals. Thus pollutants climb up the food chain.
Source: Columbia University


Recently, scientists noticed that large amounts of organochlorine compounds and heavy metals are collecting in the bodies of Arctic creatures. This is called bioaccumulation. And the chemicals are not good for the animals.

The strange thing is, the Arctic has few people or sources of pollution. So these contaminants must have traveled there from other places. They were carried north by wind and water. Some of the contaminants, for example, began as ingredients in pesticides used on crops in the United States and Canada.


Oceans cover 70 percent of our globe. So vast are the seas that people once thought they could absorb anything we dumped into them. So dump we did. Humans have pumped enormous amounts of sewage and industrial pollution into the oceans. In addition, runoff from farms has carried pesticides and other chemicals into rivers, which in turn flow into the oceans.

Besides taking in pollutants, the oceans are absorbing carbon dioxide. Scientists estimate that the sea has absorbed 500 billion tons of carbon dioxide since the start of the Industrial Revolution. When the gas mixes with seawater, it creates carbonic acid. That’s the weak acid that gives soda pop its pop.

click to enlarge image
This NASA map shows carbon dioxide in the atmosphere. The redder the area, the more carbon dioxide. Much of the gas will be absorbed by the world’s oceans.

Today we’re learning that we were wrong about the oceans. They can’t handle everything we dump in them. Pollutants and carbon dioxide are having some alarming impacts. For starters, the oceans are growing more acidic. Indeed, scientists report they haven’t been this acidic in nearly a million years. By 2100, the sea may be 2.5 times as acidic as it was before the Industrial Revolution. If this trend continues, countless fishes and other species could die out.

At the same time, the ocean’s changing chemistry is boosting the growth of harmful bacteria and algae. It’s almost as if evolution is running in reverse, with simple organisms replacing complex ones. One oceanographer calls this the “rise of slime.” Sounds gross, doesn’t it. Problem is, it can be harmful too.

One can see the problem vividly along the coast of Sweden each summer. Masses of bacteria gather in the Baltic Sea, turning the water into what locals call “rhubarb soup.” This not-so-tasty dish features dead fish bobbing in yellowish water. Its ugly aroma taunts the eyes and lungs of people who come too close. Something similar happens along America’s coasts. Red tides, once rare in Florida and California have become common, boosting the number of people going to the hospital with ailments from eating contaminated fish and shellfish or with respiratory problems.


A red tide hits the California coast.
Source: NOAA



Since at least 2003, a mysterious killer has been stalking the Great Lakes. It’s a virus that causes internal bleeding and organ failure in fish. (It is not harmful to people.) The virus has killed tens of thousands of fish and threatens the survival of two dozen species.

So where does the virus come from? That’s the mystery. Scientists know, though, where it does not come from—North America. Somehow the virus made its way to the Great Lakes from another continent. One theory is that it came in water carried and dumped by ships from other places.



science_iconWhat's the dirt on dust storms?



Is global trade a good deal? back_smallnext_small What’s the bio in bioterrorism?