What is the worst environmental disaster in history?

Ironically, the worst environmental disaster in history was an oil spill that doesn't even rank among the top 50 largest oil spills [source: Lovgren]. Yet the Exxon Valdez oil spill is widely considered to be the most disastrous oil spill in the world in terms of its environmental impact [source: Exxon]. The 11 million gallons (or 257,000 barrels) of oil that eventually escaped from the tanker's hull continue to affect the surrounding area [source: Lovgren]. As soon as the ship hit Bligh Reef, the Alaskan body of water known as Prince William Sound became forever changed.

As you might remember, the Exxon Valdez oil tanker left Alaska on March 23, 1989, at 9:12 p.m. carrying more than 53 million gallons (1.26 million barrels) of oil. Just three hours later, after the ship ran into a reef, thousands of gallons of oil coated everything within site. All told, the amount of oil spilled was enough to fill an Olympic-sized swimming pool 125 times [source: Exxon]. While 11 million gallons was the official number given by the U.S. Coast Guard at the time, some people involved in the cleanup effort estimate that the amount of oil spilled was nearly three times that [source: Knickerbocker].

Despite the relatively small amount of oil released, several factors contributed to the spill's severity: timing, location, abundance of wildlife and substandard cleanup efforts. In comparison, one of the largest oil spills in history, the rupture of an oil well in the Gulf of Mexico that released 140 million gallons (3.3 million barrels) of oil, caused relatively little damage because it happened in the open sea where currents and winds contained it until it disintegrated [source: Stevens].

By contrast, the Exxon spill occurred inside a body of water that housed an abundance of wildlife rather than in the open ocean where oil could dissipate and be broken down by wave action. The following animals were killed by the spill:

[source: Knickerbocker]

The 10,000 square miles (25,900 square kilometers) and 1,500 miles (2,414 kilometers) of shoreline covered with oil encompassed a national forest, four wildlife refuges, three national parks, five state parks, four critical habitat areas and a state game sanctuary [source: Knickerbocker].

Ten years later, only two of 23 animal species injured by the oil slicks had fully recovered [source: Knickerbocker]. As of 2004, populations of loons, harbor seals, harlequin ducks and Pacific herring were still affected by the spill [source: Lovgren], and the entire food chain was altered.

Thousands of workers participated in the cleanup efforts, but since little was known about effective cleanup methods, the workers weren't as successful as they could have been. In addition, cleanup didn't begin until three days after the spill, after a storm had spread much of the oil onto the coastline before it could be contained. Despite the cleanup effort, several miles of shoreline are still contaminated, and up to 200 tons of crude oil remain [source: Hoare, National Wildlife]. Even in areas where the surface waters appear clear, oil often lurks beneath the surface in little pockets buried by sediment.

It may take decades for Prince William Sound to heal fully. The oil remaining in the sound is almost the same composition it was decades ago -- an unknown factor has slowed down the rate of oil decomposition to only 4 percent a year [source: Hyder].

­Other events, though less well-known, have done considerable environmental damage as well. Learn about some other ecological disasters next.

The world's insatiable demand for natural resources indirectly causes much of the damage that humans inflict on the Earth. On this page, you'll learn about two more of these far-reaching catastrophes.

Amoco Cadiz Oil Spill

In 1978, more than a decade before anyone had heard of the Exxon Valdez, a tanker named the Amoco Cadiz ruptured its tank on rocks in the English Channel. Before rescue workers could get to it, a storm split the ship, causing its entire load of 68 million gallons (1.6 million barrels) of oil to leak into the waters off the coast of Brittany, France [source: Stevens].

Like the Exxon Valdez spill, the Amoco Cadiz accident was difficult to clean up because of the violent seas. Soon after the tanker split, a dangerous patch of oil and water formed that polluted everything it drifted over. An oil slick 18 miles wide by 80 miles long (29 kilometers wide by 128 kilometers long) contaminated 250 miles (400 kilometers) of coastline and killed 300,000 birds [source: BBC].

Much of the oil worked its way into protected areas in marshes or under sediments where it didn't degrade easily. Scientists on the scene observed entire species wiped out. Bottom-dwelling creatures like urchins and clams suffered "massive mortality," according to a study published by the National Research Council, and the growth rates of several species of fish subsequently slowed. At the time, researchers estimated the ecosystem would not return to pre-spill levels for several decades, and indeed, 20 years later animal populations still showed the effects [source: Stevens, Cedre].

Baia Mare Cyanide Spill

Oil, however, is not behind every toxic spill. On Jan. 30, 2000, the dam restraining contaminated water from a gold mining operation in Romania broke. The 26 million gallons (100 million liters) of polluted liquid and waste contained 55 tons to 110 tons of cyanide and various other heavy metals. The spill travelled through the rivers of Romania, Hungary and Yugoslavia, eventually reaching the major waterway of the Danube River. Both Hungary and Yugoslavia observed massive amounts of dead fish killed by the toxic metals. Hungary reported 1,367 tons of them [source: UNEP/OCHA].

Cyanide is an extremely toxic pollutant that blocks oxygen absorption; fish are almost one thousand times more sensitive to it than people [source: UNEP/OCHA]. Exposure can cause death, reproductive problems and a reduced ability to swim and fight off predators. In addition to the fish killed, plankton also were completely wiped out. However, due to cyanide's short life span, they recovered relatively soon after.

Although cyanide does not remain in the environment for long, the other heavy metals released by the dam do. Zinc, copper, lead and other metals build up in organisms over time and increase in toxicity, posing a long-term threat. For example, copper levels after the accident were at least 1,000 times higher at four different locations tested and lead levels two times to thirty times higher. Each of these metals is toxic to plants [source: UNEP/OCHA].

The spills discussed in this article are just the tip of the iceberg. Countless other environmental disasters, like wars, wildfires and tsunamis, have occurred and continue to occur that don't meet our narrow criteria. To learn more about how these disasters affect the world, look into the links on the following page.