Untitled Flashcards Set

Oil pollution comes from multiple sources

47-5 What are the sources of oil pollution?

The pollution of Earth’s oceans and shorelines from crude oil and other petroleum products is an ongoing problem that can have large economic consequences on recreation, tourism, and the fishing industry. Oil is a persistent substance that can spread below and across the surface of the water for hundreds of kilometers and leave shorelines with a thick, viscous covering that is extremely difficult to remove. It is highly toxic to marine organisms, including birds, mammals, and fish, as well as to algae and microorganisms that form the base of the aquatic food chain. For example, exposure to oil can cover the feathers of birds and the fur of mammals, such as seals and otters. This sticky outer layer of oil is difficult to remove and is not only toxic, but also reduces the animals’ layer of insulation so they cannot stay warm. It also impairs their ability to swim and fly. Whales and dolphins can inadvertently inhale the oil, causing it to get into their lungs, or inadvertently consume the oil as they capture their prey in the water. It can also sink to the ocean bottom where it smothers and kills bottom-dwelling organisms. In this section, we will examine the many sources of oil pollution and then talk about some of the ways currently used to clean up oil and to reduce its harmful effects.

Sources of Oil Pollution

There are many different sources of oil pollution in water. Oil and other petroleum products can enter the oceans as spills from oil tankers or pipelines. One of the best-known spills involved the tanker Exxon Valdez that ran aground off the coast of Alaska in 1989 (FIGURE 47.10). The ship spilled 42 million liters (11 million gallons) of crude oil that spread across the surface of several kilometers of ocean and along hundreds of kilometers of coastline. The accident killed 250,000 seabirds, 2,800 sea otters, 300 harbor seals, and 22 killer whales. Cleanup efforts went on for 2 decades.

FIGURE 47.10 The Exxon Valdez oil spill. In 1989, the oil tanker ran aground and spilled millions of liters of crude oil onto the shores of Alaska, where the oil killed thousands of animals and harmed many others such as this red-necked grebe (Podiceps grisegena) on Knight’s Island, located about 35 miles from the spill.

Twenty years after the Exxon Valdez spill, scientists evaluated the state of the contaminated Alaskan ecosystem. They concluded that the harmed populations of many species have rebounded, including bald eagles and salmon. However, several species have not yet rebounded, including killer whales (Orcinus orca) and sea otters (Enhydra lutris). Nor has the oil been completely removed from the environment. Pits dug into the shoreline suggest that approximately 55,000 L (14,500 gallons) of oil remain. It is estimated that this oil will take more than 100 years to break down and the long-lasting effects will only become apparent over the coming decades.

For its part, Exxon has paid $1 billion for the cleanup and $500 million in damages. The company also changed the ship’s name, although the ship has been banned from carrying oil in North America. The Valdez accident sparked new rules for oil tankers in North America. The Exxon Valdez had a single-hull design, but tankers must now have a double-hull design with two steel walls to contain leaking oil. As a result, the number of large oil spills from oil tankers has dramatically declined in recent decades.

Offshore drilling is another source of oil pollution. There are approximately 5,000 offshore oil platforms in North America and another 3,000 worldwide. Drilling platforms often experience leaks. The best estimate for the amount of petroleum leaking into North American waters is 146,000 kg (322,000 pounds) per year. In other parts of the world, antipollution regulations are often less stringent. Estimates of the amount of petroleum leaking into the ocean annually from foreign oil platforms range from 0.3 million to 1.4 million kilograms (0.6 million to 3.1 million pounds).

One of the most famous oil leaks from an offshore platform occurred in 2010 on a BP operation in the Gulf of Mexico. In this case, an explosion on the Deepwater Horizon platform caused a pipe to break on the ocean floor nearly 1.6 km (1 mile) below the surface of the ocean. From the time of the explosion in April until the well was sealed in August 2010, the broken pipe released an estimated 780 million liters (206 million gallons) of crude oil into the Gulf of Mexico. This spill contaminated beaches, wildlife, and the estuaries that serve as habitats for the reproduction of commercially important fish and shellfish. The magnitude of the oil spill was nearly 20 times larger than that of the Exxon Valdez. However, because much of the oil spilled into the ocean, scientists may not be able to assess the full impact of the oil spill for several decades. The accident has the potential to become one of the largest environmental disasters in history.

In addition to oil spills, oil pollution in the ocean occurs naturally. In fact, the U.S. National Academy of Sciences recently estimated that natural releases of oil from seeps in the bottom of the ocean account for 60 percent of all oil in the waters surrounding North America and 45 percent of all oil in water worldwide. FIGURE 47.11 shows the proportion of different sources of oil in water for both North American and worldwide marine waters. In the waters controlled by the United States, the ocean seeps more than 270,000 L (70,000 gallons) of oil every day. This means that when we assess the environmental impact of oil in our oceans, we must consider the combination of both natural and anthropogenic releases of oil. “Do the Math: Calculating the Magnitude of Oil Pollution” provides an opportunity to work with converting units of measurement to determine the amount of oil seepage.

FIGURE 47.11 Sources of oil in the ocean. Oil contamination in the ocean, both (a) in North America and (b) worldwide, comes from a variety of sources including natural seeps, extraction of oil from underneath the ocean, transport of oil by tanker or pipeline, and consumption of petroleum-based products.

(Data from https://sites.google.com/tamu.edu/ocean-world/)

Remediating Oil Pollution

Since the 1989 Exxon Valdez oil spill, researchers have been investigating how best to remediate oil spills. Contaminated mammals and waterfowl must be cleaned by hand. Bird feathers that are covered with oil, for example, become heavy and lose their ability to insulate. The best approach to cleaning up the spilled oil, however, is not always clear.

Oil spilled in the ocean can either float on the surface or remain far below in the form of underwater plumes. For oil floating on the surface of the open ocean, a common approach is to contain the oil within an area and then suck it off the surface of the water. Containment occurs by laying out oil containment booms that consist of plastic barriers floating on the surface of the water and extending down into the water for several meters. These plastic walls keep the floating oil from spreading further. Once the oil is contained, boats equipped with giant vacuums suck up as much oil as possible (FIGURE 47.12). In shallow areas and along the coastline, absorbent materials are used to suck up the spilled oil.

FIGURE 47.12 Oil-spill containment. Floating plastic walls can contain oil spills while the oil is sucked off the surface of the water. This worker is using a vacuum to clean up the Kalamazoo River in Battle Creek, Michigan.

A second approach to treating oil floating on the surface is to apply chemicals that help break up and disperse the oil before it hits the shoreline and causes damage to the coastal ecosystems. Although the dispersants can be effective, they can also be toxic to marine life. Current research is examining ways to make chemical dispersants more environmentally friendly.

A third approach is to burn the oil slicks. This was done during the Deepwater Horizon oil spill to rapidly remove floating crude oil. However, the burning causes a great deal of air pollution and leaves behind a thick by-product that can be harmful to wildlife.

A fourth approach to cleaning up oil uses genetically engineered bacteria. Several years ago, scientists discovered a naturally occurring bacterium that obtained its energy by consuming oil emerging from natural seeps. These bacteria were typically rare in the ocean but were very abundant in areas where oil spills or seeps occurred. Scientists are currently trying to determine the genes that confer the bacteria’s ability to consume oil and hope to insert copies of these genes into genetically modified bacteria to consume oil spills even faster.

Research on oil spill cleanups continues today. For example, researchers discovered that specially designed sponges could absorb oil while repelling seawater. These sponges can be used repeatedly and absorb 50 times their own weight. Researchers also have discovered a new method to burn oil slicks by heating the oil to allow more complete combustion with cleaner emissions from the fires.

In contrast to oil floating on the surface of the water, oil in underwater plumes persists as a mixture of water and oil, similar to the mixture of vinegar and oil in a salad dressing. In the case of the BP platform explosion in the Gulf of Mexico, scientists reported observing an oil plume moving approximately 1,000 m (3,000 feet) below the surface of the ocean. The plume was approximately 24 to 32 km (15–20 miles) long, 8 km (5 miles) wide, and hundreds of meters thick. There is currently no agreed-upon method of removing underwater plumes from the water.

When spilled oil comes to shore, the best solution in not always clear. For example, there is some debate over how to treat rocky coastlines after an oil spill. Scientists have been monitoring parts of Prince William Sound that were treated in different ways after the Exxon Valdez spill. Workers cleaned some areas with high-pressure hot water to remove the oil. Unfortunately, the hot water sprayers not only removed the oil, but also removed most of the marine life and, in some cases, the fine-grained sediments containing nutrients. Without the fine-grained sediment, many organisms were unable to recolonize the coast.

Other parts of the coastline received no human intervention. Over the years since the spill, the repeated action of waves and tides slowly removed much of the oil. However, the remaining oil existing in crevices of the rocky shoreline continues to have a negative effect on organisms that live among the rocks. Thus, leaving the oil on beaches also poses problems. At present, there is no clear consensus on the best way to respond to oil spills on coastlines.

Do the Math

Calculating the Magnitude of Oil Pollution

As we have discussed, there are many sources of oil pollution including from natural seeps, oil consumption, extraction, and transportation. Oil pollution is typically estimated in terms of metric tons of crude oil, but how does this translate into gallons of oil?

1

metric

ton

of

crude

oil

=

320

gallons

of

crude

oil

Given that 160,000 metric tons of oil seeps from the ocean floor surrounding North America, how many gallons of crude oil are seeping into the ocean in this region?

160,000

metric

tons

×

320

gallons/ton

=

5.12

×

10

7

gallons

If we assume that 1 gallon of crude oil can be used to make 1 gallon of heating oil (which is a simplifying assumption), and the average house in the northeastern United States uses 800 gallons of heating oil each year, how many northeastern homes could be heated by the oil that is naturally seeping into the ocean around North America?

(

5.12

×

10

7

)

gallons

÷

(

8

×

10

2

)

gallons/home

=

(

5.12

÷

8

)

×

(

10

7

−

2

)

=

0.64

×

10

5

=

6.4

×

10

4

homes

=

64

,

000

homes

Your Turn

The amount of pollution from oil extraction activities is 3,000 metric tons. How many gallons does this represent?

Using the assumptions above, how many homes in the northeastern United States could be heated by this amount of oil?

As we have seen in this module, humans are impacting ecosystems by adding a wide variety of chemical pollutants that impact the health and performance of animals and humans. In the next module we continue with this theme by examining how human activities contribute excess nutrients to ecosystems and how these excess nutrients have harmful impacts on ecosystems.