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Oil Spill Reduction

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So exactly what is in that stuff spewing into the Gulf of Mexico?

We all know that a whole lot of oil is being pumped into the gulf. Exactly how much is up for grabs: BP and the government claim about 5,000 barrels per day, while some scientists estimate that it may be as much as 600,000.

Some might be unconcerned about this gap -- hey, who cares about a factor of 10 or more when you are up to your eyeballs in oil? But consider this: depending on whether you take the lower or upper limit, between about six million and 73 million gallons of oil have spilled into the Gulf of Mexico from the Deepwater Horizon oil rig disaster so far.

Is That a Lot of Oil?

Oil Spill Update
"The day we've been fearing is upon us," announced Louisiana Governor Bobby Jindal yesterday after observing the gulf oil slick's arrival along his state's coast.
In the meantime scientists have observed oil at the surface penetrating into the so-called loop current that can carry it around the Florida Keys and up into the North Atlantic Ocean. (For details, see here and here.)
Scientists have also discovered deep, miles-long plumes of oil beneath the surface spreading across the gulf.

One way to answer that question is by comparing it to other major spills.

  • In 1989, the Exxon Valdez emptied 11 million gallons into Alaska's Bristol Bay.
  • The largest spill in the Gulf of Mexico, from the offshore oil rig Ixtoc 1 in 1979, released 140 million gallons over the course of nine months.

What's in the Oil

Another way is to consider what's in the oil that's spewing into the gulf.

Crude oil is primarily a mixture of hydrocarbons -- that is, compounds made of hydrogen and carbon. The simplest hydrocarbon, with only one carbon atom, is methane (CH4) -- the gas that is believed to have caused the explosion of the Deepwater rig. The hydrocarbons in crude oil range from simple ones with a few carbon atoms to bigger ones with as many as 40 carbon atoms or more.

Source: NASA/Wikimedia Commons

In addition to hydrocarbons, crude oil has organic compounds that contain nitrogen, sulfur, and oxygen as well as carbon and hydrogen. It also contains trace mineral salts and metals. The most common metals are nickel, vanadium, iron, and copper, but can also include very small amounts of metals like uranium, arsenic, and mercury.

That widely variable composition means not all oil is created equal. There's heavy and light and sweet and sour. Heavy crude tends to have more impurities like salts and metals than light crude. Sweet crude tends to have less sulfur than sour crude. Generally speaking, when you're looking to make gasoline, light sweet crude has traditionally been preferred because there is less refining needed.

I haven't seen a chemical analysis of the oil flowing from the Deepwater rig, but the general assumption has been that it is a light sweet crude. I'll use that assumption in the discussion below.

Focus on Polycyclic Aromatic Hydrocarbons

A wide array of toxic chemicals is found in oil -- and in gasoline by the way, so be careful when you fill your tank and definitely try not to breathe in the fumes. Let's focus here on one of those toxins: polycyclic aromatic hydrocarbons (PAHs). PAHs are compounds where the carbon atoms are arrayed in a series of six-sided hexagons called rings.

A 2003 study by the National Academy of Sciences found that of all the typical hydrocarbons in crude oil, polycyclic aromatic hydrocarbons (PAHs) pose the greatest risk to the environment.

There are at least three things that make PAHs worrisome:

Rough Estimate of PAH Contamination Released into the Gulf from the Deepwater Disaster

Estimated metric tons of PAHs from the Deepwater rig spill as of May 19, 2010: 270-3,300 *

For comparison:

Estimated metric tons of PAHs from the two World Trade Towers' collapse: 100 and 1,000

Estimated metric tons of PAHs [pdf] emitted yearly in the United States as air pollution: 8,600-32,000

That's right -- if not capped soon, the amount of PAHs put into the Gulf of Mexico may approach the amount of PAHs we put into the atmosphere across the entire United States over an entire year. Better get your gulf shrimp and oysters while you can.


*Estimate of the PAH content of the Deepwater crude is based on calculations made in the National Academy of Sciences report Oil in the Sea III.

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