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On Wednesday night, a toxic spill of 'bunker fuel' spread throughout Vancouver's English Bay. What is bunker fuel, and what are its effects on the environment? Read on...

The Science Behind the Spill: What is bunker fuel and how does it affect the environment?


Scott Sutherland
Meteorologist/Science Writer

Friday, April 10, 2015, 11:00 AM - On Wednesday night, a toxic spill of 'bunker fuel' spread throughout Vancouver's English Bay, with the most likely source being the tanker ship Marathassa. What exactly is bunker fuel, and what are its effects on the environment and on us?

The Bottom of the Barrel

When your average barrel of crude oil goes through the refining process, several useful products are distilled out of it in the end. 

Lighter molecules get drawn off 'the top' to become fuels like propane and gasoline.

After that, slightly heavier molecules are removed to produce jet fuel, diesel fuel and heating oils (like kerosene).

With a little more than half the barrel gone now, even heavier molecules are made into the lubricating oils we use to keep engines running smoothly.

Below that, just one step up from the bitumen that gets rolled into the asphalt that covers our highways, is 'residual fuel oil' or 'bunker oil', which is burned in the engines that drive large ships, like the tankers that deliver the crude oil across the oceans.

Not As Bad As A Crude Oil Spill, But Certainly Not Good

First off, any oil spill is bad for the environment.

When we hear about a crude oil spill, like the Exxon Valdez accident in 1989 or the Deepwater Horizon disaster in 2010, the spill is a combination of all the above products being dumped into the ocean. The lightest parts - what goes into making propane, gasoline and jet fuel - evaporate within a couple of days (at the most), and can never be recovered. The heavier products - from what becomes diesel fuel, down to what goes into lubricating oils - can be effectively cleaned up, if it is done quickly.

However, when we see scenes on our television of beaches covered in black oil, and birds floundering, unable to fly because they're coated in the stuff, requiring an army of volunteers to clean them with dish-soap, that is the 'residuals' - part bunker oil and part bitumen.

NOAA - the US National Oceanic and Atmosphere Administration - lists the following properties for this residue:

  • Little or no evaporation or dissolution.
  • Heavy contamination of intertidal (above water at low tide/below water at high tide) areas likely.
  • Severe impacts to waterfowl and fur-bearing mammals (coating and ingestion).
  • Long-term contamination of sediments possible
  • Weathers (changes chemical composition due to physical and biological factors) very slowly
  • Shoreline cleanup difficult under all conditions.

According to NOAA:

"...very 'heavy' oils (like bunker oils, which are used to fuel ships) look black and may be sticky for a time until they weather sufficiently, but even then they can persist in the environment for months or even years if not removed. While these oils can be very persistent, they are generally significantly less acutely toxic than lighter oils. Instead, the short-term threat from heavy oils comes from their ability to smother organisms whereas over the long-term, some chronic health effects like tumors may result in some organisms.
Also, if heavy oils get onto the feathers of birds, the birds may die of hypothermia (they lose the ability to keep themselves warm). We observe this same effect if sea otters become oiled. After days or weeks, some heavy oils will harden, becoming very similar to an asphalt road surface. In this hardened state, heavy oils will probably not harm animals or plants that come in contact with them."

Avoid Contact

In general, coming into contact with this spill should be avoided as much as possible, and until the exact source of the spill is positively identified, the product of the spill should be considered toxic.

Any vapours coming off the bunker fuel could be harmful if inhaled, and it may have other effects such as skin and eye irritation. If the spill contains 'fresher' oil, the effects could be worse.

The liquid components of bunker fuel can also cause skin irritation or rash, especially if a person is particularly sensitive to the chemicals in it. There can also be long-term effects from prolonged exposure, as it is considered potentially carcinogenic for humans, and it could damage the fertility of adults or possibly harm an unborn child. Again, this is only for bunker fuel. If the spill also contains crude oil, there may be other effects.

If contact does occur, such as for anyone curious enough to interact with it, it is recommended that the affected area be washed with soap and water as soon as possible. Any clothing exposed to it should be laundered as soon as possible (especially before wearing again).

However, as stated above, and by several other sources, it is best to avoid all contact with this spill.

Sources: CBC | NOAA | Shell | CBC

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