French and Spanish specialists are still scrambling to tackle an oil spill in the Bay of Biscay after a cargo ship sank there two weeks ago. How can we clean up this thick layer of oil to prevent further damage?
After the Grande America cargo vessel sank on March 12 some 300 kilometers (186 miles) off the French coast, clean-up teams are still racing to contain its oil spill. Within days, the spill had dispersed within the Bay of Biscay, with the slicks initially drifting eastward towards the French coast.
Some of that heavy fuel has now been recovered. First ships carrying the oil have arrived in La Rochelle. Local maritime authorities are now analyzing and classifying the oil in order to find out how it can be recycled.
Experts are now also focusing on Spain as the sheet of oil is moving further south. They are trying to tackle the spill before it reaches land, where its environmental impact would be much worse.
How to tackle oil spills
The method for tackling oil spills depends on several factors, including the type of oil spilled, the amount of it, the location of the spill and the weather conditions at the time.
"Once the oil comes to shore, the more intensive the cleaning technique. You can risk causing further damage," said Nicky Cariglia, Senior Technical Adviser at ITOPF, an organization funded by the shipping industry to advise on response to oil spills.
"For example, in an ecologically sensitive area, if you wanted to remove every last trace of oil, you would need to high pressure wash it, which would be much more damaging than leaving small traces of oil there," Cariglia told DW.
Because oil normally has a lower density than water, it floats on the surface of the ocean. This means that for clean-up action to be most effective, it should happen very quickly after a spill, before the oil disperses.
1. Scooping it all up
One method of controlling oil spills, which is being used in the wake of the recent incident in the Bay of Biscay, is essentially scooping up the oil from the water's surface.
This is done using equipment called booms, which act like a barrier to prevent the oil from spreading. Once it's contained, boats equipped with so-called skimmer machines can suck up the oil and separate it from the water. After being processed, the oil can even be re-used.
It seems like a simple method, but it only works when the oil is in one place – and under the right conditions. "Encountering enough oil can be difficult," said response adviser Cariglia. When that's the case, the specialized vessels needed for the process can also make this an expensive and logistically challenging method.
2. Burning oil off water
In certain conditions, burning the oil off the water's surface can be the most appropriate method. In arctic or ice-covered waters, for example, it might be the only option.
In situ burning (ISB) would also be used to tackle an uncontrolled oil leak, where a lot of oil is leaking fast. When the Deepwater Horizon offshore oil rig caught fire and sank in April 2010, oil gushed from the seabed causing the largest accidental oil spill in history. ISB proved to be a highly effective technique in responding to the disaster.
Oil burns during a controlled fire in the Gulf of Mexico after the Deepwater Horizon disaster in 2010
But the method also produces toxic fumes which can have a negative impact on the environment.
And it comes with challenges too. "It can be difficult to herd enough oil to make it thick enough to burn," Cariglia said. "If the oil had dispersed over many days, it would not be an option."
3. Soaking up oil
Absorbents can be kinder to the environment: they work by soaking up the spilled oil, like a sponge. But they're more useful for clearing small amounts of oil on land, and are not usually effective in tackling an oil spill out at sea. In fact, employing these materials on the water can create further pollution.
"Recovering and disposing of these oiled materials requires a lot of energy," Cariglia told DW. "There's a risk that oiled debris will get lost at sea."
Workers are throwing absorbents into the Han River in Seoul to clean up an oil leak from a sinking cruise ship
Experts also disagree over the effectiveness of different absorbent materials, which can range from natural products like straw to highly-engineered synthetic materials developed by scientists for the purpose of tackling oil spills.
Cariglia is wary of solutions purporting to suck up slicks. "It's not that they don't work," she said. "In lab experiments, they can work very well. But in real life, the oil has spread at sea."
4. Letting nature take care of itself
When the area of the oil spill is difficult to reach or very far out to sea, nature itself can help tackle the issue. Wind and waves will naturally disperse the oil over time, parts of it will evaporate, and naturally occurring microbes will also do their work to start breaking down the oil.
But this is a slow and unreliable process, and needs to be closely monitored and "it should not be confused with 'sitting down and doing nothing,'" according to Marine Insight, a maritime industry information site.
Chemical agents can also be used to aid this process. Cariglia is keen to allay environmental fears. "Toxicity tests are designed so that the only things that are approved are milder than the soap you would use at home," she told DW.
While the dispersants themselves are not toxic, environmental problems can occur when they are used in sheltered or shallow locations. In that situation, using dispersants can mean that the oil spreads around more of the delicate marine environment. "For example, in locations where there are coral reefs, it would be better if the oil stayed on the surface," Cariglia added.
Bacteria can also be used to help clean up oil spills, in a method known as bioremediation. It's a process that makes use of microbes which consume hydrocarbons, contained in crude oil, helping to decompose it. These microbes are naturally present in marine environments, but after a spill, clean-up teams can add fertilizers to the water, encouraging the bacteria to grow, and therefore work harder to tackle the spill. This method is generally used to treat recovered oil to process the waste.
When it comes to tackling oil spills, "there is no single miracle cure," Cariglia said.
The best method is to prevent such spills in the first place.