North Sea accident: What are the environmental risks?

London: The crash between a cargo ship and a tanker carrying jet fuel in the North Sea off the coast of England has raised fears of coastal pollution and damage to marine protected areas.

What pollutants were on the ships?

The Stena Immaculate tanker, which was anchored around 13 miles (20 kilometres) off the northeast Yorkshire coast when it was hit by the cargo ship Solong, was carrying around 220,000 barrels of kerosene, a petroleum derivative used as jet fuel, according to the specialist company Lloyd's List Intelligence.

Crowley, the ship's operator, said one of its tanks containing kerosene had been ruptured, and that a leak had been reported.

The cargo being carried by Solong is not known at the moment.

Its owner, the German company Ernst Russ, on Tuesday denied reports that sodium cyanide, a chemical compound that produces a highly flammable and toxic gas when in contact with water, was on board.

The Solong was carrying empty containers that had previously contained the "hazardous chemical", it added.

Both ships are also carrying their own fuel, which could be "marine diesel oil" or "heavy fuel oil", said Nicolas Tamic, deputy director of Cedre, a French centre specialising in accidental water pollution.

The former is lighter and dissipates more quickly in the environment.

If it is heavy fuel oil and has not yet burned off, then "the problem will have to be dealt with", said Tamic.

What are the environmental risks?

The area where the collision took place is close to the Southern North Sea and Holderness marine protected areas, whose seabeds are known for their rich fauna and flora.

The coastline around the Humber Estuary is home to many species of birds, particularly waders and other waterfowl.

"Chemical pollution resulting from incidents of this kind can directly impact birds, and it can also have long-lasting effects on the marine food webs that support them," said Tom Webb, lecturer in marine ecology at the University of Sheffield.

Martin Slater, Director of Operations at Yorkshire Wildlife Trust, also said he was "very concerned" about the threat to birds, particularly colonies of puffins, razorbills, gannets and kittiwakes, which were gathering offshore before nesting season.

"If pollution spillage enters the Humber, this could potentially be devastating for the wildlife of the estuary, including important fish stocks and tens of thousands of overwintering and migrating birds who use the mud flats."

Is there a risk of an oil spill?

According to experts, the risk of an oil spill remains low and the UK government said Tuesday that there is presently "no sign of pollution" from the two ships.

Kerosene is "not persistent" like crude oil, Ivan Vince, director of the firm ASK Consultants, specialising in environmental risk security, told AFP.

"Most of it will evaporate quite quickly. And what doesn't evaporate will be degraded by microorganisms.

"So we're talking about a week or two, and it should be all gone," he added.

Nancy Kinner, director of the Center for Spills in the Environment at the University of New Hampshire, said that jet fuel's volatility means it "does not tend to make tarballs, evaporates from the surface faster, and tends to dissolve into the water column faster than crude oil.

"The severity of the impacts definitely depend on the amount of fuel that is released upon the surface unburned. The magnitude of the fire suggests that much of the fuel burned in place," she added.

The probability of the toxic hydrocarbons making it to wildlife refuges on the coast depends on the water currents, she said.

"What could be a bigger problem is if the sea birds land, fly close to the surface, or feed on materials they mistake for food on the water that contains the jet fuel slick," she told AFP.

But while kerosene does not tend to cause oil spills, it creates "atmospheric pollution when burned," said Tamic.