The UK's lifeboat service reported on Sunday seeing "a sheen that we now know to be plastic nurdles" close to the Wash, a large bay on the east coast of England, around 43 miles (70 kilometres) south of the site of last week's crash, according to the coastguard.

Nurdles are 1-5 millimetre (0.04-0.2 inch) pellets of plastic resin used in plastics production. They are not toxic but can damage wildlife if ingested.

"Some nurdles have now also been identified on the shore," said chief coastguard Paddy O'Callaghan.

"Retrieval has started today. This is a developing situation and the Transport Secretary continues to be updated regularly," he added.

The nurdles likely entered the water at the point of collision, the coastguard added.

The manager of the Titchwell nature reserve in Norfolk said Monday that clumps of nurdles had appeared in the area that is home to rare and threatened species of birds.

"Currently the pollution is on the tideline, but we only have a few days to get this off the beaches before rising tides disperse the debris and it is washed back into the sea and into the food chain," said Steve Rowland in a statement, calling the situation "a real race against time."

The crash triggered huge fires aboard the two ships, which took several days and a massive firefighting effort to extinguish.

- Russian captain arrested -

Thousands of barrels of jet fuel were "lost" to fire and impact, one of the operators said Sunday, but called the extent of damage limited.

It remains unclear why the Portuguese-flagged Solong ran into the US-flagged Stena Immaculate about 20 kilometres (13 miles) from the English port of Hull on March 10.

One crew member from the Solong, identified by state prosecutors as 38-year-old Filipino Mark Angelo Pernia, is presumed dead.

At the time of the crash, the US military-chartered Stena Immaculate was carrying around 220,000 barrels of aviation fuel, at least one of which ruptured, prompting concern from environmentalists.

But surveillance after the crash showed that there did "not appear to be any pollution" leaking from either of the vessels, according to officials.

In a statement, the tanker's US-based operator Crowley said: "Based on an assessment by the salvage team, it has been confirmed that 17,515 barrels of Jet-A1 fuel have been lost due to the impact and fire. The remaining cargo and bunkers are secure."

Salvage teams determined that the extent of the damage was limited to a fuel tank and water tank, the statement added.

The operator praised "heroic action" by the crew to take fire precautions before abandoning ship.

The Solong's Russian captain was charged over the weekend with gross negligence manslaughter.

While the financial costs incurred from the incident are not clear, the Morningstar DBRS credit ratings agency estimates that total insured losses could range from $100 million to $300 million.