Iranian oil tanker Sanchi burns in the East China Sea on January 13 2018. Picture: REUTERS/Shanghai Maritime Search and Rescue Centre
Iranian oil tanker Sanchi burns in the East China Sea on January 13 2018. Picture: REUTERS/Shanghai Maritime Search and Rescue Centre

Beijing — The spill from a sunken Iranian tanker off China’s east coast has spawned four oil slicks as authorities prepared to send robots to the wreckage to assess the environmental damage.

The Sanchi, which was carrying 136,000 tonnes of light crude oil from Iran, sank in a ball of flames in the East China Sea on Sunday, a week after colliding with Hong Kong-registered bulk freighter the CF Crystal.

The bodies of only three out of 30 Iranian and two Bangladeshi crew members have been found.

The State Oceanic Administration of China said late on Wednesday that it was monitoring four slicks with a total area of almost 101km², roughly the same size as Paris. The office is attempting to "control the spread of the oil spill and is carrying out work to estimate its impact on the marine ecological environment", it said on its website.

The type of condensate oil carried by the Sanchi does not form a traditional surface slick when spilt, but is nonetheless highly toxic to marine life and much harder to separate from water. The cargo amounted to nearly 1-million barrels of oil.

Japan’s coast guard said on Thursday that a patrol ship and plane examined the oil spill and found it was spreading 30km east and 8km north-west from the wreck, with a maximum width of 800m.

"The swathe of oil slick is being diffused and disappearing," the coast guard said in a statement. "Chinese and other patrol ships continue to look for missing [crew] members and are carrying out oil removal missions."

On Tuesday, China had reported two slicks measuring about 69km² and an additional 40km² area of "scattered" oil. The transport ministry said late on Wednesday that the vessel lay at a depth of about 115m and that robots would be deployed to explore the wreck.

The area where the ship went down is an important spawning ground for species such the sword-tip squid and wintering ground for species such as the yellow croaker fish and blue crab, among many others, according to Greenpeace.

It is also on the migratory pathway of numerous marine mammals, such as humpback and grey whales. In addition to the light crude oil, the Sanchi also carried a fuel tank able to accommodate some 1,000 tonnes of heavy diesel. If all of the Sanchi’s cargo spills into the sea, it would be the biggest oil slick from a ship in decades.

By comparison, in the sixth-worst spill since the 1960s, the Odyssey dumped 132,000 tonnes some 700 nautical miles off Canada’s Nova Scotia in 1988, according to figures from the International Tanker Owners Pollution Federation website.

Richard Steiner, an Alaska-based oil spill consultant, called on the Chinese government to conduct a survey of the sunken vessel as soon as possible, citing concerns about the possibility of continued leakage.

"It is critical to know if any condensate remains on board," he said in an e-mail, adding that instead of evaporating it could create a "more concentrated toxic underwater plume. If the entire 1-million barrel cargo is released (which seems likely at this point), this will be the largest condensate spill in history."


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