国际英语新闻:Sources of persistent sheen in Gulf of Mexico remain unknown: U.S. officials

HOUSTON, Dec. 18 (Xinhua) -- The U.S. Coast Guard said on Tuesday that underwater inspections at the site of BP's 2010 rig explosion have failed to identify the sources of a persistent sheen on the surface of the Gulf of Mexico.

Meanwhile, it said that recent inspections confirmed BP's Macondo well is secure and not leaking any oil, according to a report on the website of The Houston Chronicle.

The Coast Guard said that remote-operated vehicles investigating the sheen concluded operation on Saturday, and that no sources of leaking oil were identified.

However, investigators collected samples of a white, cloudy substance that appeared to be coming from several areas near the rig wreckage. The substance is not believed to be oil, said the report.

A prior sheen was reported on Sept. 16 in waters near the site of the 2010 spill. It was later determined to have originated from a steel containment dome that was used in the early stages of the response in the 2010 spill to trap oil and methane hydrates from a leaking drill pipe in an attempt to funnel it to the surface.

A cap and plug were successfully put in place and no further oil emissions from the containment dome have been observed, the Coast Guard said later.

The 2010 blowout of BP's Macondo well in the Gulf of Mexico triggered an explosion that killed 11 rig workers and unleashed the worst oil spill in U.S. history.