英语文摘：Oil spill raise arsenic levels in ocean: study

LOS ANGELES, July 3 (Xinhua) -- Oil spills can raise arsenic levels in the ocean, creating an additional long-term threat to the marine ecosystem, a new study suggests.

Oil spills can partially block the ocean's natural filtration system and prevent this from cleaning arsenic out of the seawater, according to the study published in the July issue of Water Research, an influential academic journal published in the U.S.

The study sheds light on a new toxic threat from the Gulf of Mexico oil leak, said researchers from the Imperial College London.

In the study, the researchers discovered that oil spills and leakages clog up sediments on the ocean floor with oil, which prevents the sediments from bonding with arsenic and burying it safely underground with subsequent layers of sediment.

A supply vessel passes through oil floating near the site of the Deepwater Horizon oil spill in the Gulf of Mexico off Louisiana on May 31.

This shutdown of the natural filtration system causes arsenic levels in seawater to rise, which means that it can enter the marine ecosystem, where it becomes more concentrated and poisonous the further it moves up the food chain, according to the study.

The scientists say their work demonstrates how the chemistry of sediments in the Gulf of Mexico may be affected by the current oil leak.

Arsenic is a poisonous chemical element found in minerals and it is present in oil. High levels of arsenic in seawater can enable the toxin to enter the food chain. It can disrupt the photosynthesis process in marine plants and increase the chances of genetic alterations that can cause birth defects and behavioral changes in aquatic life. It can also kill animals such as birds that feed on sea creatures affected by arsenic.

Arsenic occurs naturally in the ocean, but sediments on the sea floor filter it out of seawater, which keeps the levels of naturally occurring arsenic low. However, arsenic is also flushed into the ocean in wastewater from oil rigs and from accidental oil spills and leakages from underground oil reservoirs.

"We can't accurately measure how much arsenic is in the Gulf at the moment because the spill is ongoing," said Professor Mark Sephton, from the Department of Earth Science and Engineering at Imperial College London. "However, the real danger lies in arsenic ' s ability to accumulate, which means that each subsequent spill raises the levels of this pollutant in seawater." "Our study is a timely reminder that oil spills could create a toxic ticking time bomb, which could threaten the fabric of the marine ecosystem in the future," said Sephton.