The explosion happened while the men were welding and there was no pollution, the Coast Guard reported.

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Researchers from Portland State University and Washington State University, Vancouver, looked at caffeine pollution off the coast as part of a broader study of contaminants in the water.

CNN: Researchers find caffeine in waters off Oregon

The decision to resume the Nautile's operation came as fresh incidences of pollution were reported on the coast of the French region of Brittany.

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Other concerns include potential impacts to groundwater in the event of a spill and high pollution from refineries along the Gulf Coast that would process the bitumen.

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After taking samples from 21 spots along the coast, researchers expected to find the most caffeine pollution in areas near wastewater treatment plants, large population centers or rivers and streams emptying into the ocean, said Elise Granek, assistant professor of Environmental Science and Management at Portland State.

CNN: Researchers find caffeine in waters off Oregon