In a startling revelation, man-made toxic mercury pollution has made its way to the deepest part of the ocean in the Marianas Trench. Researchers from China and US used robots to identify mercury in fish in the western Pacific Ocean and found it 11,000 metres below the ocean's surface. Fossil fuels, mining and manufacturing are sources of mercury in the atmosphere and may have entered the ocean through rainfall. Even the most remote marine ecosystems have now been hit by human-released mercury, the researchers noted. Once it enters the food-web, it can be toxic when ingested.