Up to 10 million gallons (38 million liters) of crude oil from the 2010 Deepwater Horizon oil spill has settled at the bottom of the Gulf of Mexico, where it is threatening wildlife and marine ecosystems, according to a new study.

The finding helps solve the mystery of where the «missing» oil from the spill landed. Its location had eluded both the U.S. government and BP cleanup crews after the April 2010 disaster that caused about 200 million gallons (757 million liters) of crude oil to leak into the Gulf.
«This is going to affect the Gulf for years to come,» Jeff Chanton, the study's lead researcher and a professor of chemical oceanography at Florida State University, said in a statement. «Fish will likely ingest contaminants because worms ingest the sediment, and fish eat the worms. It's a conduit for contamination into the food web.» 

The researchers took 62 sediment cores from an area encompassing 9,266 square miles (24,000 square kilometers) around the site of the Deepwater Horizon spill. Unlike other sediment on the ocean floor, oil does not contain any carbon-14, a radioactive isotope. Therefore, sediment samples without carbon-14 indicate that oil is present, Chanton said.

The scientists avoided areas with natural oil seeps, features in which oil slowly leaks onto the ocean floor through a series of cracks. In these areas, the sediment cores would have a lack of carbon-14 throughout the sample. In areas that don't normally have oil, «the oil is just in the surficial layer, like in that 0 to 1 centimeter [0 to 0.39 inches]» interval," Chanton told Live Science.