Officials spent hours on Thursday morning searching for a container that was emitting low levels of radiation near Pier J in the Port of Long Beach before eventually finding it and determining the source was an element commonly used in mining, according to authorities.

The initial call occurred around 9 a.m. and LBFD Capt. Jack Crabtree said hazmat crews joined in around 10 a.m. to help agencies including the U.S. Coast Guard and Port crews to find out which container was emitting radiation.

It took about four hours for emergency workers to locate the container, according to Lee Peterson, a spokesperson for the Port. But Peterson said that the effort wrapped up around 1 p.m. and that U.S. Customs and Border Protection had taken over the investigation. Peterson said the container is not a hazard to the public.

Peterson said that the substance that was eventually detected was Thorium-232, a naturally occurring substance that is commonly found in mining operations.

It’s not clear why the substance was in the container, “But Customs and Border Protection will do an investigation just to be on the safe side,” Peterson said.

It’s not clear how the Thorium-232 was detected, what the country of origin was or if it was on a ship when it was found.

Peterson said that most of the container terminals have devices that monitor for radiation to ensure that containers that are leaving the port are safe for transport.

Peterson said it would be up to the federal agency when the container can be moved.