Washington, D.C. ? One of the nation’s largest stockpiles of toxic mercury will remain locked up instead of oozing into the world market.

After mulling a potential sale for several months, the U.S. Department of Energy confirmed Tuesday that it will keep nearly 1,300 tons of mercury in storage, increasing pressure on private companies to follow the same policy.

Once used to process materials for hydrogen bombs, the government’s mercury has been in storage since alternative methods were developed in the early 1960s.

Some of it has been sold over the years. But as scientists have become more aware of the dangers of mercury exposure, government officials and corporate executives have increasingly faced pressure to keep it out of the environment.