The Environmental Working Group has written a letter to ask BART to test trains for asbestos after the hazardous minerals turned up in the Washington, D.C., Metro system.
A BART spokesperson told SFGate the public shouldn't be concerned and that tests found no asbestos in the 439 original rail cars that were rebuilt between 1997 and 2005.
But asbestos has been found in various BART stations more recently.
A project to remove it from Powell Street Station in San Francisco began in October as part of an overall improvement plan that also includes fixing water leaks.
Asbestos was also found at Oakland's MacArthur Station, where the decontamination of work areas was to be completed prior to beginning a 12-week process of replacing security grilles at the station entrance in June.