Asbestos is a problem when you try to scrap a ship like that. Airborne fibers are toxic. It's not a problem when you sink it. Unfortunate, that's a huge amount of metal that could be recycled. The residual oil can be mitigated by scrubbing tanks and reservoirs before scuttling. It may still leave an oil slick, but I think that's more of a cosmetic problem than long term environmental issue.