The thing they removed was sulfur. It comes up naturally with the oil, so it is not really an additive. It is cheaper to leave the Sulphur in the bunker fuel that the ships burn so that is what they did for many years. Nowadays they extract the extract the Sulphur and it ends up in big piles. Some of the Sulphur is sold to make various products, but often there is too much to sell and so it just piles up. Sometimes you may spot one of these giant yellow piles when traveling.

https://live.staticflickr.com/2786/4448449049_f5da3bbcea_z.j...

Elemental Sulphur is not very toxic, but I would not recommend eating a bowel of it.