Spaceflight

Maser said that ocean dumping has historically been a short-sighted solution that’s comparable, he explained, to 80 years ago when it was considered a good idea to dump unused ammunition from World War II in the oceans. “Today, it turns out that the ammunition is corroding and spreads its explosives into the marine environment,” he told SpaceNews.

Munitions dumping was on a much larger scale and much more hazardous compounds. Tens of thousands of tons in close proximity against coastlines.

I imagine reentry is going to effectively incinerate everything except very large chunks of metal, and we regularly deliberately sink steel ships to produce artificial reefs. There's unlikely to be any quantities of plastics or fuel oils left unlike what you get in even minor marine incidents.

Any more advanced disposal plan is going to involve putting a lot more mass into orbit, which means burning a lot more propellant.