[Quai]

I'm not a chemist nor physicist nor biologist, but..

What do you mean with "inert"? I'm pretty sure most radioactive elements are quite happy to react with other chemicals, like salt water.

Some of the new compounds will be water or fat solvable, and can find it's way in to our food chain. The gasses and particles from the nuclear tests around the world was also fairly localized, and if something was spread, it was diluted in a vast vast amount of air. Still, there was long lasting effects on humans and animals, some of which we are still discovering.

[RealityVoid]

I mean inert in both the physical sense - they do not move and the chemical sense - sure, metal rusts but the rate is really really slow compared to the liquid dispersion.

Look at the wiki entry linked above by the OP, most things dumped in the ocean are solid waste.

The look at the environmental impact studies done on the dump sites. They found no or negligible environmental impact. If OP wanted to make an argument against ocean dumping of certain nuclear waste, the wiki articles fails at this, on the contrary, careful reading makes it sound like a really good alternative for certain kinds of waste.

[derivagral]

To support this point, we're discovering today that perhaps some of that was not localized at all.

https://www.sciencemag.org/news/2021/04/nuclear-fallout-show...