[pjc50]

Greenpeace did a lot of work in the 80s and 90s against the dumping of nuclear waste, including direct action against the ships doing the dumping. This led to the London Dumping Convention.

More recently, see e.g. Trafigura https://www.bbc.co.uk/news/world-africa-10735255 (and what they've tried to hide with libel lawsuits)

The WW2 stuff is bad but seems now to be inert, although occasionally someone finds a phosphorous shell on a beach in Scotland. https://www.chemistryworld.com/news/a-dangerous-guide-to-bea...

More seriously, there is the SS Richard Montgomery, not dumped but sank during the war, carrying a thousand tons of explosives ... right next to London. https://en.wikipedia.org/wiki/SS_Richard_Montgomery