Well that was a sad article to read on a Monday morning. If this is what we've just scratched the surface on - I'm nervous to what we don't know in terms of ocean dumping.
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
https://www.smithsonianmag.com/science-nature/decaying-weapo...