There used to be -- and really still is -- this cavalier attitude about dumping stuff into the sea, because it gets diluted so much. Disposing nuclear waste this way has only been banned since 1993[0]. And of course more recently, the ocean was where much of the pollution from the Fukushima incident was directed.
Or take sea-faring ships, who dump both grey and black water (ie. untreated sewage) into the sea; I understand this is slowly being subject to some regulation. Ships also run with heavy oil which has its own set of issues (mostly sulfur content and NOx); in terms of CO2 emissions shipping is super efficient though.
"Or take sea-faring ships, who dump both grey and black water (ie. untreated sewage) into the sea; I understand this is slowly being subject to some regulation. "
Some? Some? Talk to a sailor about that one. The coast guard does not screw around with that at least in territorial waters and what exactly can be dumped where is highly regulated.
I wouldn't worry about the untreated sewage, after all, a lot of fish poop in the sea every day. The city I work in has determined its cheaper to pay EPA fines and dump raw sewage right off shore every time it rains, rather than make the substantial civil engineering investments to fix the system. I'd worry more about dish washing detergents and cooking oils and the like, unlike plain old sewage, the environment has very little natural experience with that kind of stuff.
I recall reading some proposal for dumping nuclear waste in the Marianas Trench. The rational had something to do with tectonic shifting eventually pushing the waste into the Earth's mantle.
The subduction zone off Vancouver, BC is also a place for this, and off Chile is even better.
The problem is the subduction zones are very slow -- on the order of 25 meters per 100 years, at most. The waste isn't particularly threatening past 10-20k years.
I still believe in reprocessing as the best solution.
Or take sea-faring ships, who dump both grey and black water (ie. untreated sewage) into the sea; I understand this is slowly being subject to some regulation. Ships also run with heavy oil which has its own set of issues (mostly sulfur content and NOx); in terms of CO2 emissions shipping is super efficient though.
[0] http://en.wikipedia.org/wiki/Ocean_disposal_of_radioactive_w...