There is sure a lot of water in the ocean, but it's still possible to poison stuff locally, wherever you drop the stuff is going to have higher concentration, at least for a short while.
>The process for releasing typically dilutes to a standard level before releasing into the ocean/ other water way. So when it's released, it's already at a level you could swim in (drink?), there's no process for it accumulating into a more concentrated form in the ocean, and it has a half-life of 12 years.
