radiation-wise you're correct, but I'm not sure the same holds true for some of the isotopes themselves. Admittedly, I'm neither physicist nor biologist, so my knowledge here is limited at best, but as far as I'm aware, certain particles can bio-accumulate and bio-magnify along food-chains and make entire species inedible as a result. The radiation doesn't even have to be that strong, once that shit is inside of you, there will be cancer. I'm thinking for example of mushrooms in Germany after Chernobyl - the radiation levels in forests overall were mostly fine shortly after the disaster but mushrooms remained (and I think, remain to this day, at least in certain regions?) inedible due to the accumulation of isotopes they manage to accomplish through their wide-and-deep-reaching mycelium networks. Of course, anything eating the mushrooms also becomes inedible. Which literally lead to radioactive hogs, but that's for another time.

As long as nature lives, there are constant accumulation processes happening and they may just end up gathering all that finely diluted stuff together again. Again, I'm no expert and I'm sure the experts have taken at least some of this into account - and still I remain skeptical in regards to the harmlessness of this release, just because dumping nuclear waste-water in statistically-negligible and expert-certified safe manner has been a pretty standard procedure for the UK nuclear sector - and over the years I've heard enough critiques of that, to at least remain skeptical. Maybe anger is misguided, sure, it often is - but maybe unquestioning acceptance of it as the only rational thing to do, is too.