For some perspective: I don't have a full breakdown of the release materials on hand, but according to Wikipedia of the 45 PBq you quoted something like 20 PBq of that was Iodine-131 and 5 PBq of Cs-137. That's about 4.3 grams of I-131 and 1.6 kg of Cs-137. In radiological terms that's a LOT if they were concentrated in a small area, not so much when diluted into the entire ocean.

Not to downplay the risks or consequences, people need to decide that for themselves and the dynamics of how this material ends up dispersed in the environment are complicated, but talking in terms of mass helps put things into perspective.