[RWebb]

sea water might dilute and absorb most all of the radioactive elements

BUT, C-137 might well be in airborne dust

both C-137 & I-131 can also be transported by living things - plants, animals, etc. in the air or water column AND the concentrations could increase in things we eat (food chain concentration and accumulation in certain (maybe preferred) parts of an animal's body)

overall, not much worry for US even if there is a meltdown but that is just my guess