The concentration at which it is released is already internationally regarded as safe. They aren’t dumping a high concentration that, by nature of distribution in the ocean, will eventually reach a safe concentration. They’re diluting it to safe levels before they even release it. I’m going to copy part of another comment I made in this thread here:

Here’s an IAEA overview as of February 2023,

The discharge of the ALPS treated water into the sea will be conducted after i) purification/re-purification to meet regulatory standards set based on international standards with an exception of tritium and ii) to allay the concerns of the consumers, the target concentration of tritium should be the same as the operational target (less than 1,500 Bq/L, that is less than 1/40 of the regulatory standard value for tritium) by sufficient dilution (more than 100 times) by sea water, prior to the discharge into the sea, and iii) The total annual amount of tritium to be discharged will be at a level below the operational target value for tritium discharge of the Fukushima Daiichi NPS before the accident (22 trillion Bq/year).

This release will represent less ocean irradiation than did the operating Fukushima plant.