You're right that this isn't an exactly viable comparison. Though there do seem to be signs that tritium too, is subject to biomagnification. I've posted a link below

Edit: for clarity, here's the link again. The main takeaway for me is that phytoplankton can make tritium bio-available and that this bio-available form of tritium is both getting bio-magnified up the food-chain and is entirely disregarded by current legislation, since the bio-available form of tritium is technically in a different chemical configuration. If I'm getting any of this wrong, feel free to correct me, everyone