Saying this with 100% certainty.
Of the Potassium K40 on earth, only a vanishingly miniscule portion is from any nuclear explosions, nuclear reactors, medical reactors, or spontaneous fission.
Like .000000000000001 % is "man made"
It is ALL primordial made, except for completely ignorable "newish" K40 in such low quantities as to be a joke, like 1 Bq per million M3 (million cubic meters) maybe even less.
And K40 is ionizing radiation, whether from the near 100% "natural" aka primordial source, or the miniscule vanishingly small "manmade" K40
And quoting bo quoting code, and as I believe that one reason that K40 does not do much damage is because it is evenly spread out through 70 trillion cells that make up our body. K40 has been around forever, and its in all living things, so all living thing either had to do well with K40 or they wouldn't be around.
We do have cellular level repair methods that work quite well on K40.
Other man made isotopes such as Cesium, Strontium, Plutonium do not spread out uniformly throughout the body, instead they concentrate in particular organs or in bone. Repeated attacks of the same cells in a localized area causes huge damage.
OK so here is the bo/code analogy
Potassium is like the grains of sand on a beach spread uniformly. It might be a mild annoyance if the wind pelts you with some sand, but thats it. Cesium 137 is, thinking of that same beach, a pile of large jagged glass that will do alot of damage as you run over the top of it.--------------------------------------------
Sure, there is a lot more sand than glass, but the glass is going to do way more damage.
Finally, "admitting" that there is a lot of natural radiation in the ocean and in our bodies, IN NO WAY is any type of admission that the "hormesis theory" may be true.
I am not even sure how that assumed line of thinking came about
I also can't see any direct correlation to the LNT theory
And since we are here, let me weigh in on the LNT theory.
LNT is a "theory" and a useful for setting conservative guidelines for human protection. That is it's only real purpose. But LNT has also been twisted by the Nuke Cartel to be a strawman of sorts, it's easy to knock down.
It literally says that the damage to exposure curve is Linear and there is No Threshold (LNT).
But anyone understanding physical processes could easily postulate that damage to exposure is very unlikely to be exactly linear, and there very well may be a threshold.
And that threshold will be completely different based on whether the radiation isotope is internal or external to your body. And instead of a linear relationship it is way more likely to be a curve, not a perfect straight line.
And that curve will be different for each isotope, AND for whether it is external or internal.
And for combinations of radio-isotopes it should be readily apparent that the presence of both is likely to be synergistic in a greater negative way. And so this would be yet another curve.
For instance, with both strontium 90 and Plutonium in your body, the strontium will go to the bones, and the plutonium will go the bones, liver, and maybe lungs. But when they are both "working" on the bones it is going to be more damage than just the addition of each one alone.
Think of it this way. Let say you are kind of trained in fighting, but you are up against a Jujitsu guy who has a little more power than you. You are going to take some damage, but you will walk away without having to go to the hospital. Then another day, you are up against a Tae Kwon Do expert, and you are going to take some damage, but still get out of there alive.
The third day you show up and find out to your surprise that you are in a cage match with the Jujitsu guy and the Tae Kwon Do guy. They each attack you in a different way, and at the same time. Sorry, but you are going out of there on a backboard to the ambulance.
So the new damage curve can't be made simply by adding up mSV, the sum of the parts. It's more complicated than "they" make it out to be. In fact, it's even worse than that, because some of these radio-isotopes are not poison just through their radiation, but they are poisons as chemicals and sometimes heavy metals
But just because it is complicated, that doesn't mean that we throw our hands up and says it's too complicated so lets just not even worry about radiation until we can see an obvious and immediate effect.
So we know that the LNT theory is just a theory, and beyond that, it will not accurately describe each isotope and especially combinations of isotopes. LNT is easy to "knock down" if you are pretending that it is highly accurate to predict damage compared to dose. But that was never it's purpose. It's purpose was to set a meaningfully safe level of radiation to regulate to so that innocent people were not unduly exposed to ionizing radiation.
So what the members of the well paid Radiation Cartel are up to now is to "knock down the LNT model as a straw man" and then pretend that because LNT can be shown to be wrong sometimes, that we simply replace LNT with "Hormesis, radiation is actually good for you". It's really quite an absurd course to take, but nuclear is dying under economics and its own weight of being overly complex, they are desperate.
A quick word on "Hormesis"
In the current NRC filing by 3 "people" with highly vested interests (they get paid lots of money to dose people with radiation), they state that "Some amount of radiation is good for you". One of them tries to back it up with references, which for the most part fall flat on their face, but most people will never read the references. Out of 30 references, a huge percent are based on studies showing large doses of X-rays and their effects. They bastardize this with their own version of LNT showing that the large doses at one time, if they were spread out over time, therefore show that low doses on an ongoing basis are OK.
And I call Balderdash on that. It is very likely that a large one time Xray dose (but not overly large) would do less harm than a continuous string of "small attacks".
Let's go back to the "fighter" analogy. You get out of your car in Chicago and immediately get attacked by 2 muggers that hit you, and knock you down to the ground. You are not permanently injured, and you are set back, but you recover and living properly you actually come back stronger and smarter and more cautious.
Now a different scenario. You leave your apartment, and everyday a bully hits you with a good kidney punch. You can still continue on and go to work and go about your business, although your body is not filtering poisons quite as well. As the weeks go by, the damage builds up and your body is even less able to repair itself. After a year of this daily torture, your kidneys no longer even work and you are on dialysis.
Small continuous attacks can definitely be worse than 1 large attack. So using the "large dose Xray" as a support for hormesis is a terrible example, and it doesn't support their case, but for those just passing a glance at what appears to be a scientific backup, it could appear to be good support.