Wasn't said ever-present background radiation only a thing after the nuclear bomb tests? I read a while ago that steel from old ships that sunk deep is highly valuable because it's not irradiated yet.
To a first approximation all matter on earth radiates because all matter is present with some isotopes that will eventually decay. Don't forget that we're sitting on top of a huge ball of molten metal kept hot by ongoing nuclear decay. That process produces all kinds of isotopes that eventually make their way to the surface.
The bomb tests did increase background radiation for us; irresponsibly so in my opinion. But so does burning coal. We have been lifting the level of background radiation over the natural level for centuries by now.
I don't see how sunk steel would be any more valuable than steel from freshly mined ore. But I like to be surprised about these things :-)
> I don't see how sunk steel would be any more valuable than steel from freshly mined ore. But I like to be surprised about these things :-)
Steel production uses air from the atmosphere. Thus it picks up the increased background radiation while it is refined. It may be possible to scrub the radioactive components from the air to avoid contanimating the steel, but I expect the cost would be prohibitive (at the very least, more expensive than getting it from old battleships).
It is low-backgroud steel([0]), not no-backbround steel. Potassium-40, for example, is a naturally occurring radioisotope. See Banana equivalent dose ([1]).
Amount of seawater on Earth: 1.338 billion km^3 (according to Wikipedia). Assuming 1.0 kg/L, this is 1.338 * 10^18 ton.
Seawater is about 0.04% potassium, so this is about 5.35 * 10^14 ton of potassium.
Potassium contains naturally occurring radioactive isotope (40K): the radioactivity of potassium is 31 Bq/g. Hence the natural radioactivity of all potassium in seawater is 1.66 * 10^22 Bq.
For comparison, again according to Wikipedia:
> In May 2012, TEPCO reported that at least 900 PBq had been released "into the atmosphere in March last year [2011] alone"
...which is 9 * 10^17 Bq, or about 1/18,000 of naturally occurring radioactivity in the ocean due to potassium alone.
(We didn't even start on stuff that are commonly considered "radioactive", like all the uranium and thorium lying beneath where you are.)
* Meanwhile we're busy burning fossil fuels, increasing the amount of CO2 in the atmosphere by ~30%.
On global scale it negligibly increased ever-present background radiation. It's not a good thing, but far from poisoning.