@Mike: yeah, I've heard quite a number of accounts of
underwater discharge systems accumulating a brown
muck at the bottom (or at the electrodes) and/or
brownish 'spume' on top of the water... I seem to recall
most of those did use carbon (graphite) rod electrodes.
@Forest: well, yeah, exotic electron+proton=>neutron
fusion could explain it I guess... But that is not really
considered to be a common reaction...
I would guesstimate it is due to absorption of neutrons
from the water. Possibly even absorption of multiple
protons and neutrons. After all, if the water contains
deuterium, deuterium-hydrogen nuclear fusion may occur
(if the fields and energies are right), which as we all
know should produce a nucleus with 2 protons and 1 neutron,
which is a Helium nucleus a.k.a. alpha particle.
But I must admit it is quite a large jump to get from Carbon
to Iron: Carbon has 6 protons and 6 neutrons (98.9% of it does,
1.1% of it has 7 neutrons but is still stable, only trace amounts
just above 0% are unstable C14 with 8 neutrons and decays into
Nitrogen14 after a near 6000 year halflife) while Iron has 26
protons and 30 neutrons (91.7% of it does, while theoretically
any range between 28 and 34 neutrons will still form Iron,
of which only Fe57 and Fe58 (with 31 resp 32 neutrons) is
stable along with Fe56. All the others decay, although Fe54
with 28 neutrons has a halflife of approx. 3000 billion billion years,
if I'm not mistaken. So it's not stable but I wouldn't really call
it very instable either.
In any case, my point is: to get from 6 protons and 6 neutrons
to 26 protons and 30 neutrons, we'd clearly need to add another
20 protons and another 24 neutrons... And if we'd need to get
all those from Deuterium and Tritium, we'd need something like
16 Deuterium atoms and 8 Tritium atoms, which would give us
16 proton+neutron pairs and 8 neutron-proton-neutron triplets,
resulting in the necessary 20 p and 24 n.
That's a hell of a lot of heavy water getting cemented together
into one iron atom!
Seems highly unlikely...
Let's assume 4 carbon nuclei can join the fusion dance...
then we'd already have 24 protons and neutrons, and we'd only need
2 more protons and 6 more neutrons...
Sigh... Well, IDK.
But it sure looks like it can't just be the water providing those huge amounts
of neutrons... Or you'd have some damn heavy water running from your taps!