Baron says...

You are absolutely correct about the relatively small quantity of cobalt
exposure. The reason the EPA has no limit on cobalt in drinking water is
that it has not been recognized as a problem. At least, not yet. It seems
like every year, another limit is placed on some contaminant, for good or
bad.

I don't know of any maximum contaminant level (MCL) regulation that is
unreasonable. If a water source has an MCL violation, you can rest
assured that the concentrations of that contaminant are very high
compared to what is normally encountered with clean water.
Concentrations of cobalt are typically in the microgram/liter (ppb)
range for clean drinking water, so an MCL regulation would probably be
nearer the mg/L (ppm) range considering its low toxicity by ingestion,
if such a regulation were ever instituted. It would all depend on what
conclusions were on the study that prompted the hypothetical regulation.
But what I've been able to dredge up from the Net is that continued
ingestion of more than 30mg per day is required to see negative health
problems.

The term "heavy metal" is a really soft term that was applied to just a
few metals many moons ago. Since that time, it has come to mean anything on
the Periodic table that is left after chopping off the appropriate groups
like halogens, alkali metals, etc. As a result, the term includes so many
metals that it is essentially worthless.

A useless media coined term. Gold is heavier in atomic weight and
denser compared to arsenic, yet it is non-toxic and inert. There are
many other examples. I don't see how manganese at 25 on the periodic
table and cobalt at 27 could be considered heavy metals, whatever that
means. Of course, Andy Dingley didn't mention that term in his post,
but others have in previous threads.

As for finishes being food safe once fully cured, that is correct. The
issue is the term "food safe". That means the finish can be in contact with
food. It does not mean that the finish is safe to eat. As was pointed out,
lead paint was banned because children were actually eating it. It also
happens that lead from various pigments can be leached out when in contact
with acidic food so it really was not "food safe". The metallic driers in
modern finishes are safe when used in a finish that fully cures and the
finish is not actually eaten.

Yes, but in my worst case scenario I wanted to assume that part of the
finish is actually ingested. Yet even in this worst case scenario
exposure levels were in the microgram range. I think we can forget
about manganese entirely since both of the multi-vitamins in my house
have 2mg of manganese per tablet, a couple of orders magnitude greater
than my worst case scenario. Also the driers are used only in
polymerizing finishes and even if small chips of the finish were
consumed, it isn't at all clear to me that those polymers are digestible
or that the driers could be leached from them. So not only are the
driers safe for ingestion, the exposure amounts are at worst small, but
quite possibly negligible.