Hax Planx wrote:
Andy Dingley says...

On Thu, 09 Jun 2005 19:59:28 -0700, David wrote:


Even oils with metallic driers?

Which metal ? What's "food safe" ?

A few decades age we had a reaction against lead-pigmented paint in
childrens' toys. Now that's a pretty sensible reaction -- 20%-30% of the
paint might be a lead pigment, and they're getting chewed.

For oil though, the drying agent is about 0.25% and it's likely to be
used on items where the finish is left undisturbed (barring marauding
chinchillas). So even lead-dried oils are nothing like the toxicity
hazard of pigmented paints - however the upper lead limit on a saleable
finish is something like 0.2%, so they're still forbidden.

Lead oils (for centuries) were usually a mixture of lead and manganese
driers, as this gives the best resultant oil. Shrinkage is reduced and
they dry in all weathers. When lead fell from favour, the first response
was to simply omit the lead and use manganese alone. The problem with
these is that they need a dry climate to cure and will remain
perpetually sticky on the surface if used in Wales or Seattle. They're
also too inflexible to be used on oilcloth, and have some tendency to
shrinkage cracking.

The modern replacement for lead was cobalt. This is an effective drier,
although the resultant finish isn't as robust as a lead-dried oil. We're
recently starting to see toxicity concerns over cobalt too - the element
itself is regarded most dubiously, although I haven't heard too much
concern raised yet over its use as a drier.


Good information, but I would take exception to the scare over cobalt.
It's a little known exotic sounding element, so it must be toxic, right?
Not necessarily. I am a chemist and I worked for three years testing
drinking water for EPA regulated contaminants. Last I heard, there was
no maximum contaminant level regulation for cobalt and only recommended
concentration goals for manganese. Neither are acutely toxic in the
same sense as some other so-called 'heavy metals' such as lead, mercury,
cadmium, thallium and arsenic. The term heavy metal is an artifact of
the media as far as I can tell, and was never mentioned at any point in
my long, grueling years as a chemistry student. There may have been
some cases of industrial workers being debilitated by breathing large
amounts of the dust, but similar health catastrophes can happen with
coal dust (black lung), rock dust (silicosis) or even wood fiber dust.
I have heard of other health effects like enlarged thyroid with cobalt
and restricted iron uptake with manganese, but exposure levels must be
hundreds of times what is normal in food and water over a long period of
time. Both are essential minerals for the maintenance of life and
probably have much the same function in our bodies as they do in
oxidizing finishes as catalysts. Too much of just about anything can
have adverse health reactions including calcium and some vitamins.

So let's do some math on what we might be exposed to using a salad bowl
finished with something that contains these driers. 0.25% = 2500ppm
(parts per million). If we use 1/20 of a liter of finish for our bowl
and assume that the density is about 80% that of water, then our bowl
has about 100mg of combined cobalt and manganese in its finish. If we
further assume that only 1/2 the surface is food contact area and we
consume 0.1% of the finish with each use, then our exposure to combined
cobalt and manganese comes to about 0.05mg per meal. That would be
approximately the same as drinking a liter of good quality treated
water, with the additional point that neither of these metals is
regulated with a maximum contaminant level from the US EPA. Conclusion:
intake of cobalt and manganese from food contact items using finishes
containing these driers would only be a fraction of normal intake from
food and water. We all have much bigger fish to fry for improving our
health than this.


Fish? If you are a fisherman or hunter, you have
much more to worry about, especially if the
streams have any contamination from insecticides
and herbicides and the fields are sprayed with the
same. One fish out of the Snake River or any
other river used for irrigation would have a
larger dose of any "heavy metal" in organic form
than your salad bowl coating. Heck, eating
recommendations for Pheasant in some places is
down to 1 every 2 week or none for pregnant women.