[Clayart] Cobalt toxicity

Robert Harris robertgharris at gmail.com
Wed Sep 1 23:50:23 UTC 2021


Absolutely your tests show you fall well below safe limits.

I wrote a lengthy e-mail which I decided not to send (too technical and too
nuanced) which basically said that none of the agencies whether here or in
Europe have enough data to make any real determination about safe levels of
most metals. (The obvious ones such as Lead, Cadmium, Selenium etc
excepted). The problem is that all of our (human) data deals with acute not
chronic exposure. (And in this case mice are really too different to be
confident in extrapolating their data).

If you look at the CDC guidelines for Barium for example, there is a lot of
internal documentation which explicitly states that they pulled the number
for Barium out of their asses (which is why it differs from the EU
guidelines). Effectively what they did is take some numbers for acute
exposure to Barium, make up a "safe" limit for acute exposure (presumably
based on drinking several liters of water a day), then completely
arbitrarily divide by 100. There may have been some mouse experimental data
involved too, but as I recall they threw it out because it made safe levels
too high. There are several publicly available documents written by CDC
scientists essentially excoriating the process.

All of which goes to say ... take everything from the CDC/EPA with a hefty
pinch of salt and think through the safety aspects yourself.


On Wed, 1 Sept 2021 at 14:02, Cynosure -Arts <cynosure_arts at hotmail.com>

> Thank you to all who weighed in on my earlier post (especially Ron Roy).
> After much additional googling, this is the best I could find for
> recommended maximum exposure to cobalt taken orally:
> Although the US Food and Drug Administration (FDA) has not developed an
> acceptable daily intake for cobalt, the United Kingdom Expert Group on
> Vitamins and Minerals concluded that supplementation with 1400 μg Co/d was
> unlikely to cause adverse health effects in adults (8). The European Food
> Safety Authority has suggested a safe intake of 600 μg Co/d for
> noncarcinogenic effects.
> (American Journal of Clinical Nutrition)
> Further, the EPA has NO guidelines for cobalt concentration in drinking
> water. for comparison.
> The test I had run on the Rhodes Black glaze fired to Cone 10Redux (see
> glazy.com) at BSC Labs showed a result of .278 mg/L (or 278 ug).
> This seems to fall well within 'safe' guidelines.....am I reading that
> right?
> Of course, all the other variables of application and firing may make
> these results inapplicable for other users, but it does imply the glaze is
> generally acceptable as a food surface.  And I'll also add that the home
> alkali test (simmered in a soda ash solution) produced no surface change,
> so okay for the dishwasher.
> Eric Newman
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