Over 50 years ago, a Toepler pump that I had glass-blown myself
developed a crack that caused several kilos of mercury to hit tha
ceiling and give me a shower. Fortunately I did not then know how
poisonous it was and suffered no ill-effects
George
On 12.09.2017 19:46, James Holton wrote:
One more correction,
It seems brominated vegetable oil (BMO) really does contain Br atoms!
I could have sworn I read in some reputable source long ago that the
process of "bromination" was an old term for general reduction of
double bonds and did not necessarily involve bromine. Usually
hydrogen. I remembered this because I thought it was hugely
counter-intuitive. Now, of course, I cannot find that reference. So,
who am I to pit the validity of my memory against Wikipedia and a long
list of links to health-nut web blogs? Guess I was wrong about that.
The Mountain Dew I am drinking right now has a very faint X-ray
fluorescence peak that could be Br. Hard to be sure above
background. So I will have to get a sample of neat BMO to sit next to
my shampoo, pepto and sunscreen on my shelf of heavy atom compounds
that are on the FDA's GRAS list:
https://www.fda.gov/food/ingredientspackaginglabeling/gras/
Remarkably, the MSDS for BMO is less scary than that of ordinary
vegetable oil. This raises more than one interesting topic, but the
most relevant here I think is "bio-availability". Selenomethionine is
much much more bioavailable than selenium sulfide, which is the active
ingredient in my dandruff shampoo. Apparently, humans don't absorb it,
but microorganisms can mistake it for a source of sulfur.
I expect the bio-availability of Hg in pizza is pretty high
considering how it bio-amplifies in fish, so I stand by my APE. But it
is always prudent to read the MSDS before you open a bottle, and then
read the MSDS of something similar just to put it in perspective.
-James Holton
MAD Scientist
On 9/6/2017 12:59 PM, James Holton wrote:
Was just pointed out to me off-list that my anchovy data was off, so
I just double-checked the FDA website:
https://www.fda.gov/food/foodborneillnesscontaminants/metals/ucm115644.htm
Turns out the latest number for anchovies is 0.016 ppm, or 0.5 ug per
ounce (28g).
So, if you use a whole 2 oz can, that's still ~ 1 microgram Hg as the
Anchovie Pizza Equivalent.
And it looks like one piece of bigeye tuna sushi could be as much as
~14g*1.816ppm = 25 APEs
-James Holton
MAD Scientist
On 9/6/2017 11:44 AM, James Holton wrote:
Something that could perhaps be of use here is what I like to call
the "Anchovie Pizza Equivalent" (APE), which is about 1 microgram of
mercury. According to the Food and Drug Administration website here
in the USA the average mercury content of anchovies is 0.34 ppm,
which is about 1 microgram per ounce of fish. Tuna can be higher,
but varies a lot from fish to fish. My point here is that most
institutions regard the amount of mercury you bring onsite for
purposes of eating for lunch, be it sushi or pizza, as small enough
to be negligible. I tend to agree. So, one could argue that 1
microgram of Hg per day is a "safe amount". Especially if you don't
eat it.
In terms of protein crystals, a 100 micron wide cube has a volume of
1 nanoliter, and if it were soaked to a final concentration of 50 mM
Hg that is 1e-9 L * 50e-3 mol/L *200 g/mol = 10 ng. So, 100 protein
crystals soaked with Hg add up to roughly 1 APE. Please note that I
am in no way encouraging you to eat your protein crystals, and
especially not the solutions you soak them in. You should do your
own APE calculations for those. But I do think it important to note
just how tiny the amount of metal in our crystals really is.
Now, mercury is purportedly the second-most-toxic metal after
Plutonium. But Pu derivatives are uncommon. In fact, until
recently (4zhd) Pu derivatives were unheard of. The authors I'm sure
will tell you 4zhd involved no small amount of paperwork. But as
long as you are not working with Pu, you can regard every other
metal as less toxic than Hg.
Another good example is selenium; by far the most common metal
derivative. Although toxic, Se is also a dietary requirement. I
suppose this is an excellent demonstration of what "moderation"
really means. The Recommended Daily Allowance (RDA) of selenium in
the USA for adult men and pregnant women is 55-60 micrograms per
day. In crystals, one Se atom per 100 amino acids at 50% solvent
comes to an overall concentration of 50 mM. So, a 100 micron
crystal contains about 4 ng of Se. It would take 15,000 such
crystals to add up to the US RDA. The synchrotrons I work at don't
go thought that many crystals every day. But even if they did, I'd
stick to my commercially available multivitamin to get my dietary
selenium.
So, although it is never a good idea to be sloppy with chemicals in
the lab, I think it is also important to do the math and think about
not just the toxicity of the things we work with on the bench, but
the everyday items all around us. It is never a good idea to be
antagonistic with regulators about such things. They are only trying
to do their job, and all they are trained to know about are LD50s
and how to stay as far below them as possible. A little
gently-pointed-out insight into non-lethal applications of heavy
metals can be helpful all around. The over-the-counter drug Pepto
Bismol (bismuth subsalicylate) is almost 50% bismuth by weight, a
metal that is right next to mercury on the periodic table.
Brominated vegetable oil contains no bromine, by the way. And
dandruff shampoos such as Selsun Blue make an excellent and
surprisingly radiation-hard reference for the selenium edge.
-James Holton
MAD Scientist
On 9/4/2017 3:13 AM, Dr Stephen Graham wrote:
Hi all,
(This email is aimed primarily at my UK colleagues, but feel free to
read on and gloat that you don't have to write safety forms in your
lab/country!).
I need to sort out written risk assessments for heavy atom soaking of
crystals in my lab. I wondered whether anyone would be willing to
share the risk assessments they have in their institute/company so
that I can seek inspiration and make sure I'm keeping up with best
practice.
Many thanks,
Stephen
--
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-33021 or -33068
Fax. +49-551-39-22582
