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
>>
|