FMF - Friends of Minerals Forum, discussion and message board

[Vitomorim]

I have a question, are arsenate minerals like Erythrite and Roselite dangerous since they have Arsenic in their composition? What cautions should I take?

[Riccardo Modanesi]

Hi Vitomorin!
Usually I involve these minerals (as well as asbestos) in a plastic transparent sheet, so that I should have no problem (and so far I hadn't, more than 30 years are over since then!). I hope I was useful for you.
Greetings from Italy by Riccardo.

[Vitomorim]

Thank you Riccardo. I followed your advice and got them in two sealed transparent plastic bags. If anyone has more advices, you can share them here.

[Jordi Fabre]

Recommended reading: Sensitive minerals

[Vitomorim]

Thank you for the link Jordi. I checked the mindat health warning before coming here but information from experienced people is never too much.

[Jordi Fabre]

Tracy is a major expert in Arsenic and Arsenate, but currently she is in vacation. She will probably keep on touch with this topic when she returns...

[Roger Warin]

That's my opinion on the toxicity of cobalt arsenate.

The toxicity of a mineral depends on its ability to pass through the human body.
Most often, the poison is ingested by aqueous solution (mineral) or gaseous form.
In general, a collection of mineralogy is not toxic because you do not drink the water used to wash minerals and often do not breathe the vapors.
If they did growth in nature, it is because they were insoluble. As they are salts, their vapor pressure is very low.
But there are exceptions. If the mineral decomposes, it often produces gaseous products. For example, sulfides or arsenides may undergo oxidative hydration with release of various toxic gases. But then the mineral specimen breaks.

Chemists define the proportions of ions in solution in the water by a constant (depending on the temperature, etc..) called the solubility product Ksp. The smaller, more salt is insoluble.
For erythrite Co3 (AsO4) 2, Ksp = 6.80 E-29.
I do not know the value for roselite Ca2Co (AsO4) 2, but I believe that this compound does not exist in the dissolved state. It is a crystalline construction.
The amounts of anions AsO4 in solution are accordingly low.
The toxicity of arsenic depends also on the degree of oxidation. It is lowest for arsenate.
In very small doses, this anion is a drug!
Paracelsus said: "All things are poison and nothing is without poison, only the dose makes a thing not a poison."
In general, all heavy elements are toxic. They all have a great opportunity to react with organic molecules.
And plutonium is more toxic by its chemical aspect than radioactivity, however great.
Roger.

[Jordi Fabre]

And even more info here -> How to minimize Arsenic on Realgar

[cascaillou]

I just reviewed mineral toxicity and storage/handling precautions on mindat.org:

https://www.mindat.org/mesg-62-338876.html

[Vitomorim]

So, from all of this information I can say that after cleaning a mineral specimen (to avoid the its dust) the best choice is too put it in a sealed plastic box for better protection and presentation. We can choose too handle it with our hands if we follow simple rules as washing our hands after playing with it, but for those who have children or other people that may touch the mineral specimen the best thing is the sealed plastic box.

[cascaillou]

I wouldn't consider a plastic box to be required for storing erythrite.
However, erythrite is an arsenate which contains 25% As(V) and 30% Co(II) and it is HCl soluble which means that poisoning may occur from oral absorption.
Washing hands after manipulating a specimen can't hurt.

For comparison, arsenolite is an arsenic oxide which contains 75% As(III) and it is water soluble. Therefore arsenolite is best stored inside a transparent sealed plastic box. Store arsenolite away from children reach, do not put your hand to your mouth (or eat/drink/smoke) during the manipulation of the mineral, and thoroughly wash your hands (with soap) after manipulation. Clearly, arsenolite is way more hazardous than erythrite.

More detailed safety precautions for handling/storage of hazardous minerals are available in the link I provided.

[Tracy]

Interesting discussion...but I think a bit of perspective is needed here.

I do not understand why arsenic should be considered more likely then any other atom to jump out of a mineral specimen and be absorbed by the body. Lead is poisonous too, so why not shield all of our galenas? And what about the mercury in cinnabar? As Paracelcus said (see Roger's post), all substances are poisons (though not all substances are drugs...all substances are chemicals or combinations of chemicals) and it is the dose that makes the poison. Even water is a poison at a high enough dose. So why do people worry more about arsenic?

There are thousands of arsenic-bearing minerals, and some of these are water-soluble, and some have arsenic in valence states that are more toxic than others (not to mention inorganic versus organic arsenic compounds). But I highly doubt that the amount present in a collector's specimens contain enough arsenic in them to cause toxicity to the owner, a possible exception being if s/he were to collect boulders of native arsenic. I'm also skeptical that the arsenic would separate easily out of a complex molecular structure. In my opinion, as long as we treat our specimens with equal care (that is to say we do not eat the specimens or drink water used to wash them, rub the specimens vigorously on our skin, or crush specimens and inhale the dust), then we should be safe from harm.

The risk of toxicity is a function of both the hazardous properties of the substance and the potential for exposure to it. Hazard alone is not enough to cause concern. I would submit that careful handling of specimens - most notably, grasping them on the matrix instead of on the crystals themselves, keeping them safe from damage either on shelves or in boxes, controlling climate as much as possible, etc - is more than enough to keep exposure potential to a minimum. With minimal exposure potential comes minimal risk of toxicity! Washing hands after handling is always good advice, though I think this too might be an unnecessary precaution under ordinary circumstances of handling specimens.

I would emphasize that I am focusing my response on arsenic, not on other mineral types that MIGHT be further protected by some form of shielding (for strong radioactives) or extra ventilation (for highly fibrous/fraying asbestos specimens). For most of these specimens, the "special precautions" could also be seen as excessive, but not for all - it depends on the situation at hand and the exposure potential.

One last thing to note about arsenic is that its toxicity is usually CHRONIC in nature - that is to say, long-term repeated exposure to small amounts of arsenic can cause a variety of adverse symptoms leading ultimately to death. ACUTE arsenic poisoning requires exposure to large amounts (= toxic doses) all at once, and were this to happen, the main effect would be stomach upset (diarrhea, vomiting, cramps). More serious acute effects could occur if the intoxication is great enough. However, in the context of collecting specimens, this simply isn't a realistic scenario (as long as you don't eat your specimens every day ;) ). It is more likely that an arsenic specimen would degrade (eg with prolonged exposure to light/moisture) than that a collector might be poisoned by it.

In sum: arsenic in mineral specimens is not, in my opinion, something to worry about. Arsenic carries a bad reputation, but it isn't really different from most other elements in the periodic table. Sensible, delicate handling is all that is required, that which one would do for all of his/her specimens. Anything more I would regard as being at the discretion of the individual more than as highly recommended.

- Tracy

[cascaillou]

You cannot compare inorganic arsenic toxicity to inorganic lead toxicity:
-inorganic lead shows rather low acute toxicity and high chronic toxicity potential
-organic lead shows high acute toxicity and high acute chronic toxicity potential (organic lead is way more toxic than inorganic lead)
-inorganic arsenic shows high acute toxicity and high chronic toxicity potential
-organic arsenic shows high acute toxicity and high chronic toxicity potential (although organic arsenic toxicity is slightly less than for inorganic arsenic).
-As(V) compounds tends to be slightly less toxic than As(III) compounds, although both As(V) and As(III) are highly toxic.
In other world, in terms of acute toxicity (which is the main exposure concern for the arsenic minerals collector), inorganic lead isn't of much concern while inorganic arsenic is seriously poisonous.


However, it is very important to understand that for a given toxic element, not all compounds of that elements will show same level of toxicity.
For instance, in the arsenic minerals familly, arsenolite (arsenic trioxide, which is as much as 75% As3+) acute toxicity orally in rats is about 50 times greater than for native arsenic (100% As), which is mostly due to the difference in solubility between these two compounds. In humans, 200mg arsenolite can be enough to cause death, and of course you can get seriously sick from much less than the lethal dose, and considering that it is a dense compound we're are talking of quantities not much bigger than a grain of rice!

[Tracy]

Cascaillou, I was not comparing lead toxicity to arsenic toxicity. I was simply pointing out that all elements have their own inherent toxicities, and used lead as one example.

My main point is that it is virtually impossible to get a lethal dose of arsenic, however small, from the ordinary handling of a specimen. You are describing a scenario in which a specimen, or a fragment of a specimen, is accidentally eaten. I don't imagine that anyone who takes pride in his/her collection will carelessly handle specimens while cooking lunch, and not notice or care if a piece breaks off and falls in the pot. I suppose it is theoretically possible, but I think the odds are rather small! Similarly, I can't imagine a collector aggressively rubbing specimens on the skin until a lethal dose of arsenic is absorbed (dermal absorption of inorganic arsenic is <10%, so you would have to rub at least 2 grams of arsenolite to accomplish this) or otherwise willfully damaging a specimen. Yes, arsenic has significant toxicity potential...but the likelihood that conditions would favor a toxic exposure is very, very low.

While I'm not a chemist (I'm a toxicologist), I also can't see situations where a specimen of erythrite (for example), which has the chemical formula Co3(AsO4)2·8H2O, would release enough free arsenic to poison anyone, especially if it is handled as gently as one would/should handle any other specimen.

If it makes you feel more comfortable to handle an arsenic specimen with gloves and in a well-ventilated enclosure, by all means go ahead and do so. However, my personal and professional opinion is that taking extra precautions just because arsenic is part of a specimen's chemical makeup is unnecessary.

- Tracy

[cascaillou]

well, I don't know but I think a compound that is water soluble with oral LD50 in rat lower than 15mg/kg (thus labelled as "highly toxic") should be regarded as potentially hazardous.

Also keep in mind that arsenolite has been found in large samples, see this specimen: https://www.mindat.org/photo-405990.html

However, most minerals that shows such high toxicity are "fortunately" very rare species essentially occuring as very small (often microscopic) crystalline formations, so that it's rather unlikely to absorb a dose big enough to cause serious toxicity.

Now, back to the subject, I do agree that erythrite and native arsenic arn't too much of a concern (although toxic if ingested) which is precisely what I was pointing to when comparing these to arsenolite (my point was precisely to underline that all arsenic compounds do not represent an equal hazard). Actually, I have a sample of native arsenic on hand that has some size to speak of, and I'm not much worried about it (I don't handle it more than necessary, and I simply wash my hands after handling).

ps: as a toxicologist, you might explain me something I'm curious about. If an inorganic compound of a given metal or metalloid is ingested, and if this compound isn't soluble in water nor in hydrochloric acid, can it still be absorbed by the body through other processes?