Sanitary nature of synthetic whetstones within the kitchen

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May 21, 2018
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(This topic is strictly regarding big name stone brands like Naniwa, Shapton, King, etc, not random cheapo mystery stones intended for rough grinding tools in a workshop. It is also keeping in mind a common-sense approach to having things generally tidy during the process; wiping down surfaces used after, washing knives properly after, etc.)

I've always been under assumptions that the use and mess from most whetstones isn't really an issue in the kitchen if you have a proper setup. Either with sufficient paper towels/rags, or a professional level water basin with stone holding device overtop. A further assumption would be that since water is a primary element involved during use, no airborne particulate from the steel or the stone would be an issue over time, since it should all be contained within the water (with proper disposal of it after).

Even with a good seemingly clean & tidy setup, could it be possible that tiny micro amounts of leftover debris (on surfaces or in the air) could be causing some level of contamination within the kitchen?

Heavy metal poisoning is a thing I know very little about, but that comes to mind.
If anything I'd again ASSUME that the stone/slurry debris isn't as much of a potential harm as metallic particulates coming off of certain steels could be. ...or perhaps some abrasive compounds could potentially be worse..I have no idea.

I know a lot of high-end professional restaurant kitchens use them regularly within the same room(kitchen) that food-prep and cooking takes place, but this could simply be something not fully tested/analyzed, or otherwise overlooked by chefs/management and certain sanitary standardization organizations.

I'd just like to know for certain that consistent use of whetstones within the kitchen is indeed harmless if kept clean & tidy in the general sense - on more of a hard science/medical/biological level, does anyone have access/links to any documentation or other data proving it either way?

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I don’t have any scientific proof for my answer, it’s based on my knowledge about chemistry and physiology, so take this with a grain of salt:

As most common abrasives like aluminiumoxide and the likes are insoluble in water and pretty inert, they should leave your body unaltered in case you ingest them. (Not sure about binders though)
Iron, the most obvious contaminant that’s set free while sharpening is pretty hard to metabolize and should be safe as well.
Alloy elements like chrome and nickel are primarily harmful if inhaled as anorganic compound (salts) which should be no issue either.

Lastly I think it’s safe to say, that the amount of heavy metals ingested during regular food intake is much higher than numerous sharpening sessions can yield, provided you don’t eat the slurry [emoji4].

Anyone please feel free to correct me if I’m wrong.
There shouldn't be any heavy metals in a quality knife (just think abou the logic for a second)....

heavy metals are a problem because your body cannot get rid of them (lead, or mercury in fish, etc)
non-heavy metals to a certain extent are a different class.

Other issues like breathing in silica dust are problem but not with water on the stone;
you can get terrible complications from breathing (dry) stone dust other wise.

You should alwys clean and wash your hands and knife and work area to avoid
cross contamination. You do not want to eat metal grindings or stone slurry.

That part is just common sense, IMHO.
Not sure of the safety of synthetic stones, but there are differing opinions on the safety of oral exposure to aluminum. It's generally considered safe, but it's also been linked to Alzheimer's. That may be a specious association, however, and no mechanistic rationale for why it would promote neurodegeneration has been proposed to my knowledge.

Natural stones are a crapshoot, because there could be any number of elements in there.

Steels contain several alloying elements that are regulated in food and drugs. Vanadium, nickel, and cobalt are tightly regulated in drug products, and may be present in significant amounts in many alloys. Chromium can be extraordinarily toxic in certain oxidation states, so wiping up your slurry with bleach might be problematic. Molybdenum is generally less toxic than these other elements, but is still closely regulated in drug products if they are injected or inhaled.

Not sure where the notion that metallic impurities cannot be in steel came from. There is no such thing as pure steel, and the quantity and type of elemental impurities remaining in a given steel will depend on the source or ore and how it was made.
Just wanted to clarify, I was usign the term 'heavy metals' in the way many people do to refer to a subset of them that are inherently toxic.
Wikipedia shows the term can also be used in other ways, so better to just clarify what I was meaning.

The term heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations. Examples of heavy metals include mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl), and lead (Pb).

That being said, chroumium in stainless steel isn't really
a "source" of environmental chromium.

In the same way that table salt (sodium chloride, NaCl) isnt a source
of (free or elemental) sodium (Na) which can be quite dangerous as well.
I think the more common practice of steeling knives in western kitchens is likely more problematic. Generally right over the prep surface and I've noticed watching butchers and working the line, too often the blade isn't so much as wiped down before going straight to cutting. I've seen visible steel residue in the first cuts watching butchery demos on YouTube, etc. Gross!
Iron is essential to life. There are literally iron filings added to fortified cereal. You can blend the cereal in water and extract the iron with a magnet. There is a significant amount present.
Re: Exposure to various elements found in knife steel alloys due to sharpening in kitchen via ingestion?

Yay. Something down my alley.

Wisdom of the ancients: "The dose makes the poison". If FDA hasn't bothered to kick over it, I'm hoping the doses are so small that it's been found to be non problematic- But the "cutting edge" of materials science may now use elements in kitchen knife alloys the FDA never thought to consider when writing current federal codes?

What is the exposure, how much, what oxidation states are the elements in? (hexavalent chrome is truly bad, other oxidation states are not AS bad)

The very fine swarf on stones and tiny curls of steel off of grooved steels have a large surface area:volume ratio. This equates to high reactivity with the hydrochloric acid in your stomach if ingested.

I'm going to disregard C, S, P, Si, N as minor constituents (and elements your body is QUITE competent in dealing with in any quantity likely from this source)

So, I assume chlorides of Fe, Cr, Ni, V, Mn, Mo, W, Co. Did I miss anything, I don't see much about, say, rare earth elements in kitchen knife steel alloys I've looked at?

Of these, from prior experience? Cr and W ions in some of their oxidation states are probably the worst as far as carcinogenicity. Tungsten has an AMAZING number of oxidation states, getting particles of pure metalic tungsten embedded in your body is right up there with having radioactive particles embedded for carcinogenicity, if you live long enough after, there will likely be an issue.

The Israelis use of plastic bonded DHMEX (explosives heavily salted with Tungsten powder instead of HE wrapped in pre fragmented steel) for "surgical strikes" on people they don't like among the Palestinians is NOT going to be remembered as a better idea than the collateral dammages from traditional (steel cased) munitions when someone with no axe to grind eventually does the epidemiology on that population- I suppose it could be a feature rather than a bug if you're a Zionist, for the rest of the world, probably not so much.

I'll quit describing my ASS U ME ptions for now, I'll be doing some quick checks on likely chemistry before I go further.

For some basics on problems with heavy metals in the environment, this is a good introduction:
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This will be another ASSumption, but I'll bet that compared to knives, people ingest much more metal over the years from stainless steel prep bowls and stainless lined cookware, both from abrasion with utensils and chemical leaching. Basic kitchen cleanliness, including washing and wiping down a knife after sharpening or "steeling," shouldn't be an issue.

The stainless cookware on the other hand.... I know there is some risk there, and we do use a lot of stainless bowls and stainless-lined cookware in our home kitchen. But one study I read showed that the surface abrasion loss of metal tapers off with older cookware, and I'm careful about not letting acidic sauces sit too long in a pan.
I'd speculate that leaching of metal is far greater issue
with reactive pans like carbon and cast Iron,

not to mention all of the kinds of plastic food storage
and water storage, etc in a kitchen, endocrind distuptors,etc

interesting discussion there are so many ways
to get sick these days :(
I'd speculate that leaching of metal is far greater issue
with reactive pans like carbon and cast Iron,

not to mention all of the kinds of plastic food storage
and water storage, etc in a kitchen, endocrind distuptors,etc

interesting discussion there are so many ways
to get sick these days :(

Totally agreed.
I'd speculate that leaching of metal is far greater issue
with reactive pans like carbon and cast Iron,

not to mention all of the kinds of plastic food storage
and water storage, etc in a kitchen, endocrind distuptors,etc

interesting discussion there are so many ways
to get sick these days :(

I'm not an expert on this stuff, but I think carbon steel pans and cast iron pans are safer than stainless steel, because basic carbon steel doesn't have anything nasty in it. Stainless steel on the other hand, has the bad stuff like nickel and chromium that can leach out, or be abraded over time, and never leaves the body.

I'm still cooking with stainless-lined heavy copper pans because it hasn't killed me yet, and the advantages are just too great to ignore. I don't know what I'd use instead of large stainless steel prep bowls either. Aluminum would be worse and wouldn't last as long. You can get copper bowls (great for whipping egg whites), but bare copper isn't that great for ingestion either.

And yeah, plastic food storage is the other thing to watch out for. I've read that the plastic used in name brand bags like Ziplock, or Foodsaver for vacuum pack and sous vide is safe. So avoiding off-brand bags is the main thing to watch out for. But who knows, long-term. I'm not going to give up sous vide for the few things it really works for, even though I don't love the amount of plastic waste it generates.
Quick followup to this thread to share some research I fell into, for the benefit of the next person to care about this –

I'm attaching a 2017 paper by the University of Messina that shows some leaching of Ni into acidic dishes – tomato sauce and lemon meringue. The leached Ni generally falls below allergy thresholds but people with extreme sensitivities will take the position that the only safe amount is 0.

One review reads:
I got them because my hair was falling out and so nickel-free cookware was recommended. Within a month, my hair stopped falling out! I can't tell you how happy this makes me!

A couple of brands sell 18/0 cookware: HomiChef and SolidTeknics.

Carbon steel and (enameled) cast iron are the obvious alternatives, but for those who are into exotic steels, you can find nitrogen-hardened cast iron, which claims more corrosion resistance, at, or in Asia as "Nitrigan" under the brand La Gourmet. You can read all about the metallurgy, as always, at KnifeSteelNerds's post about nitrogen-alloyed steels.


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