"Mineral spirits might just contain the same compounds (and other well-tolerated ones like octane and xylene) but they also might have novel compounds humans don't tolerate as well. And you can't usually tell from the label; just as with turpentine, what you get depends on where it comes from. Typically the MSDS will tell you the major components, but not the impurities thought to be harmless."

Right, I agree. It's necessary to say where I am and that's Australia. It's important because I've lived and worked in both the US and in Europe and from experience nomenclatures and formulations of these substances vary substantially from country to country.

The term 'mineral spirit' for mineral turpentine (aka mineral turps) is rarely used here. If one went to any hardware store and asked for mineral spirit the person serving would likely be quite confused and ask for clarification 'do you mean Shellite?', or whatever.

BTW, Shellite† is our version (concoction) of naphtha, it's much more flammable ('explosively' so) than turps.

Here, labels on containers of mineral turps are always titled with the name 'Mineral Turpentine' followed by its UN number and description, ie: UN-1300, Turpentine substitute. The UN-1300 MSDS is: https://advancechemicals.com.au/wp-content/uploads/2021/03/0....

As with all SDSs, almost every warning possible is described but for mineral turps two particularly relevant points stand out which are 'Mutagenicity: Not mutagenic' and 'Carcinogenicity: Limited evidence…'.

Despite the usual danger warnings to not inhale it, to avoid skin contact and avoid long exposure to it etc., the facts are that in practice there's little evidence of any serious harm coming to those who are exposed to it on a regular basis—so long as they take reasonable safety precautions. Here, painters use it as their primary most-used solvent for linseed oil-based paints. Go to any hardware shop and you'll see 1, 4 and 20-litre containers of it everywhere. Paint shops stock mineral turps along with acetone and DCM. At a guess, for every litre of DCM there'd be 5 litres of acetone and 20-50 litres of mineral turpentine.

I'd always have several litres of mineral turps at home. Today, I used about 300ml to wash out dirt from an old clock, here it's a household solvent with a multitude of uses. I've a range of pre-mixed solutions—mixed with Shellite, with ~5℅ EtOH and trace H2O, etc; they're used for degreasing, stain removal, etc.

EtOH is the safest chemical I use on a day-to-day basis (I've always about 10 litres of 95% available—unlike the US, denatured EtOH is readily available here). The next safest solvent I use is mineral turps, yes I avoid deliberately sniffing it or getting it on my skin but I take no other special precautions (that's the procedure most here would adopt).

It's worth noting that mineral turpentine that's available here is very consistent in its formulation, benzene and other toxic impurities never exceed 0.1%, and I'm reliably informed levels are usually much lower. I cannot speak for stuff that's called mineral spirits that I've seen in the US and in Europe. I've not done an assay but I know they differ significantly to our local product, for starters they have quite dissimilar odors (here, all brands have an identical odor).

I'm in no way trying to whitewash the dangers of mineral turps but in this highly regulated country it comes in as one of the solvents of least concern. On past evidence it draws pretty much the least attention.

I say that as someone who considers ALL aromatic hydrocarbons as potentially dangerous, especially so if they've benzene rings. DCM is considered significantly more toxic than mineral turps, trichloromethane is now unavailable to the GP, and CCl4 was banned years ago, and righty so (but when I was a kid evey dry-cleaning shop used it, walk nearby a store and one would always smell it).

Turning now to gum/wood turps, from your description it seems the stuff to which you are referring is very different to the type that's available over here. Reckon they're different substances, the only similarity seems to be in name only.

Over here, gum turps is at least four to five times more expensive than mineral turps, at minimum it costs around $28/litre versus $5-6/litre for the mineral stuff. Some art supplies even sell it for upwards of $11/100ml that's around 20 times as much! At that exorbitant price no normal person is going to use it as a general purpose solvent.

Here's gum's MSDS: https://diggersaustralia.com.au/wp-content/uploads/sds/16012....

Comparing their harmful effects they're as different as chalk and cheese with gum turps being substantially more toxic. Obviously, I'm unfamiliar with chemical regulations in your jurisdiction but you'll note from the MSDSs that here there's much greater concern over gum turps than there is for the mineral stuff, in fact the gum turps MSDS is a frightening read. Gum's MSDS sums it up as 'Hazardous', it goes on to say that one must wear gloves, protective clothing, eye protection with side shields and a respirator. It also makes the point I remarked upon in my earlier post, that is:

"…essential oils can consist of up to several hundred constituents, which can vary considerably depending on many factors (e.g. genus, species, growing conditions, harvest period, processes used). Therefore, a description of the main constituents is often not sufficient to describe these substances. …"

As someone who does some carpentry, I've often heard stories from fellow woodworkers never to use the stuff. Some have told me from experience that its effects on the skin are as bad as urushiol if not worse and it produces rashes and blistering that can take weeks to heal; and that's just the effects on one's skin, breathing or ingesting it are much, much worse.

All up, it's little wonder the stuff has a nasty reputation in this part of the world.

Again, it seems to me the only explanation for our differing accounts is that we're discussing two different substances. Perhaps where you are regulations are much more stringent for the product. Perhaps also it's distilled from a genus that has compounds that are low in toxicity and or that post-distillation purification further reduces the amount of its toxic compounds to safe levels.

"as with cyanide, the humans evolved with frequent exposure to small amounts of plant terpenes, …"

I'm not a toxicologist but I know that a main function of the liver is to metabolize various toxins including those produced by one's body; eg, alcohol dehydrogenase enzymes mop up the small amounts of EtOH produced during digestion, same goes for numerous other 'nasties' including various terpenes. As chemistry teaches, concentration matters. Similarly, as we evolved to eat fruit, so we've adapted to the small quantity of toxic amygdalin glycoside that's in some fruit kernels one metabolite of which is HCN and our bodies have learned to mop it up quickly..

Incidentally, as a young teenager who was keen on processing my own films, I recall a darkroom experience when reducing the amount of Ag in negatives with HCN. To be dark the room had to be almost airtight and the HCN got to me. Fortunately, I was aware of its effects and staggered from the room. A short time later I was quite OK.

I'd like to discuss the impurities 'triangle' with you as it's a fascinating subject but this comment is already too long.

___

† Here's Shellite MSDS: https://diggersaustralia.com.au/wp-content/uploads/sds/Shell....

Here's an anecdote that's somewhat off topic but given it's about Shellite and that it's so memorable I couldn't help but to recall it here. Quite some years ago during a prolonged strike of some weeks by petroleum workers I kept my car running on Shellite—at least so for most of the strike's duration. At the time I had access to a number of 20-litre drums of it, and it was marvelous to drive around without almost any other traffic on the roads except for emergency vehicles (they had special reserves of fuel available). Having the normally bottlenecked roads in a large busy city with a population of millions almost all to myself for several weeks was a strange and unforgettable experience—and a very pleasant one.

That said, unfortunately about two-thirds way through the strike I ran out of Shellite. Well, not to be deterred I resorted to using any flammable liquid that I could lay my hands on including EtOH, kerosene and mineral turpentine mixed in various ratios depending on what 'fuels' were available on the day. Initially, the car ran quite well on the combo mixture—albeit a little rough—that is, so long as I had enough EtOH in the mixture. Trouble was, soon I also began to run short of EtOH and each day I had to reduce its percentage which made the vehicle very difficult to start. Eventually, the ratio of EtOH to the 'oils' was so out of wack that the vehicle wouldn't start, there just wasn't enough of it in the mix to get ignition.

What to do next? Fortunately, the uni's physics school had lots of sealed tins of Et2O, so I resorted to pouring a small amount directly into the carburetor and that solved the issue of the engine not starting, but then (as I expected) another problem arose. Unfortunately, kero/turps mixtures are not that dissimilar to diesel fuel and engine run-on became a problem, to stop the engine I'd turn off the ignition and then put my hand over the carburetor's air intake to choke it. :-)