Are we all debating the same thing? Let us look at the question of whether it is safe for home extractors to use relatively cheap 99% Isopropyl for extraction, vis a vis expensive and heavily taxed Ethanol.
On average I opine/proffer that unlike commercial extractors with high capital investments and EPA VOC constraints, home extractors have less access to things like refluxing stills for recovering 190/200 proof Ethanol, and in the worst case scenario will be using simple evaporation and heat without vacuum assist.
That leads us to the issue of final purging to ensure residual solvents are below FDA standards for pharmaceuticals. They FDA considers both Ethanol, Isopropyl, and Acetone to all be Class 3 solvents.
Solvents in Class 3 (Table 3) may be regarded as less toxic and of lower risk to human health. Class 3 includes no solvent known as a human health hazard at levels normally accepted in pharmaceuticals. However, there are no long-term toxicity or carcinogenicity studies for many of the solvents in Class 3. Available data indicate that they are less toxic in acute or short-term studies and negative in genotoxicity studies. It is considered that amounts of these residual solvents of 50 mg per day or less (corresponding to 5,000 ppm or 0.5 percent under Option 1) would be acceptable without justification. Higher amounts may also be acceptable provided they are realistic in relation to manufacturing capability and good manufacturing practice (GMP).
Further regulated by CFR-Code of Federal Regulations Title 21 for food additives for Ethanol versus Isopropyl:
Ethanol: eCFR :: 21 CFR 184.1293 – Ethyl alcohol.
Isopropyl: CFR - Code of Federal Regulations Title 21 (fda.gov)
As you note, the FDA approves both Ethanol and Isopropyl for pharmaceutical extraction, providing residual solvent standards are met.
Also noting that nowhere does it approve drinking either, or ingesting higher quantities. While there are LD-50 levels where half the population died, established for both Ethanol and Isopropyl, they are approximately 4200% and 3600% of PDE respectively.
The LD-50 also doesn’t address chronic or long-term effects, nor percent of the tested population that didn’t die but were damaged for life.
Interestingly the chronic effects of Ethanol are one of the most closely studied of them all because of chronic alcoholism, which has enlightened us to the fact that its Acetaldehyde metabolite is a carcinogen, genotoxin, and a teratogen. If we had actual long term human studies of other solvent abuses, we might find they also have additional insalubrious side effects.
Both the PDE and LD-50 numbers clearly show Isopropyl is more toxic, but poison is in the dosage. Our bodies are equipped to deal with amounts at or below PDE. IE: Metabolize Isopropyl into Acetone, which our bodies produce naturally burning fat.
To verify my understanding, I contacted my favorite Pharm D and asked their opinion, which was that the PDE numbers are a good order of magnitude rule of thumb, keeping in mind that they were “calculated” based on animal studies, as human subjects are not used to establish the limits.
If dosages below PDE are not of concern, how probable it is that the average home extractor can meet Class 3 residual solvent standards of 5000 ppm, not to exceed 50 mg/day, without analyzing equipment beyond his nose.
ASSuming average human odor threshold, Isopropyl alcohol is detectable around 200 to 40 ppm. I can still smell and taste the sweetness and flavor of the Isopropyl if the extraction is simply evaporated away using air flow, but after decarboxylation, it was no longer detectable.
9.4.8.1 QWISO - GrayWolf’s Lair (graywolfslair.com)
Part of Doug at Cannabis Home Sciences presentation are easy ways to further clean the Iso extract to remove not only the residual Iso, but also the waxes and lipids. All using readily available equipment and ingredients.
I’ve sampled his RICE oil and can tell you that I was unable to detect any Isopropyl, so I believe the levels to be at least below 200 ppm. At 40 ppm to 200 ppm residual Iso and one gram per day concentrate dosage, residual solvent would be 0.000006 grams to 0.0002 grams per day.
I no longer have a GC, but I still have a sample of the Rice if anyone wants to test it for residual
Better off rexing it in ethanol after and then getting it tested for methanol residuals before you smoke or eat the result.