I am writing this to the welcome area since as a new member I do not have the permissions to post it to the Chemistry section where I feel it would better go. Several threads discussing Lye (NaOH) warn against using industrial grade NaOH in extraction as it may contain unknown impurities, in particular heavy metals. Despite rather extensive investigation, I have not found definitive answers to the following:

1. What is the expected maximum heavy metal content in industrial grade lye (EC number 215-185-5).

2. How efficiently do the heavy metals and/or their salts pass the extraction process? Are they actively absorbed in the final spice, passively travel through extraction steps along with other material, or are effectively filtered out in the extraction.

3. Is it really safe to use industrial grade NaOH for freebase extraction (considering heavy metal content in the final spice). Some threads claim that it is ok to use industrial grade NaOH if the announced purity is >98% but I have not found substantive factual evidence supporting this claim. On the other hand some people absolutely seem to discourage the use of industrial grade NaOH due to potential heavy metal content. I have not seen a genuine consensus emerging in the community yet.

I have found some promising pointers:


Maximum concentration of heavy metals in industrial grade NaOH:

Industrial grade NaOH is sold under the EC Number 215-185-5 but the maximum level of impurities mentioned for this standard differ between sources. The European Commission risk assessment report (http://publications.jrc.ec.europa.eu/repository/bitstream/JRC41941/sodiumhydroxidesum416.pdf) mentions the following purity for EC 215-185-5: sodium chloride (≤ 2%), sodium carbonate (≤ 1.0%) and sulfate (≤ 0.2%). The concentration of other impurities is less than 0.1%. In some other sources that I can't trace back any more I have seen that the concentration of other impurities in 215-185-5 could be up to 0.5% but I can't verify this. I have identified one manufacturer who says in the lye pellet container for industrial grade NaOH is 'c. 100%' (I assume it is not good to discuss specific brands here?). Given that other impurities than heavy metals are formed easily in NaOH manufacture processes it seems safe to assume that the heavy metal concentration in industrial grade NaOH is in general around the magnitude of <0.1%.


Theoretical maximum heavy metal concentration in the final spice:

Then 50g MHRB extraction takes 50g NaOH, which is now assumed to contain <50mg heavy metals. Assuming a 2% yield the extraction will produce 1g of spice. Assuming that all heavy metals would pass the extraction process, this would mean 50mg * 50/1000 = 2.5mg of heavy metals per 50mg of spice. However this would mean that the heavy metals are actively and completely aborbed in the non-polar solvent and in the spice. On the other hand, if the heavy metals are not actively absorbed in the final spice, we could assume that their concentration in the final spice is at most the same than in the starting NaOH ie. 0.1% which would yield 0.05mg ie. 50ug heavy metals in the spice. If heavy metals are blocked in the extraction process then the final heavy metal concentraction is even lower.


Safe baseline heavy metal concentration

The total heavy metal content in cigarettes has been reported to be in the order of 1-10ug per cigarette (I checked a couple of research papers and can add refs later) so one bag of cigarettes would contain 20-200ug i.e. <0.2mg of heavy metals. This I consider a relatively safe baseline and the theoretical maximum heavy metal content in one portion of spice would exceed this by a factor of 10-100. However if the heavy metals are not actively absobed by the extraction process, or if they are blocked by the extraction process then the potential heavy metal concentration in the final spice is around the baseline levels that a regular cigarette smoker is absorbind daily.



To what extent the (potential) heavy metal residues may pass the extraction?

Perhaps only minor proportion of potential heavy metals can theoretically pass the extraction process, or perhaps a step could be added to ensure this. If there are plausible arguments indicating so then it would seem relatively safe to use >98% industrial grade NaOH in the extraction despite the potential heavy metal impurities. I have so far seen only personal opinions of some forum members that >98% industrial grade NaOH is pure enough because many people are using it anyway, and other opinions that it should not be used. But the facts to back either position are missing.

If there is any sense to the issues you raise, then they would more rightly fit in the Safety section IMO.


Do you know of any inorganic heavy metal compounds formed in highly alkaline conditions that are also soluble in naphta? If an extraction is performed correctly, that would be the only vector for any heavy metal compound to remain in the end result.

While I'm not an expert on the above matters, I think that your worries are unfounded and that any (hypothetical) heavy metals will not get into the naphta.

If you are unsure of the purity of your extraction result you can always recrystallize from clean naptha.

Thanks ! This sounds promising and is exactly my concern: are heavy metal compounds soluble in naptha (or more generally in other non-polar solvents that are generally used for extractions) and to what extent?

I would like to find references, however, if it is an established fact that heavy metal compounds formed in highly alkaline solutions are not soluble in NPS to any remarkable extent.

Good to do research about potential risks.

Probably the risk to having effect on your health is low.
Food grade sodium hydroxide would be a nice option. Its readily available and eliminates the worrying about potential contamination.

A bit off-topic:
It's all about the amount of intake of heavy metals. For instance at my property a company performed some soil tests beforeIi bought it. It came out that there was a heightened Cadmium level. Not too disturbing and within legal limits but still there. My neighboring land is biological farm land. That produce is available on the Biologic food-market at the city centre. Still it's the same soil with the same pollution and with certain vegetables that cadmium is absorbed. People eat their nice " healthy " biological veggies with some cadmium without even knowing it. The previous owner of the property had a veggie garden which the whole family ate from year in year out. She's 88 and still lives.
That doesn't say a thing though. A big time heavy metal intaker could reach the age of 90 while a health guru dies of cancer at 40.

Industrial grade NaOH is more readily available from ordinary shops, food grade mostly in online shops.

If the typical >97% industrial grade NaOH really does not pose any risk then I do not see any practical difference. So far I have only seen personal views, both for and against using >97% industrial grade NaOH (I understand the case can be quite different with 50% industrial liquid NaOH that is also common).

Yes the level of exposure is what matters. Therefore I would like to calculate the theoretical maximum potential intake from >97% NaOH based on scientific literature and then compare this to the intake associated with ordinary cigarette smoking (for vapo), and established vegetable safety levels (for oral). There are various opinions but the lack of scientific references about actual heavy metal solubility in NPS from alkaline solution is the bottleneck for exact calculations.

Just wash your extraction solvent with distilled water. Not much of an issue as long as you don't half ass the extraction.

Tnx 1ce.

So you have the impression (or knowledge?) that any heavy metal compounds that may be present in the solvent after the pulls are largely absorbed in the polar layer (water) rather than the non-polar one (solvent)?

This sounds good. Many people are using industrial grade NaOH (>97%) for extractions at a regular basis. Therefore this is an important safety concern where verifiable claims regarding potential heavy metal contamination would be valuable. If any references and/or more exact quantification is available that would be quite useful to back up these comments.

If there are heavy metals in your non-polar to begin with, then you are using the wrong solvent (don't use leaded gasoline) and should not worry about the lye. If the solvent is clean, then any hypothetical heavy metals will likely not be dissolved in the aqueous layer either, as most heavy metal ions will precipitate as oxides or hydroxides in strongly alkaline conditions.


You could contribute a lot yourself by helping to find such references.

Excellent, thanks pitubo.

I am getting convinced that no considerable health risk are associated with potential heavy metals with >97% industrial grade NaOH. Perhaps it is just my lack of knowledge in chemistry making it hard to identify appropriate refs. Will certainly post these if I find.


In any case here some references for heavy metal concentrations in air and cigarettes that I mentioned above are in [1-3]. For instance Bernhard & Rossmann state following concentrations in cigarettes (assuming cigarette contains around 2-3g tobacco):

Aluminium 699-1200 ug/g (ie. 1000-3000ug/cigarette);
Cadmium 0.5-1.5 ug/cigarette;
Chromium 0.0002-0.5 ug/cigarette;
Copper 156 ug/g (ie. 300-500 ug/cigarette);
Lead 1.2 ug/cigarette;
Manganese 155-400 ug/g (ie. 300-600 ug/cigarette);
Mercury 5-7 ng/cigarette;
Nickel 0.078-5 ug/cigarette;
Selenium (present; amount not given);
Vanadium (average 1.11 ug/cigarette);
Zinc 24 ug/g (ie. 50-80 ug/cigarette);


[1] Bernhard, D., Rossmann, A. and Wick, G. (2005), Metals in cigarette smoke. IUBMB Life, 57: 805–809. doi: 10.1080/15216540500459667 PMID:16393783

[2] Islam E ul, Yang X, He Z, Mahmood Q. Assessing potential dietary toxicity of heavy metals in selected vegetables and food crops . Journal of Zhejiang University. Science. B 2007;8(1):1-13. doi:10.1631/jzus.2007.B0001.

[3] Labile and bioaccessible fractions of heavy metals in the airborne particulate matter from urban and industrial areas. Atmospheric Environment 36(22)3583-3590 D Voutsa, C Samara

You're more likely to find practically relevant data in inorganic chemistry textbooks and CRC data books than in a bunch of scientific articles like you quoted. Search engines are not yet an easy and sufficient substitute for reading books.


These numbers are about combusting whole plant materials containing heavy metals and measuring the amounts of heavy metals in the smoke and ash dust that is inhaled. That is not relevant here, because we want to know how much of these heavy metals can work its way through an extraction into the end result. Only then can we consider how much of that can eventually enter the human body as a result of the various methods of administration.

EDIT: and by the way, if you look into the amounts of crap you inhale daily as a result of living in industrialized urban areas, that puts a lot of these fears in perspective.

Yes exactly, the goal is to check whether possible heavy metal exposure with various ingestion methods differs from baseline levels in cigarette smoke / air in cities / eating vegetables from mildly polluted soil etc. The references above can help with such comparison once estimates of the heavy metal concentration in spice are available.

What about flouride and other gunk in tap water? Soluable in Naphtha?

In fact the calculations in my first post indicate that if heavy metals (or other crap) are not *actively absorbed* in the NPS but just passively transmitted there in minute quantities (in concentrations that are same or lower than in the alkaline solution), then their concentrations in spice will be around the same orders of magnitude (or probably lower) than in a single cigarette. Assuming this is the case, I do not think it makes much difference safety-wise whether these traces are vaped (as with spice) or smoked (as with tobacco).

Any fluoride in the water converts into sodium fluoride during basification (if lye or sodium carbonate is used) calcium fluoride (if calcium hydroxide is used), ammonium fluoride (if ammonia is used) etc.

No chance of any of this getting in the final smoking product.