Product Refinement Safety & Compliance

Residual Solvents in Extraction Products

Lance Griffin
Written by Lance Griffin

Residual solvents may adversely affect cannabis concentrate quality and the consumer’s health. Generally they are the result of unpurified extract; vacuum ovens are one tool to remove hydrocarbon solvents. Residual solvents may also be introduced during cleaning (e.g., isopropyl alcohol). State-level cannabis testing regulations require at least some analytical testing for residual solvents in legal cannabis. The United States Pharmacopeia (USP) <467> provides guidelines that inform some programs. Nonetheless, cannabis testing requirements vary by region.

Residual solvents requiring testing may include chloroform, benzene, acetone, methanol, toluene, and many others with varying degrees of toxicity. [1,2] The tables below summarize the requirements of seven different states for five residual solvents to illustrate regulatory differences (the list is by no means exhaustive).

Butane

State Residual Limit (ppm) Products
Alaska 800 Solvent-based concentrates
California 5,000 All
Maine 5,000 All
New Mexico 800 Solvent-based
Oklahoma 1,000 Food/infusions
Pennsylvania 5,000 Extraction-based
Utah 5,000 All

Propane

State Residual Limit (ppm) Products
Alaska N/A N/A
California 5,000 All
Maine 5,000 All
New Mexico 800 Solvent-based
Oklahoma 1,000 Food/infusions
Pennsylvania N/A N/A
Utah 5,000 All

Hexane

State Residual Limit (ppm) Products
Alaska 10 Solvent-based concentrates
California 70

290

Inhalable

All other

Maine 290 All
New Mexico 250 Solvent-based
Oklahoma 60 Food/infusions
Pennsylvania N/A N/A
Utah 290 All

Ethanol

State Residual Limit (ppm) Products
Alaska N/A N/A
California 5,000 All
Maine 5,000 Oral & topical products exempt
New Mexico N/A N/A
Oklahoma N/A N/A
Pennsylvania 5,000 Extraction-based products
Utah 5,000 All

Benzene

State Residual Limit (ppm) Products
Alaska 1 Solvent-based concentrates
California 1 All
Maine 1 All
New Mexico 2 Solvent-based
Oklahoma 2 Food/infusions
Pennsylvania N/A N/A
Utah 2 All

The 5,000 ppm limits for hexane, propane, and ethanol reflect USP <467>, which considers these solvents less harmful and defers to Good Manufacturing Practice guidelines. Extractors must nonetheless be aware that more harmful solvents may co-occur. For example, purified ethanol may contain small amounts of benzene. Butane may also contain harmful contaminants. This is one reason why programs require rigorous testing for trace amounts of solvents that seem irrelevant.

Although ethanol is sometimes considered a non-priority, at least one study has suggested that inhaling residual ethanol may cause dependence and other negative effects. [3] Sufficient levels are known to intoxicate and potentially damage lung tissue.  On the other hand, a 2019 case study profiled the case of an 18-year-old individual who suffered severe pneumonitis after using illicit butane hash oil. [4] The injury was likely due to “an unknown level of pure butane.” [4] Ultimately, untested concentrates are dangerous.

References

  1. Valdes-Donoso P, et al. Costs of cannabis testing compliance: Assessing mandatory testing in the California cannabis market. PLOS ONE, 2020;15(4): e0232041.doi:10.1371/journal.pone.0232041. [Impact Factor: 2.740; Times Cited: n/a]
  2. Nate S. Cannabis contaminants: Regulating solvents, microbes, and metals in legal weed. Environ Health Perspect. 2020;127(8):82001. doi:10.1289/EHP5785. [Impact Factor: 8.05; Times Cited: 2]
  3. MacLean RR, et al. Inhalation of alcohol vapor: Measurement and implications. Alcohol Clin Exp Res. 2017;41(2):238-250. doi:10.1111/acer.13291. [Impact Factor: 3.235; Times Cited: 16]
  4. Anderson RP, Zechar K. Lung injury from inhaling butane hash oil mimics pneumonia. Respir Med Case Rep. 2019;26:171-173. 2019. doi:10.1016/j.rmcr.2019.01.002. [Impact Factor: n/a; Times Cited: 21]

Image: Kevin King, CC By-2.0

About the author

Lance Griffin

Lance Griffin

Leave a Comment