Safety/Toxicology Profiles of Extraction Solvents

Solvent safety in cannabis extraction must not be underestimated. The harsh toxicology of naphtha and other solvents led to to their decline. Consumers and extractors want safe solvents.

Inhalation of airborne vapors is a major consideration. Acute Exposure Guideline Levels (AEGL) are published by the National Academies of Science to help measure the toxicity of certain airborne chemicals:

AEGL-1: airborne concentration that causes discomfort in the general population; effects are transient and reversible

AEGL-2: airborne concentration that causes irreversible or serious health effects in the general population

AEGL-3: airborne concentration that causes death or catastrophic health effects in the general population

Airborne chemicals are usually reported in parts per million (ppm). Different time periods of exposure are also tracked, namely 10 minutes (min), 30 min, 1 hour (h), 4 h, and 8 h. The Occupational Safety and Health Administration (OSHA) and the American Conference of Governmental Industrial Hygienists (ACGIH) also publish limits for certain airborne chemicals.

Cannabis extractors must also be aware that flammable vapors can cause cataclysmic explosions. Lower explosive limit (LEL) refers to the lowest concentration of vapor (as a percent of volume in air) required to spread fire given an ignition source. The extractor may not experience any negative health effects with levels of vapor capable of igniting.

Monitoring vapor levels, using closed-loop extraction systems, and testing for residual solvents are fundamental. Without further ado, here is the data for the four most common cannabis extraction solvents:

Butane (C₄H₁₀)

Hydrocarbon solvents are petroleum-derived organic compounds composed of carbon and hydrogen molecules. Butane is perhaps the most common hydrocarbon solvent in cannabis extraction today.

Overall Toxicity: Low

• 10-min AEGL-1: 10,000 ppm
• 1-h, 4-h, and 8-h AEGL-1: 5,500 ppm
• 10-min AEGL-2: 24,000 ppm
• 30-min, 1-h, 4-h, and 8-h AEGL-2: 17,000 ppm
• 10-min AEGL-3: 77,000 ppm
• 30-min, 1-h, 4-h, and 8-h AEGL-3: 53,000 ppm

Symptoms: Drowsiness and slowed speech; pulmonary distress; unconsciousness; central/peripheral nervous system and cardiac effects; brain damage.

Flammability: Extremely flammable

• LEL: 1.9% (or 19,000 ppm)

Notes: Requires Class I Division I set-up, per National Fire Code. Butane may cause severe brain damage in developing fetuses. Vaporizing residual butane in cannabis oils produces cancerous byproducts.

Propane (C₃H₈)

Propane may be the second most common hydrocarbon solvent used in cannabis extraction. Some extractors combine propane and butane.

Overall Toxicity: Low

• 10-min AEGL-1: 10,000 ppm
• 30-min AEGL-1: 6,900 ppm
• 1-h, 4-h, and 8-h AEGL-1: 5,500 ppm
• AEGL-2: 17,000 ppm (all time periods)
• AEGL-3: 33,000 ppm (all time periods)

Symptoms: Vertigo; burning sensation; nausea; fever; respiratory distress; central nervous system depression; cardiac sensitization (e.g., cardiac arrhythmia).

Flammability: Extremely flammable

• LEL: 2.3% (or 23,000 ppm)

Notes: Requires Class I Division I set-up. Air displacement and asphyxia are a significant concern.

Ethanol (C₂H₆O)

Many extractors use ethanol (aka ethyl alcohol, or simply alcohol) as a standalone polar solvent; others use ethanol as part of post-processing (i.e., winterization).

Overall Toxicity: Low

• OSHA regulatory limit: 1,000 ppm (8-hour time weighted average)

Symptoms: Eye and skin irritation, headache, sensation of heat; rapid inebriation and narcosis; vomiting; lung irritation and injury; liver and kidney damage; central nervous system depression.

Flammability: Highly flammable

• LEL: 3.3% (or 33,000 ppm)

Notes: Requires Class I Division I set-up. The consumption of alcohol is associated with various forms of cancer and severe brain damage to fetuses; acute/chronic vapor exposure may pose similar dangers.

Carbon Dioxide (CO₂)

Extractors modulate the temperature and pressure of CO₂ (to sub- or super-critical states) to extract phytochemicals from cannabis. CO₂ is ubiquitous in the natural world and present in fresh air at roughly 300 ppm (0.03%).

Overall Toxicity: Very low

• OSHA regulatory limit: 5,000 ppm (8-hour time weighted average)
• 10-min ACGIH limit: 30,000 ppm

Symptoms: Personality changes; reduced cognitive performance; flushed skin; vision impairment; hyperventilation/respiratory stimulation; asphyxiation and convulsions; unconsciousness; respiratory failure; circulatory arrest; coma. [1,2]

Flammability: Non-flammable

Notes: Carbon dioxide is odorless and readily displaces oxygen. Unconsciousness can occur within one minute of over-exposure. [2] Accumulation of CO₂ in the blood is known as hypercapnia.

References

1. National Research Council. “Chapter 3: Carbon Dioxide.” Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 1, 2007, The National Academies Press, https://www.nap.edu/read/11170/chapter/5.
2. Permentier, Kris, et al. “Carbon Dioxide Poisoning: A Literature Review of an Often Forgotten Cause of Intoxication in the Emergency Department.” International Journal of Emergency Medicine, vol. 10, no. 1, 2017, doi:10.1186/s12245-017-0142-y. Journal Rank: 0.434, Times Cited = 8 (ResearchGate)