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Residual solvents

Solvents, or chemicals, left in a cannabis concentrate after the extraction process. The bulk of solvents are purged from a concentrate after extraction, but trace amounts are usually still present—these are residual solvents. Legal cannabis markets regulate how much residual solvents are allowed in concentrates before they can be sold.

“I only dab rosin so I can be sure there aren’t any residual solvents to bother my lungs.” 

What are residual solvents?

Chemical solvents are used for some cannabis extraction processes and then purged out when the process is done. The trace amounts of chemicals left in the extract are residual solvents.

Common solvents used in cannabis extraction are ethanol, butane, propane, hexane, pentane, and xylene. Depending on the method of extraction, multiple solvents be used, so residual solvents can be more than one chemical. 

States with legal, regulated cannabis industries generally have rules establishing a legal limit for residual solvents in products before they can be sold. Regulations differ depending on the state, the solvent, and the type of cannabis product. Testing for residual solvents is critical for determining the safety of consuming cannabis extracts. 

It is important to note that residual solvent testing is only required in legal, regulated markets, and products in illicit cannabis markets are not tested. Additionally, there are reports of licensed cannabis businesses that also sell products in the illicit market, which could be products that failed testing. 

Safety of residual solvents

There are many dangers from consuming contaminants in cannabis, and residual solvents are no exception, with different medical risks posed by each solvent. Research shows that if butane is inhaled at high levels it can lead to cardiac damage and organ failure, among other serious harms. Residual butane inhalation can also be a contributing factor to severe lung injury, but normally the BHO in question was obtained illegally rather than from a regulated market. 

Benzene is a known carcinogen with risks of damage to bone marrow, and vaporized xylenes can cause central nervous system depression, with symptoms including nausea, headache, dizziness, and vomiting. Hexane can have similar effects if inhaled in high amounts. 

Shimadzu, a leading manufacturer of cannabis lab testing equipment, recommend using gas chromatography (GC) paired with a flame ionization detector (FID) when testing for residual solvents in cannabis products. Increasingly, GC is being paired with mass spectrometry (MS) because it allows for better identification of unknown impurities. 

Some cannabis consumers avoid residual solvents altogether by consuming rosin, ice water hash, or other concentrates which are made without chemical solvents.