Cannabis products in the state of California are legally required to undergo residual solvent testing. Testing is especially important for cannabis extracts such as oils, concentrates, waxes, shatters, etc. Presently, there are residual solvents and processing chemicals (Category II) that can be legally used in cannabis production if the chemicals meet certain detection limits. In July 1 2018, Category 1 residual solvents & processing chemicals were restricted from use for cannabis production. For a more detail list, including the detection limits, please visit: Residual Solvents & Processing Chemicals Testing Requirements for Cannabis Products in State of California.

Some common residual solvents related to cannabinoid extraction are:

  • Acetone
  • Butane
  • Ethanol
  • Heptane
  • Hexane
  • Isopropanol
  • Propane

Repeated exposure to such solvents has been shown to cause significant consumer health issues. Some of the potential effects on the human body include allergic reactions, headaches, and nausea. Acetone, for example, can cause irritation of the throat and nasal passages, nausea, vomiting, and headaches. It can also damage to the eyes and create confusion, dizziness, or even unconsciousness. Butane is another dangerous residual solvent which can cause long term damage to the nervous system, respiratory failure, liver and kidney failure, and in some cases, even death.

These solvents are typically used during extraction of the cannabinoids from the physical plant material, and they are divided into three categories.

  • Class 1 Solvents are to be completely avoided because they are known carcinogens, suspected carcinogens, and environmental hazards.
  • Class 2 Solvents are to be limited. These may be possible causative agents or another irreversible toxicity like neurotoxicity.
  • Class 3 Solvents have low toxic potential and should be the only solvent used for extracting cannabinoids from cannabis materials.

Effectively testing for residual solvents

Residual solvent testing is typically analyzed by gas chromatography combined with flame ionization or mass spectroscopy. Together, these analytical procedures will allow cannabis researchers to detect and quantify harmful residual solvents in concentrated cannabis products and ensure that the producer be aware of such hazards in their products. Without such testing, consumers are at risk of potential exposure to such hazardous components and, growers are also at risk of possible legal action if the state requires such. This may be true, regardless of whether or not a consumer has been exposed.  With new regulations developing rapidly and more states making cannabis legal, the the need for testing has never been greater.

Below are Examples of Residual Solvents Considered to be Unsafe Over a Certain Detection Limit or Illegal for Cannabis Production

Residual SolventAllowed for Use?Type / DescriptionCause and Effects
1,2-DichloroethaneNo1,2-Dichloroethane is a common synonym for ethylene dichloride.The chemical formula for ethylene dichloride isC 2 H 4 Cl 2Its molecular weight is 98.96 g/mol. (1) Ethylene dichloride occurs as a colorless, oily, heavy liquid that is slightly soluble in water. (1)Ethylene dichloride has a pleasant chloroform-like odor, with an odor threshold of 6-10 ppm. (1)Inhaling concentrated ethylene dichloride can induce serious health concerns, such as:Effects on the human nervous systemLiver, and kidneys, as well as respiratory distressCardiac arrhythmiaNausea, and vomiting*While there is limited, to no information available, in terms of chronic exposure in humans, animal studies show that the effects include effects on the liver and kidneys.** While no information is available on the reproductive effects of ethylene dichloride in humans, animal studies show a decrease in fertility, as well as, higher embryo mortality.
BenzeneNoThe chemical formula for benzene is C6H6It has a molecular weight of 78.11 g/mol.Benzene occurs as a volatile, colorless, highly flammable liquid that dissolves easily in water.Benzene has a sweet odor (2, 3)Acute (short-term) exposure of humans to benzene may cause:DrowsinessDizzinessHeadachesSkin, and respiratory tract irritationAt high levels, unconsciousness. *Chronic (long-term) inhalation exposure has caused:Various disorders in the bloodReproductive effects have been reported for women exposed by inhalation to high levelsAdverse effects on the developing fetus have been observed in animal tests.EPA has classified benzene as known human carcinogen for all routes of exposure. (2, 3)
AcetoneYes if it meets action level thresholdAcetone is a colorlessvolatile, flammable organic solvent. Acetone occurs naturally in plants, trees, forest fires, vehicle exhaust and as a breakdown product of animal fat metabolismAcetone is toxic in high doses (4)Can irritate the nose and throat.At high concentrations: can harm the nervous system. Symptoms may include headache, nausea, dizziness, drowsiness and confusion. A severe exposure can cause unconsciousness.May cause mild irritation on skin. Can be absorbed through the skin, but harmful effects are not expected.Effects of Long-Term (Chronic) Exposure:Can cause dry, red, cracked skin (dermatitis) following skin contact. May harm the nervous system.(5)
ButaneYes if it meets action level thresholdFormula C4H10Butane is a colorless gasHas a faint disagreeable odorIt is poorly soluble in water (5)High exposure to butane may cause:Effects on the central nervous system and Cardiac effectsCase studies also reveal serious brain damage in fetusesUnderdeveloped organs can occur in fetuses in case of high single exposures during the week 27 or 30 of pregnancy. (5)


  • Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for 1,2-Dichloroethane.
  • Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Benzene. U.S. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. 2007.
  • American Conference of Governmental Industrial Hygienists (ACGIH). 1999 TLVs and BEIs. Threshold Limit Values for Chemical Substances and Physical Agents. Biological Exposure Indices. Cincinnati, OH. 1999.
  • Robinson RC, Shorr RG, Varrichio A, Park SS, Gelboin HV, Miller H, Friedman FK: Human liver cytochrome P-450 related to a rat acetone-inducible, nitrosamine-metabolizing cytochrome P-450: identification and isolation. Pharmacology. 1989;39(3):137-44.
  • This document was prepared by the AEGL Development Team composed of Peter Bos (RIVM, The Dutch National Institute of Public Health and the Environment), Julie M. Klotzbach (Syracuse Research Corporation), Chemical Managers Jonathan Borak and Larry Gephart (National Advisory Committee [NAC] on Acute Exposure Guideline Levels for Hazardous Substances), and Ernest V. Falke (U.S. Environmental Protection Agency). The NAC reviewed and revised the document and AEGLs as deemed necessary. Both the document and the AEGL values were then reviewed by the National Research Council (NRC) Committee on Acute Exposure Guideline Levels. The NRC committee has concluded that the AEGLs developed in this document are scientifically valid conclusions based on the data reviewed by the NRC and are consistent with the NRC guidelines reports