Every batch of legal cannabis must be tested by licenced laboratories, according to Health Canada’s guidelines for allowable limits of pesticides, microbials, mould, and heavy metals. THC and CBD testing (and labelling) is also mandatory, with some licenced producers choosing to test for other cannabinoids and terpenes as well.
“Cannabinoid potency and terpene testing doesn’t have standard described methods. There’s literature out there, but no standard description of how you prepare samples and how you measure,” says Jodi McDonald, president & founder of Keystone Labs. “But when we talk about heavy metals, microbial, and pesticide testing there are published methods that describe how to prepare samples and measure for the absence of those contaminations.”
Testing is done on the final packaged product, with different labs opting for different methods depending on individual preference and type of product. Variations in results occur due to different methodology and varied methods of sampling and may lead to LPs ‘shopping around’ for a lab that suits their needs.
Flowers from the same batch vary in both potency and water content.
“Challenges for labs do include some error due to measurement, instrument, or human error, but primarily due to sample variability,” says Denise Johnson, Head of Laboratory at Pura Labs. “For example, flowers from the same batch vary in both potency and water content. Flowers at the top of a plant can be as much as 100% more potent than the bottom buds (e.g. 10% THC at bottom and 20% THC at top). Larger buds can have higher water content than smaller buds, etc. The higher the water content, the lower the THC potency by weight.” Ideally, LPs submit a large sample size of between 10-25 g for flower or 1-5 g for extracts/concentrates. In the case of flower, it should come from several parts of the plant to provide a better representation.
“More variability exists in edible products just by nature,” says Johnson. “Serving sizes vary within a batch as well as homogeneity (how well dispersed the cannabinoids are) of the product. Infused, well-mixed products offer the best accuracy and consistency, while coated products can be highly variable from sample to sample. Oil tinctures are typically homogenous if infused with a soluble cannabis extract. If infused with insoluble flower parts, results can be variable.”
Cannabinoid Profile and Potency
‘Potency’ is a contentious term as some people think it’s incorrect to refer to THC/CBD profiles as being the determinator of potency in a product (due to the ‘entourage effect’ of terpenes and other cannabinoids, etc.). Semantics aside, cannabis labels must display the total amount of THC/THC-A, and CBD/CBD-A by law. Other cannabinoids (and terpenes) are optional and labs can generally test for up to 16 cannabinoids, including the increasingly popular CBN and CBG.
“We have to magically change that solid dried flower into liquid form, so we do a really simple extraction in the lab and mix the dried flower with solvent then mix together vigorously,” explains McDonald. “The dry material, now mushy, settles on the bottom. The beauty of the cannabinoids is that they really enjoy being in the solvent and they don’t mind letting go of the plant material.” There are two main methods of testing for THC/CBD and both involve separating the cannabinoids using high pressure liquid or gas to see which cannabinoids are present. Using a process called High Pressure/Performance Liquid (or Gas) Chromatography (HPLC/GC), the extract is injected into a stainless-steel straw column and chemically exploited to make the cannabinoids flow through at various times. “We use the key chemical structure of cannabinoids and their characteristics to separate them in time,” says McDonald. “Think of opening your piggy bank and using one of those coin separators that looks for a different size for the loonies and toonies—some stay in the top layer or drop down through to the next level. It’s kind of the same idea for how we do things in chromatography. We use the size and physical characteristics of each compound.” GC tends to be used more for flower, rather than edibles or topicals, as the high heat means that only the decarboxylated THC/CBD can be measured, whereas the liquid method allows for THC-a and CBD-a, the acids that have potential to become THC/CBD when heat is applied.
Terpenes are often measured using GC due to their volatile nature. There’s no legal requirement for terpene testing from Health Canada, but it’s increasingly important to LPs trying to move away from the THC-only model of potency.
Heavy Metals Testing
“Heavy metals testing is really fun as we take starting material—it can be plant or oil—and we do a super concentrated acid digestion in a microwave oven, and the only thing that’s left at the end is acid and metal,” says McDonald. “We then use ICP-MS (Inductively Coupled Plasma – Mass Spectrometry) to do the imaging part of it. The instrument has a plasma flame, which ionizes everything going through plasma. On the other side of the plasma are a series of lenses that allow us to selectively identify the metals based on their mass.”
Heavy metal analysis is required by Health Canada to check for lead, which must be less than 500 ppb/parts per billion, and mercury, arsenic and cadmium, which all must be less than 200 ppb. Typically, labs use ICP-MS or another faster and simpler technique (with no sample prep) called X-Ray Fluorescence, but this has significantly higher start-up costs for labs.
Health Canada’s allowable limits for contaminants such as heavy metals are determined based on permitted daily exposure and concentration limits, and the ‘intended and reasonably foreseeable use of the cannabis product’ because the toxicity of heavy metals can vary greatly depending on whether the product is orally ingested versus inhaled.
Testing for microbial contaminants falls broadly into two camps. One is a rapid method that is popular for a quick turnaround (48 hours) and is based on looking at the DNA of the sample. The other old-school method involves plating the material onto a growth medium and waiting five days to see what fungal spores grow. Fungi likes a moist atmosphere to grow on plant matter and this can result in spores growing after packaging (hence why Health Canada sets moisture limits at 10%).
Cannabis is also screened for mycotoxins (Aflatoxins B1, B2, G1, G2, and G3), which are toxic and potentially carcinogenic chemicals produced by some types of mould. Microbial contamination tests look for total yeast and mould count, total aerobic bacteria count, and total bile tolerant gram-negative bacteria. There are no allowable limits for Salmonella, E. coli, Pseudomonas aeruginosa, Shigella, and Staphylococcus aureus.
Screening can include traditional plating methods that use specific media to promote the growth of the target organism over several days or rapid tests that can produce results within 24-48 hours. The Q-PCR (Quantitative Polymerase Chain Reaction) test amplifies the DNA of a specific pathogen if detected, then compares it to a positive control. “New advances with this technique can enzymatically remove any microbial contamination that has been irradiated so that “dead” DNA will not amplify and be detected,” says Johnson. Liquid media culture is another technique that is like plating, but also produces faster results as colonies are automatically counted via a fluorescence sensor and are updated hourly using computer software.
Health Canada’s regulations also require third-party mandatory testing for 96 pesticides, which are detected as parts per billion. Pesticide levels must be within agreed parameters and from a list of approved pesticides.
“While there may be variations in results between labs, each one must show and document that a known result can be detected using the given method within a range of plus or minus 20% (e.g. if a THC level is spiked at 100 mg/g (10%) then the results should fall between 90 and 110 mg/g),” notes Johnson. “Labs typically run duplicate or triplicates of some samples to verify results, ensure proper sample prep, and document sample result variability, known as RSD% (Relative Standard Deviation).”
Understanding the importance of testing cannabis can help retailers explain the rigorous testing procedures to consumers, which will make them feel more confident about purchasing products exclusively from licensed stores.