Standardization News

Representative Sampling of Cannabis

A critical issue in the growing field of cannabis and hemp is how to take a representative sample of a crop for testing. Help is on the way.
Kathy Hunt

Over the past 20 years, public opinion on cannabis has seen a slow but steady shift. Once considered a gateway to further drug use, cannabis is now lauded for its ability to help manage pain, regulate seizures, and aid with anxiety and sleep disorders. Prescribed by physicians and used by over two million U.S. patients in 2018, medical marijuana has entered the mainstream. 

To date, 46 countries have legalized medical cannabis. Of these, more than 30 have also decriminalized its recreational use. Four countries, including Canada, as well as 11 U.S. states and Washington, D.C., have legalized both recreational and medical marijuana. More are expected to follow suit. 

Hemp has seen a similar shift. Used in textiles since ancient times, this cannabis variety has gained widespread recognition for its durable cellulosic and woody fibers, wholesome oil, fast growth, and ability to control erosion. Today, over 30 countries, including the United States, produce industrial hemp. 

Increased use means increased production, which in turn necessitates standards for sampling and testing cannabis batches to ensure product quality and consumer safety. To address this need, the subcommittee on laboratory (D37.03), part of the cannabis committee (D37), is developing 26 laboratory-related and testing standards, including the practice for the sampling of cannabis/hemp post-harvest batches for laboratory analysis (WK64336). The proposed standard describes how to gather representative samples of cannabis/hemp inflorescence — the flowering part of the plant, including stalks and stems — for post-harvest lab analysis. 

FOR YOU: Two Cannabis Standards You Should Know About

The Complexities of Post-Harvest Batch Sampling

Developing standards for cannabis is no easy task. Cannabis is a complex plant genus with two primary varieties: cannabis sativa and cannabis indica. The plants contain a wealth of chemical compounds, including the familiar cannabinoids tetrahydrocannabinol (THC) and cannabidiol (CBD). THC and CBD, the most predominant and commonly occurring cannabinoids, are extremely similar in molecular makeup. Yet, THC produces a high or sense of euphoria that CBD does not. Because CBD has some of THC’s therapeutic benefits but none of its particular psychoactive effects, it is used to treat an array of health disorders. 

Within a given plant, the amount of cannabinoids present can be influenced by an assortment of factors, including the gender of the plant, individual strain, temperature, water, sunlight, condition of the soil, and the plant’s exposure to chemicals. The cannabinoids’ location in a plant also may vary. THC levels may be higher in the buds but lower in the stalks of a specific plant. Yet, in a neighboring plant of the same cultivar, the reverse may be true.  

As a result of these irregularities, accumulating representative samples can be difficult. David Vaillencourt is recording secretary for the laboratory subcommittee, CEO of The GMP Collective, and a member of the International Society for Pharmaceutical Engineering.  He points out that, similar to tomatoes, which grow in slightly different shapes and sizes, cannabis varies not only from harvest to harvest but also from plant to plant. “We have to remember that this is a natural product. Therefore, you have to create a batch size that allows you to take a representative sample by helping to homogenize or eliminate some of that variability,” he says. 

Batch sample size can also be problematic, especially for growers. In sampling, the grower must lose a portion of his or her financially valuable crop. Whatever goes into a batch for sampling cannot be sold. The larger the sample, the more product and money the farmer loses. The subcommittee is still considering the actual size of post-harvest batches, and the published standard will include a suggested appropriate amount.

Another complexity is that the basic definition of a cannabis/hemp harvest batch differs across the United States. According to Connecticut’s Department of Consumer Protection, a batch is “a specific harvest of marijuana or marijuana products that is identifiable by a batch number.” Meanwhile, California law describes it as a “specifically identified quantity of dried flower or trim, leaves, and other cannabis plant matter that is uniform in strain, harvested at the same time, and, if applicable, cultivated using the same pesticides and other agricultural chemicals, and harvested at the same time.” 

Cary Black, CEO and principal consultant of CK Black Group and chair of D37’s subcommittee on accreditation, certification, and training (D37.06), is working on this standard, among several others. He notes these discrepancies. “Right now it’s the ‘Wild West’ out there. You have different states with different regulations and different protocols. Many times the analyses that labs conduct are very different. You could send one batch of cannabis to three different labs and get three different results. Standardized sampling has been a clear need right from the beginning. It minimizes the probability of error propagation. It’s very important for accuracy and understanding what you have in your product and what people are putting into their bodies,” Black says. 

Process of Representative Sampling

The process of representative sampling can be destructive and costly. New standards aim to help.

Best Practices for Cannabis/Hemp Sampling

To establish a best practice for sampling cannabis, the subcommittee first outlined a series of steps that should be followed. These are covered in WK64336. 

First, the person doing the sampling must have access to the full post-harvest batch. That individual then randomly samples the batch of harvested cannabis, visually assessing the samples to help ensure that they represent the entire batch. If the cannabis buds appear consistent in color and state, sampling can continue. If some look brownish and deteriorated while others are green and fresh, the sampling should stop at this point. From a visual perspective, representativeness has been lost.

“There is always a continuous verification of the representative nature of the batch from a visual perspective,” says Black. “Representativeness needs to be continued as the samples get to the lab. These need to be homogenized properly and have the same techniques used so that you’re not introducing bias. The end result is having a sample that’s representative of the characteristics of that batch. We’re really trying to minimize the introduction of errors, at least on the sampling side of it.”

What Testing Cannabis Reveals

When testing post-harvest batches, laboratories look at cannabinoid potency, particularly that of THC. In the United States, where federal law categorizes THC as a Schedule 1 controlled substance, the legal THC potency level is less than 0.3%. Any crops over the legal THC limit are considered “hot crops.” They cannot be used for human consumption and must be destroyed. Not doing so would result in fines to the grower and possible prosecution. 

Other countries have much less stringent regulations regarding cannabinoid potency. In the Netherlands, where the government oversees the distribution of medical cannabis through the Office of Medicinal Cannabis, THC amounts are based on a patient’s need. Prescribed in the Netherlands for a range of conditions including cancer and tics resulting from Tourette’s Syndrome, cannabis can possess a THC level ranging from less than 1% up to 22%.  

Along with cannabinoid strength, lab testing of post-harvest batches determines microbiological activity, including the presence of mold, fungi, and bacteria in the cannabis. Testing also indicates the concentration of trace metals, pesticides, and terpenes. As part of the plants’ essential oils, terpenes give cannabis its complex fragrance and flavor.

Black says that various factors can impact the plant and its usefulness. “There are many potential toxic moieties that could be associated with pesticides. The plant itself has a very high absorptive proclivity to pull in heavy metals from the soil that it grows in. It is prone to mold growth and aflatoxins. All of these represent significant hazards to consumers. It’s really important for it to be screened adequately and to be sure that batch samples are representative to ensure consumer safety,” he says. 

Ultimately, lab testing and its associated results can impact cannabis quality control and regulatory requirements. This work can provide transparency and truth in labeling, two things that are lacking in the current cannabis market, says Darwin Millard, co-chair of the industrial hemp subcommittee (D37.07) and founder and owner of TSOC LLC. 

READ MORE: Why Cannabis Standards Are Needed

According to Millard, another hurdle for the cannabis industry is that it does not always assist consumers trying to make sound, informed decisions. Currently, the industry tests for THC but not always for CBD content. As a result, CBD levels can fluctuate widely, with producers inaccurately stating how much CBD is in their product. This can lead consumers to believe that the CBD content is higher or lower than it actually is. 

A 2019 study conducted by Ellipse Analytics (Denver, Colorado) found that over half of the 240 products tested by its lab did not possess the amount of CBD indicated by the producer. In many instances, little to no CBD was present. In some cases, though, the product had up to six times the amount of CBD listed on its label. 

“It’s one thing to require certain information on a label, but if the data isn’t representative of the product inside the package, then what good is it? This sampling standard is only one part of a larger set of standards that can be used to support each other in ensuring product quality and environmental and public health and safety,” Millard says. 

“As federal legalization and increased cannabis usage become more predominant, the need for transparency becomes critical,” Black says. “As consultants/stakeholders in the industry and the creators of standards, we are working with people at the individual state levels and at the federal level to bring all these disparities together in a unified whole. This unification will be driven by standardization and support transparency.”

An Integral Part of a Larger Series of Standards

While valuable on its own, the proposed sampling standard (WK64336) plays an equally important part in a series of proposed standards from the laboratory subcommittee. Among this series is the proposed practice for sampling of field and bulk harvest lots of cannabis for laboratory analysis (WK73730). This proposed standard details strategies for in-the-field, pre-harvest sampling. It includes procedures designed to minimize the variability intrinsic to cultivated cannabis.  

Another related proposed standard is the guide for representative sampling of cannabis extracts and derivatives for analytical testing (WK64646). According to Black, the work item covers typical, manufacturing-based, quality-control sampling standards as defined by traditional military sampling plan standards and codified in American National Standards Institute (ANSI)/American Society for Quality (ASQ) documents (ANSI/ASQ Z1.4 and ANSI/ASQ_Z1.9). The subcommittee references these ANSI/ASQ standards in WK64646. Similar to the proposed standard on sampling field and bulk harvest lots, this proposed standard aims to minimize the lack of homogeneity in cannabis

“We are hoping to promote a way of sampling that optimizes the representativeness of the sampling exercise, taking into account those areas that provide the greatest variability in testing results, such as potency and phytochemistry,” Black says. 

He adds that there are sampling standards in the works for hemp seeds, which fall under the jurisdiction of the industrial hemp subcommittee (D37.07). The group developing WK64336 is working with this subcommittee and others to ensure harmonization across ASTM cannabis-sampling standards. 

“When it comes to standardization of the cannabis industry, there is a lot of analysis and a lot of science needed to verify product safety,” Black says. “As the industry progresses, follow specific safety guidelines will be required, whether they’re from the FDA, EU, or the like. The more we can do to standardize those elements, the more seamless it will be to go into a regulated industry.”  

“What we find nearly every day, as we go through the development process of standards, is the need for a supporting standard or a supporting research and development effort,” says Millard. “This is just the tip of the iceberg, so to speak. The work has only just begun. We need help, and we need subject matter experts who have the passion and drive to shape this industry to join ASTM International and D37.” 

The committee and subcommittees officially meet twice a year. However, ad hoc meetings of members engaged in the standards development process are held all year long. If you are interested in becoming part of the conversation about and assisting with the development of cannabis standards, please contact:

Cary Black, CK Black Group Inc.
tel +1.989.737.4486

Darwin Millard, TSOC LLC
tel +1.720.839.0559 ) 

Robert Morgan, ASTM
tel +1.610.832.9732

Kathy Hunt is an East Coast-based journalist and author.

Industry Sectors:

Issue Month: 
Issue Year: