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A Recap of ASTM’s Workshop on Measuring Elemental Contaminants in Cannabis and Hemp Consumer Products

By Robert Thomas

Published: Aug 05, 2021   
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If you attended the recent virtual “ASTM Workshop on Elemental Contaminants in Cannabis and Hemp Consumer Products,” you would have come away with the distinct impression that to only monitor the “big four” heavy metals is completely inadequate to ensure the safety of cannabis consumer products. It was clear based on many of the 22 talks over the three days of the workshop that researchers were not only finding elevated levels of the traditional heavy metals, such as lead and cadmium, but they were also finding additional elemental contaminants in the cannabis and hemp flower and in the finished consumer products.

The take-home message was that the industry needs to be carrying out a complete risk assessment study to better clarify the real-world sources of elemental contaminants throughout the entire cultivation, extraction, production, packaging and delivery processes. Guidance from the pharmaceutical industry should also be heeded, even if it took over 20 years for the industry to get a comprehensive understanding of elemental impurities in drug and nutraceutical products under federal oversight from the US Food and Drug Administration (FDA).

So, before I give an overview of the event, let’s remind ourselves of the reasons for holding the workshop and the serious nature of heavy metal toxicity and its impact on the safety of cannabis consumer products.

Heavy metal toxicity

Long term exposure to heavy metals, irrespective of the source can have serious adverse effects on human health. They can interact with DNA and interrupt regular cellular functions, causing cell mutations, carcinogenesis, and apoptosis (cell death). Heavy metal toxicity affects virtually every system in the human body and often occurs with no distinctive symptoms. It can damage the central nervous system, kidneys, and reproductive system, and, at higher levels, can cause comas, convulsions, and even death. Many metals, such as lead and mercury, are neurotoxins, which means they readily cross over the blood-brain barrier and affect the development and growth of brain neurons, so even at low levels they are associated with reduced brain development, lower intelligence, and learning disabilities.

Consumer safety

As a result, heavy metals are a known consumer safety hazard that have largely been unaddressed by the cannabis/hemp industry. Currently, only four heavy metals (lead, cadmium, arsenic, mercury) are required by the vast majority of the thirty-six states in the United States (and Canada) where consumption of cannabis/hemp consumer products is legal. However, there is compelling evidence in the public domain that at least another ten elements could be derived from the cultivation environment, including soil, fertilizers, and water. Moreover, the production of various cannabinoids can also lead to a further increase in these levels of elemental contaminants through the extraction, purification, concentration, and filtration processes, as well as picking up additional elements from the manufacturing, packaging, and delivery equipment, which can represent significant safety risks to consumers. 

In addition, it has been widely reported that cannabis/hemp dried flower, extracts and diluent oils used in electronic cannabis vaping delivery systems (ECDS) are corroding internal metallic components. Researchers are finding elements such as iron, chromium, nickel, aluminum, zinc, and lead in the vaping liquid, which are derived from a variety of alloys inside the vaping devices, such as stainless steel, brass, nichrome, kanthal, solder, and other metal-based materials. At vaping temperatures of 200-300°C, these metal particles are finding their way into the vaping aerosol and being delivered to the users’ respiratory pathways and potentially causing long term damage to the lungs.

Workshop objectives

This workshop was therefore put together to provide a broad perspective and awareness of the current knowledge of elemental contaminants in cannabis/hemp consumer products, communicate their significance, and educate users, cultivators, processors, testing labs, and regulators within the cannabis/hemp community of the metals’ potential risks to human and environmental health. The goal of the workshop was to address the following critical areas:

  • The most current research detailing the mechanisms for metal uptake into a cannabis plant based on growing conditions and soil chemistry.
  • Optimization of analytical methodology used to measure heavy metals in cannabis/hemp consumer products.
  • Lessons learned from regulating heavy metals in drug products and using a scientifically risk-based approach to predict elemental impurities derived from the manufacturing process.
  • Toxicological impact of heavy metals and the industry’s responsibility for ensuring consumer health and safety.
  • The current state of the art research in phytoremediation and phytoextraction techniques.
  • The most recent research in characterizing elemental contaminants in vaping liquids and aerosols produced by electronic nicotine delivery systems (ENDS) and electronic cannabis delivery systems (ECDS).

Workshop overview

So, with this as background information, allow me to give a summary of the workshop proceedings and to focus on some of the excellent presentations which aligned with the workshop objectives. The full workshop agenda, speaker bios and program abstracts can be found at the following link, but first let me give a breakdown of the major themes of the workshop. The 22 talks were broadly classified under the following categories:

  • Lessons learned from the pharmaceutical industry.
  • ICP-MS analytical testing methodology.
  • Measurement of elemental contaminants in cannabis.
  • Characterizing of elemental contaminants in vaping liquids/aerosols.
  • Uptake of elemental contaminants from the grow medium.
  • Heavy metals phytoremediation capabilities of hemp.
  • Standardization/validation procedures.

They all emphasized the importance of monitoring elemental contaminants and in particular to have a better understanding of the impact of heavy metals on human health, from the perspective of the many types of consume products available in the marketplace today.

There were three contributions dedicated to regulating elemental impurities in drug products and substances. They emphasized very strongly the fractured nature of state-based regulations, which, apart from a few exceptions, are mostly based on monitoring only the big four heavy metals, lead, cadmium, arsenic, mercury. They produced compelling evidence that these are not a true reflection of the real-world of cannabis products and that an expanded list needs to considered based on assessing the risk of the likelihood of finding other contaminants at various stages of the cultivation and production processes.

There were two talks on ICP-MS methodology, which covered writing of standardized methods as well as developing optimized instrumental conditions specifically for measuring heavy metals in cannabis-related samples. There were also three presentations about measuring an expanded list of elemental contaminants in cannabis and consumer products, which suggested that up to 20 metals could be justified.

On the same theme, there were four talks specifically focused on measuring elemental contaminants in both electronic nicotine delivery systems (ENDS) and electronic cannabis delivery systems (ECDS), commonly known as vapes. One study even found a correlation between the metals in e-cigarette vaping aerosols with a significant accumulation of several neurotoxic metals in mouse brains. Based on these researchers’ data, it was very clear that whether the dry flower, liquid extract, or the vaped aerosol was being characterized, elements were being found related to the internal metal components of these devices which could do serious harm to the users’ airways and lungs. It was also evident that the methodology required to get meaningful data on vaping aerosols was an order of magnitude more complex than just monitoring the dry flower or liquid extract in the vape tanks.

There were four presentations dedicated to measuring the uptake of heavy metals by the plant from the soil and grow medium, and how the pH and soil chemistry could have a major impact on the rate, amount, and number of heavy metals being absorbed. These talks were further subdivided into looking at ways of minimizing the uptake for using the cannabis/hemp plants biomass and flowers as a source of cannabinoids and also maximizing the uptake to use the plants for phytoremediation purposes to clean up toxic waste sites contaminated with heavy metals and radionuclides.

Finally, there was a very important talk about developing cannabinoid and hemp toxic metal certified reference materials (CRMs) to help testing labs get validated and more consistent data. There was some debate about what panel of elements should be included on the certificate. However, this contributor argued that because cannabis and hemp are natural plants, it was important to base that decision on historical evidence in the public domain of heavy metals found in other plants, such as food crops and tobacco.

Workshop presentations

To supplement the overview of the event, here are the 22 presentation titles given (in order) over the three-day workshop.

Day 1

  • Regulating Heavy Metals in Cannabis: What We Can Learn from the Pharmaceutical Industry: Robert Thomas, Scientific Solutions.
  • Heavy Metals in Hemp Extract Products: Dianne Picket and Dr Serena Giovinazzi, Florida Department of Agriculture and Consumer Services.
  • Validation of an Expanded List of Elements in Cannabis and Hemp Flower by Microwave Digestion and ICP-MS Analysis: Aaron Hineman, PerkinElmer Inc.
  • Toxicological Impact of Heavy Metals: The Role of United Natural Hemp Extracts in Ensuring Public Health and Safety: Dr Joseph Dzisam, United Natural Hemp Extracts (UNHE).
  • Phytoremediation of Radionuclides with Hemp (Cannabis sativa L.): Hannah Rheay, PhD student, New Mexico State University.
  • Essential Practices for Quality Analyses of Metal Concentrations in Hydrophilic and Hydrophobic Vaping Liquids and Aerosols: Dr R. Steven Pappas, Centers for Disease Control and Prevention (CDC).
  • Examination of Cannabis Hemp Oil Products for Heavy Metal Contamination: Patricia Atkins, Spex Certiprep.

Day 2

  • Beyond the Big Four, Determination of Heavy Metals in a Variety of Cannabis and Cannabis-Derived Products: Dr Jenny Nelson, Agilent Technologies.
  • Phytoremediation Potential of Hemp, Identification of Genetic Modifications Leading to the Development of Hemp Strains for Enhancing its Phytoremediative Properties: Dr David Cornett and Cary Black, National Hemp Growers Cooperative.
  • Heavy Metals Analysis of Cannabis Related Products by ICP-MS: Optimizing and Troubleshooting a Method for Improved Efficiency and Accuracy: Jonathan Peters, Shimadzu Scientific Instruments.
  • Control of Elemental Impurities in Drug Substances: Dr Donglei Yu, Office of Pharmaceutical Quality, US Food and Drug Administration (FDA/CDER).
  • Trace Metal Profiling of Commercially Available Hemp Derived CBD Oils: Dr Tom Gluodenis, Lincoln University.
  • Vaping, Metals, and Health Effects, Lessons for Cannabis Products: Dr Markus Hilpert, Department of Environmental Health Sciences, Columbia University.
  • Cadmium Accumulation in Industrial Hemp (Cannabis sativa L.); Amanda Olbrick Marabesi, University of Georgia, PhD student.
  • Elemental Analysis of Tetrahydrocannabinol and Nicotine E-Liquids: Dr Kevin Kubachka, US FDA, Forensic Chemistry Center.

Day 3

  • Status of ASTM - WK74576 Method, Analyses of Trace Elements in Cannabis and Related Products by Inductively Coupled Plasma-Mass Spectrometry: Dr William Lipps, Shimadzu Scientific Instruments.
  • Cannabis Vaping Aerosols, Non-Polar Methods for Collection and Analysis of Ten Metals: Dr Amber Wise, Medicine Creek Analytics.
  • Effect of the Surrounding Contamination on the Heavy Metals Content of Cannabis Sativa: Dr Murad Ali Khan, Kohat University, Pakistan.
  • Challenges in Development of a Cannabis Reference Material for Trace Elements: Dr Charles Barber, Chemical Sciences Division, National Institute of Standards and Technology (NIST).
  • USP Perspectives on the Limits of Elemental Contaminants in Cannabis/Hemp: Dr Nandakumara Sarma, United States Pharmacopeia.
  • Metals in the Flower, Is It Safe? A Look at Which Metals Cannabis Should be Tested for to Maximize Consumer Safety: Elizabeth Sherburne, All Set Analytical.
  • Evaluation of Propensity of the Canadian Hemp Varieties to Accumulation of Elevated Heavy Metal Levels in Grain: Dr Jan J. Slaski, InnoTech Alberta.

Final thoughts and the path forward

When I came into the industry in the summer of 2019 to explore the possibility of writing a book about the measurement of heavy metals in cannabis and hemp, I was surprised to find that there was not a great deal known about the sources of elemental contaminants. So I spent about three months talking to as many people in the industry as possible including cultivators, growers, processors, manufacturers, regulators, and testing labs. I also went to a number of conferences and noticed there were never any talks on heavy metals. So, I decided to survey the symposium landscape and submitted abstracts on the topic to see if I could get the attention of conference organizers. Slowly, I started getting noticed, and over the next 12-18 months I was fortunate to be invited to give talks on the topic and to contribute numerous articles as well as publish my new book, “Measuring Heavy Metal Contaminants in Cannabis and Hemp,” in October 2020. There is no question that the research I carried out over the past two years gave me the incentive to be involved with the ASTM workshop, as I realized that it was critically important to educate the industry on this topic and to use this forum to advance our understanding and knowledge of heavy metal contaminants in cannabis/hemp products to better protect consumer safety.

I believe the workshop could be a pivotal moment for the industry. It has shown that there are researchers who are equally passionate about the topic as I am, as witnessed by the 80-100 attendees for each of the three days. I’m convinced we are ready to move past the big four to an expanded list of elemental contaminants. Hopefully it will stimulate further research into the topic and encourage cultivators to better understand the chemistry of their soil and adopt ways to reduce heavy metal uptake by their plants, and for cannabinoid producers and manufacturers to find ways to optimize the extraction process to minimize the metals being carried over into the concentrates.

If we are to produce cannabinoids that are as clean as drug products, the cannabis industry needs to be looking at how the pharmaceutical industry did this by abandoning its 100-year-old sulfide colorimetric test for lead and adopting testing procedures using plasma spectrochemistry with a comprehensive set of validation protocols. In addition, pharma arrived at a panel of elemental toxicology data for up to 24 elemental impurities, using well-established animal models and by classifying them based on their likelihood of being found at different stages of the drug manufacturing process. So now is the time for the cannabis industry to move on this extremely important topic. The ASTM Committee D37 on Cannabis is working diligently to develop standards to ensure safe consumer products, so this type of expertise is needed more than ever in shaping the appropriate content of marketplace-relevant standards. There is no question that addressing these challenges through dialogue and consensus can make a significant difference and produce results that federal regulators will embrace.

I’d like to leave you with one final thought. A representative from GW Pharmaceuticals – the company that makes Epidiolex, the only CBD-based FDA-approved prescription drug to treat seizures and epilepsy in young children – was in the workshop audience. In a discussion I had with him after the workshop, he told me when they were seeking approval for the drug with the FDA, they had to show compliance by meeting permitted daily exposure (PDE) limits for all Class 1, 2A and 3 elemental contaminants (lead, cadmium, arsenic, mercury, cobalt, vanadium, nickel, lithium, antimony, barium, molybdenum, copper, tin, chromium) as defined in USP Chapter 232/ICH Q3D guidelines before they could get approval. This is a strong indication that when the federal government eventually gets oversight of the cannabis industry, this is likely to be the panel of elements they will initially start regulating. However, if you also include the additional elements regulated by Maryland (chromium, selenium, barium, silver) and New York (nickel, chromium, copper, antimony, and zinc) and the panel of elements in the new NIST hemp CRM (lead, cadmium, arsenic, mercury, beryllium, cobalt, vanadium, chromium, manganese, molybdenum, nickel, selenium, uranium), you realize that list could be even longer. It should also be pointed out that GW Pharmaceuticals has also initiated the first US phase III clinical trial study on nabiximols, another cannabinoid-based prescription drug (administered as an oral spray) for the treatment of multiple sclerosis (MS) spasticity. Nabiximols is also known as Sativex in Europe and has been approved in over 25 countries to treat MS. To me, it clearly shows that the FDA recognizes the benefits of cannabinoids to treat certain diseases, so it’s only a matter of time before cannabis is taken off the list of the DEA Schedule 1 drugs and the cannabis industry is going to be under the microscope. It better have its ducks in a row or this “wild, wild west” might have to deal with a new sheriff in town!

Link reference:

Workshop on Measurement of Elemental Contaminants in Cannabis and Hemp Consumer Products: Sponsored by ASTM Committees D37 on Cannabis: Program booklet of agenda extended abstracts, and speaker bios.

Robert Thomas

Principal of Scientific Solutions

Rob is a heavy metals expert and has written for Analytical Cannabis on the subject since 2019. Through his consulting company Scientific Solutions, he has helped educate countless professionals in the cannabis testing community on heavy metal analysis. He is also an editor and frequent contributor of the Atomic Perspectives column in Spectroscopy magazine, and has authored five textbooks on the principles and applications of mass spectrometry. Rob has an Advanced Degree in Analytical Chemistry from the University of Wales, UK, and is a fellow of the Royal Society of Chemistry and a chartered chemist.


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