Beyond Potency: The Importance of Measuring Elemental Contaminants in Cannabis and Hemp: Page 3 of 3

October 24, 2019
Abstract / Synopsis: 

On a daily basis, the average person around the world is subjected to doses of heavy metals and other contaminants from a variety of sources. One of the most insidious sources of routes of exposure is through food, beverages, and other sources of oral consumption (that is, nutraceuticals, pharmaceuticals, and so on). The World Health Organization contends that food may be the source of the largest contribution to the intake of contaminants. Many agricultural products may naturally contain heavy metal and other contaminant compounds, from either natural biochemical processes or from bioaccumulation from the environment. Other products become contaminated by natural, agricultural, or industrial sources or poor hygiene methods of production and storage. Finally, there are food and beverage products that are intentionally adulterated or counterfeited with materials containing contamination. In this column, we look at different sources of potential contamination exposure that may be of concern to both the cannabis industry and the cannabis consumer from the perspective of an analytical industry professional with decades of experience in metals analysis. The guest author of this installment, Robert Thomas, has worked as an analytical chemist in the field of trace element analysis for more than 45 years, including 24 years for an inductively coupled plasma-mass spectrometry (ICP-MS) manufacturer and 19 years as principal of his own consulting company.

The Smoking of Cannabis

It’s worth pointing out that, historically, most consumers of recreational cannabis use it by the inhalation or smoking route. Smoke chemistry has been predominantly investigated in tobacco products, but many studies over the past 10 years have highlighted the qualitatively similar carcinogenic chemicals contained within both tobacco and cannabis smoke (17). In a recent study, the International Organization for Standardization and Health Canada analyzed tobacco and cannabis cigarettes. The heavy metals contained in both smoked products included: mercury, cadmium, lead, chromium, nickel, arsenic, manganese, and selenium (18). Quantitatively, there were lower heavy metal concentrations in cannabis smoke condensates, due mainly to the fact that the cannabis supply was grown hydroponically. In addition, the soil-less growth medium of the cannabis plants required water and water-soluble hydroponic vegetable fertilizers which contain nitrogen in the form of nitrates. So with no soil-based heavy metals to be extracted during the growth cycle of the cannabis, it was the liquid fertilizers used in the hydroponic systems that contributed mostly to the heavy metal levels. It should also be emphasized that in any hydroponic growing process, the elemental impurities in the water supply should be below the U.S. Environmental Protection Agency (EPA) maximum contaminant levels (MCL), otherwise the plant will pick up heavy metals from the water. This could be a real concern with old buildings that perhaps have been using lead pipes, or copper and iron pipes connected with lead-based solder. There is a great deal of information in the public domain about the uptake of heavy metals into tobacco and the resulting content in tobacco products, such as nicotine and electronic nicotine delivery (END) devices (19,20).

Testing Procedures

As a result of the high likelihood of heavy metals being present in hemp and cannabis products, the correct sampling and testing for heavy metals is absolutely critical. The most suitable and widely used technique is inductively coupled plasma-mass spectrometry (ICP-MS), which is a very sophisticated multielement analytical technique that can easily measure down to parts per trillion (ppt) detection levels. However, it requires an analytical chemist with a reasonably high level of knowledge and expertise to fully-understand the nuances of ultra-trace elemental analysis, including laboratory cleanliness, sources of contamination, sample preparation, digestion techniques, instrumental method development, interference corrections, calibration routines, use of reference materials, and validation procedures. In other words, in the hands of an inexperienced user it could easily generate erroneous results. For that reason, the expertise of the testing laboratory and the people running the instrumentation is of prime importance, and in particular to have an intimate knowledge of working in the ultra-trace environment and to be aware of all the potential sources of elemental contaminants outlined below (21).

Sources from the Laboratory Testing Procedure and Methodology

  • Cleanliness of sample preparation test area and equipment
  • Laboratory dust or dirt of unknown origin (for example, old Pb-based paint)
  • Cleanliness of sample digestion procedure
  • Quality of the deionized water
  • Purity of analytical reagents, acids, and solvents
  • Impurities in laboratory glassware and plastic vessels or containers
  • Purity of the plastic tubing used in delivering the sample to the instrument
  • Contaminants from the analyst including clothing, cosmetics, lotions, perfumes, shampoo, jewelry, smoke
  • Laboratory drywall or plasterboard walls and partitions made from flue gas desulfurization (FGD) waste products—some of these contain high levels of heavy metals because they have been made with “clinker” produced by scrubbing emissions from coal-fired power plants

I have become very familiar with the demands of the pharmaceutical community and, in particular, their trace element impurity requirements, so I have a very good perspective of how the industry approached the problem of tracing sources and pathways of heavy metals in raw materials and drug products. This topic was the focus of my most recent book entitled Measuring Elemental Impurities in Pharmaceutical Materials: A Practical Guide, which was published in the spring of 2018 (22). In the three years it took me to research and write this book, I realized the pharmaceutical manufacturing industry were not really familiar with ICP-MS, so they needed educating about how to generate high quality data when working at the ultra-trace level. After I published the book, on the suggestion from many people within the pharmaceutical and herbal supplements industries, I turned my attention to the cannabis and hemp industry and started interviewing cultivators, growers, producers, processors regulators, and testing laboratories to get a better understanding of what the industry needs with regard to its heavy metals’ testing requirements. As a result of that background research, I have begun the process of writing the book, which will be entitled Measuring Heavy Metal Contaminants in Cannabis and Hemp: A Practical Guide (5).

Final Thoughts

Our environment has been severely polluted by heavy metals, which has compromised the ability of our natural ecosystems to sustain and foster life. Heavy metals are known to be naturally occurring compounds, but anthropogenic activities introduce them in extremely large quantities into our agricultural growing and cultivation systems. Nowhere is this more evident than in the delicate balance of growing cannabis and hemp for commercial, medicinal, and recreational uses. Unfortunately, the demand for cannabinoid-based products is moving so fast that the scientific community is not keeping up with it; whether it’s the testing of the products to make sure they are safe for human consumption or the medical research required to understand the biochemistry that is fundamental to treating a particular disease or ailment. The industry is both exciting and chaotic at the same time, but because of its unparalleled growth there appears to be very little incentive to bring in sensible regulations. There clearly needs to be a more comprehensive suite of elemental contaminants tested and to set the maximum limits on toxicological data based on the manner and the quantity that cannabis products are consumed. For that reason, researchers who are trying to raise the bar now will be rewarded when the FDA eventually starts to regulate the industry. However, in the meantime, I’m firmly committed to educating state regulators to better understand the potential sources of heavy metals in cannabis and hemp and to help the laboratory testing community improve the quality of its results.

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  2. Cannabis Consumer Report, New Frontier Data Analytics (2019).
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  5. R.J. Thomas, Measuring Heavy Metals in Cannabis and Hemp: A Practical Guide (CRC Press, Boca Raton, Florida, to be published in summer 2020).
  6. Marijuana Policy by State:
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  20. M. Halstead,, J. Anal. Toxicol. in press (2019).
  21. P. Atkins, Cannabis Science and Technology 1(4), 40–49 (2018).
  22. R.J. Thomas, Measuring Elemental Impurities in Pharmaceuticals: A Practical Guide (CRC Press, Boca Raton, Florida, 2018).

About the Guest Author

Robert ThomasRobert Thomas is the principal of Scientific Solutions, a consulting company that serves the training, application, marketing, and writing needs of the trace element user community. He has worked in the field of atomic and mass spectroscopy for more than 45 years, including 24 years for a manufacturer of atomic spectroscopic instrumentation. He has served on the American Chemical Society (ACS) Committee on Analytical Reagents (CAR) for the past 19 years as leader of the plasma spectrochemistry, heavy metals task force, where he has worked very closely with the United States Pharmacopeia (USP) to align ACS heavy metal testing procedures with pharmaceutical guidelines. Rob has written almost 100 technical publications.

About the Columnist

Patricia AtkinsPatricia Atkins is a Senior Applications Scientist with SPEX CertiPrep and a member of both the AOAC and ASTM committees for cannabis.

How to Cite This Article

R. Thomas, Cannabis Science and Technology 2(5), 22-30 (2019).