Metals in Cannabis and Related Substances—Regulations and Analytical Methodologies: Page 4 of 4

March 1, 2018
Abstract / Synopsis: 

Evolution in the legislation regarding the production and consumption of cannabis and related products for medicinal and recreational uses has led to emerging regulations regarding the potency, terpene profiles, and impurity content of such products. Among the impurities, or contaminants, that require testing are metals. Because of their toxicity and carcinogenicity, most jurisdictions are, at a minimum, requiring testing for arsenic, lead, cadmium, and mercury. Metals accumulate in plant material through normal metabolic processes. Furthermore, some plants are capable of hyperaccumulating metals to concentrations well above those in the soils and waters that nourish them. Some such metals are beneficial or nutritional in nature, whereas others show varying levels of toxicity. As such, testing for metals, particularly ones that are toxic, are important for products destined for human consumption. Quantitation of metals within cannabis materials can be accomplished through a variety of analytical techniques. Such amenable technologies include atomic absorption (AA) spectroscopy, inductively coupled plasma-optical emission spectroscopy (ICP-OES), and inductively coupled plasma-mass spectrometry (ICP-MS). As with all aspects of analytical instrumentation, each method has its advantages and disadvantages. Here, we present an overview of analytical methodologies, challenges facing the analyst, and notes on regulatory stipulations.


The rapid changes in the legal status of cannabis and related products have necessitated regulations on their chemistry, including potency, residual solvents, pesticide contamination, and metals content. Because of metals’ potentially harmful biological effects, metals analysis of cannabis and its related products is critical to minimizing risk to the consumer. Although such regulations vary between states and jurisdictions, the majority require testing for arsenic, cadmium, lead, and mercury (at a minimum) because of their particularly hazardous properties.

Metals analysis can be conducted using a variety of instrumentation and methodologies—including AA, ICP-OES, and ICP-MS—each with their individual strengths and weaknesses. Atomic absorption spectroscopy benefits from low costs, but suffers from slower sample throughput; ICP-OES offers similar detection limits and more rapid sample processing than AA at a slightly higher cost; and ICP-MS offers exceptional sensitivity and throughput, but at the highest initial and operating costs.

Despite the higher costs and analytical complications associated with the method, most laboratories are pursuing ICP-MS as their technique of choice because of the high sensitivity, high sample throughput, and adaptability to other methods and industries. Because the technique has long been used in testing of food, water, and pharmaceutical products, contract laboratories with existing ICP-MS systems are viewing cannabis testing as a supplemental revenue stream. Alternatively, as cannabis testing evolves, laboratories may use their ICP-MS instruments for detection of metals in cannabis growth media, soils, fertilizers, water for hydroponic growth, and so on. Furthermore, as regulations evolve and are codified, it is likely that the number of metals requiring testing will increase and acceptable concentrations of said metals will decrease, necessitating the use of fast and sensitive analytical techniques, such as ICP-MS.

Andrew P. Fornadel, PhD, Daniel L. Davis, Robert H. Clifford, PhD, and Scott A. Kuzdzal, PhD, are with Shimadzu Scientific Instruments in Columbia, Maryland. Direct correspondence to: [email protected]

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How to Cite This Article

A.P. Fornadel, D.L. Davis, R.H. Clifford, and S.A. Kuzdzal, Cannabis Science and Technology 1(1), 36-41 (2018).