Tag Archives: arsenic

Heavy Metals Testing: Methods, Strategies & Sampling

By Charles Deibel
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Editor’s Note: The following is based on research and studies performed in their Santa Cruz Lab, with contributions from Mikhail Gadomski, Lab Manager, Ryan Maus Technical Services Analyst, Laurie Post, Director of Food Safety & Compliance, and Charles Deibel, President Deibel Cannabis Labs.


Heavy metals are common environmental contaminants resulting from human industrial activities such as mining operations, industrial waste, automotive emissions, coal fired power plants and farm/house hold water run-off. They affect the water and soil, and become concentrated in plants, animals, pesticides and the sediments used to make fertilizers. They can also be present in low quality glass or plastic packaging materials that can leach into the final cannabis product upon contact. The inputs used by cultivators that can be contaminated with heavy metals include fertilizers, growing media, air, water and even the clone/plant itself.

The four heavy metals tested in the cannabis industry are lead, arsenic, mercury and cadmium. The California Bureau of Cannabis Control (BCC) mandates heavy metals testing for all three categories of cannabis products (inhalable cannabis, inhalable cannabis products and other cannabis and cannabis products) starting December 31, 2018. On an ongoing basis, we recommend cultivators test for the regulated heavy metals in R&D samples any time there are changes in a growing process including changes to growing media, cannabis strains, a water system or source, packaging materials and fertilizers or pesticides. Cultivators should test the soil, nutrient medium, water and any new clones or plants for heavy metals. Pre-qualifying a new packaging material supplier or a water source prior to use is a proactive approach that could bypass issues with finished product.

Testing Strategies

The best approach to heavy metal detection is the use of an instrument called an Inductively Coupled Plasma Mass Spectrometry (ICP-MS). There are many other instruments that can test for heavy metals, but in order to achieve the very low detection limits imposed by most states including California, the detector must be the ICP-MS. Prior to detection using ICP-MS, cannabis and cannabis related products go through a sample preparation stage consisting of some form of digestion to completely break down the complex matrix and extract the heavy metals for analysis. This two-step process is relatively fast and can be done in a single day, however, the instruments used to perform the digestion are usually the limiting step as the digesters run in a batch of 8-16 samples over a 2-hour period.

Only trace amounts of heavy metals are allowed by California’s BCC in cannabis and cannabis products. A highly sensitive detection system finds these trace amounts and also allows troubleshooting when a product is found to be out of specification.

For example, during the course of testing, we have seen lead levels exceed the BCC’s allowable limit of 0.5 ppm in resin from plastic vape cartridges. An investigation determined that the plastic used to make the vape cartridge was the source of the excessive lead levels. Even if a concentrate passes the limits at the time of sampling, the concern is that over time, the lead leached from the plastic into the resin, increasing the concentration of heavy metals to unsafe levels.

Getting a Representative Sample

The ability to detect trace levels of heavy metals is based on the sample size and how well the sample represents the entire batch. The current California recommended amount of sample is 1 gram of product per batch.  Batch sizes can vary but cannot be larger than 50 pounds of flower. There is no upper limit to the batch sizes for other inhalable cannabis products (Category II).

It is entirely likely that two different 1 gram samples of flower can have two different results for heavy metals because of how small a sample is collected compared to an entire batch. In addition, has the entire plant evenly collected and concentrated the heavy metals into every square inch of it’s leaves? No, probably not. In fact, preliminary research in leafy greens shows that heavy metals are not evenly distributed in a plant. Results from soil testing can also be inconsistent due to clumping or granularity. Heavy metals are not equally distributed within a lot of soil and the one small sample that is taken may not represent the entire batch. That is why it is imperative to take a “random” sample by collecting several smaller samples from different areas of the entire batch, combining them, and taking a 1 g sample from this composite for analysis.


References

California Cannabis CPA. 12/18/2018.  “What to Know About California’s Cannabis Testing Requirements”. https://www.californiacannabiscpa.com/blog/what-to-know-about-californias-cannabis-testing-requirements. Accessed January 10, 2019.

Citterio, S., A. Santagostino, P. Fumagalli, N. Prato, P. Ranalli and S. Sgorbati. 2003.  Heavy metal tolerance and accumulation of Cd, Cr and Ni by Cannabis sativa L.. Plant and Soil 256: 243–252.

Handwerk, B. 2015.  “Modern Marijuana Is Often Laced With Heavy Metals and Fungus.” Smithsonian.com. https://www.smithsonianmag.com/science-nature/modern-marijuana-more-potent-often-laced-heavy-metals-and-fungus-180954696/

Linger, P.  J. Mussig, H. Fischer, J. Kobert. 2002.  Industrial hemp (Cannabis sativa L.) growing on heavy metal contaminated soil: fibre quality and phytoremediation potential. Ind. Crops Prod. 11, 73–84.

McPartland, J. and K. J McKernan. 2017.  “Contaminants of Concern in Cannabis: Microbes, Heavy Metals and Pesticides”.  In: S. Chandra et al. (Eds.) Cannabis sativa L. – Botany and Biotechnology.  Springer International Publishing AG. P. 466-467.  https://www.researchgate.net/publication/318020615_Contaminants_of_Concern_in_Cannabis_Microbes_Heavy_Metals_and_Pesticides.  Accessed January 10, 2019.

Sidhu, G.P.S.  2016.  Heavy metal toxicity in soils: sources, remediation technologies and challenges.   Adv Plants AgricRes. 5(1):445‒446.

The Practical Chemist

Instrumentation for Heavy Metals Analysis in Cannabis

By Chris English
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Determination of Toxic Metals in Cannabis

Heavy metals are common environmental contaminants often resulting from mining operations, industrial waste, automotive emissions, coal fired power plants, amount other sources. Several remediation strategies exist that are common for the reduction/elimination of metals in the environment. Phytoremediation is one method for removing metals from soil, utilizing plants to uptake metals which then bioaccumulate in the plant matter. In one study, cesium concentrations were found to be 8,000 times greater in the plant roots compared to the surrounding water in the soil. In 1998, cannabis was specifically tested at the Chernobyl nuclear disaster site for its ability to remediate the contaminated soil. These examples demonstrate that cannabis must be carefully cultivated to avoid the uptake of toxic metals. Possible sources would not only include the growing environment, but also materials such as fertilizers. Many states publish metal content in fertilizer products allowing growers to select the cleanest product for their plants. For cannabis plant material and concentrates several states have specific limits for cadmium (Cd), Lead (Pb), Arsenic (As) and Mercury (Hg), based on absolute limits in product or daily dosage by body weight.

Analytical Approaches to Metals Determination

Inductively Coupled Plasma, Ionized Argon gas stream. Photo Courtesy: Sigma via Wikimedia Commons

Flame Atomic Absorption Spectroscopy (Flame AA) and Graphite Furnace Atomic Absorption Spectroscopy (GFAA) are both techniques that determine both the identity and quantity of specific elements. For both of these techniques, the absorption in intensity of a specific light source is measured following the atomization of the sample digestate using either a flame or an electrically heated graphite tube. Reference standards are analyzed prior to the samples in order to develop a calibration that relates the concentration of each element relative to its absorbance. For these two techniques, each element is often determined individually, and the light source, most commonly a hollow cathode lamp (HLC) or electrodeless discharge lamp (EDL) are specific for each element. The two most common types of Atomic Emission Spectroscopy (AES) are; Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and ICP-Mass Spectrometry (ICP-MS). Both of these techniques use an argon plasma for atomization of the sample digestates. This argon plasma is maintained using a radio frequency generator that is capable of atomization and excitation of the majority of the elements on the periodic table. Due to the considerably higher energy of the plasma-based instruments, they are more capable than the flame or furnace based systems for measurement of a wide range of elements. Additionally, they are based on optical emission, or mass spectrometric detection, and are capable of analysis of all elements at essentially the same time.

Technique Selection

Flame AA is easy to use, inexpensive and can provide reasonable throughput for a limited number of elements. However, changes to light sources and optical method parameters are necessary when determining different metals. GFAA is also limited by similar needs to change the light sources, though it is capable of greater sensitivity for most elements as compared to flame AA. Runtimes are on the order of three minutes per element for each sample, which can result in lower laboratory throughput and greater sample digestate consumption. While the sensitivity of the absorption techniques is reasonable, the dynamic range can be more limited requiring re-analyses and dilutions to get the sample within the calibration range. ICP-OES allows the simultaneous analysis of over 70 elements in approximately a minute per sample with a much greater linear dynamic range. ICP-OES instruments cost about 2-5 times more than AA instruments. ICP-MS generally has the greatest sensitivity (sub-parts-per-trillion, for some elements) with the ability to determine over 70 elements per minute. Operator complexity, instrument expense and MS stability, as well as cost are some of the disadvantages. The US FDA has a single laboratory validated method for ICP-MS for elements in food using microwave assisted digestion, and New York State recently released a method for the analysis of metals in medical cannabis products by ICP-MS (NYS DOH LINC-250).

The use of fertilizers, and other materials, with low metal content is one step necessary to providing a safe product and maintaining customer confidence. The state-by-state cannabis regulations will continue to evolve which will require instrumentation that is flexible enough to quickly accommodate added metals to the regulatory lists, lower detection limits while adding a high level of confidence in the data.