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Cbd oil tested for heavy metals

Heavy Metals Testing: Methods, Strategies & Sampling

Analyzing cannabis samples for heavy metals requires a very low detection limit; the various matrices may not have heavy metals evenly distributed so the sample sizes may skew results.

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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.

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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.


California Cannabis CPA. 12/18/2018. “What to Know About California’s 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.

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. Accessed January 10, 2019.

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How to Test for Heavy Metals in Cannabis

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Cannabis collects heavy metals. It “absorbs heavy metals from the soil, water and air,” says Bob Clifford, general manager at Shimadzu Scientific Instruments. These elements—arsenic, cadmium, lead, mercury and others—can trigger a range of health problems, including cancer and heart disease. Although cannabis for human consumption or smoking should be as free from heavy metal contamination as possible, that’s not always the case. When Sammy Hagar wrote “sparks fly in the middle of the night,” little did he know that this line could describe not just heavy-metal music, but the concerns of testing of cannabis for these elements.

Today’s ‘sparks’ fly around the need and necessary extent of testing cannabis for heavy metals. “Heavy-metal contamination will vary from farm to farm and different strains will have different uptake rates of metals, thus the importance of testing,” Clifford explains.

Regardless of where cannabis comes from, it can include heavy metals. “All agricultural products, including cannabis, contain some amount of heavy metals,” says GenTech Scientific. “The use of things such as fertilizers and pesticides in agricultural applications increase the abundance of these metals in soils and water.”

Beyond coming from natural sources and agricultural methods, heavy metals can infiltrate cannabis-based products in other ways. As an example, GenTech Scientific notes: “Contamination can also occur during the processing of cannabis.”

Despite the wide range of potential sources of heavy metals, it is not inevitable that every cannabis sample includes these elements—at least not at high levels. “With the correct atmosphere, clean soil and water, and limited use of pesticides and fertilizers, you can keep your levels below the acceptable safe limit,” according to GenTech Scientific. Nonetheless, this company adds, “It is important for growers to monitor the levels to ensure their products are in compliance with their state’s regulatory guidelines.” And those can vary considerably.

Where regulators do require testing cannabis for heavy metals, the list usually includes arsenic, cadmium, lead and mercury. “Other states, like Maryland, include additional elements to be tested for such as barium, chromium, selenium and silver,” Clifford says.

Testing tools

Cannabis can be tested for heavy metals in many ways, such as various forms of atomic spectrometry, including atomic absorption (AA), inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). “For AA, the method used would have to be the more sensitive graphite furnace atomic absorption—GFAA—since the flame AA method would not be sensitive enough for most elements,” Clifford explains. “Also, mercury must be measured by a method called cold vapor atomic absorption spectroscopy—CVAAS—due to poor sensitivity by AA.”

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In general, flame techniques can measure elements at low parts per million, and GFAA goes down to low parts per billion. “Also, the AA method usually measures one element at a time,” Clifford says. “ICP and ICP-MS are techniques capable of measuring multiple elements simultaneously.” Nonetheless, using ICP to test cannabis for heavy metals, often requires a way to enhance its sensitivity, such as introducing the sample with an ultrasonic nebulizer (USN). “The USN can increase sensitivity up to a factor of 10,” Clifford says.

From Aeos Labs, analytical chemist Anya Engen says, “ICP-MS offers the best sensitivity and is the method used in our lab.” She adds, “The FDA and United States Pharmacopeia have standardized methods for heavy-metals analysis, which are very useful resources in the fledgling cannabis-testing industry, where regulation is slow to catch up.”

To test for arsenic, scientists often need special sample preparation, such as liquid chromatography (LC), because arsenic can be in inorganic or organic forms. The inorganic form is more toxic. “If one wants to test for the different forms, LC-ICP-MS is utilized to separate and detect the different compounds,” Clifford says. “States currently only require total arsenic, so speciation of this compound is not required.”

Tomorrow’s testing

Not all regulators even require heavy-metals testing for cannabis at the moment. “We test for heavy metals in the USA’s food supply system, enforced by FDA and USDA, so why would we not test for other consumed products like cannabis, especially when involving immune-compromised patients?” Clifford asks. “There needs to be federal oversight of testing for heavy metals, as well as pesticides, residual solvents, mycotoxins and other contaminates so testing is harmonized throughout the United States.”

When asked if any testing improvements would be useful, Engen says, “Measuring heavy-metal levels in the soil and water where cannabis is grown and correlating the data to cannabis-generated data would be helpful in illustrating an overview of possible contamination sources.” She adds, “Being in Hawaii with an active volcano, the heavy metals produced and dispersed by the volcano is a possible source of contamination in Hawaii-grown cannabis.”

Without testing cannabis for heavy metals, sparks could fly from more than guitars as customers insist increasingly on safe, tested products.

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