How Clean is Your Cannabis?

Under a new program announced in Canada, strict guidelines have been imposed on the medical marijuana industry to ensure that the final product doesn’t contain significant levels of heavy metals, aflatoxins, pesticides or microbial contamination. These guidelines weren’t created specifically for cannabis: They’re the same Pharmacopoeia-based standards used by Health Canada for other dried natural-health products derived from plants (i.e., echinacea, ginseng and so on).

While the regulations were designed to protect Canadian consumers, it’s actually quite difficult to meet these “dried product” standards by growing, drying and curing cannabis using the traditional methods. Many microbes that occur naturally in plants and soil can be flagged by such sensitive microbial tests. For example, the common Pseudomonas aeruginosa is one of the primary causes of hospital infections and can also be found on cannabis. Even a small amount of fungal sporulation, whether during growth or post-harvest, can lead to a failed test. As a result, some of the world’s largest medical marijuana producers have opted to sterilize their cannabis using gamma radiation. While other, less invasive techniques exist to ensure product safety, each harvested batch must be tested independently by an outside lab prior to sale.

In the United States, the Food and Drug Administration has regulations similar to Health Canada’s for most plant-based medicines. As attitudes toward cannabis undergo profound social change, there’s a growing demand for lab tests to ensure the safety not only of medical marijuana, but recreational cannabis as well.

To many seasoned users, the idea of requiring such tests seems almost ludicrous. When cannabis is grown properly, without harsh chemical fertilizers or inorganic pesticides, and dried and cured in a clean environment, it’s generally safe for consumption by any method. Indeed, it’s not too surprising that no one is getting sick from cannabis, considering the method of consumption used by most people: Biological organisms do not typically survive the combustion or baking process.

However, several cases of illness and even death have been reported due to aspergillosis of the lungs following the smoking of cannabis contaminated by fungi. While it’s difficult to prove that the infection was directly due to cannabis use, it should be noted that all of these cases involved people with compromised immune systems, such as transplant recipients or HIV/AIDS patients. And as other methods of ingesting cannabis become more popular (topicals, raw juicing, etc.), the risks of microbial infection may increase. People employing these methods should be much more concerned about whether there are infectious microbes such as E. coli on their plants.

While bacteria and fungi pose potential risks, we need to pay attention not only to the immediate short-term consequences of using contaminated cannabis, but also the long-term effects, which are often difficult to correlate with any single factor. When smoking, for example, there is always the risk of inhaling toxic vapors from the combusted material. Heavy metals, aflatoxins, mycotoxins, and residues from fertilizers, pesticides and fungicides can all be inhaled following combustion. Even vaporization can potentially release a number of these elements. Though a single low-dose exposure appears relatively harmless, long-term exposure to these physically damaging and even carcinogenic agents should be a matter of serious concern.

This question becomes more acute when we ask to what extent these substances are being concentrated during the creation of cannabis extracts. There has been a sharp increase in extract production in recent years: Dabs, oils, waxes, budders, shatters and medical extracts are all increasingly available. However, unlike concentrated pharmaceutical drugs, many of the people making these extracts are not accredited scientists working in laboratory settings.

It’s essential that you know how the concentrates that you ingest are produced.

Testing for residual solvents has been one of the main focuses of quality control when it comes to cannabis extracts. However, this is only the obvious first thing to look for, since solvents are a major input in the extraction process. For this reason, solvent testing is extremely important, especially when substances are used that are not really safe for human consumption—for example, naphtha, a common solvent used in lighter fluid. The MSDS (material safety data sheet) for naphtha specifies that “vapors or mists from this material may cause central nervous system depression such as dizziness, drowsiness, headache, and similar narcotic symptoms,” which can also resemble the effects of a cannabis “high.” For this reason, it is important to ensure that the solvent used in creating the concentrate has been properly removed.

For most of the extracts, residual solvent testing is the only safety analysis performed. Yet there are other concerns. Saving time or money can tempt concentrate producers to take shortcuts or make other compromises if they don’t directly perceive a negative consequence. The people making these potentially hazardous decisions may not even be aware of their danger—but ignorance is not an excuse for compromising people’s health.

I assume, for example, that most concentrate producers use high-quality solvents or gases. Yet the difference in cost between a 99.99 percent pure substance and something that is relatively pure is considerable. Further, pure solvents or gases are much harder to acquire—and “pure,” in these cases, doesn’t always mean pure. Both the liquids and gases used in extraction often contain impurities. Typically, around 20 percent of the volatile gas found in butane is actually other gases such as hexane, heptane, ethyl mercaptan, benzene or some other potentially toxic substance.

One of the first things taught about compressed gases in a certification course is that it’s not only important to know the source (i.e., supplier) of your gas, but also to know that the tank in which it arrives has been properly cleaned and stored. These tanks can be made from a variety of different metals, and each typically has to be cleaned in a different fashion. Even more important is knowing what other gases have previously been stored in the tank. Many industrial suppliers of compressed gas simply take an empty tank and replace it with a filled one. This new tank could have been previously filled with any number of gases that may have toxic impurities. Keep in mind that when a tank is “empty,” it still contains gas—just not compressed at that point. The extent to which these leftover residues end up in concentrates needs to be further investigated.

Concentrates and Contaminants

I set out to determine the extent to which common contaminants would accumulate in a basic extraction process. To do this, I used cannabis that had become moldy in the final stages of growth. Three separate samples were taken from these plants. Sample 1 consisted of the moldy dried flowers and had only biological contaminants (BC). Sample 2 was sprayed with a fungicide and two pesticides (FP) prior to harvest. Sample 3 contained toxic pollutants (TP) and was intended to represent potential post-harvest contamination; it included 1 gram of dried paint flecks, 1 milliliter (ml) of motor oil, 1 ml of bleach, 1 ml of dish detergent and 1 ml of rusty water.

These samples were extracted using the standard 99% isopropyl-alcohol process commonly used to make cannabis oil. After soaking overnight, the liquid was filtered and evaporated off. Each 100-gram sample yielded from 15 to 17 grams of cannabis oil. This was sent to an accredited third-party laboratory to test for aflatoxins, elemental components and pesticide residues.

The results were not encouraging (see table). Aflatoxins were found above acceptable limits in the two samples not treated with fungicide. This demonstrates that the toxins produced by fungi did accumulate in the extract. At the same time, pesticides were detected in Sample 2, demonstrating that these also accumulate during the extraction process.

Heavy metals were detected in Samples 2 and 3—specifically, charged metal ions like aluminum, cadmium, copper, lead, magnesium, nickel, strontium, tin and zinc. Regardless of whether these levels can be considered “safe,” the continuous inhalation of such particles over time cannot be good. These simple tests demonstrate the potential for toxic impurities to accumulate during the extraction process.


While many people make their own high-THC extracts, the interest in CBD has sparked a whole new industry surrounding this molecule and its potential medical benefits. Not only have breeders begun to focus on strains with high levels of CBD, but those looking to commercialize such extracts are able to create inexpensive CBD concentrates using industrial hemp.

One of the first and largest American producers of a high-CBD extract claims to be using raw hemp material grown in Canada. Similar extracts can now be purchased cheaply from other countries, such as China and the Czech Republic.

It didn’t take me long to track down a number of extracts coming from China. While a supplier in Chicago claims to possess a certificate of analysis (CA) ensuring the safety of the product, I was able with relatively little effort to trace the source of the raw material: It was being shipped by a company in Hong Kong that acquired the hemp from China’s Heilongjiang province.

Google Earth reveals a disturbing fact: The crops are being grown in a mountain valley that has mines all around. The runoff from these mines directly feeds the hemp crops. This raises serious concerns regarding the potential contaminants in these plants.

Is Chinese hemp toxic?

Many plants—including cannabis—have been shown to absorb heavy-metal ions and other toxins from the soil or water. Precisely because of their capacity to hyper-accumulate toxic elements, these plants are used to clean up contaminated areas through a process known as photo-remediation. Plants also exchange air with the atmosphere, essentially breathing in any toxins that may be present. Fungicides and pesticides can leave residues as well.

A lack of strict environmental controls leads to contaminated soil. In the past six months, The New York Times has published two articles detailing how soil and water pollution in China have ended up in the food supply. Heavy-metal concentrations in plants grown in wastewater-irrigated soil were also significantly higher, exceeding the permissible limits set by the Environmental Protection Agency and the World Health Organization. The extent to which these toxic substances are accumulating in Chinese hemp—and especially the concentrates made from it—have yet to be determined.

The disturbing reality is that without knowing exactly who grew your plants, what chemicals they used and how they produced the extract, you are taking a gamble with your future health. Aflatoxins and heavy metals are among the most carcinogenic substances known to science. Hitting a dab or using a concentrate with high levels of these substances is relatively unnoticeable over the short term, yet it will drastically increase the risk of cancer down the road. With new research coming out showing that cannabis smoking does not necessarily increase cancer rates—and may even play a preventative role—it would be detrimental to the cannabis movement to see a reversal of these statistics due to the consumption of contaminated extracts.

Darryl Hudson is president of DOC Solutions, which specializes in agricultural consulting and specialty fertilizers. He holds a PhD in plant molecular biology and genetics.
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