Cannabis, Fertilizers, and Heavy Metals

In today’s world, it seems that people are inclined to quickly choose a side. Whether it’s politics, social issues, religion, science, you name it: we often take a stance one way or another and then blindly discount any arguments from the opposition as not credible or just flat out wrong. This tendency is as much polarizing as it is unproductive since no progress can be made when each side refuses to recognize and consider any valid points from that which they deem an antagonist.

The choosing of sides and the creation of intellectual schisms is not only found in things like politics and social issues. It can be found in the fertilizer world as well. I see it daily. A person will proudly boast that only organic (or synthetic) fertilizers are the best and that the other side is inferior in every single way. This is a very narrow-minded way of thinking because almost nothing in this world is simply black and white. There are variables that must be considered in every case. At the end of the day, a person can provide pretty basic arguments that show how inorganic or synthetic fertilizers are not all bad and that organic fertilizers are not completely perfect. A great way to illustrate this point is by looking at the connection between cannabis, fertilizer, and heavy metals.

Plants That Remove Contaminants

Phytoremediation is the use of plants for the removal of contaminants in soils, other terrestrial lands, and waterways. There are a wide range of materials that can contribute to this contamination, but one of the most prevalent and important contaminants in the environment are heavy metals. There are several ways the ground can become contaminated with heavy metals ranging from poor soil management to industrial pollution. Regardless of how the materials got there, the importance of removing the contaminants and remediating the land is paramount as heavy metals can be toxic to living organisms. The type of phytoremediation used to remove heavy metals is referred to as phytoextraction, and it is achieved with the help of specialized plants called hyperaccumulators.

Hyperaccumulators are plants that have the ability to uptake high amounts of toxins, such as heavy metals, without them overly affecting plant growth and development in a negative way. Simply put, these plants have exceptional metal-accumulating capacity while at the same time still being able to grow in a normal fashion. Every plant has the ability to uptake metal ions, such as iron and copper, which they use to develop and reproduce. The same mechanisms involved in the root uptake of metals and elements that are essential to plant growth are also used in the accumulation of heavy metal ions that have no known benefits. What makes hyperaccumulators different from an average plant like a tomato is its ability to do so and continue growing as if nothing was wrong. There are multiple species of plants that have hyperaccumulation abilities but for this article, I want to focus on just one.

Cannabis for Cleanup

The cannabis (hemp) plant is a known hyperaccumulator that has been used to clean up contaminated lands for years. Most notably is the use of cannabis to help remediate the radionuclide-polluted lands at the Chernobyl nuclear disaster site. Cannabis makes for an ideal candidate for phytoremediation because it is relatively fast-growing, has an extensive root system, and is for the most part unaffected by the heavy metals and toxins it takes in and accumulates. When the plants start to reach the end of their growth cycle, they are uprooted, usually burned, and then the contaminated ashes are properly disposed of. Cannabis plants are by no means the only hyperaccumulators available, but they are quite efficient at the job.

Metals in Fertilizers

At this point, you may be wondering to yourself what all of this has to do with fertilizers? I’ve spent nearly the last 15 years of my life working for fertilizer companies. Throughout the years, I’ve sent countless fertilizer materials and blends of all types to well-respected labs to not only determine their nutrient contents but heavy metals concentrations as well. Judging by what I’ve read from others on social media platforms and growing forums, the results we receive may surprise many of you.

There appears to be a misconception that inorganic or synthetic fertilizers contain higher levels of heavy metals than organic fertilizers. In my experience, this is most often not the case. First off, it is important to state that pretty much all fertilizers will have some amount of heavy metals. Even if the amounts are below the minimum detection level of the analysis, there are likely still trace amounts present. What I’ve noticed is that granular organic fertilizer products will, more often than not, have higher levels of heavy metals and generally higher levels than their liquid organic counterparts. On the other end of the spectrum, the water-soluble and concentrated liquid inorganic or synthetic fertilizers almost always have the lowest amounts of heavy metals with many clocking it at the non-detectable level.

The reason for these differences is the source. The granular organic fertilizers that are derived from animal matter tend to have the highest levels. This is likely linked to the type of diet they consume. Plant-based organic fertilizers come in next in regard to heavy metals. The levels will vary depending on the plant because not all plants take in metals in the same amounts. I think almost anyone would be surprised at the arsenic levels of a standard sea kelp extract. Basically, anything that is alive and consuming food and nutrients from the surrounding environment will begin to accumulate heavy metals. This is all very natural.

On the other hand, inorganic or synthetic fertilizers usually come from specifically mined mineral sources where heavy metals are found in much smaller amounts. The levels found in these fertilizers are often a direct reflection of the purity of the mineral source. Food and pharmaceutical-grade inorganic minerals have a much higher purity level than cheaply-mined sources and such quality will come at a price but the difference will be extremely noticeable. In turn, they will be more soluble in water and have better uptake into plant roots. It is also important to keep in mind that some heavy metals, such as zinc and manganese, are essential plant nutrients as well.

All of this may be contrary to what many of you have heard before, but I urge you to not just take my word for it. There are ways for consumers to check the heavy metals content for the products they use. Both the California Dept. of Food & Agriculture (CDFA) and the Washington State Dept. of Agriculture (WSDA) have online databases for all registered fertilizer products sold in their respective states that have the heavy metals contents listed along with the nutrient analysis. Each company that sells a fertilizer product into these states is required to submit a heavy metals analysis from a reputable third-party lab as part of the product registration product. A consumer can also contact the product manufacturer and request information on the heavy metal concentrations. If the company refuses to supply such information, I would view them as suspect, with something to possibly hide.

So how does this all tie in together with cannabis? At the moment most current regulations in states that have legalized either medicinal or recreational cannabis usually require testing end-user products for the following: cannabinoids (i.e. THC/CBD), solvents, residual pesticides, microbiological impurities (i.e. salmonella/e-coli). Only 7 of the 30 states (plus D.C.) actually test cannabis products for their heavy metal contents. The metals tested are typically arsenic (Ar), cadmium (Cd), lead (Pb), and mercury (Hg). Unbelievably, some states don’t require producers to test their products for any of the above.

Cannabis and Heavy Metals

To me, the concern about cannabis and heavy metals lies in the fact that it is a hyperaccumulator and that it is often grown in the same soil each season (especially outdoors) with many growers using strictly organic fertilizer inputs. This coupled with the fact that only a small handful of states actually require that the products be tested for heavy metals is a bit concerning. When hemp cannabis is used for phytoremediation, there is a common understanding that it should not later be used for food or medicine, especially if the plant is to be concentrated into oil or similar products. If a plant is contaminated with heavy metals or other toxins, they will be present in the finished product and even more so in a concentrated material. Oils and other concentrates are steadily becoming more popular than normal flowers, so I see this as a potential issue that should be addressed.

I must be completely clear that I am in no way saying one type of fertilizer is better or safer than another. In fact, the plant itself technically doesn’t really know the difference between organic and synthetic. At the end of the day, the plant really only sees elemental plant nutrients as ions needed for development. I’m simply trying to illustrate that not every situation is completely black and white, cut and dried. Obviously, there are many variables involved in every situation. In this particular situation, I see the importance of testing all cannabis products for heavy metals as paramount and that the health of the consumer is worth the extra scrutiny.