Can Avid Hyperaccumulating Plants Like Hemp Realistically be Used as a Source of Medicinal Cannabinoids? Part 1: The Conflicting Personality of Hemp

Hemp is such a diverse and flexible plant that not only is it a prolific source of cannabinoids and terpenes, but it can also be used to manufacture industrial products such as concrete, rope, paper, plastic, textiles, biofuels, and insulation materials. Additionally, it is a wonderful source of nutritional seeds that are very high in protein. However, its diverse nature for manufacturing one product, can also be detrimental in its use for another. For example, how is it that a plant that is known to be an excellent phytoremediator to clean up soil contaminated with heavy metals can also be used as a rich source of CBD oil that is strictly regulated for heavy metals in the state where it is grown?

This two-part article will take a closer look at the conflicting personality of hemp in an attempt to get a better understanding of how it can be safely used for many different applications. Part one will focus on the phytoremediation properties of hemp and why it has been used to clean up toxic waste sites where other types of remediation have failed. The second part will examine its more recent industrial applications and, in particular, its use as a prolific source of cannabinoids for medicinal purposes. Moreover, it will emphasize the importance of regular testing, which is imperative to ensure the product is suitably utilized for the optimum application and does not have a negative impact on consumer safety.

Hemp as a hyper-accumulator

Cannabis and hemp are known to be avid hyperaccumulators of contaminants in the soil. That is why they have been used to clean up toxic waste sites where other kinds of remediation attempts have failed. In the aftermath of the Chernobyl nuclear meltdown in Ukraine in 1986, industrial hemp was planted to clean up the radioactive isotopes that had leaked into the soil and ground waters ¹. The phytoremediation properties of botanical species are well-recognized. It has been reported that close to 400 plants, shrubs, flowers and trees have the ability to absorb extremely high levels of metal contaminants out of the soil ². Of course, Chernobyl is an extreme example of metal and radionuclide contamination, but as a result of normal anthropogenic industrial activities over the past few decades, including mining, metal refining/smelting, power generation and use of fertilizers, heavy metal pollution has become one of the most serious environmental problems today.

Even though much of the farmland in the US is perfectly suitable for growing agricultural crops, even low levels of heavy metals can end up in the plant material. A recent report showed that popular infant food had unacceptably high levels of Pb, Cd, As and Hg derived from the vegetables used in the manufacturing process, which had escaped the scrutiny of the US FDA ³. And, with all the diverse and varied soil conditions used for growing hemp for consumer products such as medicinal cannabinoids, edible seeds and industrial fibers, it will be very difficult to eliminate all these potential sources of pollution in order to reduce their impact on the plant’s biology. So can hemp, which is predominantly grown outdoors – and one of the best plants for soil phytoremediation purposes be realistically and safely used as a source for all these wonderful products? Let’s take a closer look.

Chernobyl nuclear disaster

On April 26, 1986, a sudden surge of power during a reactor system test destroyed Unit 4 of the Chernobyl nuclear power plant in Pripyat, Ukraine, part of the former Soviet Union. The accident and the fire that followed released massive amounts of radioactive material into the environment and caused the worst nuclear disaster the world had ever seen. Thirty-one people perished as an immediate result of the accident, with a further 29 dying within weeks from horrific effects of radiation poisoning. Hundreds of thousands of people were affected by the long-term impact of the accident. The radioactive fallout was so serious that local farmers were deeply concerned that the soil would be irrevocably harmed by the toxic metals leaching into the soil. The site was left for several years to allow the radioactivity to subside. Then in the early 1990s scientists began growing industrial hemp around the abandoned Chernobyl nuclear power plant, and found it significantly reduced radionuclide soil toxicity ⁴. Fast forward 10 years to 2001 and a team of researchers in Germany confirmed the Chernobyl results by showing that hemp was able to extract lead, cadmium and nickel and other heavy metals from a plot of land contaminated with sewage sludge ⁵. All of a sudden industrial hemp became a viable option for cleaning up many industrial contaminated sites around the world as it offered many benefits over traditional remediation approaches.

Traditional soil remediation

Heavy metal accumulation in soil has been rapidly increasing due to various natural processes and industrial activities. As heavy metals are toxic and non-biodegradable, they persist in the environment, have the potential to enter the food chain through crop plants, and eventually may accumulate in the human body through long-term exposure and biomagnification. As a result, heavy metal contamination has posed a serious threat to human health and the ecosystem. It is therefore necessary to take remediation measures to prevent heavy metals from entering terrestrial, atmospheric, and aquatic environments, and to mitigate the contaminated land ⁶.

A variety of remediation approaches have been developed to reclaim heavy metal-contaminated soil, which are mainly based on mechanical or physio-chemical techniques, such as soil incineration, excavation and landfill, soil washing, solidification, and electric field application. However, there are limitations to these approaches such as high cost, inefficiency when contaminants are present at low concentrations, irreversible changes to the physicochemical and biological properties of soils which lead to the deterioration of the soil ecosystem, and the introduction of secondary pollutants. Therefore, there is clearly a need to develop cost-effective, efficient, and environmentally-friendly remediation technologies to reclaim heavy metal-contaminated soil.

Principles of phytoremediation

Phytoremediation is a plant-based clean-up approach, which involves the use of plants to extract and remove elemental pollutants or lower their bioavailability in soil. Plants have the ability to absorb ionic compounds in the soil even at low concentrations by extending their root system into the soil matrix and establishing a rhizosphere ecosystem to accumulate heavy metals and modulate their bioavailability, thereby reclaiming the polluted soil and stabilizing soil fertility. Phytoremediation has many advantages, which include:

• Economically feasible, requiring only a source of carbon, nitrogen and solar energy for metabolic synthesis.
• Relatively simple to manage, with low cost of installation and maintenance.
• Environmentally friendly—it can reduce exposure of pollutants to the environment and ecosystem.
• Prevents erosion and metal leaching through stabilizing heavy metals, reducing the risk of spreading of contaminants.
• Improves soil fertility by releasing various organic matter into the soil.
• Extremely efficient for many contaminants.
• Applicability over large areas and plants can easily be disposed of.

Phytoremediation efficiency

A great deal of research has gone into molecular mechanisms behind heavy metal tolerance and uptake by plants. It has been well-studied and, as a result, the process of phytoremediation is optimized and extremely efficient ². It has been reported that there are over 400 plants that can be called hyperaccumulators, many with properties that are metal specific. For example, alfalfa is an excellent remediator for the classic heavy metals and studies have shown it can extract up to 43,000 mg of Pb per kg of the plant and still remain healthy. While other plants such as alpine pennygrass work better for transition metals and studies have reported it can remove up to 51,000 mg/kg Zn from the soil ². 

Hemp is not as efficient as other metal-specific phytoremediators but appears to be a plant that has good hyperaccumulation properties for a broad range of contaminants including heavy metals, transition metals and radionuclides. A recent scientific study showed that industrial hemp could absorb over 1000 mg/kg of cadmium without affecting its growth ⁷. Its very long root system and high biomass, means the metals are absorbed quickly and reside in many different parts of the plant, including roots, shoots, stems, leaves, flowers, etc. As a result, it is widely used to clean up contamination from sources such as mining waste, metal refining, coal-fired power plants, sewage sludges, and polluted nuclear reactor sites such as Chernobyl. It’s also worth noting that following the devastating damage by the tsunami that caused the Fukushima nuclear plant meltdown in Japan in 2011, scientists considered using hemp to aid their clean-up efforts. However, due to the Cannabis Control Law forced into Japanese law by the US after the second world war, hemp can only be grown under license, so is highly restricted and difficult to obtain. It looks like these restrictions will soon be lifted in order to take advantage of hemp’s phytoremediation properties to help the clean-up ⁸. As a result of these restrictions, sunflowers were first used to clean up cesium-137 and Strontium-90 from the soil immediately after the meltdown. Sunflowers are another hyperaccumulator plant with the added benefit of growing very tall for maximum absorption of the contaminant. In addition, they are inexpensive, plentiful in Japan, and perfectly suited for the local climate ⁹.

In conventional phytoremediation, once the plants have absorbed the maximum level of contaminants, they are usually destroyed (typically incinerated). However, in some applications, the extracted material is then processed to remove the metal. This is a relatively new science called phytomining, which is phytoextraction applied to the extraction of various metals from waste sites using different plants, including hemp ¹⁰. For example, rare earth metals are being extracted from acid drainage sites that contain waste effluents leftover from the refining of rare earth minerals. This is attracting a great deal of attention, particularly from China and South Africa, where most rare earth mining is carried out today. It is a way of both cleaning up the waste site and also extracting the rare earth metals, which would otherwise have been treated and dumped ¹¹.

The second part of this article will examine the many industrial and therapeutic applications of hemp including its use for the production of CBD products and emphasize the importance of regular testing for heavy metals, to ensure maximum consumer safety.

Further reading 

1. Back to Chernobyl, Lila Guteman, New Scientist, April 10, 1999, https://www.newscientist.com/article/mg16221810-900-back-to-chernobyl/ 
2. Phytoremediation: A Promising Approach for Revegetation of Heavy Metal-Polluted Land, An Yang et al., Front. Plant Sci., 30 April 2020, https://www.frontiersin.org/articles/10.3389/fpls.2020.00359/full 
3. New Report Finds Toxic Heavy Metals in Popular Baby Foods: FDA Failed to Warn Consumers of Risk: L. Railey, Washington Post, Feb 4, 2021, https://www.washingtonpost.com/business/2021/02/04/toxic-metals-baby-food/ 
4. Phytoremediation of radio cesium-contaminated soil in the vicinity of Chernobyl, Ukraine, Slavik Dushenkov et.al., Environmental Science & Technology, 33, 3, 469-475, (1999)
5. Health Effects of Chernobyl, German Affiliate of International Physicians for the Prevention of Nuclear War (IPPNW), Sebastian Pflugbeil et. al., April 2011, https://www.ippnw.org/pdf/chernobyl-health-effects-2011-english.pdf 
6. Phytoremediation: Principles and Perspectives, Joan Barceló and Charlotte Poschenriede, CONTRIBUTIONS to SCIENCE, 2 (3): 333-344 (2003), https://www.researchgate.net/publication/28076724_Phytoremediation_Principles_and_perspectives 
7. Cannabis sativa L. growing on heavy metal contaminated soil: growth, cadmium uptake and photosynthesis. Peter Linger et. al., BIOLOGIA PLANTARUM 49 (4): 567-576, 2005, 
8. Hemp Vs. Nuclear Waste, HERB Website, December 2019, https://herb.co/news/culture/hemp-vs-nuclear-waste/?fbclid=IwAR0kvJbReeguUrmtRaYWr2DKcY5sPGbS2qgWuNE8AwsUuZLWMduD--khpao 
9. Scientists Are Using Sunflowers to Clean Up Nuclear Radiation, Molly Beauchemin, Garden Collage magazine, May 12, 2016, https://gardencollage.com/change/sustainability/scientists-using-sunflowers-clean-nuclear-radiation/ 
10. Phytomining, Robert Brooks et.al., Trends in Plant Science, Volume 3, Issue 9, Pages 359-362, 1 September 1998, https://www.sciencedirect.com/science/article/abs/pii/S1360138598012837 
11. Phytoextraction of rare earth elements from ion-adsorption mine tailings by Phytolacca Americana: Effects of organic material and biochar amendment, Wen Shen Lui et. al., Journal of Cleaner Production, Volume 275, 122959, 1 December 2020 https://www.sciencedirect.com/science/article/abs/pii/S0959652620330043