Hemp and phytoremediation

Hemp science is now advancing in leaps andbounds compared to the stagnation of the previous few decades. One significantarea of research that is currently receiving particular attention isphytoremediation, or decontamination of soil—although the fact that hempdecontaminates soil has been known for some time.

Hemp and the Chernobyl PhytoremediationProject

For almost two decades, industrial hempgrowing in the environs of the abandoned Chernobyl nuclear power plant inPripyat, Ukraine has been helping to reduce soil toxicity.

In 1990, just four years after the initialexplosion, the Soviet administration of the time requested that theInternational Atomic Energy Agency (IAEA) assess the environmental situation.In the 30km exclusion zone surrounding Chernobyl, high concentrations ofvarious toxic metals including lead, cesium-137, strontium-90 and plutoniumwere found in the soil, as well as in the tissues of plants and animals.

In response, it was decided that aconcerted effort to reduce soil contamination through the use of beneficialplants would be undertaken. This process, known as phytoremediation, wasimplemented almost immediately.

Hemp and the Decontamination of RadioactiveSoil

Hemp has been found to decontaminate soilat a very high rate

Which Plants are Useful inPhytoremediation?

Various plants have been utilized inChernobyl for their ability to take up specific contaminants—two brassicavarieties to remove chromium, lead, copper and nickel, maize to take up lead(various studies have demonstrated the excellent lead-uptake capability of thisimportant crop), and more recently, sunflower and hemp.

Sunflower plantings began in 1996subsequent to the development of a variety that promised hitherto unheard-ofefficiency of decontamination; hemp plantings soon followed, in 1998. SlavikDushenkov, a research scientist with Phytotech, one of the organisations behindthe hemp plantings, stated that “hemp is proving to be one of the bestphyto-remediative plants we have been able to find”.

As well as in Ukraine, rural areas inneighbouring Belarus were affected by the Chernobyl incident., Authoritiesthere have also considered the use of hemp as a decontaminant. However, it isnot clear if any programs involving hemp were ever implemented.

Hemp and the Decontamination of RadioactiveSoil

The Chernobyl exclusion zone, site of theworld’s worst nuclear disaster, is slowly being returned to health as plantsand animals begin to reclaim the land

Where Else is Hemp Used inPhytoremediation?

In Puglia, Italy, industrial hemp is beingused on a wide scale to assist in the decontamination of some of Europe’s mostpolluted soils. The Ilva steel plant, the largest of its kind in Europe, haspoisoned local soil, plants, animals, and human residents for decades with itstoxic emissions. Within a 20km radius of the plant, grazing livestock isprohibited.

Since 2012, when the extent of the crisisbecame apparent, farmers have planted millions of cannabis plants in an effortto decontaminate the soil. In that time, the local area of hemp cultivation hasincreased from 3 to 300 hectares. Around 100 farmers are growing hemp, and themovement has even proved to be an economic stimulus. A new hemp processingplant has opened to convert the harvest into fibre for clothing andconstruction.

Since the devastating Fukushima Dai-ichinuclear power plant accident in 2011, there have been calls for Japan toimplement hemp phytoremediation. However, due to the Cannabis Control Lawforced into Japanese law by the occupying U.S. powers in 1948, hemp may only begrown under license – and these are highly restricted and difficult to obtain.

A few months after the incident, Fukushimaresidents began to plant millions of sunflowers, as well as field mustard andamaranth, in an attempt to soak up cesium and other toxins from the soil. TheJapan Aerospace Exploration Agency also began an experimental project involvingsunflowers in 2011, and various projects since have investigated algae,buckwheat and spinach for their uptake abilities. But it seems that hemp hasnot been utilized to date.

Research Into Hemp as a Soil Decontaminant

There is extensive research into theability of hemp to act as a phytoremediator. An Italian study published inPlant and Soil in 2003 showed that hemp had the ability to absorb cadmium,chromium and nickel from soil, and that high concentrations of the heavy metalshad little effect on plant morphology.

In fact, “an increase in phytochelatin andDNA content was observed during development” of the hemp plants, suggesting“ability to avoid cell damage by activating different molecular mechanisms”.

In 2005, a German study published inBiologia Plantarum concluded that hemp was unaffected by root concentrations ofcadmium as high as 800 mg/kg, but that leaf and stem concentrations of 50 – 100mg/kg “had a strong effect on plant viability and vitality”. This study alsonoted that soil pH affected the rate of cadmium uptake.

In 2010, a Chinese study investigated eightcrops, including hemp, for their ability to uptake zinc. Zinc is a heavy metalthat is beneficial in trace amounts but potentially phytotoxic at higherconcentrations.

According to this study, “all crops, exceptsunflower, could grow quite well under 400–800 mg kg?1 Zn stress”. Hemp showed “small inhibitions in plant growth”, indicating “a strong tolerance to high Zn concentrations”.

Hemp and the Decontamination of RadioactiveSoil

As vegetation slowly reclaims formerlyinhabited areas, adding species such as hemp to decontaminate the soil can aidin ecosystem rejuvenation

Transgenic Hemp Varieties forPhytoremediation

More recently, a Pakistani study publishedin 2015 identified several genes in hemp associated with tolerance of heavymetals including nickel, cadmium and copper. These results may assist in thedevelopment of transgenic hemp varieties with improved ability to uptakemetals.

The use of genetically-modified hemp inphytoremediation projects may not be without precedent. In 2017, the Universityof Virginia announced a collaboration with a biotechnology company known as22nd Century, which “has developed proprietary hemp plants that areparticularly well-suited for use in phytoremediation”.

Phytotech, the biotechnology companyinvolved with the Chernobyl company, used “specially selected and engineeredplants”, although there appears to be little information available regardingthe development of the hemp varieties used.

It is not clear whether these varietieswere developed through marker-assisted breeding or are truly transgenic(involving the transfer of genes from one organism to another), or – in thelatter case – what the potential implications of this would be.

How Can Hemp From Contaminated Soil SitesBe Safely Used?

In 2012, a Romanian study investigated thenutritional safety of hemp seed produced from plants grown in soils containingcadmium, magnesium, iron and various other metals. The study found that fivedistinct Romanian hemp strains developed different nutritional profilesaccording to uptake of the various metals in the soil.

Ominously, all varieties also tested abovethe safe legal limit for cadmium—despite the soil testing within the safelimit. Levels were particularly high in the Armanca and Silvana strains.Cadmium is a toxic heavy metal that can cause various serious healthcomplications. Excessive dietary intake can lead to joint and bone deformities,respiratory illness, anaemia, and kidney failure.

However, in 2009 another Chinese studyshowed that cadmium concentration was 25-29.5 times higher in the roots of hempcompared to the shoots, “suggesting the plant can be classified as a Cdexcluder”.

Thus, even if hemp used to remove cadmiumfrom contaminated soil is unsafe for consumption, its fibre can still be usefulfor textile and construction applications. As well as this, hemp biomass can beused in a number of other industrial applications, such as for biofuel.

Hemp could benefit hundreds of thousands ofcontaminated sites

As a proven, valuable tool in the fight torepair human-inflicted damage to our soils and ecosystems, hemp couldpotentially benefit hundreds of thousands of sites across the globe. It isestimated that in the USA alone there are 30,000 sites requiring remediation.

For many years, US restrictions on hempcultivation precluded any large-scale operations from being implemented.However, now that restrictions on hemp cultivation are lifting in many USstates, this situation is changing.