Hemp science is now advancing in leaps and bounds compared to the stagnation of the previous few decades. One significant area of research that is currently receiving particular attention is phytoremediation, or decontamination of soil—although the fact that hemp decontaminates soil has been known for some time.

Hemp and the Chernobyl Phytoremediation Project

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

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

In response, it was decided that a concerted effort to reduce soil contamination through the use of beneficial plants would be undertaken. This process, known as phytoremediation, was implemented almost immediately.

Which Plants are Useful in Phytoremediation?

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

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

As well as in Ukraine, rural areas in neighbouring Belarus were affected by the Chernobyl incident., Authorities there have also considered the use of hemp as a decontaminant. However, it is not clear if any programs involving hemp were ever implemented.

Where Else is Hemp Used in Phytoremediation?

In Puglia, Italy, industrial hemp is being used on a wide scale to assist in the decontamination of some of Europe’s most polluted soils. The Ilva steel plant, the largest of its kind in Europe, has poisoned local soil, plants, animals, and human residents for decades with its toxic emissions. Within a 20km radius of the plant, grazing livestock is prohibited.

Since 2012, when the extent of the crisis became apparent, farmers have planted millions of cannabis plants in an effort to decontaminate the soil. In that time, the local area of hemp cultivation has increased from 3 to 300 hectares. Around 100 farmers are growing hemp, and the movement has even proved to be an economic stimulus. A new hemp processing plant has opened to convert the harvest into fibre for clothing and construction.

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

A few months after the incident, Fukushima residents began to plant millions of sunflowers, as well as field mustard and amaranth, in an attempt to soak up cesium and other toxins from the soil. The Japan Aerospace Exploration Agency also began an experimental project involving sunflowers in 2011, and various projects since have investigated algae, buckwheat and spinach for their uptake abilities. But it seems that hemp has not been utilized to date.

Research Into Hemp as a Soil Decontaminant

There is extensive research into the ability of hemp to act as a phytoremediator. An Italian study published in Plant 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 metals had little effect on plant morphology.

In fact, “an increase in phytochelatin and DNA 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 in Biologia Plantarum concluded that hemp was unaffected by root concentrations of cadmium as high as 800 mg/kg, but that leaf and stem concentrations of 50 – 100 mg/kg “had a strong effect on plant viability and vitality”. This study also noted that soil pH affected the rate of cadmium uptake.

In 2010, a Chinese study investigated eight crops, including hemp, for their ability to uptake zinc. Zinc is a heavy metal that is beneficial in trace amounts but potentially phytotoxic at higher concentrations.

According to this study, “all crops, except sunflower, 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”.

Transgenic Hemp Varieties for Phytoremediation

More recently, a Pakistani study published in 2015 identified several genes in hemp associated with tolerance of heavy metals including nickel, cadmium and copper. These results may assist in the development of transgenic hemp varieties with improved ability to uptake metals.

The use of genetically-modified hemp in phytoremediation projects may not be without precedent. In 2017, the University of Virginia announced a collaboration with a biotechnology company known as 22nd Century, which “has developed proprietary hemp plants that are particularly well-suited for use in phytoremediation”.

Phytotech, the biotechnology company involved with the Chernobyl company, used “specially selected and engineered plants”, although there appears to be little information available regarding the development of the hemp varieties used.

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

How Can Hemp From Contaminated Soil Sites Be Safely Used?

In 2012, a Romanian study investigated the nutritional safety of hemp seed produced from plants grown in soils containing cadmium, magnesium, iron and various other metals. The study found that five distinct Romanian hemp strains developed different nutritional profiles according to uptake of the various metals in the soil.

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

However, in 2009 another Chinese study showed that cadmium concentration was 25-29.5 times higher in the roots of hemp compared to the shoots, “suggesting the plant can be classified as a Cd excluder”.

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

Hemp could benefit hundreds of thousands of contaminated sites

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

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

The biotech company 22nd Century has stated: “Because there are more than 30,000 sites that require soil remediation in the United States alone, phytoremediation is expected to become a significant area of business for 22nd Century”.

We will continue to follow this topic and will issue more updates as soon as new information becomes available.