How does marijuana help regenerate the soil?

Marijuana is a plant that finds multiple uses, both medicinal and utilitarian, and it continues to generate controversy. A final study has shown that this plant can be useful for the restoration of soils contaminated by heavy metals.

Also known as hemp (cannabis sativa), this controversial plant which because of its misuse is an addictive drug, nevertheless has proven pharmacological properties. It is also known to be useful as a source of natural fiber for textiles, livestock feed, and even papermaking.

But the most innovative is its use in the field of environmental protection through phytoremediation, which consists of using plants to recover a natural environment disturbed by pollutants. It is a cost-effective and reliable technology for removing a wide range of organic and inorganic chemicals, including heavy metals, as well as radioactive contaminants.

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heavy metals

Contamination of soil and water by heavy metals during the 20th century has become one of the biggest environmental problems. These are substances that persist for a long time in the natural environment because they are not biodegradable or chemically degradable. Some can pass to living beings, accumulate in them and pass from one to another through food relations, integrating into food webs.

The marijuana plant can be very useful in helping to decontaminate environments that accumulate heavy metals. It has been proven that this plant has the property of absorbing and accumulating nickel, lead, cadmium, zinc, copper and chromium in its tissues, especially in its leaves. It has been proven that a single kilogram of plant can accumulate more than 150 milligrams of cadmium, about 123 milligrams of nickel, up to 1.5 grams of copper and up to 4.4 grams of lead.

Of course, the toxicity of these products leads to weaker growth of the plant, which would affect its extraction capacity. Its effectiveness is therefore limited to moderately contaminated soils. There is a limit to the concentration of heavy metals in the soil, depending on the plant, its genetics and the environmental conditions in which it grows, beyond which hemp is no longer viable.

One way to facilitate the extraction of these contaminants by the plant is the application of biodegradable chelating agents. These types of substances are so useful that it has been observed experimentally that by using hemp it is possible to go from just under 130 grams of lead per hectare to more than 26 kilograms.

hemp, cannabis, marijuana, soils, heavy metals, earth, fibers, pharmaceuticals

The role of genetics

Recently, several plant genes related to the ability to grow under heavy metal contamination conditions have been identified.

Specifically, it has been observed that in the presence of heavy metals there is greater expression of two genes, RSG and the PLD𝛼. The expression of these genes induces the production of antioxidant enzymes that protect plant cells from oxidative stress. This work is particularly important under stressful conditions, as free radicals are released from oxygen which can cause serious damage to cells and tissues. These genes are therefore associated with the defense mechanisms of plants against the stress produced by these pollutants.

Genetic manipulation could facilitate the production of strains of marijuana – or other species – with greater genetic expression RSG Yes PLD𝛼, that they can grow better in even more polluted conditions, that they are planted where current varieties do not grow, and that they help eliminate the heavy metals accumulated in these soils.

What to do after?

Removing heavy metals from the soil is a difficult task, which can be greatly facilitated by the use of plants. However, we are left with a problem. What do we do with plants with all this contamination retained in their tissues? Can they themselves be an environmental problem?

Luckily, hyperaccumulator plants — that’s what we call plants that can hold high concentrations of heavy metals in their tissues — tend to taste unpleasant to herbivores, so it’s hard for these metals to end up. in food webs. However, if they die and decompose, they release the metals into the ground and the problem is by no means solved.

However, this problem opens the door to a new solution. It is enough to carry out a good surveillance of the plants and to eliminate them, once they have accumulated the maximum of tolerable contaminant for them. These plant remains, properly treated, can become a source of metals of some commercial value, and be reincorporated into the industrial system, thus reducing soil treatment costs.

REFERENCES:

Ahmad, R. et al. 2016. Phytoremediation potential of hemp (Cannabis sativa L.): Identification and characterization of heavy metal-responsive genes.

CLEAN – Soil, Air, Water, 44(2), 195-201. DOI: 10.1002/clen.201500117

Alufasi, R. et al. 2018, March 9. Potential applications of Cannabis sativa in Environmental bioremediation. A review. 6th Internationally-Involved Scientific Conference on People: Challenges for Science and Education, Slovenia.

Awa, SH et al. 2020. Heavy Metal Removal in Contaminated Soils by the Phytoremediation Mechanism: A Review. Water, air and soil pollution, 231(2), 47. DOI: 10.1007/s11270-020-4426-0

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