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Cannabis and Heavy Metal: It’s Deeper Than You Think As Study Shows Potential for Hemp in Cleaning Toxic Old Mines

Cannabis pulls toxins from the Soil

Cannabis can be used to clean up acid waste and heavy metals from abandoned mine dumps.

Wits University master’s student Tiago Campbell, has demonstrated how planting hemp on old mine dumps pulls the toxicity out of the soil.

He says a programme of hemp mine rehabilitation could open up new areas for human settlement in Gauteng and the Free State where abandoned mines pose a threat to the environment.

Campbell says the hemp could then be processed into building material as it would be unfit for human or animal consumption.


The polluted areas are within the Witwatersrand Basin, one of the world’s largest gold deposits that stretches for 400 kilometers through the Gauteng, Free State, and North West provinces.

South Africa’s Federation for a Sustainable Environment said there are at least 380 abandoned mining areas in Gauteng Province containing “elevated levels of toxic and radioactive metals” including arsenic, cadmium, cobalt, copper, zinc and uranium.


Campbell’s initial findings were published in Hemp Today on 11 November 2021.

His research so far has confirmed hemp as a “heavy metal hyper-accumulator” in comparison to other plants studied for their phyto-remediation potential – Indian mustard, water hyacinth, alfalfa and sunflower. The “hyper-accumulator” characteristics of hemp were proven in cleanup efforts in the 1990s when Ukraine’s Institute of Bast Crops documented the plant’s ability to absorb heavy metals such as lead, nickel, cadmium, zinc and chromium in the Chernobyl nuclear fall-out zone.


Irresponsible mining has left a polluted legacy

Campbell says that in South Africa, 130 years of irresponsible mining practice have resulted in acid mine drainage and concentrations of runoff of heavy metals known to be hazardous to human health and wildlife.

He said harvested hemp containing the pollutants could not be used for food or other products intended for human consumption, but could be suitable as raw material for other secondary products such as bioplastics, textiles and construction materials.

(Italian researchers have suggested, for example, that hurd from hemp planted to cleanse the soil of heavy metals can be considered safe for building material such as hempcrete, and that biomass from phytoremediation efforts could be an energy source.)


The U.S. Environmental Protection Agency has estimated the cost of phytoremediation as a technique for removing hazardous heavy metals from soil ranges from 20-50% of outlays required for conventional methods that employ physical, chemical or thermal technologies. 


Campbell’s project, which also includes the study of plant growth and genetics, is being funded by the University of the Witwatersrand.


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