Hemp probed to wash land in South Africa’s poisonous gold mining areas

A South African researcher is investigating the potential of hemp cultivation to clean the soil in abandoned, heavily polluted former gold mining areas and how hemp cultivation could boost economic development in largely uninhabited regions.

Tiago Campbell, Masters candidate in environmental science at the University of the Witwatersrand, examines the potential for the remediation of land affected by more than 130 years of irresponsible mining practices in areas near Johannesburg in Gauteng Province. Pollution is the result of acid mine drainage and levels of heavy metal runoff, which are known to be dangerous to human health and wildlife.

Legacy of gold mining

The polluted areas are located in the Witwatersrand Basin, one of the world’s largest gold deposits, stretching 400 kilometers through the provinces of Gauteng, Free State and North West. The South African Federation for a Sustainable Environment said there are at least 380 abandoned mining areas in Gauteng province that contain “elevated levels of toxic and radioactive metals,” including arsenic, cadmium, cobalt, copper, zinc and uranium.

Campbell said harvested hemp, which contains the pollutants, cannot be used in food or other products intended for human consumption, but could be useful as a raw material for other secondary products such as bioplastics, textiles and building materials. (For example, Italian researchers have suggested that hemp, grown to cleanse the soil of heavy metals, can be considered safe for building materials like hempcrete, and that biomass from phytoremediation efforts could be a source of energy.)

Clearing the land could also make the generally uninhabited rural areas in Gauteng Province suitable for settlement, Campbell suggested.

‘Hyperaccumulator’

Campbell’s previous research has confirmed hemp as a “heavy metal hyperaccumulator” compared to other plants that have been studied for their phytoremediation potential – Indian mustard, water hyacinth, alfalfa and sunflower. He said nearly 1,000 cannabis plants placed in the soil collected from the polluted countries grew normally in laboratory tests.

The “hyperaccumulator” properties of hemp were demonstrated during clean-up operations in the 1990s when the Ukrainian Bast Plant Institute documented the plant’s ability to absorb heavy metals such as lead, nickel, cadmium, zinc and chromium in the Chernobyl nuclear fallout zone .

The U.S. Environmental Protection Agency has estimated the cost of phytoremediation as a technique to remove hazardous heavy metals from the soil at 20-50% of the cost of conventional methods that use physical, chemical, or thermal technologies.

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