Certain native plant and grass species can uptake or retain high concentrations of metals, including those toxic to the soil and general environment, Phumudzo Munyai, of the University of Venda, said on October 25, at the 2022 Council for Geoscience Summit in Durban.

She described phytoremediation as “an environment-friendly technique that uses green plants to reduce or remove environmental toxins, primarily those of anthropogenic origin, to restore sites to a condition suitable for private or public use”. 

Having presented a poster that outlined research into the phytoremediation of gold tailings at the Klein Letaba tailings storage facility (TSF), she explained that high concentrations of heavy metals, such as those found at the TSF can lead to metal poisoning through dust inhalation and ingestion. 

Some of the metals identified in her, and others’, research indicate that trace elements such as lead, chromium, arsenic, nickel, copper and cobalt, occur in the tailings, in order of abundance. 

Previous studies at Klein Letaba recommended rehabilitation of the tailings dam to prevent further heavy metal dispersion in the environment.

Munyai explained that the research objectives were to identify the existing plant species growing on the TSF; determine the metal concentration in plants; determine the metal concentration in tailings; and seasonally compare the rate of metal uptake and plant phenology.

Random samples of both the tailings and the surrounding plants were conducted in the summer and winter seasons. Three native plant species were identified, namely, Combretum imberbe, Cynodon dactylon and Sporobolus africanus.

The research noted that metal uptake, in order of abundance was roots, stem, and then leaves, with Combretum imberbe absorbing particularly high concentrations when compared with the grass (Cynodon dactylon) species, in summer. 

In winter, in the plant species, the metal concentration was highest in the leaves, then the stem and lastly the roots, whereas in the grass species, the concentration was higher in the roots, followed by the shoot.

Munyai noted that the study met its objectives in that it determined that the native plants and native species of grass can be deemed “hyper-accumulators as they can uptake high concentrations of metals and store them”.

She explained that this study could lead to an effective means of rehabilitating and stabilising the TSF by using plant species – a relatively cost-effective endeavour compared with other forms of rehabilitation, especially as the plants occur naturally and need not be introduced into the local environment.

Moreover, as they are all native species, they will not adversely affect the ecosystems or biodiversity of the surrounding environment. Ongoing studies will focus on phytomining from these native plant species.