Looking for crop that can tolerate heavy metal
UNIVERSITY of the Western Cape (UWC) research helps combat the impact of metals in soils. Next time you use a good quality pair of pliers or a spanner, take a closer look at what it’s made from. Chances are, it will be steel, strengthened with vanadium.
South Africa is home to the world’s biggest known supply of vanadium, and second only to China as a current producer of this heavy metal. Unlike many other metals and minerals, vanadium is not mined by itself, it is found in areas with rich iron ore deposits and is a by-product of the mining process.
But not all the by-products of mining are equally beneficial. As other metals and minerals are mined, acid mine drainage changes the pH of rivers, streams and soils and releases the vanadium.
What happens next is the subject of study by Dr Marshall Keyster, deputy head of UWC’s Department of Biotechnology. The research was funded by the Centre of Excellence in Food Security’s Innovation Programme headed by the university’s Professor Ndiko Ludidi.
“Acid mine drainage makes vanadium soluble, and that means it is present in the soil in quantities that have an effect on the crops that are grown and on our food safety. And it does not just affect the areas around the mines. Research has shown vanadium is present in the Cape Town aquifer,” he said.
Although there are some laws regarding the presence of metals such as vanadium in drinking water, there is currently no legislation to determine an acceptable limit to the amount of vanadium in the country’s soils.
Keyster and his team have been investigating different canola cultivars to establish if any would be suitable to be used as phyto-remediation for soils with high banadium levels.
“Research indicated that members of the Brassica family were potentially efficient in phyto-remediation,” he said.
“We conducted experiments with two contrasting Brassica napus – rapeseed or canola – genotypes (Agamax and AV Garnet). We assessed both the impact of vanadium on plant growth and development, as well as the ability of the plants to store vanadium in their roots and leaves.”
The ideal phyto-remediation candidate would be a plant that keeps harmful materials in its roots rather than transporting them to the leaves or seeds. This would mean that, in the case of an important food crop such as canola, the farmer would potentially be able to harvest (while) remediation was under way.
“We found that the Agamax had a greater tolerance to vanadium stress,” he said. “It held a much higher amount of the metal in its roots compared to AV Garnet.
“Our conclusion was that AV Garnet could be used for remediation only, but that Agamax was a better candidate for both remediation and food production. We need to do further research to determine the cycle of remediation versus crop years, but Agamax would potentially be able to produce a safe crop and be used for phytoremediation at the same time.”