C·I·B researchers at the University of the Witwatersrand
recently demonstrated that the invasive aquatic weed, water hyacinth (Eichhornia crassipes), can be used to remove metal pollutants
from water. Through a process called phytoremediation — literally a “green” technology — plants are used to remove
pollutants from the environment by absorbing them into their roots.
Solomon measuring the removal of metal salts from water by the invasive weed, water hyacinth
(Eichhornia crassipes) (Photo credit: Solomon Newete)
Water hyacinth is characterised by fast growth and despite being a notorious and aggressive invader, it has been widely
researched as a potential agent for phytoremediation. Its efficiency, however, relies on the type of contaminant, concentration and eventual
storage site in the plant tissues.
In the study, C·I·B researcher, Marcus Byrne
and post-doctoral fellow, Solomon Newete, performed a series
of experiments on water hyacinth to see whether it is able to remove metal salts from water; where it stores the metal pollutants and how it
responds to metal toxicity. Experiments were conducted as single element trials with one each for gold (Au), copper (Cu), iron (Fe),
mercury (Hg), manganese (Mn), Uranium (U) and zinc (Zn).
The results showed that over 80% of the metal contaminants in the water were removed by water hyacinth. Up to 98% were
accumulated in the roots, of which 30% - 52% was adsorbed to the root surface.
“Tolerant plants retained most of the heavy metals in their roots, where the toxicity is minimal, while others
reduce the metal toxicity in the shoots by excreting the cations. This is a strategy by which water hyacinth avoids toxic metals reaching the
more susceptible shoots,” explains Solomon, lead author of the paper published in the journal
Environmental Science and Pollution Research.
Bioconcentration is a process by which the quantity of a chemical in an aquatic organism exceeds that of its concentration in
the water surrounding that organism. The bioconcentration factor of copper (Cu), mercury (Hg), gold (Au) and zinc (Zn) in the study exceeded
1 000, meaning that water hyacinth is a hyper accumulator with regards to these metals. The study found that water hyacinth was generally
tolerant to all the metal contaminants, except for copper (Cu) and mercury (Hg).
“Although water hyacinth has the potential for many phytoremediation roles, this must be weighed up against its ability
to invade waterways,” says Solomon “knowing whether metals are adsorbed, or assimilated in the plant and their allocation
between the roots and shoots will inform decisions how to re-treat the biomass for metal recovery, or safe disposal after phytoremediation.”
Click here to read the paper in
Environmental Science and Pollution Research
Newete, S.W., Erasmus, B.F.N.,
Weiersbye, I.M. and Byrne, M.J. 2016. Sequestration of precious and pollutant metals in biomass of cultured water hyacinth (Eichhornia
crassipes). Environmental Science and Pollution Research 23: doi:10.1007/s11356-016-7292-y
Click here for a related
article by Solomon Newete in Biological Control
Newete, S.W., Erasmus, B.F.N.,
Weiersbye, I.M. and Byrne, M.J. 2016. The effect of water pollution on biological control of water hyacinth. Biological Control.
Volume 79, Pages 101–109. http://dx.doi.org/10.1016/j.biocontrol.2014.08.006
For more information, contact Solomon Newete at Solomon.Newete@wits.ac.za