Following a 37-year academic career at Sheffield University, Alan Baker was Professor of Botany (Ecology and Environmental Science) at the University of Melbourne, Australia, from 2000 until 2008. He now lives back in the UK but continues his active engagement with many research institutions around the world.
It was while at Sheffield that his interest in the relationship between plants and metals was sparked by the many old mine workings in the Peak District.
Some plants, which grow near mines, absorb lead or copper from the soil and the toxicity kills them. Other plants are resistant to the metals and continue to grow. These plants are called metallophytes.
Other metals, which are absorbed by metallophytes, are cobalt, nickel, manganese, zinc, and some metalloids such as arsenic and selenium are also absorbed by some plants. Alan showed us pictures of a plant in New Caledonia which had its bark slashed. A bright blue liquid ran out of the slash. This showed that sap in the plant was saturated with nickel.
The metals are absorbed by the roots from the soil, transported to the shoots in the xylem and dumped in the leaves of the plants.
It seems that the roots actually seek the contaminated soil. A lab test was done using a planter in which the left half contained soil with a high zinc concentration and the right half contained normal soil. A plant was put in the middle and left to grow for some weeks then was uprooted.
The left half showed many more roots that the right half as if the plant favoured the zinc soil and sent more roots in its direction.
Examination of plants that were often eaten by caterpillars showed holes in the leaves of plants grown in normal soil, but no holes in the leaves of plants grown in high zinc concentration soil. It seems as if the plants chose to absorb the zinc to protect themselves from caterpillars.
Trials have been carried out on plants to see which have a high metal uptake and also which have a multiple metal uptake. The reason was to grow many of these plants in order to use them to decontaminate the land around old mines and it has been very successful in China, removing arsenic and zinc in some areas.
They also wanted to know how many years it would take before the land was fit to grow other plants.
In other places thy have tried to grow metallophytes to absorb metals from the land in order to “mine” metals. They have collected seeds and planted hundreds of plants around metal-contaminated areas to see if they can get enough leaves to put in a smelter to produce the metals. Apparently there has been some small success so it may become commercially possible!
This could be used to make metals like platinum and gold if the right metallophytes could be found and grown in sufficient quantity in the right place.