Question:

I’ve just been reading about the advantages of short rotation in issue 8 of Alternatives; one being the ability of some plants to fix heavy metals. Which plants are these and are they able to fix lead, cadmium, etc.? How can we recover these heavy metals? Aren’t we cleaning up one form of pollution to create another?

Answer:

The trees that do the best job of fixing heavy metals are willows, poplars and eucalyptus. Cultivated plants include reeds and certain herbaceous varieties (especially Thlaspi caerulescens, commonly known as alpine pennycress). For example, these plants can concentrate up to 3% of their weight of heavy metals like cobalt, lead and nickel, but only 0.01% of cadmium. Absorbed via the roots, these metals concentrate in the above-ground stems and leaves, and can be recovered by burning them in facilities that generate no secondary pollution. Between 2 and 13 kg of metals can be extracted from one hectare of land in the space of one year using this method.