coppice willow photo courtesy of http://woodlands.co.uk
Some metals, such as zinc (Zn) and copper (Cu) are micronutrients needed in small amounts by plants, animals and humans alike, for optimum health. Others, such as cadmium (Cd), aluminium (Al) and lead (Pb) are not needed and can be toxic to humans, animals and ecosystems. Thankfully, there are plants called hyperaccumulators that can remove these metals from the soil and store them, usually in the vacuole, out of the way. The accumulated metal serves no apparent purposes to the plant, but some believe (e.g. Rascio and Navari-Izzo 2011) it serves as a defence against natural enemies, such as herbivores.