Similar to
phytoremediation but more profitable, this is the use of plants to
purify metals. Recovering from land that is impregnated with metal ions is a costly and time consuming effort. By planting
modified trees that absorb the metals and concentrate them in their leaves you can do the same job more quickly and efficiently.
This might seem an odd ability to put into a plant, but many metals that are needed by plants can be absorbed by the roots. Changing the specificity of the transporter is not too hard, and pathways for internal transport already exist. Alternatively, in the case of gold, the metal accumulatees in the soil around the roots and can be more easily removed by soil extraction.