Phytoextraction
Phytoextraction involves plants uptaking pollutants from soil, water, or sediments by their roots and transferring them to aboveground biomass where they accumulate, such as in shoots or other harvestable parts PubMed Central. This is also known as phytoaccumulation, and represents one of the most studied phytoremediation approaches. Hyperaccumulators sequester high concentrations of heavy metals in aerial parts through enhanced active metal transport ScienceDirect. The underlying process is complex: it involves enhanced translocation across biological membranes, including transport through cytoplasmic membranes and uploading/unloading of xylem vessels PubMed Central.
There is rapid and active translocation of heavy metals to the shoot via the xylem, which is upregulated by transpiration, and metals are detoxified through complexation with amino acids, organic acids, or metal-binding peptides and sequestered into vacuoles ScienceDirect. Hyperaccumulating plants can contain more than 1% of a metal in their dry biomass Nature, and the contaminants are physically removed from the environment when plants are harvested. It is even possible to extract metals from harvested biomass in a process termed phytomining Nature. However, the main limitation is low biomass production of many natural hyperaccumulators PubMed Central.
Suitable species vary by target metal. Alpine Pennycress (Thlaspi caerulescens) is effective for Zn, Cd, and Ni hyperaccumulation, whilst Indian mustard (Brassica juncea) can accumulate Cd, Pb, Cu, Cr(VI), Zn, Ni, and Se ScienceDirect. For arsenic contamination, Pteris vittata is notable as a hyperaccumulator, capable of accumulating up to 20 mg per gram of dry weight ScienceDirect. The technique is primarily used for heavy metals including Cd, Zn, Ni, Cu, Pb, As, and Se.