Practice question

Phytostabilization aims to reduce mobility and bioavailability of heavy metals not readily degradable without removing mass, establishing persistent vegetative cover immobilizing pollutants in root zone and preventing off-site migration via wind or water. Tolerant grasses Festuca rubra, Agrostis stolonifera and Buchloe dactyloides plus legumes fix nitrogen achieve stabilization through raising rhizosphere pH via carbonates causing precipitation as hydroxides and phosphates, stimulating sulfate-reducing Desulfovibrio producing sulfide precipitating PbS and ZnS with Ksp 10^-28, binding to root cell wall pectic carboxyl and vacuolar storage as phytochelatin complexes via synthase, accumulation of humic matter complexing metals, and hydraulic control limiting infiltration. Accumulation mainly in roots with translocation factor below 0.1 avoiding grazing chain. Outcome is decreased dust, runoff and leaching to groundwater, suitable for large mine tailings and smelter sites where excavation cost-prohibitive, differing from phytoextraction harvesting metals and phytovolatilization releasing to atmosphere, often implemented with soil amendments lime and compost enhancing immobilization long term.