Ni Phytoaccumulation in Mentha aquatica L. and Mentha sylvestris L.

Ni phytoaccumulation in Mentha aquatica L. and Menthasylvestris L., two hydrophytes that had shown high Ni accumulation potential in previous screenings, was evaluated forpossible inclusion in aquatic phytoremediation systems. The plants were grown for 14 days in full-strength (FS) and half-strength (HS) Hoagland's solutions spiked with 1, 2, 4, and8 mg L-1 Ni. Roots and shoots were harvested and analysed for Ni. Ni accumulation and bioconcentration factor (BCF) generally increased with increasing external Ni levels, except for shoot Ni in HS solution at 8 mg L-1, which was lower than at 4 mg L-1. We suggest that a mechanism may exist tocontrol Ni entry to the shoot at high external Ni levels in orderto reduce injury. Ni phytoaccumulation and BCF were consistentlylarger in the HS solution, probably resulting from interaction between Ni and other nutrients, and indicating that manipulationof the nutrient concentration is a possible avenue for improvingthe efficiency of aquatic phytoremediation. Due to their large growth rates and biomass, both species accumulated Ni in the roots to levels equal or superior to those of known phytoremediator plants (8327 for M. aquatica and 6762 mg kg-1 for M. sylvestris), indicating their adequacy foruse in phytoremediation systems.