Are Lemna spp . Effective Phytoremediation Agents ?

Lemna spp. of the family Lemnaceae have been widely studied for their potential application in phytoremediation. A few Lemna species are already being adopted to enhance natural attenuation for both organic and inorganic pollution in polishing ponds of wastewater treatment facilities, and constructed wetland designed for decontamination of metal pollution. In view of this growing interest, we review in this article the potency and limitation of Lemna species as effective phytoremediation agents. We find that Lemna species have many unique properties ideal for phytoremediation plants species: they are have fast growth and primary production; high bioaccumulation capacity; ability to transform or degrade contaminants; ability to regulate chemical speciation and bioavailability of some contaminant in their milieu; resilient to extreme contaminant concentration; and can be applied on multiple pollutants simultaneously. In addition, they have properties significant for public health likewise livestock production and aquaculture, and ecological function. However, we also find a few important limitations of Lemna as an ideal phytoremediation agent. The plants are small in size and floating in nature. Hence, they are easily blown off the water surface resulting in transferring contamination to uncontaminated sites because Lemna biomass degrades easily thereby readily releasing the contaminant back into the water pathway. This also results in both low sedimentation and contribution to humic material in the benthic. Further, Lemna has very high wet-dry biomass ratios which may be deceiving to believe that they have high bioaccumulation on one hand, while on the other, the energy required to dewater the biomass may be equivalent to conventional treatment plants. Nevertheless, Lemna species remain one of excellent plants for studying process in phytoremediation, and a good phytoextraction agent for application in shallow and small polishing ponds. _____________________________________________________________________________________________________________