Macrophytes in Phytoremediation of Heavy Metals in Aquatic Ecosystems - An Overview

The discharge of heavy metals into aquatic ecosystems has become a matter of grave concern globally in the last few decades. These pollutants are introduced into the aquatic systems in significant amounts as a result of various industrial operations. The pollutants of concern include lead, chromium, mercury, uranium, selenium, zinc, arsenic, cadmium, gold, silver, copper and nickel, which may be derived from mining operations, refining ores, sludge disposal, fly ash from incinerators, the processing of radioactive materials, metal plating or the manufacture of electrical equipment, paints, alloys, batteries, pesticides or preservatives. Unprecedented pollution in aquatic ecosystems needs eco-friendly cost-effective remediation technology. To this effect, macrophytes are potent tools in the abatement of heavy metal pollution in aquatic ecosystems. They are preferred over other bio-agents due to low cost, frequent abundance in aquatic ecosystems and easy handling. Both the living and dead biomass of aquatic macrophytes can be used for removal of heavy metal contaminants from the aquatic ecosystems. Physico-chemical factors like temperature, pH, light, salinity and presence of other heavy metal may affect the metal uptake.

Aquatic macrophytes usually follow the mechanism of rhizo-filtration for metal removal and are more suitable for polluted water treatment than terrestrial plants because of their faster growth and larger biomass production, relative higher capability of pollutant uptake, and better purification effects due to direct contact with contaminated water. Typha, Phragmites, Eichhornia, Azolla, Lemna, and other aquatic macrophytes are some of the potent macrophytes for heavy metal phytoremediation while Pteris, which grows in moist conditions, is known to be an effective hyperaccumulator for arsenic. Biodiversity prospecting with the objective of finding more effective hyperaccumulators with the ability to accumulate, translocate and concentrate high amounts of toxic elements is recommended for a sustainable green technology.