This article published in the Journal of Ecobiology describes the technique of phytoremediation, which is increasingly being adopted wherein certain plants are used to adsorb or degrade the pollutants from soil and water.

The discharge of heavy metals in the environment has been a matter of concern with rapid industrialization and intensification of agricultural activities over the last few decades. The pollutants are introduced into the environment without appropriate treatment in most localities. Heavy metals released into the environment today come from uncontrolled emissions by metal smelters and other industrial activities, unsafe disposal of industrial wastes and lead in water pipes, paint  and gasoline.

Heavy metals that are hazardous are lead, mercury, cadmium, arsenic, copper, zinc and chromium. Such metals are found naturally in the soil in trace amounts. Increased concentrations due to anthropogenic activities in particular areas pose serious threat to all living organisms. Arsenic and cadmium, for instance, can cause cancer. Mercury can cause mutations and genetic damage, while copper, lead, and mercury can cause brain and bone damage.

Metal ions are commonly removed from dilute aqueous streams through chemical
precipitation, reverse osmosis and solvent extraction. These techniques have disadvantages such as incomplete metal removal, high reagent and energy requirements, generation of toxic sludge or other waste products that again require disposal.

The search for alternate and innovative treatment techniques has focused attention on the use of biological materials for heavy metal removal and recovery technologies (Biosorption) and has proved efficient in the removal of heavy metals and economically viable compared to conventional treatment.

Phytoremediation is a general term used to clean up contaminants using plants, or remediate sites by removing pollutants from soil and water. Plants can break down or degrade organic pollutants or contain and stabilize metal contaminants by acting as filters or traps. Phytoremediation involves growing plants in a contaminated matrix, for a required growth period to remove contaminants from the matrix or facilitate immobilization or degradation (detoxification) of the pollutants. The plants can be subsequently harvested, processed and disposed off in an environmentally sound manner.

The article argues that the development and application of phytoremediation as
an environmentally sound technology however, involves a number of challenges
that include capacity building and establishment of regulatory framework. Mostly, there is a lack of data, performance standards and cost-benefit analysis regarding phytoremediation technologies. Hence there is a need for:

• More research on appropriate phytoremediation technologies and techniques applicable to different geographic regions with varied climatic conditions
• More research on site characterization, clean-up and technology selection criteria
• Need for evolving assessment and evaluation methods that can determine the applicability of various phytoremediation techniques
• Capacity-building on the planning and implementation of phytoremediation technology.