**2.5 Phytofiltration**

Plants absorb soil ionic compounds by their root system through capillary action even at low concentrations. Phytofiltration is a phenomenon where plant roots (rhizofiltration), shoots (caulofiltration), or seedlings (blastofiltration) absorb water along with minerals and pollutants from contaminated or wastewaters [36].

Plants broaden their root system in search of water which deepens in the soil profile. It can establish a network in the root ecosystem. As it mounts up contaminants it aids in regaining the polluted soil and stabilizing soil fertility through the plant exudates. Root exudates often involve in altering the pH of rhizosphere, precipitating ions of heavy metals on plant root and minimizing the movement of heavy metals to underground water. When the roots become saturated, they are harvested and disposed of which minimize the soil contamination but can be dumped from one form to another form. Ideally, plants used for rhizofiltration should have a dense root system, high biomass production, and be tolerant to heavy metal.

In general the terrestrial and aquatic plants can be used for rhizofiltration. Plants cultivated in specific condition achieve biomass with effective root system while other potential submerged organs concentrate on the contaminants, especially heavy metals, radioactive elements and organic pollutants from contaminated water bodies. The plants kept in a hydroponic system absorb the concentrated contaminants when the effluents are passed and 'filtered' by the roots (Rhizofiltration) [17, 37]. Plants with high root biomass or high absorption surface with more accumulation capacity (aquatic hyperaccumulators) and tolerance to contaminants will achieve the best results. Promising examples include *Helianthus annus*, *Brassica juncea*, *Phragmites australis*, *Fontinalis antipyretica* and several species of *Salix*, *Populus*, *Lemna,* and *Callitriche* [38, 39].

Some terrestrial plants such as Indian mustard (*Brassica juncea*) and sunflower (*Helianthus annuus*) have longer, deeper and hairy root systems with good capacities to accumulate heavy metals during rhizofiltration [40, 41]. Unpredictably woody species make easy accumulation of heavy metals in their shoot system above the soil level. Their deep root system, participate effectively in preventing the soil erosion as well as the distribution of the contaminated soil to the surrounding [42]. In this concern biofiltration, bioaccumulation and biomagnification are threats related to the food chain and food web. Because of their in-edible nature this approach prevents the availability and probability of the heavy metals entering into the food chain through trees [43].
