When we think of a polluted site, we can only think of removing the pollutants by some mechanical method. But do you know that living organisms can remove pollutants? Yes, bioremediation is the process that uses organisms to remove or neutralize pollutants.

 According to the United States EPA, bioremediation is a “treatment that uses naturally occurring organisms to break down hazardous substances into less toxic or non toxic substances”. The contaminated material can be treated on the site (in situ) or can be taken elsewhere for its treatment (ex situ).

But microorganisms are not capable of removing all kinds of contaminants. Few heavy metals such as Cadmium & lead are not absorbed by microorganisms. The assimilation of metals such as mercury into the food chain causes mercury poisoning. Phytoremediation is useful in these circumstances because natural plants or transgenic plants are able to bioaccumulate these toxins in their above-ground parts, which are then harvested for removal. A recent experiment, suggests that the removals of pollutants (nitrate, silicate, chromium and sulphide) from tannery wastewater were studied in batch experiments using marine microalgae. The heavy metals in the harvested biomass may be further concentrated by incineration or even recycled for industrial use.

Arbuscular mycorrhizal fungi (AMF) can be used to assist phytoremediation of soil hydrocarbon contaminants (Rajtor M, Piotrowska-Seget Z; July 2016). Arbuscular mycorrhizal fungi (AMF) form mutualistic associations with the roots of 80-90% of vascular plant species and may constitute up to 50% of the total soil microbial biomass. AMF have been considered to be a tool to enhance phytoremediation, as their mycelium create a widespread underground network that acts as a bridge between plant roots, soil and rhizosphere microorganisms. Abundant extramatrical hyphae extend the rhizosphere thus creating the hyphosphere, which significantly increases the area of a plant's access to nutrients and contaminants. They focused on

 (1) an impact of hydrocarbons on arbuscular mycorrhizal symbiosis, 

(2) a potential of AMF to enhance phytoremediation, 

(3) determinants that influence effectiveness of hydrocarbon removal from contaminated soils. 

This knowledge may be useful for selection of proper plant and fungal symbionts and crucial to optimize environmental conditions for effective AMF-mediated phytoremediation. It has been concluded that three-component phytoremediation systems based on synergistic interactions between plant roots, AMF and hydrocarbon-degrading microorganisms demonstrated high effectiveness in dissipation of organic pollutants in soil.

Heavy metals can be removed from wastewater by aquatic plants (Rezania S, Taib SM, Md Din MF, Dahalan FA, Kamyab H ; July 2016) . Environmental pollution specifically water pollution is alarming both in the developed and developing countries. Heavy metal contamination of water resources is a critical issue which adversely affects humans, plants and animals. Phytoremediation is a cost-effective remediation technology which able to treat heavy metal polluted sites. This environmental friendly method has been successfully implemented in constructed wetland (CWs) which is able to restore the aquatic biosystem naturally. Nowadays, many aquatic plant species are being investigated to determine their potential and effectiveness for phytoremediation application, especially high growth rate plants i.e. macrophytes. Based on the findings, phytofiltration (rhizofiltration) is the sole method which defined as heavy metals removal from water by aquatic plants. Due to specific morphology and higher growth rate, free-floating plants were more efficient to uptake heavy metals in comparison with submerged and emergent. The following four well known species (hyper-accumulators) were investigated:

1)Pistia stratiotes

 2)Eicchornia spp., 

3) Lemna spp. 

 4) Salvinia spp. 

Limited research is done on bioremediation of heavy metals by plants. Though few species of plants have been identified which can take up heavy metals but it is not mentioned clearly that in which part of the plant the heavy metals will be accumulated, how to harvest those parts & how these metals can be extracted for industrial purpose. Also more terrestrial plant species need to be identified that can take up heavy metals. There is definitely scope for more research in this field.

References:

 1. https://en.wikipedia.org/wiki/Bioremediation

2. Heavy metals removal by diverse aquatic plants species from wastewater 

    Rezania S, Taib SM, Md Din MF, Dahalan FA, Kamyab H  (July 2016)

      http://www.ncbi.nlm.nih.gov/pubmed

3. Arbuscular mycorrhizal fungi (AMF) assist phytoremediation of soil hydrocarbon         contaminants.

   Rajtor M, Piotrowska-Seget Z (July 2016)

    http://www.ncbi.nlm.nih.gov/pubmed