Dear Joseph,

Not all contaminants are easily treated by bioremediation using microorganisms. For example, heavy metals such as cadmium and lead are not readily absorbed or captured by microorganisms. A recent experiment, however, suggests that fish bones have some success absorbing lead from contaminated soil. Bone char has been shown to bioremediate small amounts of cadmium, copper, and zinc. 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 assimilation of metals such as mercury into the food chain may worsen matters. 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.The heavy metals in the harvested biomass may be further concentrated by incineration or even recycled for industrial use. Some damaged artifacts at museums contain microbes which could be specified as bio remediating agents. The use of genetic engineering to create organisms specifically designed for bioremediation has great potential. The bacterium Deinococcus radiodurans (the most radioresistant organism known) has been modified to consume and digest toluene and ionic mercury from highly radioactive nuclear waste. Releasing genetically augmented organisms into the environment may be problematic as tracking them can be difficult; bioluminescence genes from other species may be inserted to make this easier.

It should be emphasized that bioremediation provides a good cleanup strategy for some types of pollution, but as you might expect, it will not work for all. For example, bioremediation may not provide a feasible strategy at sites with high concentrations of chemicals that are toxic to most microorganisms. These chemicals include metals such as cadmium or lead, and salts such as sodium chloride.

References:

Kris S. Freeman (January 2012). "Remediating Soil Lead with Fishbones". Environmental Health Perspectives.

http://coastguard.dodlive.mil/2012/07/battling-lead-contamination-one-fish-bone-at-a-time/.

Huan Jing Ke Xue (February 2007). "Chemical fixation of metals in soil using bone char and assessment of the soil genotoxicity".

Adam s. "marine Biology and ocenography".

 Meagher, RB (2000). "Phytoremediation of toxic elemental and organic pollutants". Current Opinion in Plant Biology 3 (2): 153–162. 

Jump up ^ Francesca Cappitelli; Claudia Sorlini (2008). "Microorganisms Attack Synthetic Polymers in Items Representing Our Cultural Heritage". Applied and Environmental Microbiology 74: 564–9. 

Olapade, OA; Ronk, AJ (2014). "Isolation, Characterization and Community Diversity of Indigenous Putative Toluene-Degrading Bacterial Populations with Catechol-2,3-Dioxygenase Genes in Contaminated Soils". Microbial Ecology 69: 59–65.

Diaz E (editor). (2008). Microbial Biodegradation: Genomics and Molecular Biology (1st ed.). Caister Academic Press. ISBN 1-904455-17-4. http://www.horizonpress.com/biod.

Lovley, DR (2003). "Cleaning up with genomics: applying molecular biology to bioremediation". Nature Reviews Microbiology 1 (1): 35–44. 

Brim H, McFarlan SC, Fredrickson JK, Minton KW, Zhai M, Wackett LP, Daly MJ (2000). "Engineering Deinococcus radiodurans for metal remediation in radioactive mixed waste environments". Nature Biotechnology 18 (1): 85–90. 

Robert L. Irvine; Subhas K. Sikdar. Bioremediation Technologies: Principles and Practice.

Hoping this will be helpful,

Rafik

It will depend on the specific contaminate and organism.  As mentioned by Rafik above, most bacteria are not used to remediate heavy metals.  If plants are used to uptake heavy metals, the fate of the metal will vary.  For instance, if all of the metals are retained in the roots/rhizomes, the metals will be 'returned' to the soil as the roots decay after the plants die.  If the metals are transferred to the above ground tissues and the plants harvested the plant mass can be disposed of or digested to recover the metals.

Bacteria are typically associated with the degradation of organics.  The extent of the degradation process (partial degradation or complete mineralization) will depend on the contaminant(s) present, concentration, sufficient bacteria, presence of needed nutrients, terminal electron acceptors, etc.  Rarely will one bacteria species be able to facilitate complete degradation of mid to complex structures. 

if its not an organic compound, which might be detoxified, "Phytoremediation is just transporting the problem from one place to another! Phytoremediation is not a solution for pollution but a suitable excuse for abuse of environment!

Thank you for these answers everyone, very much appreciated.

• I appriciate the good suggestions of Dr-Karaman ,Cutright and caution of Dr.Schnug.

Phytoremediation is just a technique of 'removing''pollutants and 'transferring' in plants.

As Dr. Schnug righty quoted, "Phytoremediation is just transporting the problem from one place to another! Phytoremediation is not a solution for pollution but a suitable excuse for abuse of environment!".

This question is very very important because in the wake of sustainable environmental management, everybody is thinking about ways to do bioremediation or biodegradation but rarely do we think about where the cells that have been used to bio-remediate end up and the effects of biodegradation products. I am currently doing a biodegradation experiment myself but one of my objectives will to find out the effects of biodegradation products.

In sewage treatment for example, there are some bacteria that are employed to remove nutrients especially phosphorous from wastewaters to prevent eutrophication in receiving water bodies. These bacteria accumulate the phosphorous in their cells and infact they are called Polyphosphorous Accumulating Organisms (PAOs). But these cells can be harvested after bioremediation and used to make fertilizers for farming..organic farming which again translates to environmental sustainability

On the other hand, I think that microbes, because these are the organisms I am well conversant with, when they accumulate nutrients during the process of bioremediation, they are capable of completely breaking down the absorbed compounds into simpler substances like water and gases as they get their energy from the exergonic processes, and the simple substances that are released can be released into the atmosphere without any harm at all

In continuation to the Dr. Schnug, I want to add that, the phytoremediation approaches should be coupled with some other biophysical techniques, through which we can extract specific heavy metals from roots and (or) shoots for recycling purpose. However, there is a need of research and experimentation to make this true at large scale in cost-effective manner.

I  appreciate  the comments of Drs Aloo and Akhtar. The Bioremediation involving microbes and phytoremidiation involving plants is much researched field as can be seen from a lage number of review articles published on this aspect.Converting bioremediation/phytoremidiation knowledge into technology is a challenge.Bioremediation has been successfully used in decontamination of organic  pollutants including petroleum spills and waste waters(recently there was news paper report of use of bioremediation technique in Ganga water purification).Phytoremidiation is intended for mildly polluted sites.The product from bioremidiating plant like flowers is not intended for animal or human consumption.The phytoremidiation is also spread over a number of years.As mentioned by colleagues the heavy metals  from plant shoot biomass can  be harvested after ignition or other processes.Bioremediation may not be possible for heavy  metal decontamination from soil but it can be used for heavy metal removal from waste waters.One of my colleagues ,Dr.M.C.Manna developed a biofilter loaded with specific microbes to trap heavy metals in waste waters.Of course I agree with Dr.Schnug that we have to pay attention to heavy metal transport in environment and also the toxcity if any of the products of organic pollutants decomposition(but many times the end product may be CO2 and water).