lable at ScienceDirect

Environmental Pollution 158 (2010) 18–23

Contents lists avai

Environmental Pollution

journal homepage: www.elsevier .com/locate/envpol

Commentaries

Knowledge explosion in phytotechnologies for environmental solutions

M.N.V. Prasad a,*, Helena Freitas b, Stefan Fraenzle c, Simone Wuenschmann d, Bernd Markert c,d

a Department of Plant Sciences, University of Hyderabad, Hyderabad, 500046, Indiab Centre for Functional Ecology, Department of Botany, University of Coimbra, 3001-456 Coimbra, Portugalc International Graduate School (IHI) Zittau, Chair for Environmental High Technology, Zittau, Germanyd Fliederweg 17, D-49733 Haren-Erika, Germany

Bioremediation using biotechnology and biodiversity - a multiscale ap

proach.

a r t i c l e i n f o

Article history:Received 25 July 2009Accepted 28 July 2009

Keywords:PhytotechnologiesBioremediationApplicabilityAssessmentOrganicInorganicContaminantsPollutantsPlant–endophytesXenobioticsPharmaceuticals

* Corresponding author.E-mail address: prasad_mnv@yahoo.com (M.N.V. P

0269-7491/$ – see front matter � 2009 Elsevier Ltd.doi:10.1016/j.envpol.2009.07.038

environmental biotechnology and is not to be confused withbiodegradation, which tackles the biological bases of the (mostly

Bioremediation (i.e., green technologies or phytotechnologieswhen relied upon plants) mainly deals with biological interventionsaimed at environmental contamination assessment and alleviatingpollution. Both industrialization and natural resource extractionresulted in the release of large amounts of toxic and wastecompounds into the biosphere. These pollutants belong to two mainclasses: inorganic and organic ones. According to EEA (EuropeanEnvironment Agency) estimates 1.4 million areas are contaminated(Puschenreiter and Wenzel, 2003). In India alone there are about20,000 abandoned mine sites covering about 60 different kinds ofminerals. Biological interventions mediated by some wide array ofbiological species (none of which will be able to ‘‘remove every-thing’’) can be used to remove unwanted compounds from thebiosphere, thus contribute significantly to the fate of toxic spills.

Phytotechnologies deal with the use of plants in pollutioncontrol and removal as well as on aspects related to plants frompolluted environments as a source of food, fodder, fuel and fertil-izer. Plants are able to indicate, exclude, accumulate,

rasad).

All rights reserved.

hyperaccumulate or metabolise toxic inorganic or organicsubstances. Thereby they contribute significantly to the fate ofchemicals, and they can be used to remove unwanted compoundsfrom the biosphere. On the other hand, chemicals can enter thefood chain via plants, which cause unwanted/causing harmfuleffects (Schroeder and Schwitzguebel, 2004).

As of May 2009, about 10,684 articles have been published onvarious aspects of bioremediation starting with only 11 in 1989(Fig. 1). Thus, there has been a steep rise in scientific investigationsand a real knowledge explosion in green technologies. An envi-ronmental watchdog survey revealed that Russia, China and Indiaare among the ‘‘top ten’’ most polluted places/countries in theworld (Anonymous, 2007). In the developed nations as well asdeveloping nations there have been several convincing evidencesfor applications of green technologies.

Therefore, the field of bioremediation belongs to the realm of

bacterial) metabolism of unusual and/or recalcitrant compounds.Depending on the degree of such intervention, bioremediation isgenerally considered to include natural attenuation (which entailslittle or no human action), or bio-stimulation (requiring addition ofnutrients, and electron donors/acceptors to promote the growth ormetabolism of certain micro-organisms), or bio-augmentation, thedeliberate addition of natural or engineered micro-organisms withthe desired catalytic capabilities.

Bioremediation is exploitation of biological interventions ofbiodiversity for purposes of mitigation (and wherever possiblecomplete elimination) of the noxious effects caused by environ-mental pollutants in a given site (Fig. 2). If the process occurs in thesame place which was afflicted by pollution then it is called in situbioremediation. In contrast, deliberate relocation of the contami-nated material (soil and water) to a different place to intensifybiocatalysis, is referred to as ex situ treatment. Biodiversity is theprecondition for bioremediation. Quite a variety of plants, natural,transgenic, and/or associated to rhizosphere micro-organisms areextraordinarily active in these biological interventions cleaning uppollutants by removing or immobilizing. Diverse microbes are themost active agents, fungi and their strong oxidative enzymes arekey players in recycling recalcitrant polymers and xenobioticchemicals as well (Loeffler and Edwards, 2006; Kawahigashi, 2009).

Fig. 1. Articles published on bioremediation based on www.sciencedirect.com.

Fig. 3. Beneficial use of plant metal interactions: a) phytoremediation, b) bio-fortification of food crops, and c) phytomining. The desirable traits are high toleranceto contaminants, hyperaccumulation, wide ecological amplitude, easy management,economics and value additives, fast-growing and high biomass producing plants, suchas Salix and Populus spp. Indicator: Plants in which uptake and translocation reflect soilmetal concentration and exhibit toxic symptoms. Accumulator: Plants in which uptakeand translocation reflect soil metal concentration without showing toxic symptoms.Excluder: Restricted uptake of toxic metals over a wide range of soil metal concen-tration. Hyperaccumulator: Plants in which metal concentration is up to 1% dry matter(this is metal dependent, most often Ni or Zn) (Baker, 1981; Markert, 1996).

M.N.V. Prasad et al. / Environmental Pollution 158 (2010) 18–23 19

Phytoremediation can be used in combination with othertraditional and innovative remediation technologies. Cleanup canbe accomplished to certain depths below ground level, within thereach of plants’ roots. Such sites need to be maintained (watered,fertilized, and monitored). Phytoremediation may yet be slowerthan mechanical cleanup methods such as excavation and properdisposal and is limited to soil depths that are within the reach ofplants’ roots. Phytoremediation can, however, be used in combi-nation with other remediation technologies.

Plant physiology, agronomy, microbiology, hydrogeology, andengineering are combined to select the proper plant and conditionsfor a specific site. Phytoremediation is a procedure that can reduceremedial costs, restore habitat, and cleanup contamination in placerather than entombing it in place or transporting the problem toanother site.

Fig. 2. Selected bioremediation processes involving some wide scale of biodiversity (for morand Schnoor, 2003).

Phytoremediation is the use of certain plants and trees to cleanupsoil and water contaminated with metals and/or organic contami-nants such as solvents, crude oil, and polyaromatic hydrocarbons(PAHs). Phytoremediation is an aesthetically pleasing, solar-energydriven, passive technique that can be used along with-or, in somecases, in place of-mechanical cleanup methods at sites with shallow,low-to-moderate levels of contamination.

Thus, phytoremediation of contaminated environment offers anenvironmentally friendly, cost effective, and carbon neutral approachfor the cleanup of toxic pollutants in the environment. Plants withabilities to hyperaccumulate, accumulate, exclude and indicate heavymetals are important in environmental remediation (Fig. 3).

e details on transformation, control and containment of contaminants see McCutcheon

Fig. 4. Biogeochemical processes and enhanced remediation to mitigate environmental contaminants and pollutants.

M.N.V. Prasad et al. / Environmental Pollution 158 (2010) 18–2320

Plants with ability to take up volatile organic compounds, andsequester pollutants have been proposed as a solution to thetreatment of toxic contamination in situ. However, the use of plant-based technologies has a number of limitations, primarily due tothe fact that plants are autotrophic and not ideally suited for themetabolism and breakdown of organic compounds. One of themajor limitations with current phytoremediation is the often slowtime-scale for remediation to acceptable levels and also toxicity to

Fig. 5. Plant–rhizosphere interactions including plant–endophytes relationships in environ

the plants themselves. To some extent, this can be addressedthrough interactions with the natural microflora associated withplants; endophytic bacteria, rhizosphere bacteria and mycorrhizaehave been shown to have the potential to degrade organiccompounds in association with plants (Dowling and Doty, 2009;Weyens et al., 2009) (Figs. 4–6).

The use and transformation of over 100,000 individualcompounds whose current locations are largely unknown have

mental decontamination (for more details see Ryan et al., 2008; Weyens et al., 2009).

Fig. 6. Detoxification of xenobiotics. Pharmaceutical residues are common contaminants of ground water in many cities (based on COST action 859, Szeged April 2009 workshoppresentations).

M.N.V. Prasad et al. / Environmental Pollution 158 (2010) 18–23 21

resulted in the establishment of new fields of research, which haveone thing in common: they link ecological, physiological, andchemical/analytical lines (Markert, 1996; Markert et al., 2008). Thiscomplex system of interactions and interrelations requires inten-sified efforts to provide integrated information on the status anddevelopment of environmental quality. Bioindicators and bio-monitors have proven to be excellent tools in many of these casesand could provide information which cannot be derived fromtechnical measurements alone (Markert et al., 2003; Prasad, 2008).

Fig. 7. Degradation of pharmaceuticals (and other organic compounds) capable of or meanronment along wastewater disposal and cattle breeding. In the very end, compounds wh[ethinylestradiol]). (based on COST action 859, Szeged April 2009 workshop presentations)

Bioindicators and biomonitors yield extensive information. Thus anincreasing knowledge of ecology gave way to the insight thatorganisms, cells and subcellular compounds likewise can be used asindicators for ecosystem qualities and for assessment of the impactof environmental stress on the composition and functioning ofecosystems. Indicators can be used to assess (environmental)quality, but also to investigate trends, e.g. monitoring systems withmeasurements to be repeated in time, what is of highest interestwith respect to any phytotechnological method in use.

t to attack micro-organisms including those in soil after their disposal into the envi-ich are refractory may show in drinking water again (including steroids such as EE2.

Table 1Selected enzymes capable of degrading organic contaminants (Husain et al., 2009).

Enzyme Target pollutant Examples of plants

Dehalogenase Chlorinated solvents Populus, Myriophyllumspicatum Nitella, Spirogyraand Anthoceros

Laccase Explosives Nitella, Myriophyllum spicatunNitroreductase Explosives Populus, Myriphyllum spicatum,

Lemna minor, NitellaPeroxidase Phenols Armoracia rusticanaPhosphatase Organophosphates Duckweeds

Cytochrome P450 Xenobiotics (PCBs) Brassica sp.

Fig. 9. Scope and limitations of bioremediation – the hierarchy of complexity (DeLorenzo, 2008; Van Aken, 2009).

M.N.V. Prasad et al. / Environmental Pollution 158 (2010) 18–2322

Biotechnology and systems biology approaches are gainingconsiderable importance in fostering bioremediation (De Lorenzo,2008; Van Aken, 2009). It is strongly believed that there are threedimensions for the effectiveness of vital bioremediation process,i.e., chemical landscape (nutrients-to-be, electron donors/acceptorsand stressors), abiotic landscape and catabolic landscape of whichonly the catabolic landscape is ‘‘genuinely’’ biological. The chemicallandscape has a dynamic interplay with the biological interventionson the abiotic background of the site at stake. This includeshumidity, conductivity, temperature, matrix conditions, redox (O2)status, etc. (De Lorenzo, 2008).

Conventionally the efficacy of bioremediation has been determinedchemically, by measuring changes in total pollutant concentrationsusually by an assemblage of sophisticated instruments. However,recently attempts have been made to use biosensors, especiallymicrobial whole-cell biosensors to monitor pollution (Fig. 7).

Information is encoded in DNA (desoxyribonucleic acid) andtransferred through RNA (ribonucleic acid) to ribosomes to makeproteins or enzymes which are used to operate systems within theorganism. In this regard enzymes are responsible for the degrada-tion of organic contaminants which is used by the bacterial cell toproduce both the building blocks of life and energy. The degrada-tion of any organic molecule, including contaminants, requires theproduction and efficient utilization of enzymes (Table 1), as a rule.

Fig. 8. Knowledge explosion in the field of bioremediation – progressing fields of advanced research.

M.N.V. Prasad et al. / Environmental Pollution 158 (2010) 18–23 23

In some instances, degradation is merely a complex oxidation/reduction reaction. The electrons or reducing equivalents(hydrogen or electron-transferring molecules) produced must betransferred to a terminal electron acceptor (¼TEA, bacteria aregrouped into three categories, namely aerobes, facultative aerobes/anaerobes and anaerobes). Herbicide phytoremediation usingtransgenics is one of the most successful examples. Transgenicplants engineered for the transformation of explosives and meta-bolic path way engineering for degradation of xenobiotics are inprogress (Van Aken, 2009).

Much progress has been made in the field of bioremediation inEurope and North America. The costs, benefits and residual risksthereafter need to be investigated to present the final outcome tothe decision makers. Further, particularly countries with vastbiodiversity and high environmental pollution must implementand evaluate the exciting and feasible biotechnological options. Theobvious approach to address some of the aforesaid limitations is theapplication of recombinant DNA technology to express specificgenes from heterotrophic organisms such as bacteria and mammalsto increase plant tolerance for metabolism of organics and decon-tamination of inorganics such as toxic trace metals (Figs. 8 and 9)(Scow and Hicks, 2005; Singh et al., 2008; Wood, 2008; Abhilashet al., 2009; Ruiz and Daniell, 2009).

Financial support through the Department of Science & Tech-nology (DST), Government of India, New Delhi (DST/INT/PORTUGAL/PO-22/04/16-7-2007) (to MNVP) and GRICES (FCT),Lisbon (to HF) in the frame work of the India–Portugal joint pro-gramme of cooperation in science and technology is gratefullyacknowledged. Part of this work has been carriedout with thefinancial assistance provided to MNVP by the Ministry ofEnvironment and Forests, Govt. of India, New Delhi [F.No.19/80/2008 RE dt 3-10-2008].

References

Anonymous, 2007. The world’s top ten most polluted places. The New Scientist 195(2622), 5.

Abhilash, P.C., Jamil, S., Singh, N., 2009. Transgenic plants for enhanced biodegra-dation and phytoremediation of organic xenobiotics. Biotechnology Advances27, 474–488.

Baker, A.J.M., 1981. Accumulators and excluders-strategies in the response of plantsto heavy metals. Journal of Plant Nutrition 3, 643.

De Lorenzo, V., 2008. Systems biology approaches to bioremediation. CurrentOpinion in Biotechnology 19, 579–589.

Dowling, D.N., Doty, S.L., 2009. Improving phytoremediation through biotech-nology. Current Opinion in Biotechnology 20, 204–206.

Husain, Q., Husain, M., Kulshrestha, Y., 2009. Remediation and treatment oforganopollutants mediated by peroxidases: a review. Critical Reviews inBiotechnology 29 (2), 94–119.

Kawahigashi, H., 2009. Transgenic plants for phytoremediation of herbicides.Current Opinion in Biotechnology 20, 225–230.

Loeffler, F.E., Edwards, E.A., 2006. Harnessing microbial activities for environmentalcleanup. Current Opinion in Biotechnology 17, 274–284.

Markert, B. (Ed.), 1996. Instrumental Element and Multielement Analysis of PlantSamples – Methods and Applications. John Wiley & Sons, Chichester, New York,Tokyo.

Markert, B., Breure, A., Zechmeister, H. (Eds.), 2003. Bioindicators and Biomonitors –Principles, Concepts and Applications. Elsevier, Amsterdam, New York, Tokyo.

Markert, B., Wuenschmann, S., Fraenzle, S., Wappelhorst, O., Weckert, V.,Breulmann, G., Djingova, R., Herpin, U., Lieth, H., Schroeder, W., Siewers, U.,Steinnes, E., Wolterbeek, B., Zechmeister, H., 2008. On the road from environ-mental biomonitoring to human health aspects: monitoring atmospheric heavymetal deposition by epiphytic/epigeic plants: present status and future needs.International Journal of Environment and Pollution 32 (4), 486–498.

McCutcheon, S.C., Schnoor, J.L. (Eds.), 2003. Phytoremediation – Transformation andControl of Contaminants. Wiley Interscience.

Prasad, M.N.V. (Ed.), 2008. Trace Elements asContaminants and Nutrients, Consequencesin Ecosystem and Human Health. John Wiley & Sons, Chichester, New York, Tokyo.

Puschenreiter, N., Wenzel, W., 2003. Pflanzen als Metall-Schlucker. LandlicherRaum, online – Fachzeitschrift des Bundesministeriums fur Land- undForstwirtschaft, Wien, Osterreich. www.laendlicher-raum.at.

Ruiz, O.N., Daniell, H., 2009. Genetic engineering to enhance mercury phytoremediation.Current Opinion in Biotechnology 20, 213–219.

Ryan, R.P., Germaine, K., Franks, A., Ryan, D.J., Dowling, D.N., 2008. Bacterialendophytes: recent developments. FEMS Microbiol Letters 278, 1–9.

Schroeder, P., Schwitzguebel, J.P., 2004. New cost action launched: phytotechnolo-gies to promote sustainable land use and improve food safety. Journal of Soilsand Sediments 4 (3), 205.

Scow, K.M., Hicks, K.A., 2005. Natural attenuation and enhanced bioremediationof organic contaminants in groundwater. Current Opinion in Biotechnology 16,246–253.

Singh, S., Kang, S.H., Mulchandani, A., Chenm, W., 2008. Bioremediation:environmental clean-up through pathway engineering. Current Opinion inBiotechnology 19, 437–444.

Van Aken, B., 2009. Transgenic plants for enhanced phytoremediation of toxicexplosives. Current Opinion in Biotechnology 20, 231–236.

Weyens, N., van der Lelie, D., Taghavi, S., Vangronsveld, J., 2009. Phytoremediation:plant–endophyte partnerships take the challenge. Current Opinion in Biotech-nology 20, 248–254.

Wood, T.K., 2008. Molecular approaches in bioremediation. Current Opinion inBiotechnology 19, 572–578.