The term "phytotechnologies" broadly refers to the use of plants to address contamination in the environment, including soil, groundwater, surface water, sediment, and waste streams such as leachate, acid mine drainage, and wastewater (Pivetz, 2001)1. Phytotechnologies are considered a green technology (ITRC, 2009; Mench et al., 2010). They are generally less energy-intensive, and less costly and require less operation and maintenance than more active treatment methods, such as excavation or pump and treat (Henry et al., 2013; Pivetz et al., 2001). Plant-based technologies also tend to be an aesthetically pleasing treatment alternative (U.S. EPA, 2004; ITRC, 2009).
Plant-based technologies can be applied to help achieve a remedial objective of contaminant remediation2, containment, or both (ITRC, 2009). Due to the limited reach of plant roots, phytotechnologies are best-suited for addressing large areas of shallow contamination, although some phreatophytes and hybrid approaches have proven effective for treating aquifers at greater depths (USGS 2007; Gestler et al., 2019). Because high levels of contaminants may be toxic to plants and inhibit growth, phytotechnologies are best applied to low and moderate levels of contamination, used with other treatment methods, or applied as a final polishing step (U.S. EPA, 2006). Because plants make take several years to establish and grow, phytotechnologies are not generally selected to address acute risks to human or ecological receptors (Tangahu, et al., 2011).
Phytotechnologies are typically applied in situ (Conesa et al. 2012; Mench et al. 2010) although ex situ applications such as hydroponic systems and constructed treatment wetlands (U.S. EPA, 2004; Horst, et al., 2020; Pittarello et al., 2017; Ali et al., 2020) are available. Plant-based technologies can address a range of organic contaminants including petroleum hydrocarbons, gas condensates, crude oil, chlorinated compounds, pesticides, and explosive compounds, as well as inorganic contaminants such as heavy metals, metalloids, radioactive materials, and salts (ITRC, 2009). In addition, there is ongoing research into the potential of phytotechnologies to treat per- and polyfluoralkyl substances (PFAS) and other emerging contaminants (Huff, et al., 2020; Huff, 2019; Gobelius, et al., 2017; Huang S. and P.R. Jaffe, 2019; Wang et al., 2020).
Many site-specific features, such as the soil, climate, availability of suitable plant species, associated rhizosphere microbes, and types and levels of contaminants, factor into the selection and performance of phytotechnology systems. Systems are designed, installed, and operated to accommodate a site's unique characteristics (ITRC 2009). For example, the suitability of a plant species is determined based on its ability to grow and survive given the soil, contaminants, climate, USDA hardiness zone, altitude, and water availability of the site. In addition, the plant must be able to take up, extract, or treat the contaminants of concern. Other factors-growth rate, habit (perennial, annual, biennial, deciduous, evergreen), form (grass, flowering plant, shrub, tree), rooting depth, disease/pest resistances, tolerances, and the potential to introduce non-native and/or invasive species-must be considered as well (Pivetz, 2001; ITRC 2009).
Six major mechanisms are employed by phytotechnologies to remove, destroy, transfer, stabilize, or contain contaminants:
Typical plants used in phytoextraction (e.g., Indian mustard, Alpine pennycress, sunflowers, ferns, grasses) are most effective in the top one foot of soil because of their shallow root systems and generally slow growth (Mahar et al. 2016). Plants that accumulate contaminants may require periodic harvesting and proper disposal to avoid recontamination of soil when the plants die or drop their leaves (Pivetz, 2001; Suman et al., 2018). Though with the use of plants known as hyperaccumulators (e.g. Sebartia acuminata, alpine pennycress), there is less need for frequent harvesting because these plants are able to withstand the elevated concentrations of contaminants (less phytotoxicity) by accumulating them in their above-ground parts (Suman et al. 2018).
Phytoextraction typically applies to inorganic contaminants, such as metals, metalloids, and radionuclides (Suman et al., 2018), because organic contaminants are more likely to be transformed rather than accumulated within the plant tissue. Testing suggests that phytoextraction can even prove useful for extracting valuable metals for reuse (Corzo Remigio, et al., 2020; Yang, et al., 2017; Anderson, 2013). However, scientists have identified plants that are capable of extracting chemicals, such as chlordane, 2,2-bis(p-chlorophenyl), and 1,1-dichloroethene (1,1-DCE), and storing them in their roots, leaves, and fruits (U.S. EPA 2006).
Phytodegradation typically applies to organic contaminants (Yadav et al. 2018). Uptake is affected by the contaminant's hydrophobicity, solubility, and polarity. Moderately hydrophobic and polar compounds are more likely to be taken up after they have sorbed to plant roots. Chlorinated solvents, herbicides, insecticides, polyaromatic hydrocarbons (PAHs), pentachlorophenol (PCP), polychlorinated biphenyls (PCBs), and munitions constituents can potentially be phytodegraded (U.S. EPA 2006; RTDF 2005; Dixit, et al., 2011).
Phytovolatilization typically is used to treat groundwater but also can treat soluble contaminants in soil. It is applicable to the treatment of volatile organic compounds, although phytovolatilization of inorganic (e.g., selenium, mercury, arsenic) contaminants is possible (Limmer, et al., 2016; Wang, et al., 2012). Simply transferring a contaminant to the air by transpiration may not be an acceptable alternative, and it is preferable that phytodegradation or transformation of contaminants to less toxic compounds occurs prior to transpiration. Note, however, that degradation of some contaminants such as TCE may produce even more toxic compounds (e.g., vinyl chloride) to be transpired (U.S. EPA 2006; RTDF 2005).
Once in the atmosphere, sunlight can photodegrade the transpired compounds. The potential advantages and disadvantages of phytovolatilization must be assessed on a site-specific basis (U.S. EPA 2006; RTDF 2005).
Rhizodegradation is considered "plant-assisted bioremediation." The presence of plant roots moderates soil moisture and increases soil aeration, making conditions more favorable to microbial habitats and thus, bioremediation. Root exudates (substances secreted by the plant) stimulate microbial communities or induce specific enzymes in organisms to enhance rhizodegradation (Dzantor, 2007). The rhizosphere is small, extending about one millimeter from the roots. At any given time, the percentage of soil in the rhizosphere is small and it can take time for new root growth to reach contaminated areas (Pivetz, 2001).
Rhizodegradation may treat soil contaminants amenable to bioremediation, such as petroleum hydrocarbons (Hoang, et al., 2021), PAHs, pesticides, BTEX, chlorinated solvents, PCP, PCBs, and surfactants. Rhizodegradation breaks down contaminants in the soil and, in some cases, completely mineralizes them; thus, plant harvesting and disposal is not necessary. The success of this technique is site-specific, however, and laboratory microcosms may not reflect the microbial conditions encountered in the field.
Phytosequestration limits the migration of contaminants, mainly metals, through adsorption of metals to plant roots, formation of metal complexes, precipitation of metal ions (e.g., due to a change in pH), or a change to a less toxic redox state. Conditions that promote phytosequestration occur when plants alter the chemical and microbial makeup of the soil (e.g., through the production of exudates [fluids, generally sugars and amino acids, emitted by roots] or carbon dioxide), which impacts the fate and transport of the soil metals (U.S. EPA 2006). Although transport proteins within the plant facilitate the transfer of contaminants between cells, plant cells contain a compartment called the "vacuole" that acts, in part, as a storage and waste receptacle for the plant. The vacuoles of root cells can sequester contaminants, preventing further translocation to the xylem (ITRC 2009, RTDF 2005).
Because phytosequestration retains contaminants in the soil, plant harvesting and disposal are not required; however, evaluation of the system is necessary to verify that translocation of contaminants into the plant tissue is not occurring. Due to the continuing presence of contaminants in the root zone, plant health must be monitored and maintained to ensure system integrity and prevent future release of contaminants. Phytosequestration also can be used to prevent migration of soil contaminants with wind and water erosion, soil dispersion, and leaching (U.S. EPA 2006).
Plant canopies intercept some precipitation. The water is held on leaves, stems, and branches where it evaporates before reaching the ground and groundwater and mobilizing contaminants. Plants also transpire water taken in through the root system, which limits downward migration of precipitation and groundwater. The horizontal migration of groundwater can be controlled or contained using deep-rooted species, such as prairie plants and trees, to intercept, take up, and transpire water. Trees classified as phreatophytes - deep-rooted, high-transpiring, water-loving organisms - are best for implementing phytohydraulics. Phreatophytes send their roots into regions of high moisture and can survive in conditions of temporary saturation. Typical phreatophytes include species such as cottonwoods, poplars, and willows (ITRC 2009; RTDF 2005).
Ali, et al., 2020. Application of floating aquatic plants in phytoremediation of heavy metals polluted water: A review. Sustainability 2020, 12, 1927; doi:10.3390/su12051927
Anderson, C.W.N., 2003. Hyperaccumulation by Plants. Chapter 5 in Element Recovery and Sustainability. (Abstract)
Conesa, H. M. et al., 2012. A Critical View of Current State of Phytotechnologies to Remediate Soils: Still a Promising Tool? The Scientific World Journal, 2012. (Abstract)
Corzo Remigio, A. et al., 2020. Phytoextraction of High Value Elements and Contaminants from Mining and Mineral Wastes: Opportunities and Limitations. Plant and Soil. 449, pp 11-37. (Abstract)
Delil, A.D., et al., 2020. Recovery of Heavy Metals from Canola (Brassica napus) and Soybean (Glycine max) Biomasses Using Electrochemical Process. Environmental Technology & Innovation. Vol. 17. (Abstract)
Dixit et al., 2011. Phytodegradation of PAHs (Anthracene) by Transgenic Tobacco Plants. Journal of Hazardous Materials. 1:15, pp 270-276. (Abstract)
Dzantor, E.K., 2007. Phytoremediation: The State of Rhizosphere 'Engineering' for Accelerated Rhizodegradation of Xenobiotic Contaminants. Chemical Technology and Biotechnology 82:3. (Abstract)
Gestler et al., 2019. Engineered Phytoremediation of Contaminated Aquifers - Adapting a Natural System to Meet Remedial Goals. Geosyntec Consultants. RemTech 2019.
Gobelius, L. et al., 2017. Plant Uptake of Per- and Polyfluoroalkyl Substances at a Contaminated Fire Training Facility to Evaluate the Phytoremediation Potential of Various Plant Species. Environmental Science & Technology. 51(21):12602-12610. (Abstract)
Henry, H.F., 2013. Phytotechnologies - Preventing Exposures, Improving Public Health. International Journal of Remediation. 15(9), 889-899. (Abstract)
Hoang, S. A., et al., 2021. Rhizoremediation as a Green Technology for the Remediation of Petroleum Hydrocarbon-Contaminated Soils. Journal of Hazardous Materials. Vol 401. January.
Horst, J., et al., 2020. Nature-Based Remediation: Growing Opportunities in the Harnessing of Natural Systems. Groundwater Monitoring & Remediation. 40:1 pp14-23 (Abstract)
Huang, S., and P.R. Jaffe, 2019. Defluorination of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) by Acidimicrobium sp. Strain A6. Environ. Sci. Technol. 2019, 53, 19, 11410-11419.
Huff, D.K., et al., 2020. Accumulation of Six PFAS Compounds by Woody and Herbaceous Plants: Potential for Phytoextraction. International Journal of Phytoremediation [Published online 10 July 2020 prior to print] (Abstract)
Huff, D., et al., 2019. Final Report: Phytoremediation of Perfluoroalkyl Substances (PFAS) via Phytoextraction. Small Business Innovation Research - Phase 1 EPA Contract number: 68HE0D18C0018.
ITRC (Interstate Technology & Regulatory Council), 2009. Phytotechnology Technical and Regulatory Guidance and Decision Trees, Revised. Phyto-3
Limmer M., et al., 2016. Phytovolatilization of Organic Contaminants. Environmental Science and Technology. 50:13. Pp 6,632-6,643. (Abstract)
Mahar, A., et al., 2016. Challenges and Opportunities in the Phytoremediation of Heavy Metals Contaminated Soils: A Review. Ecotoxicology and environmental safety, 126, pp.111-121. (Abstract)
Mench, M., et al., 2010. Successes and Limitations of Phytotechnologies at Field Scale: Outcomes, Assessment and Outlook from COST Action 859. Journal of Soils and Sediments, 10(6), 1039-1070. (Abstract)
Pittarello, et al., 2017. Possible developments for ex situ phytoremediation of contaminated sediments, in tropical and subtropical regions-review. Chemosphere. 182 (2017). pp. 707-719. (Abstract)
Pivetz, B., 2001. Ground Water Issue: Phytoremediation of Contaminated Soil and Ground Water at Hazardous Waste Sites. EPA-542-S-01-500. U.S. EPA Office of Solid Waste and Emergency Response, February.
RTDF (Remediation Technologies and Development Forum), 2005. Evaluation of Phytoremediation for Management of Chlorinated Solvents in Soil and Groundwater. EPA 542-R-05-001. January
Suman, J., et al., 2018. Phytoextraction of heavy metals: a promising tool for clean-up of polluted environment? Frontiers in Plant Science, 9, p.1476. (Abstract)
Tangahu, B.V., et al., 2011. A Review on Heavy Metals (As, Pb, and Hg) Uptake by Plants through Phytoremediation. International Journal of Chemical Engineering.
U.S. EPA. 2006. In Situ Treatment Technologies for Contaminated Soil: Engineering Forum Issue Paper. EPA 542-F-06-013.
U.S. EPA, 2004. Constructed Treatment Wetlands. EPA 843-F-03-013. August.
USGS, 2007. Application of Phreatophytes to Remediate Contaminated Groundwater Before Discharge to Protected Surface-Water Systems. South Atlantic Water Science Center.
Wang et al., 2020. https://pubs.acs.org/doi/10.1021/acs.est.9b05160?fig=tgr1&ref=pdf
Yadav, et al., 2018. Mechanistic Understanding and Holistic Approach of Phytoremediation: A Review on Application and Future Prospects. Ecological engineering, 120, pp.274-298. (Abstract)
Yang, Y., et al., 2017. Phytoextraction of Cadmium-Contaminated Soil and Potential of Regenerated Tobacco Biomass for Recovery of Cadmium. Scientific Reports 7210.
Community Guide to
EPA 542-F-21-020, 2021
Phytoremediation Advances Fact Sheet
Naval Facilities Engineering Command, 4 pp, 2021
Accumulation of Six PFAS Compounds by Woody and Herbaceous Plants: Potential for Phytoextraction (Abstract)
Huff, D.K., L.A. Morris, L. Sutter, J. Costanza, and K.D. Pennell.
International Journal of Phytoremediation [Published online 10 July 2020 prior to print]
Applying Rhizobacteria Consortium for the Enhancement of Scirpus Grossus Growth and Phytoaccumulation of Fe and Al in Pilot Constructed Wetlands (Abstract)
Ismai, N.I., S.R.S. Abdullah, M. Idris, S.B. Kurniawan, et al.
Journal of Environmental Management 267:110643(2020)
Arsenic Phytovolatilization and Epigenetic Modifications in Arundo Donax L. Assisted by a PGPR Consortium (Abstract)
Guarino, F., A. Miranda, S. Castiglione, and A. Cicatelli.
International Phytotechnology Society
Website for the International Phytotechnology Society, a nonprofit, worldwide professional society, includes news, projects and upcoming conferences and events.
Performance Evaluation of Microbe and Plant-Mediated Processes in Phytoremediation of Toluene in Fractured Bedrock Using Hybrid Poplars
Ben-Israel, M., Ph.D. thesis, The University of Guelph, 163 pp, 2020
Phytoextraction of High Value Elements and Contaminants from Mining and Mineral Wastes: Opportunities and Limitations (Abstract)
Corzo Remigio, A., R.L. Chaney, A.J. M. Baker, M. Edraki, P.D. Erskine, G. Echevarria, A. van der Ent.
Plant and Soil. 449, pp 11-37, 2020.
Phytoremediation: A Promising Approach for Revegetation of Heavy Metal-Polluted Land
Yan, A., Y. Wang, S.N. Tan, M.L.M. Yusof, S. Ghosh, and Z. Chen.
Frontiers in Plant Science 11:359(2020)
Trace Element Phytoextraction from Contaminated Soil: A Case Study Under Mediterranean Climate (Abstract)
Guidi Nissim, W., E. Palm, S. Mancuso, E. Azzarello.
Environmental Science and Pollution Research volume 25, pp. 9114-9131(2018)
Phytoextraction of Heavy Metals: A Promising Tool for Clean-Up of Polluted Environment? (Abstract)
Suman, J., O. Uhlik, J. Victorova, T. Macek.
Frontiers in Plant Science, 9:1476(2018).
Plant Uptake of Per- and Polyfluoroalkyl Substances at a Contaminated Fire Training Facility to Evaluate the Phytoremediation Potential of Various Plant Species (Abstract)
Gobelius, L., J. Lewis, and L. Ahrens.
Environmental Science & Technology 51(21):12602-12610(2017)
Phyto: Principles and Resources for Site Remediation and Landscape Design (Abstract)
Kirkwood, N. and K. Kennen.
Routledge, New York. ISBN: 978-0-415-81415-7, 346 pp, 2015
Phytoremediation of Explosive-Contaminated Soils
Kiiskila, J.D., P. Das, D. Sarkar, R. Datta.
Current Pollution Reports 1:23-34(2015)
Phytotechnologies - Preventing Exposures, Improving Public Health
Henry, H.F., J.G. Burken, R.M. Maier, L.A., Newman, S. Rock, J. L. Schnoor, and W.A. Suk.
International Journal of Remediation. 15(9), 889-899(2013)
Field Scale Phytoremediation Experiments on a Heavy Metal and Uranium Contaminated Site, and Further Utilization of the Plant Residues (Abstract)
Willscher, S., D. Mirgorodsky, L. Jablonski, D. Ollivier, D. Merten G. Buchel, J. Wittig, and P. Werner.
Introduction to Phytoremediation of Contaminated Groundwater: Historical Foundation, Hydrologic Control, and Contaminant Remediation (Abstract)
Springer, New York. ISBN: 978-94-007-1956-9, 436 pp, 2011
A Review on Heavy Metals (As, Pb, and Hg) Uptake by Plants through Phytoremediation
Tangahu, B.V, Sheikh Abdullah, S.R., H. Basri, M. Idris, N. Anuar, M. Mukhlisin
International Journal of Chemical Engineering, 2011
Handbook of Phytoremediation
Golubev, I.A. (ed.).
Nova Science Publishers, ISBN: 978-1-61728-753-4, 815 pp, 2011
Heavy Metal Hyper-Accumulating Plants: How and Why Do They Do It? And What Makes Them So Interesting? (Abstract)
Rascio, N., and F. Navari-Izzo.
Plant Science 180.2 (2011): 169-81. SCOPUS. Web. 16 October 2011
The Role of Aquatic Ecosystems in the Elimination of Pollutants (Abstract)
Moore, M.T., R. Kroeger, and C.R. Jackson.
Ecological Impacts of Toxic Chemicals. Bentham Science Publishers, Ltd. eISBN: 978-1-60805-121-2, Chapter 11:225-237, 2011
From Brownfields to Greenfields: A Field Guide to Phytoremediation
Urban Omnibus (2010)
Phytotechnologies for Site Cleanup
EPA 542-F-10-009, 2010
Phytotechnology Technical and Regulatory Guidance and Decision Trees, Revised
Interstate Technology & Regulatory Council (ITRC) Phytotechnologies Team.
PHYTO-3, 187 pp, 2009
Effects of Soil Amendments on the Bioavailability of Heavy Metals from Zinc Mine Tailings (Abstract)
Misra V., Tiwari A., Shukla B., Seth C.S.
Environmental Monitoring Assessment 155, pp. 467-475, 2008
Environmental Cleanup Using Plants: Biotechnological Advances and Ecological Considerations (Abstract)
Pilon-Smits, E.A.H., and J. L., Freeman.
Frontiers in Ecology and the Environment. 4:203-210, 2006
Phytoremediation and Hyperaccumulator Plants
W.A. Peer, I.R. Baxter, E.L. Richards, J.L. Freeman, and A.S. Murphy.
Chapter 7 in Molecular Biology of Metal Homeostasis and Detoxification. Springer, Berlin. ISBN-10: 3-540-22175-1, pp 299-340, 2006
Constructed Treatment Wetlands
EPA Office of Water, EPA 843-F-03-013, 2 pp, 2004
D. Tsao (ed.).
Springer, New York. ISBN: 978-3-540-43385-9, 206 pp, 2003
Phytoremediation: Transformation and Control of Contaminants (Abstract)
S.C. McCutcheon and J.L. Schnoor.
J. Wiley, New York. ISBN: 9780471273042, 987 pp, 2003
Ground Water Issue: Phytoremediation of Contaminated Soil and Ground Water at Hazardous Waste Sites.
EPA-542-S-01-500. U.S. EPA Office of Solid Waste and Emergency Response February
Introduction to Phytoremediation
EPA 600-R-99-107, 2000
Phytoremediation of Organic Contaminants: A Review of Phytoremediation Research at the University of Washington (Abstract)
Newman, L.A., S.L. Doty, K.L. Gery, P.E. Heilman, I. Muiznieks, T.Q. Shang, S. T. Siemieniec, S. E. Strand, X. Wang, et al.
Journal of Soil Contamination. 7:4, pp. 531-542, 1998
The commonly used term "phytoremediation" refers to remediation mechanisms (i.e., those that remove or reduce the toxicity of contaminants). ↩
The commonly used term "phytoremediation" refers to remediation mechanisms (i.e., those that remove or reduce the toxicity of contaminants). ↩