Removal of Heavy Metal Pollutants Removal of Heavy Metal Pollutants by Wetland Plantsby Wetland Plants

Therese Frauendorf

Aquatic Conservation: Global Freshwaters, Science, and Policy

Overview

• Introduction

• Mechanism of Heavy Metal Removal by Wetland Plants

• The Effectiveness of Constructed Wetlands Compared to Wastewater Treatment Plants

• Conclusion

• Questions

Introduction• Goals

Understand how heavy metals are removed from the water by wetland plants

Understand the effectiveness of wetland plants

• Wetlands: a lowland that is saturated with water

• Heavy Metals in Water: Lead, Cadmium, Zinc, Mercury, Nickel, Copper

• Most Studied and Effective Heavy Metal Removal Plants: Water hyacinth (Eichhornia

crassipes) Cattails (Typha)

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www.arcatapet.com

Overview

• Introduction• Mechanism of Heavy Metal Removal

by Wetland Plants• The Effectiveness of Constructed Wetlands Compared to

Wastewater Treatment Plants• Conclusion• Questions

Plant Requirements

• Heavy Metal Tolerance (Natural Selection) → metal specific

• Shallow-rooted Plants: high metal uptake rate

• Deep-rooted Plants: small metal uptake rate

• Emergent vs. Surface Floating Plants

• Heavy Metal Absorbance Rate: roots > rhizomes > shoots > leaves

Mechanism: Roots & Rhizomes

• Extended Root System fractionates & dissolves Organic Matter

→ decreases Turbidity

→ increases Electrical Charges

• Optimize uptake by: pH, organic matter content, temperature, redox potential, turbidity

Pb2+

Hg2+

Cd2+

Zn2+

Cu2+

Diffusion: Cations

H2O

H2O

Osmosis: Water

Mechanism: Leaves, Petioles & Shoots

• Passively absorbed → Stoma Cells & Cracks in Cuticle Apparent Free Space (AFS):

→ Water Free Space: (WFS) absorbs H2O molecules & free mobile ions → Donnan Free Space: (DFS) absorbs free mobile ions through cell wall

Actively absorbed → Cytoplasm: move into vacuoles & various other cells via Plasmadesmata

decrease in cell size

A. Cross section of leaf of water hyacinth control plant B. Cross section of leaf of water hyacinth experimental plant (100x)

(Mahmood et al 2005).

A

B

Translocation

• Transport of Solutes in Plants• Movement of Metal Containing

Sap from Root to Shoot Takes place by root pressure

or leaf transpiration Slower than absorption by

roots → limiting factor in uptake of metal

• Movement of Oxygen from Shoot to Root Induces Oxygen leaks to the

reduced environment Promotes Oxyhydroxide (Fe3,

Mn2) release → absorption sites for heavy metals

or Phloem

Metals

O2

Metals

Oxyhydroxide

O2

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Plant Aid

• Plant metallothioneins: induced by metals like Cd and Cu and are part of the plant’s tolerance

Participate in uptake, transport and regulation of metals → Thionein protein binds to metal for transportation

Detoxify mercury and other heavy metals by binding to them

• Rhizospheric bacteria and fungus increases feasibility and efficiency of phytoremediation by promoting accumulation of metals

• Additional treatment with antibiotic Oxytetracycline (OTC) increases efficiency further (So et al 2993)

• Microorganisms + Plants = BiosorptionPassive & metabolism-independent mechanism that removes

metals by interactions with microbial biomass

Overview

• Introduction• Mechanism of Heavy Metal Removal by Wetland Plants• The Effectiveness of Constructed Wetlands Compared

to Wastewater Treatment Plants• Conclusion• Questions

The Benefits and Costs of an Artificial Constructed Wetland

Pros:Pros:• Aesthetics• Habitat Creation for

Wildlife• Increased Cost-

Efficiency• Little Maintenance

Cons:Cons:• Susceptible to

Climate and Disease• Limited Life

Expectancy• Creation of Toxic

Wetlands

Tres Rios Constructed Wetlands

• Demonstration Project near Phoenix, AZ Upgrade of Water Treatment

Plant: $625mill

Cost of creation of the Wetland: $3.5mill

Cost of Water Treatment Plant Maintenance/Month: $1000

Cost of Wetland Maintenance/Month:“little to nothing” (Gelt 1997)

• Project for Treatment of Organic Matter → Estimate for Heavy Metal Removal

• Water Hyacinth & Cattails – high reproductive rate and very inexpensive (Weeds)

(Gelt 1997)

Toxic Wetlands?

Try to transform toxic heavy metals into mobile forms by changing physical & chemical characteristics:

• Concentrating heavy metals in plant for convenient extraction → proper disposal or reuse of heavy metals → ex: Water Hyacinth

• Detoxification: Metallothioneines Balance of surface charge by free floating anions (HPO4

2-) and cations (K+)

Ingestion and metabolistic use of toxic metals by Microorganisms

?

Problems

• High concentrations of Heavy Metals can be toxic to plants → decrease of plant growth

→ harvesting of plants

• Disposal of accumulated metal stored in plants → need of another disposal facility?

Conclusion

• Wetland plants limit the spread of Heavy Metals by storing them

• The basic mechanism of Heavy Metal uptake by wetland plants like the water hyacinth and the cattails is well known

• Further Research needs to be conducted: Conduct a study to see the effectiveness of wetlands removing

heavy metals compared to a wastewater treatment plant Key role of the collaboration between wetland plants,

microorganism and bacteria to maximize uptake Cost-effective method to increase uptake (OTC) Develop a cost-effective and efficient way to dispose wetland

plants containing heavy metals Increase detoxification of Heavy Metals (Metallothioneins)

?

Questions

Citations• Briggs, G.E., and R.N. Robertson. 1957. Apparent free space. Annual Review of Plant

Physiology 8: 11-12.• Gelt, J. 1997. Constructed wetlands: using human ingenuity, natural processes to treat

water, build habitat. Arroyo 9 (4): 23-37.• Heathcote, I. Dr. 2000. Artificial wetlands for wastewater treatment. Pearson Education

Company. Prentice-Hall Inc, New Jersey, USA.• Karbiscak, M.M, L.R. Whiteake, J.F. Artiola, and K.E. Foster. 2001. Nutrient and heavy

metal uptake and storage in constructed wetland systems in Arizona. Water SciTechnol. 44 (11-12): 455-462.

• Kong, K.F., and J.S.H. Tsang. 1998. Nucleotide sequences of cDNAs (Accession nos. AJ010160, AJ010161 and AJ010161) encoding a Type 2 metallothionein-like protein from water hyacinth Eichhornia crassipes. (PGR98-176) Plant Physiol. 118: 1101.

• Kosolapov, D.B., P. Kuschk, M.B. Vainshtein, A.V. Vatsourina, A. Wießner, M. Kästner, and R.A. Müller. 2004. Microbial processes of heavy metal removal from carbon-deficient

effluents in constructed wetlands. Eng. Life Sci. 4 (5): 403-411.• Krishnan, S.S., A. Cancilla, and R.E. Jervis. 1998. Wastewater treatment for heavy metal

toxins using plant and hair as adsorbent. Sci Total Environ. 68: 267-273.• Mahmood, Q., P. Zheng, R.M. Siddiqi, E. ul Islam, R.M. Azim, and Y. Hayat. 2005.

Anatomical studies on water hyacinth (Eichhornia crassipes (Mart.) Solms) under the influence of textile wastewater. Journal of Zhejiang University SCIENCE 6B (10): 991-998.

Citations• Matagi, S.V., D. Swai, and R. Mugabe. A review of heavy metal removal mechanisms

in wetlands. Afr. J. Trop. Hydrobiol. Fish. 8: 23-35.• Pye-Smith, C. 1995. Salvation from Sewage in Calcutta marshes. People & the

Planet 4 (1): 20-22.• So, L.M., L.M. Chu, and P.K. Wong. 2003. Microbial enhancement of Cu2+ removal

capacity of Eichhornia crassipes (Mart.). Chemosphere 52 (9): 1499-1503.• Win, D.T, M.M Than, and S. Tun. 2002. Iron removal from industrial waters by water

hyacinth. AU J.T. 6 (2): 55-60.• Win, D.T, M.M Than, and S. Tun. 2003. Lead removal from industrial waters by water

hyacinth. AU J.T. 6 (4): 187-192.• Wu, L., and J. Antonovics. 1975. Zinc and copper uptake by Agrostis stolonifera,

tolerant to both zinc and copper. New Phytologist 75 (2): 231-237.• Xiaomei, L., M. Kruatrachue, P. Pokethitiyook, and K. Homyok. 2004. Removal of

cadmium and zinc by water hyacinth, Eichhornia crassipes. ScienceAsia 30: 93-103.