Azolla caroliniana A model for Arsenic Remediation

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Azolla carolinianaA model for Arsenic
Remediation
A.M. Duncan and J.F. Gottgens Department of
Environmental Sciences University of Toledo
Sponsor USDA-CSREES (2005-38894-02307) Technical
assistance ARS-USDA (Jonathan Frantz, Doug
Sturtz Greenhouse space UT Plant Science
Research Center Collaborators Defne Apul, Daryl
Dwyer, Jordan Rofkar
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WHO drinking water standard 10 ppb
In the U.S., arsenic contaminated drinking water
is a serious threat. Some 56 million people in
the U.S. have drinking water with unsafe arsenic
levels (NRCD 2001)
77 million people are drinking water in
Bangladesh with toxic levels of Arsenic (CNN 2010)
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• Due to its extreme toxicity and high prevalence
  in the environment, the Department of Health and
  Human Services has ranked arsenic as the number
  one contaminant of concern to human health.
• Arsenic has held this top spot since 1997.

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Acute and chronic exposure linked
Cancer (skin, kidney, liver, lung...)
Neurological Disorders (neuropathy)
Skin Lesions
Gangrene (Blackfoot disease)
Respiratory failure
Gastrointestinal lesions
Reproductive failure
Renal failure
Death
Diabetes
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Sources

• Natural
• Weathering of bedrock
• Volcanic eruptions
• Anthropogenic
• Agricultural pesticides
• Industrial byproducts
• leaded gasoline, combustion of fossil fuels,
  manufacturing of electronics, application of wood
  preservatives, and production of glass and
  ceramics.

Toledo Glass Company Sheet Glass
Plant (1912-1914.)
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Conventional treatment High cost, low
efficiency, chemically-intensive
Currently no inexpensive, efficient option for
removing arsenic from contaminated water.

• Wetlands may provide an alternative technology
  Use of hyper-accumulating plants

Arsenic concentrations in brake fern after 20
weeks growth in a soil containing 97ppm As.
Chinese brake fern (Pteris vittata)
Source Ma et al. (Nature, 2001)
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Optimal plants for phytoremediation

• Accumulate the contaminant effectively
• Tolerate contaminant toxicity
• Grow naturally (native) and fast within region
• Possess appropriate root type/depth for site
  conditions
• Harvest easily

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Uptake may depend on As species

• Common arsenic forms within aquatic systems
• MMAA, DMAA, arsenite and arsenate
• Primarily arsenate
• Phosphorous uptake system.
• Competes with P for ATP binding

Arsenate
Arsenate
Arsenite
Source Carbonell et al. (1999)
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ObjectiveEvaluate the arsenic phytofiltration
potential of A. caroliniana.

• Quantify uptake for four arsenic species
• Impact on Azolla growth
• Changes in mineral concentrations in tissue
• Quantify difference between absorption and
  adsorption
• Develop a mass balance model to track arsenic and
  make predictions about removal times under
  different scenarios

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ObjectiveEvaluate the arsenic phytofiltration
potential of A. caroliniana.

• Quantify uptake for four arsenic species
• Impact on Azolla growth
• Changes in mineral concentrations in tissue
• Quantify difference between absorption and
  adsorption
• Develop a mass balance model to track arsenic and
  make predictions about removal times under
  different scenarios

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Randomized block design
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• Grown hydroponically in 1 liter 10 Hoagland
  solution
• 15 g Azolla (fresh wt) per tray containing
  arsenic (1.5 mg/L)
• 12 day exposure period with solution refreshed
  every 4 days.
• Also measured pH, redox, air/water temp, light,
  humidity
• Plant/water samples digested and analyzed with
  ICP-OES
• QA/QC Standards, spikes, SRM, LOD
• Data analysis used ANOVA with Tukey post-hoc test
  in SAS

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ObjectiveEvaluate the arsenic phytofiltration
potential of A. caroliniana.

• Quantify uptake for four arsenic species
• Impact on Azolla growth
• Changes in mineral concentrations in tissue
• Quantify difference between absorption and
  adsorption
• Develop a mass balance model to track arsenic and
  make predictions about removal times under
  different scenarios

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Uptake of different As species

• Arsenic in Azolla for the control (no As)
  treatment was consistently lt the detection limit
  (10 mg kg-1).
• Letters indicate Tukey's standardized range test.
  Means with same letter are not significantly
  different. Vertical bars represent 1 STD (N3).

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Plant Responses

• Growth inhibition increased from DMAA lt As (III)
  lt MMAA lt As (V)

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Plant Responses
Frond discoloration and reduced growth with MMAA
exposure have been linked to decreases of Mg and
K in plant tissue (Carbonell et al. 1998).
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Plant Responses
Frond chlorosis as a result of arsenate exposure
has been linked to reductions in sulfur (Wong
2005)
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ObjectiveEvaluate the arsenic phytofiltration
potential of A. caroliniana.

• Quantify uptake for four arsenic species
• Impact on Azolla growth
• Changes in mineral concentrations in tissue
• Quantify difference between absorption and
  adsorption
• Develop a mass balance model to track arsenic and
  make predictions about removal times under
  different scenarios

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Arsenate Exposure

• 4 concentrations (0, 0.5, 1.0, 1.5 mg/ L)
• 21 day exposure
• 40 grams initial weight
• 5g fresh weight and 20 ml solution samples were
  collected at 0, 2, 8, 24, and 72 hours, followed
  by a 4 and 3 day sampling rotation.
• Replenished evaporative loses

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Plant Response
1.5 ppm
0 ppm
0.5 ppm
1.0 ppm
Red pigmentation (anthocyanin) increased with
increasing As levels
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Mass Balance
Goal Track the pathway of arsenic through the
experimental system and to predict uptake trends
over time.
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Average mass of As removed over time by A.
caroliniana for exposures to 500, 1000, and 1500
ppb.
Data fitted with power trendline.
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Initial conc. (ppb) Target conc. (ppb) Mean As removal rate over 21 days (ug/day) Remediation time (days) Mean As removal rate over 7 days (ug/day) Remediation time (days)
1,500 150 17.7 76 37.7 36
1,000 150 10.4 82 23.1 37
500 150 5.3 84 12.4 36
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Optimal plants for phytoremediation
v

• Accumulate the contaminant effectively
• Tolerate contaminant toxicity
• Grow naturally (native) and fast within region
• Possess appropriate root type/depth for site
  conditions
• Harvest easily

v
v
v
v
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Further work

• Longer time intervals, larger scales, and varying
  environmental factors.
• Enclosures that incorporate flow through
  conditions, sediments and additional plant
  species.
• Development of techniques to re-utilize the
  concentrated arsenic from plant tissue