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Azoll a caroliniana A 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

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azoll a caroliniana a model for arsenic remediation

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

1 cm

slide2

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)

slide3

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.
acute and chronic exposure linked
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

sources
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.)

conventional treatment high cost low efficiency chemically intensive
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)

optimal plants for phytoremediation
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
uptake may depend on as species
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)

objective evaluate the arsenic phytofiltration potential of a caroliniana
Objective:Evaluate 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
objective evaluate the arsenic phytofiltration potential of a caroliniana1
Objective:Evaluate 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
slide12

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
objective evaluate the arsenic phytofiltration potential of a caroliniana2
Objective:Evaluate 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
uptake of different as species
Uptake of different As species
  • Arsenic in Azolla for the control (no As) treatment was consistently < 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 (N=3).
plant responses
Plant Responses

Arsenate

MMAA

No Arsenic

Arsenite

DMAA

Growth inhibition increased from DMAA < As (III) < MMAA < As (V)

plant responses1
Plant Responses

MMAA

Frond discoloration and reduced growth with MMAA exposure have been linked to decreases of Mg and K in planttissue (Carbonell et al. 1998).

slide17

Plant Responses

Arsenate

Frond chlorosis as a result of arsenate exposure has been linked to reductions in sulfur (Wong 2005)

objective evaluate the arsenic phytofiltration potential of a caroliniana3
Objective:Evaluate 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
arsenate exposure
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
plant response
Plant Response

1.5 ppm

0 ppm

0.5 ppm

1.0 ppm

Red pigmentation (anthocyanin) increased with increasing As levels

mass balance
Mass Balance

“Lost”

Azolla

Solution

Harvested

Goal: Track the pathway of arsenic through the experimental system and to predict uptake trends over time.

Refreshed

slide22

Average mass of As removed over time by A. caroliniana for exposures to 500, 1000, and 1500 ppb.

Data fitted with power trendline.

optimal plants for phytoremediation1
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
further work
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