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Azoll a caroliniana A model for Arsenic Remediation

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

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  1. 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

  2. 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)

  3. 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.

  4. 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

  5. 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.)

  6. 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)

  7. 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

  8. 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)

  9. 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

  10. 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

  11. Randomized block design

  12. 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

  13. 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

  14. 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).

  15. Plant Responses Arsenate MMAA No Arsenic Arsenite DMAA Growth inhibition increased from DMAA < As (III) < MMAA < As (V)

  16. 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).

  17. Plant Responses Arsenate Frond chlorosis as a result of arsenate exposure has been linked to reductions in sulfur (Wong 2005)

  18. 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

  19. 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

  20. Plant Response 1.5 ppm 0 ppm 0.5 ppm 1.0 ppm Red pigmentation (anthocyanin) increased with increasing As levels

  21. Mass Balance “Lost” Azolla Solution Harvested Goal: Track the pathway of arsenic through the experimental system and to predict uptake trends over time. Refreshed

  22. Average mass of As removed over time by A. caroliniana for exposures to 500, 1000, and 1500 ppb. Data fitted with power trendline.

  23. 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

  24. 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

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