A.M. Duncan and J.F. Gottgens
Department of Environmental Sciences
University of Toledo
1 cm
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

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)

• 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.

Cancer (skin, kidney, liver, lung…...)
Gangrene (Blackfoot disease)
Gastrointestinal lesions
Renal failure
Diabetes
Neurological Disorders (neuropathy)
Skin Lesions
Respiratory failure
Reproductive failure
Death

– Weathering of bedrock
– Volcanic eruptions
– Agricultural pesticides Toledo Glass Company Sheet Glass Plant
(1912-1914.)
– Industrial byproducts
• leaded gasoline, combustion of fossil fuels, manufacturing of electronics, application of wood preservatives, and production of glass and ceramics.

.
• Conventional treatment: High cost, low efficiency, chemically-intensive
• 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)

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

• Common arsenic forms within aquatic systems
– MMAA, DMAA, arsenite and arsenate
– Primarily arsenate
• Phosphorous uptake system.
• Competes with P for
ATP binding
Arsenite
Arsenate
Arsenate
Source: Carbonell et al. (1999)

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. 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

• 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. 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

• 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
Arsenate
MMAA
No Arsenic
Arsenite
DMAA
Growth inhibition increased from DMAA < As (III) < MMAA < As (V)

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

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. 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

• 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

1.5 ppm
0 ppm
0.5 ppm
1.0 ppm
Red pigmentation (anthocyanin) increased with increasing As levels

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

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

Initial conc.
(ppb)
1,500
1,000
500
Target conc.
(ppb)
150
150
150
Mean As removal rate over 21 days
(ug/day)
17.7
Remediation time (days)
76
Mean As removal rate over 7 days
(ug/day)
37.7
Remediation time (days)
36
10.4
5.3
82
84
23.1
12.4
37
36

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

• 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