Phytoremediation of Arsenic Phytoremediation of Arsenic Contaminated Soils Using Contaminated Soils Using
Chinese Brake FernChinese Brake Fern
Maria Silva
Soil and Water Science Department
University of Florida
ArsenicArsenic Anthropogenic activities account for most As
contamination in soils and water;
As is carcinogenic
Remediation of As contaminated sites has become an important issue
Current remediation technologies are expensive and environmental disruptive.
The use of plants to remove, contain, or render harmless environmental pollutants.
PhytoremediationPhytoremediation
Plant biomass
Uptake
Plant species
Contaminant concentration
Use of accumulating plants to remove metals from soil by concentrating them in
harvestable parts.
PhytoextractionPhytoextraction
Chinese Brake fern (Pteris vittata L)
Natural ability to tolerate, accumulate, and translocate high concentrations of As
As high as 2.3% in fronds
Rapid growth rate
Perennial
High biomass
Capable of taking up both organic and inorganic As
Although the fern shows great
potential to be used in
Phytoremediation, many
questions still need to be
answered!!!
Research objectivesResearch objectives1. Determine the effectiveness of Chinese
Brake fern (CBF) in continuously remove As from soils over time;
2. Investigate the impacts of CBF on As mobilization and redistribution in the rhizosphere soil
3. Determine the NPK levels for optimum As removal by the fern
4. Evaluate the effect of plant maturity on As accumulation by the fern.
Experiment 1Experiment 1Effectiveness of Chinese Brake fern on
arsenic removal over time
HYPOTHESESHYPOTHESES:
1. Chinese Brake fern is capable of continuously removing As from soils;
2. Arsenic availability in soil will decrease as more available As is taken up by Chinese Brake
3. Changes in plant available As can be predicted by partitioning the soil As-pools using a sequential fractionation procedure
Materials and MethodsExperimental setup
Completely Randomized Design Six As-contaminated soils One plant per pot containing 4 kg soil Four replications Controls without plants
Sampling Harvest fronds 2-3 times a year Collect soil with plant harvest
Soil
Source of arsenic As (mg kg-1)
Marl Natural 20
Avon Cattle-dipping vat 27
CCA chromated-copper-arsenate
(CCA) wood preservative
110
CDV Cattle-dipping vat 300
Mining Mining activities 300
EDS herbicide 700
Experimental Soils
Analyses
Aboveground biomass
Total As concentrations (soil and plant)
Hot block digestion system (EPA Method 3050A)
Graphite furnace AAS
Arsenic fractionation in soil
Wenzel et al. (2001)
Fractions Extracting solution Extraction condition
SSR*
As-NAs-N: Non-specifically- bound
(NH4)2SO4 0.05M 4h shaking, 20oC 1:25
As-SAs-S:Specifically-bound
(NH4)H2PO4 0.05M 16h shaking, 20oC 1:25
As-AAs-A:Amorphous hydrous oxide-bound
NH4-oxalate buffer
(0.2 M) pH 3.25
4h shaking, 20o dark
1:25
As-CAs-C:Crystalline hydrous-oxide-bound
NH4-oxalate buffer
(0.2 M) + ascorbic acid (0.1M) pH 3.25
30 min in a water basin at 96oC with light
1:25
As-RAs-R:Residual HNO3/H2O2 Hot block digestion
1:50
SSR=soil to solution ratio
As fractionation procedure
As availab
ility
Experiment 2 Arsenic mobilization and redistribution
in the rhizosphere of two ferns
HYPOTHESESHYPOTHESES:
1. More roots of CBF will be developed in arsenic-rich soil than arsenic-free soil;
2. Changes in the rhizosphere of CBF will be greater than those of Boston fern, a non-hyperaccumulator.
Materials and MethodsExperimental setup
Completely Randomized Design
Factorial scheme (2 x 2)
2 plants (CBF and Boston fern)
2 soils (contaminated and non-contaminated)
1 plant/pot containing 2.5kg of soil
4 replications
Controls without plantsSampling
Harvest after 8 weeks of growth
Collect rhizosphere and bulk soil
Rhizopot
Rhizosphere soil
Bulk soil
45um
AnalysesPlant
Frond and root biomass Frond and root As concentration Root length density Root area density
Soil (rhizosphere and bulk) water-soluble As Total As pH and DOC As fractionation
Experiment 3Interactive effects of N, P, K and As on
plant arsenic uptake
HYPOTHESESHYPOTHESES:1. As accumulation affects plant nutrient
requirements;
2. Maximum plant As removal can be achieved through optimum application of NPK;
Materials and MethodsExperimental setup
4 factor- 5 level central composite design
N = 60 to 300 ppm;
P = 30 to 150 ppm;
K = 30 to 300 ppm;
As = 50 to 200 ppm;
one plant/pot with 1.5 kg of soil
Three replications
Sampling Harvest after 8 weeks of growth
Soil
Analyses
Plant Frond and root biomass Frond and root As concentration Frond and root macro and micronutrients
Soil (rhizosphere and bulk) Total As concentrations pH and DOC
Experiment 4Arsenic removal by Chinese brake fern
using plants of different maturity
HYPOTHESESHYPOTHESES:
1. Plant maturity affects its arsenic removal capability;
2. Maximum plant As removal can be achieved using optimum plant age;
Materials and Methods
Experimental setup Completely Randomized Design
One plant per pot with 2.5 kg of soil
Plants: 45 days, 8, 10 and 16 month-old
One As contaminated soil (150 mg kg-1)
Four replications
Sampling Harvest after 12 weeks of growth
Bulk and rhizosphere soil
Plant biomass
As concentrations in soil and plant
Soil pH and DOC in the rhizosphere and
bulk soil
Analyses
Preliminary Results
0
100
200
300
400
500
Marl Avon CCA Mining CDV EDS
Soils
Biom
ass
incr
ease
(%
)
Frond biomass in the first harvest
Initial frond biomass = 8g
Experiment 1
Fern As concentration in the first harvest
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Marl Avon CCA Mining CDV EDS
Soils
As(
mg
kg-1
)
Arsenic removed from soils by fern after one harvest
0
1
2
3
4
5
6
7
8
9
10
Marl Avon CCA mining CDV EDS
Soil
%o
fAs
rem
ov
ed
Changes in Soil Arsenic fractions after first harvest
As-N non-specifically bound, As-S specifically bound, As-A amorphous Fe and Al As-C crystalline Fe and Al As-R residual
0%
20%
40%
60%
80%
100%
Soils
As
As-R
As-C
As-A
As-S
As-N
Clean soil
As soil
Experiment 2
Clean soil
As soil
Chinese brake fern
Boston fern
Plant biomass, As concentration & removal after 8 weeks of growth
Fern specie
Biomass As concentration As remediated
(%)Frond Root Frond Root
--- g plant-1--- -- --mg kg-1 -----
Non-contaminated soil
CBF 6.33 1.98 0.58 2.65 -
Boston 2.46 0.86 0.10 0.30 -
Contaminated soil
CBF 5.54 1.84 432 116 1.03
Boston 1.75 0.60 19.7 98.0 0.04
0
0.5
1
1.5
2
C. Brake Boston No plant
Treatment
W-S
As
(mg
kg-1
)
Bulk soil Rhizosphere
Water-soluble As
a a a
C BA
6.9
77.1
7.27.3
7.47.5
7.67.7
C. Brake Boston No plant
Treatment
So
il p
H
Bulk soil Rhizosphere
Soil pH
a a a
A
B B
Summary-1
1. CBF grew well in all six soils with 195-360% biomass increase after 4 months;
2. CBF was effective in removing As from the soils, with 4- 9% reduction after one harvest;
3. The majority of soil As was associated with the amorphous fraction
Summary-2
4. Compared to Boston fern, CBF accumulated greater biomass and greater arsenic in the fronds;
5. Water-soluble As was lower in the rhizosphere of CBF than Boston fern;
6. pH was greater in the rhizosphere of CBF than Boston fern;
Special Thanks
Advisor- Dr. Lena Ma
Dr. Jorge Santos
Committee members:
Dr. Commerford
Dr. Rhue
Dr. Stamps
Dr. Bonzongo
Tom Luongo
Trace metal biogeochemistry group
Sponsorship – CAPES
Thank you
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