Speciation and Speciation and Bioavailability of Trace Bioavailability of Trace
Elements in Contaminated Elements in Contaminated SoilsSoils
Sébastien Sauvé
Université de Montréal (Montréal, QC, Canada)
email:[email protected]://mapageweb.umontreal.ca/sauves/
© Sauvé 2003
ObjectivesObjectives Determine the free metal speciation of divalent
metals in soil solutions
Identify the physico-chemical characteristics of the soil which control metal solubility and speciation
• Quantify the contributions of pH, total metal and organic matter
Propose simple semi-mechanistic regression models to estimate metal solubility and free Me2+ speciation in contaminated soils
Link within the context of a large data acquisition projet
© Sauvé 2003
SoilsSoils Multiple dataset of field-collected soils
Metals originating from smelting/battery recycling operations, long-term phosphate fertilizers, aerial deposition, sewage sludge application, diffuse and point source industrial contamination
• Montréal (QC), Ithaca (NY), Québec, France, Denmark & Colorado
Field « equilibrium », in most cases, contamination has occured at least ten years before sampling
Uncontaminated « controls »
© Sauvé 2003
Soil PropertiesSoil Properties Soil pH in 0.01 M CaCl2 or KNO3 extract (from
3.5 to 8.9)
Soil organic matter of 8.0 to 108 g C kg-1
Dissolved organic carbon 1.1 to 140 mg C L-1
Metal levels from background to high industrial range
• Soil totals of 0.1 to 56 mg Cd kg-1
• Dissolved Cd of 0.03 to 3500 µg Cd L-1
• Free Cd2+ of 10-10 to 10-5 M
© Sauvé 2003
Analytical MethodologyAnalytical Methodology «Totals» by HNO3 reflux digestion
Soil solutions obtained using 1:2 soil:0.01 M KNO3 or CaCl2 extractions filtered to <0.22µm (or <0.45µm)
• Total dissolved metal by GFAAS (Zeeman) or ICP-AES
• Electrochemically labile Cd, Pb and Zn by differential pulse anodic stripping voltammetry (DPASV)
• Free Cd2+ Pb2+, Zn2+ speciation by partitioning ASV-labile metal into inorganic ion-pairs
• Free Cu2+ by ion-selective electrode potentiometry
© Sauvé 2003
Electrochemically
active metals are
reduced into the
Hg drop electrode
Each metal has a
specific reduction
potential, peak
position identifies
metal, peak height
is proportional to
its concentration
Differential Pulse Anodic Stripping Differential Pulse Anodic Stripping VoltammetryVoltammetry
© Sauvé 2003
Calibration by comparison of known standards with samples
y = 0.0119x - 0.0002
R2 = 0.9985
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 10 20 30 40 50 60 70
DPASV Peak Height (nA)
ASV-
Labi
le Cd
(µM)
Differential Pulse Anodic Stripping Differential Pulse Anodic Stripping VoltammetryVoltammetry
© Sauvé 2003
Free CdFree Cd2+2+ Speciation Speciation
Assuming that ASV is not sensitive to metals strongly complexed with dissolved organic matter
ASV-labile Cd is composed mainly from inorganic species
)CdCdClCdNO)Cd(COCdCO
CdHCOCd(OH)Cd(OH)(CdOH ASV)by Cd Labile(2++
3-2
2303
-3
+3
02
+
Cd) LabileASV()CdBoundOM(CdDissolved
© Sauvé 2003
CuCu2+2+ by potentiometry by potentiometry
Ion selective electrode very sensitive for Cu2+
Not prone to interferences (except very high levels of chloride or mercury)
y = -0.0299x + 10.107R2 = 0.9948
2.0
4.0
6.0
8.0
10.0
12.0
14.0
-1000100200300
Electrode potential (mV)
Free
Cu
(pCu
2+)
© Sauvé 2003
Fractionation/SpeciationFractionation/Speciation
Soil total
Bound to DOM
Free metal
Cl complexes
SO4 complexes
1 mg Cd kg1 mg Cd kg-1-1
pH ~ 5pH ~ 5
MineralMineral Solubility Solubility EquilibriaEquilibria
3 4 5 6 7 8 9pH
0
2
4
6
8
10
12
p (a
ctiv
ity)
CdOH2
CdCO 3
CdSO4·2Cd(OH)2
Cd3(PO4)2
3 5 7 9
0
4
8
123 5 7 9
0
4
8
123 4 5 6 7 8 9
pH
0
2
4
6
8
10
12
Cu(OH) 2
CuO
Cu4(OH)6SO4
CuCO 3
Cu3(PO4)2·H2O
3 5 7 9
0
4
8
123 5 7 9
0
4
8
123 4 5 6 7 8 9
pH
0
2
4
6
8
10
12
Pb2(CO)2(OH)2
PbOPb(OH)2
PbSO4PbHPO4
Pb5(PO4)3OH
Pb5(PO4)3Cl
3 5 7 9
0
4
8
123 5 7 9
0
4
8
12
Sauvé S. 2002. «The Role of Chemical Speciation in Bioavailability » In: Naidu R., Gupta V.V.S.R., Kookana R.S., Rogers S., Adriano D. (Eds.),
Bioavailability, Toxicity and Risk Relationships in Ecosystems. Science Publishers Inc., Enfield, NH, pp 21-44.
© Sauvé 2003
Solid/liquid PartitioningSolid/liquid Partitioning
• Assumes a unique and constant ratio between solution and solid phases:
• Total metal is in mg/kg dry soil and dissolved metal is in mg/L, hence Kd´s are usually reported as L/kg
• Sensitive to determination method, solid:liquid ratio, extracting solution, time of extraction and filtration
MetalDissolvedMetalTotal
Kd
© Sauvé 2003
Dependence of KDependence of Kdd on pH on pH
For a compilation of literature Kd’s, 29 to 58 % of the variability depends on soil solution pH.
Soil Solution pH
2 4 6 8 10
Soil Solution pH
2 4 6 8 10
Soil Solution pH
2 4 6 8 10
Soil Solution pH
2 4 6 8 10
Soil Solution pH
2 4 6 8 10
Kd(L
kg
-1)
10-1100101102103104105106107
Cd Cu Ni
Pb
Zn
Sauvé S. Hendershot W., Allen H.E. 2000. «Solid-Solution Partitioning of Metals in Contaminated Soils: Dependence on pH, Total Metal and Organic Matter ». Environ. Sci. Technol. 34:1125-1131 .
© Sauvé 2003
Dissolved Cd - KDissolved Cd - Kdd Partitioning Partitioning(Field-collected soils only)(Field-collected soils only)
0.101.00
10.00
Soil Total Cd (mg/kg)
10
100
1000
10000
100000
Kd (
kg/L
)
A
3 4 5 6 7 8 9Soil Solution pH
3 4 5 6 7 8 93 4 5 6 7 8 93 4 5 6 7 8 9
B
1 10Dissolved OM (mg C/L)
C
Janssen et al. 1996 Data Lee et al. 1996 Anderson and Christensen 1988
© Sauvé 2003
Dissolved CdDissolved Cd
Total Cd
pH
Field & spiked datasets are similar at pH<8
KOH effect on DOM at pH>8 Field
Spiked
TYPE
© Sauvé 2003
Predictive RegressionsPredictive Regressions
Field-collected dataset
Field & spiked soils (pH<7).).(,64,001.0,759.0
)(log)07.0(77.0
)04.0(54.0)28.0(23.3)41.0)((log
2
10
10
ESnpR
CdSoilTotal
pHCdDissolved
.).(),7(,70,001.0,861.0
)(log)06.0(07.1
)05.0(57.0)28.0(54.3)40.0)((log
2
10
10
ESpHnpR
CdSoilTotal
pHCdDissolved
© Sauvé 2003
Adsorption ModelAdsorption Model
Assuming competitive binding of H+ and Me2+ to a deprotonated surface (S):
HyMeSurSurHMe y
© Sauvé 2003
Adsorption ModelAdsorption Model With some assumptions, then:
Assuming that adsorption capacity is dependent on organic matter content:
But could be oxyde content, clays, sulfides, etc.
)log(
) log(2
Surfaced
MetalTotalcpHbapMe
) log(
) log(2
MatterOrganicd
MetalTotalcpHbapMe
© Sauvé 2003
Adsorption ModelAdsorption Model
simplified further to:
) log(2 MetalTotalcpHbapMe
Applied with succes to the soil solution speciationof Cd2+, Cu2+, Pb2+ and Zn2+.
© Sauvé 2003
Free CdFree Cd2+2+
Total Cd
pH
Field & spiked datasets are similar
No apparent effects of KOH-induced DOM
FieldSpiked
TYPE
© Sauvé 2003
Predictive Regressions for Predictive Regressions for Free CdFree Cd2+2+
Spiked dataset
Field & spiked soils
.).(,102,001.0,736.0
)(log)08.0(97.0)05.0(69.0)32.0(39.4)66.0(2
102
ESnpR
CdSoilTotalpHpCd
.).(,35,001.0,822.0
)(log)11.0(76.0)07.0(66.0)27.0(96.3)51.0(2
102
ESnpR
CdSoilTotalpHpCd
© Sauvé 2003
Free CuFree Cu2+2+
Tight relationship to soil solution pH and total metal content
N=94
© Sauvé 2003
Free PbFree Pb2+2+
For Pb…
N=84
© Sauvé 2003
Free ZnFree Zn2+2+
Preliminary speciation data for a free zinc regression
N=30 (Tambasco et al., Sauvé unpublished and and Knight et al. 1999)
© Sauvé 2003
Predictive Regressions for Predictive Regressions for Free MetalFree Metal
Pb2+
Cu2+
Zn2+
Should be possible to derive similar regressions for other divalent cationic metals or anionic elements.
.).(,94,001.0,921.0
)(log)08.0(84.1)06.0(47.1)39.0(20.3)58.0(2
102
ESnpR
CuSoilTotalpHpCu
.).(,84,001.0,643.0
)(log)10.0(84.0)05.0(84.0)28.0(78.6)47.0(2
102
ESnpR
CdSoilTotalpHpPb
.).(,30,001.0,760.0
)(log)22.0(71.1)10.0(95.0)59.0(70.4)50.0(2
102
ESnpR
ZnSoilTotalpHpZn
© Sauvé 2003
Free Ion Activity ModelFree Ion Activity Model
7.58.08.59.09.5
Free Metal (pCu2+ )
0
20
40
60
80
100
% S
urv
ival
B0 1 2 3 4 5
Total Dissolved Cu (µM)
0
20
40
60
80
100
% S
urv
ival
A
Ma H, Kim S, Cha D, Allen H (1999) Effect of kinetics of complexation by humic acid on toxicity of copper to Ceriodaphnia dubia. Environ Toxicol Chem 18: 828-837.
InhibitionInhibition
1 10 100 1000
Total Pb (mg·kg -1)
0
20
40
60
80
100%
Inhi
bitio
n R2=0.127
From: Sauvé et al. 1998. Derivation of soil quality criteria using predicted chemical speciation of Pb2+ and Cu2+. Environ. Toxicol.
Chem. 17:1481-1489.
InhibitionInhibition
1 10 100 1000
Total Pb (mg·kg -1)
0
20
40
60
80
100%
Inhi
bitio
n R2=0.127
From: Sauvé et al. 1998. Derivation of soil quality criteria using predicted chemical speciation of Pb2+ and Cu2+. Environ. Toxicol.
Chem. 17:1481-1489.
© Sauvé 2003
InhibitionInhibition
6789101112
Predicted pPb2+
0
20
40
60
80
100
% In
hibi
ti on
BR2=0.409
1 10 100 1000 10000Total Pb (mg/kg)
0
20
40
60
80
100
% In
hibi
ti on
AR2=0.127
From: Sauvé et al. 1998. Derivation of soil quality criteria using predicted chemical speciation of Pb2+ and Cu2+. Environ. Toxicol.
Chem. 17:1481-1489.
© Sauvé 2003
InhibitionInhibition
6789101112
Predicted pPb2+
0
20
40
60
80
100
% In
hibi
ti on
BR2=0.409
1 10 100 1000 10000Total Pb (mg/kg)
0
20
40
60
80
100
% In
hibi
ti on
AR2=0.127
From: Sauvé et al. 1998. Derivation of soil quality criteria using predicted chemical speciation of Pb2+ and Cu2+. Environ. Toxicol.
Chem. 17:1481-1489.
© Sauvé 2003
ConclusionsConclusions Reasonable predictions of the speciation of
metals in soils can be realized from simple regressions with total metal burden, soil solution pH and other soil characteristics
Within a large sampling program, as much care should be devoted to « other » physicochemical parameters as to soil metal analyses per se.
email: [email protected]://mapageweb.umontreal.ca/sauves/