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Sources, Mobility and Bioaccessibility of Potentially Harmful Elements in UK Soils
© NERC All rights reserved
Mark CaveBritish Geological Survey
Sources of Potentially Harmful Elements in soils
• Natural geogenic sources• Anthropogenic pollution
• Point source (single identifiable source)
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identifiable source)• Diffuse pollution
(dispersed over a wide area)
Census Area Statistical Wards 2003
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Domain Area
(km2)
Area
(%)
NBC
(mg/kg)
n
Ironstone 1,300 1 220 437
Mineralisation 2,300 2 290 187
Principal 129,30
0
97 32 41,50
9
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Establishing a Normal Background
Concentration (NBC)
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Arsenic in the Ironstone domain
Domain Area
(km2)
Area
(%)
NBC
(mg/kg)
n
Urban 5,400 4 820 7,529
Mineralisation 2,900 2 2,400 347
Principal 124,60
0
94 180 34,25
7
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Domain Area
(km2)
Area
(%)
NBC
(mg/kg)
n
Urban 5,200 4 2.1 9,308
Min. Group 2 500 <1 17 224
Min. Group 1 1,600 1 2.9 95
Chalk South 6,900 5 2.5 265
Principal 118,70
0
89 1.0 4,418
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How do we measure PHE mobility?
• Geo availability – PHE fractionation, mineralogy, sequential extraction, SEM, XAFS,XANES
•
CarbonatesMn oxides
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• Bioaccessibility/bioavailability – measure in-vivo or mimic inhalation, ingestion, dermal contact.
Iron Oxides
Alumino Silicates
Organic
Ingestion
What are we trying to achieve?
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Absorption
Exposure biomarkersBiological markers (biomarkers) can be utilised to estimate
levels of exposure to harmful substances.
Following exposure, soluble arsenic is adsorbed from the gastro-intestinal tract and distributed to all bodily systems in
the blood, accumulating in many body parts.
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Toenails Fingernails Hair
Long-term (past exposure)
Blood Urine
Short-term (recent exposure)
Bioaccessibility : Unified BARGE Method (UBM)
Saliva
pH = 6.5 ± 0.5
Stomach
extractantpH = 0.9/1.0
pH =1.2 +/-.05
Centrifuge (3000 g,
5 min). Analysis by
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0.6 g soil
0.6 g soil
End-over-end
1 hour
Intestinal
extractant
End-over-end
4 hours
pH =6.3 ±
0.5pH = 6.3 ± 0.5
5 min). Analysis by
ICP-OESGastric sample
Gastro-Intestinal sample
The PBET method
Stomach and Intestine reagents are Soil samples are weighed into Soils are extracted with gastric
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Stomach and Intestine reagents are prepared according to the protocol
Soil samples are weighed into centrifuge tubes
Soils are extracted with gastric and intestine solutions in a water
bath at 370 C
Samples are CentrifugedDecanted samples are diluted and preserved in 0.1 M HNO3
Samples are analysed by ICP-
AES
Comparison of in vivo and in vitro data for NIST 2710 for the UBM inter-laboratory trial (2006/2007)
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2012,46, pages 6252-6260
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bone
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Summary of the RBA vs RBAc regression statistics for the four end points for As. Black squares show data for the ‘stomach’ phase and white triangles for the ‘stomach & intestine’
phase. Error bars represent 95% confidence limits dotted lines show benchmark values.
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0 2 4 6 8Intercept
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0.2 0.6 1.0 1.4Slope
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0.6 0.8 1.0r squared
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Summary of the RBA vs RBAc regression statistics for the four end points for Cd. Black squares show data for the ‘stomach’ phase and white triangles for the ‘stomach & intestine’
phase. Error bars represent 95% confidence limits, dotted lines show benchmark values
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-10 10 30Intercept
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0.4 0.8 1.2Slope
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0.6 0.8 1.0r squared
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Summary of the RBA vs RBAc regression statistics for the four end points for Pb. Black squares show data for the ‘stomach’ phase and white triangles for the ‘stomach & intestine’
phase. Error bars represent 95% confidence limits, dotted lines show benchmark values.
© NERC All rights reserved
-5 5 15Intercept
kidn
eyli
ver
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0.2 0.6 1.0 1.4Slope
kidn
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0.6 0.8 1.0r squared
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Rel
ativ
e bi
oacc
essi
bilit
y % 20
4060
8010
0
(a)
Stomach
2040
6080
100
(a)
Stomach & Intestine
RBAc against RBA for (a) Pb and (b) Cd for the ‘stomach’ and ‘stomach & intestine’ phases for the kidney endpoint. Bold dashed dotted line is the line of equivalence, dashed lines are
the 95% confidence intervals and the solid lines is the best line of fit
Pb
© NERC All rights reservedRelative bioavailability %
Rel
ativ
e bi
oacc
essi
bilit
y %
0 20 40 60 80 100
0
0 20 40 60 80 100
0
0 20 40 60 80 100
020
4060
8010
0
(b)
0 20 40 60 80 100
020
4060
8010
0
(b)
Cd
Rel
ativ
e bi
oacc
essi
bilit
y % 20
4060
8010
0
(c)
Stomach
2040
6080
100
(c)
Stomach & Intestine
RBAc against RBA for (c) As and (d) Sb for the ‘stomach’ and ‘stomach & intestine’ phases for the urine end point. Bold dashed dotted line is the line of equivalence, dashed
lines are the 95% confidence intervals and the solid line is the best line of fit.
As
© NERC All rights reservedRelative bioavailability %
Rel
ativ
e bi
oacc
essi
bilit
y %
0 20 40 60 80 100
0
0 20 40 60 80 100
0
0 5 10 15 20
05
1015
20
(d)
0 5 10 15 20
05
1015
20
(d)
Sb
Comparison of the Relative Bioaccessibility of As in the UK
6
5
4
s
GLAS
HUMB
LOND
NORT
SWAN
AREA
Scatterplot of LnBSAs vs LnAs: UBM analysis
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8765432
3
2
1
0
LnAs
LnBSAs
LondonSwansea
Northampton
Glasgow
Hull
Don’t just rely on the bioaccessibility test
• Always use geochemical tests to back up your bioaccessibility results.
• Helps the risk assessor put the bioaccessibility value in context.
Centrifugation
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bioaccessibility value in context.• Bioaccessibility is no longer just a ‘black
box’ or a black art in the eyes of the regulators and policy makers
• Allows decisions to be made regarding current and future land use.
• Gives the regulator added confidence in the risk assessment.
0.45 µµµµfilter
membrane leachate
How are PHE distributed in the soil components?
CISED TestChemometric Identification of Substrates and Element
Distributions
•Separate aliquots of aqua regia of increasing concentration. Centrifugation
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increasing concentration.
•Passed through the sample under centrifugal force.
•Determination by ICP-AES.
•Chemometric data processing .
•Identification of physico-chemical hosts and the metal distributions within
the sample under test.
Centrifugation
0.45 µµµµfilter
membrane leachate
Example of CISED
Fe
Fe-Al
Pb
Fe
Fe-Al
As
Fe oxide
Fe oxide
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0 20 40 60 80
Ca
K -Ca
Mn-Al
Al-Fe
Ca-Al
Fe-Na-Si-P
mg kg-10 5 10 15 20 25
Ca
K -Ca
Mn-Al
Al-Fe
Ca-Al
Fe-Na-Si-P
mg kg-1
Mn oxide
Carbonate
Al oxide
Carbonate2
Residual solutes
Organics
Northampton• Large Market town in central England
• Population of c. 200,000• Busy Road and Rail links
• Primary industrial activities were shoe making and other leather industries• Now a hub for finance and distribution
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• Now a hub for finance and distribution industries
• BGS surveyed the area as part of the G-BASE programme
• Ironstone soils, naturally elevated in arsenic• 45% of the soils have As concentrations above
the residential SGV of 32 mg mg-1
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Measurement of the diffuse reflectance spectra of soils using a mug light.
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2.5
3
3.5
4A
bsor
banc
e
281 spectra Northampton urban soils
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500 1000 1500 2000 25000.5
1
1.5
2
Wavelength, nm
Abs
orba
nce
Coefficient Value Standard Error P value % Variance
explained
Intercept -0.56 1.22 <0.64 -
pH 0.41 0.12 <0.05 22.6
MLR model of bioaccessible As using NIR spectral components and Major element compositions
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As 0.05 0.01 <0.05 37.6
Mg 0.00 0.00 <0.05 4.9
SC1 -21.1 3.6 <0.05 2.5
SC2 16.2 2.5 <0.05 16.5
R square = 0.84
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0.2
0.3
0.4
Den
sity
Bio
acce
ssib
le A
s
0.01
00.
020
0.03
0
Den
sity
Tot
al A
s
Bioaccessible AsTotal As
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0 20 40 60 80 100
0.0
0.1
As mg kg−1
Den
sity
Bio
acce
ssib
le A
s
0.00
00.
010
Den
sity
Tot
al A
s
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A Structured Approach
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