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Sources, Mobility and Bioaccessibility of Potentially Harmful Elements in UK Soils
© NERC All rights reserved
Mark CaveBritish Geological Survey
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Sources of Potentially Harmful Elements in soils
• Natural geogenic sources• Anthropogenic pollution
• Point source (single identifiable source)
© NERC All rights reserved
identifiable source)• Diffuse pollution
(dispersed over a wide area)
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Census Area Statistical Wards 2003
© NERC All rights reserved
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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
© NERC All rights reserved
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Establishing a Normal Background
Concentration (NBC)
© NERC All rights reserved
Arsenic in the Ironstone domain
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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
© NERC All rights reserved
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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
© NERC All rights reserved
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How do we measure PHE mobility?
• Geo availability – PHE fractionation, mineralogy, sequential extraction, SEM, XAFS,XANES
•
CarbonatesMn oxides
© NERC All rights reserved
• Bioaccessibility/bioavailability – measure in-vivo or mimic inhalation, ingestion, dermal contact.
Iron Oxides
Alumino Silicates
Organic
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Ingestion
What are we trying to achieve?
© NERC All rights reserved
Absorption
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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.
© NERC All rights reserved
Toenails Fingernails Hair
Long-term (past exposure)
Blood Urine
Short-term (recent exposure)
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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
© NERC All rights reserved
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
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The PBET method
Stomach and Intestine reagents are Soil samples are weighed into Soils are extracted with gastric
© NERC All rights reserved
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
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Comparison of in vivo and in vitro data for NIST 2710 for the UBM inter-laboratory trial (2006/2007)
© NERC All rights reserved
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2012,46, pages 6252-6260
© NERC All rights reserved
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bone
urin
e
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bone
urin
e
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bone
urin
e
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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.
© NERC All rights reserved
0 2 4 6 8Intercept
kidn
eyli
ver
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0.2 0.6 1.0 1.4Slope
kidn
eyli
ver
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0.6 0.8 1.0r squared
kidn
eyli
ver
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bone
urin
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bone
urin
e
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bone
urin
e
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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
© NERC All rights reserved
-10 10 30Intercept
kidn
eyli
ver
bone
| |
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0.4 0.8 1.2Slope
kidn
eyli
ver
bone
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0.6 0.8 1.0r squared
kidn
eyli
ver
bone
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bone
urin
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bone
urin
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urin
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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
eyli
ver
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0.6 0.8 1.0r squared
kidn
eyli
ver
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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
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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
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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
© NERC All rights reserved
8765432
3
2
1
0
LnAs
LnBSAs
LondonSwansea
Northampton
Glasgow
Hull
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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
© NERC All rights reserved
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
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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
© NERC All rights reserved
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
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Example of CISED
Fe
Fe-Al
Pb
Fe
Fe-Al
As
Fe oxide
Fe oxide
© NERC All rights reserved
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
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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
© NERC All rights reserved
• 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.
© NERC All rights reserved
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2.5
3
3.5
4A
bsor
banc
e
281 spectra Northampton urban soils
© NERC All rights reserved
500 1000 1500 2000 25000.5
1
1.5
2
Wavelength, nm
Abs
orba
nce
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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
© NERC All rights reserved
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
© NERC All rights reserved
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
© NERC All rights reserved