Analysis for discussion only
– do not quote
Do we have a problem with
freshwater Kd values?
B. Howard and E. Tipping
CEH, UK
ERICA
• ERICA uses Kd values to predict unknown water
or sediment concentrations
• Water conc is used with CR to predict
wholebody conc and internal dose
• Sediment conc is used for estimation of external
dose
• Some ERICA values are based on sea water
– -does this introduce larger error than for the other
values used?
D is trib u tio n
N u c lid e
a q u a tic
C o e ffic ie n t (K d ) S o u rc e
Ag
Am
C
Cd
Ce
Cl
Cm
Co
Cs
Eu
H
I
Mn
Nb
Ni
Np
E R IC A
1 .2 E + 0 5
5 .3 E + 0 5
5 .0 E + 0 0
3 .0 E + 0 4
3 .8 E + 0 5
1 .0 E + 0 0
5 .0 E + 0 3
1 .1 E + 0 5
1 .4 E + 0 5
5 .0 E + 0 2
1 .0 E + 0 0
3 .0 E + 0 2
9 .1 E + 0 4
8 .0 E + 0 5
2 .0 E + 0 4
1 .0 E + 0 1
P
Pb
Po
Pu
Ra
Ru
S
5 .0 E + 0 1
1 .0 E + 0 5
2 .0 E + 0 7
1 .4 E + 0 6
1 .5 E + 0 4
4 .0 E + 0 4
5 .0 E -0 1
Sb
Se
Sr
Tc
Te
Th
U
Zr
1 .2 E + 0 4
3 .0 E + 0 3
2 .0 E + 0 3
5 .0 E + 0 0
1 .0 E + 0 3
1 .8 E + 0 7
5 .0 E + 0 1
1 .0 E + 0 3
T R S re v
T R S re v
SR S 19 / TR S 364
TR S 422
T R S re v
e d u c a te d g u e s s
SR S 19 / TR S 364
T R S re v
T R S re v
SR S 19 / TR S 364
C o p p le s to n e e t a l 2 0 0 1
A A B a lk e m a
T R S re v
TR S 422
TR S 422
SR S 19 / TR S 364
SR S 19 / TR S 364 +
O n is h i p e rs c o m m
TR S 422
TR S 422
T R S re v
T R S re v
T R S re v
TR S 422
SR S 19 / TR S 364 +
O n is h i p e rs c o m m
TRS
TRS
SRS
TRS
TRS
SRS
SRS
422
re v
19 / TR S 364
422
re v
19 / TR S 364
19 / TR S 364
typ e
s ys te m
o rig in a l s o u rc e
ads
in s itu
fw
fw
fw
sw
C iffro y e t a l
C iffro y e t a l
O n is h i 8 1
o c e a n m a rg in T a b le II
C iffro y e t a l
fw
fw
fw
fw
O n is h i
C iffro y
C iffro y
O n is h i
fw
sw
sw
fw
C iffro y e t a l
o c e a n m a rg in T a b le II
o c e a n m a rg in T a b le II
O n is h i 8 1
fw
sw
sw
fw
O n is h i 8 1
o c e a n m a rg in T a b le II
a n a lo g u e
C iffro y e t a l
C iffro y e t a l
C iffro y e t a l
o c e a n m a rg in T a b le II
in s itu
in s itu
in s itu
in s itu
sw
in s itu
fw
sw
fw
fw
sw
fw
fw
81
et al
et al
81
O n is h i 8 1
o c e a n m a rg in T a b le II
C iffro y e t a l
O n is h i 8 1
a n a lo g u e
C iffro y e t a l
O n is h i 8 1
O n is h i 8 1
ERICA values
from Ciffroy are
AM from the
reported GM
N u c lid e
Am
Ce
Co
Cs
I
Mn
Pu
Ra
Sr
Th
E R IC A
530000
384000
106000
137000
300
90800
1390000
15200
2000
18400000
T R S 3 6 4 v a lu e ra tio E R IC A/3 6 4
5000
10000
5000
1000
10
1000
10000
500
1000
1000
Oxidising
conditions
106
3 8 .4
21
137
30
9 0 .8
139
30
2
18400
Comparison
with TRS 364
(Onishi 81)
KD
=
mol bound (g colloid)-1
mol L-1 in solution
But KD depends on:
pH
competing solutes
competing ligands
loading of the colloid
ionic strength
Modelling tries to explain variability in KD
WHAM
Mz+
-
-
10
9
Mz+
Key assumption
– binding
to
z+
M
organic matter dominates for
N metal
ions Mz+
b in d in g stren g th
8
7
6
5
4
3
2
H+
1
0
1
Model VI
Specific & nonspecific proton
& metal binding
2
3
4
5
6
N
7
m e ta l co n c
-
Mz+
8
9
H+
Humic substances
The most abundant
macromolecules on
the planet!
• Partial decomposition products of plants etc
• Principally composed of C, H and O, + N & S
• Heterogeneous, recalcitrant, yellow-to-brown
• Possess weak acid groups - COOH, phenolic-OH
• Fulvic acid MWt ~ 1000
dominant in waters
• Humic acid MWt ~ 10 000
dominant in soils
Database for WHAM / Model VI
GAP studies
FILLING: binding
strength
correlations
for metal
• Laboratory
with
isolated
HA
andionsFA
10
9
• ~ 207 data sets for protons
log K humic acid
8
6
~ 100 data sets for metals
5
4
3
Esp actinides
2
1
• Average
proton binding for FA and HA
0
1
2
3
4
5
6
7
8
9
• Average binding for 23+ metals (Mg…Cu…Eu...Cm)
log K acetic acid
Model VI and cation binding : summary
• Proton and metal binding as function of [H+], [Mz+]
• Proton-metal competition (pH dependence)
• Metal-metal competition (esp at high [M+])
• Ionic (eg Na, Cl, )strength dependence of H and M
binding due to interference with binding
Ion-binding models and their combinations
“simple”
solution
chemistry
WHAM
Humic IonBinding Models
V & VI
Na, Cl, OH, CO3, SO4
SCAMP
Clay cation
exchanger
Oxide model
AlOx SiOx
MnOx FeOx
Wham 6 set up
•Freshwaters are for 3 different [DOC] - 1, 3 and 10 mg/L
•A range of pH's is generated by titrating an initially acid
solution with Ca, to take us from pH ~ 4 to pH ~ 8.5
•Seawater is assumed to be at pH 8, and with 2 mg/l DOC
assumed ph8 for fw values also
WHAM IV
• Calculations assume that
– DOC can be represented by average isolated fulvic
acid,
– OM in particulate matter (SPM) can be represented
by average isolated humic acid
• Only organic matter in the SPM has any binding
properties (oxides, clay etc ignored)
• Calculations take into account
– competition between the element of interest and
major ions (H+, Mg, Ca, Al, Fe etc),
– complexation by inorganic ligands and natural organic
matter (dissolved and particulate)
Kd estimates
• The Kd's are calculated for suspended
particulate matter containing 10% organic
matter
• results give some idea of
– how Kd can vary with pH and [DOC],
– comparisons between FW and SW
Health warning
• Elements which form hydrolysis reactions in solution at
low pH may not be represented well as the model
assumes organic complexation (eg Pu)
• The element concentrations are set to low levels and will
be sensitive to the model's assumptions about small
numbers of strong binding sites
• The model default database has differences in the
binding strengths of fulvic and humic acid towards most
metals,
– these difference may not be real. (e.g. UO2 and PuO2)
• Some elements affected by redox, models assumes
specifi oxidation state
– Cr, Mn, Fe, Tc, Np
FeIII
1000000
No Erica value
(just WHAM)
100000
Kd l/kg
10000
1000
[DOC] = 1
[DOC] = 3
100
[DOC] = 10
sw pH 8
10
1
CrIII
3
4
5
6
7
8
9
pH
10000000
1000000
Onishi
10000
Fe – 5000
[DOC] = 1
[DOC] = 3
1000
Cr low
[DOC] = 10
100
sw pH 8
Zn - 500
10
1
Zn
3
4
5
6
7
8
9
pH
100000
10000
sw value similar to
fw predictions at
relevant pH
Kd l/kg
Kd l/kg
100000
1000
[DOC] = 1
[DOC] = 3
100
[DOC] = 10
sw pH 8
10
1
3
4
5
6
pH
7
8
9
Erica - Ciffroy
Am – ERICA high
over most pH
range
Am
10000000
1000000
Kd l/kg
100000
Sw – lower
10000
[DOC] = 1
1000
[DOC] = 3
[DOC] = 10
100
Onishi 100x lower
than ERICA
ERICA value
10
sw pH 8
1
3
4
5
6
7
8
9
pH
Th
Th – ERICA much
higher
100000000
[DOC] = 1
10000000
[DOC] = 3
[DOC] = 10
1000000
TRS – much lower
Onishi (c.20000)
ERICA value
sw pH 8
100000
Kd l/kg
Sw – lower, similar to
fw model
10000
1000
100
10
1
3
4
5
6
pH
7
8
9
PuIV
10000000
ERICA Ciffroy
1000000
[DOC] = 1
100000
[DOC] = 3
Kd l/kg
10000
[DOC] = 10
1000
ERICA value
100
sw pH 8
10
1
0.1
0.01
3
4
5
6
7
8
9
pH
PuO2
10000000
Onishi – 100x
lower
Kd l/kh
1000000
100000
[DOC] = 1
10000
[DOC] = 3
[DOC] = 10
1000
ERICA value
100
sw pH 8
10
1
0.1
0.01
3
4
5
6
pH
7
8
9
Mn
100000
[DOC] = 1
Erica - Ciffroy
[DOC] = 3
10000
ERICA value
1000
sw pH8
100
10
1
3
4
5
6
7
8
9
Co
pH
1000000
Onishi
100000
[DOC] = 1
[DOC] = 3
10000
Kd l/kg
Mn 100 x lower
[DOC] = 10
ERICA value
1000
sw pH 8
Co 20 x lower
100
10
Sr - same
1
3
Sr
1000
100
[DOC] = 1
[DOC] = 3
[DOC] = 10
10
ERICA value
sw pH 8
1
3
4
5
4
5
6
pH
10000
Kd l/kg
Kd l/kg
[DOC] = 10
6
pH
7
8
9
7
8
9
Eu (Onishi)
ERICA Onishi
100000
[DOC] = 1
1000
[DOC] = 3
[DOC] = 10
100
ERICA value
sw pH 8
10
1
3
4
5
6
7
8
9
pH
Cm (Onishi)
1000000000
100000000
Kd l/kg
Kd l/kg
10000
10000000
[DOC] = 1
1000000
[DOC] = 3
100000
[DOC] = 10
ERICA value
10000
sw pH 8
1000
100
10
1
3
4
5
6
pH
7
8
9
UO2
[DOC] = 1
[DOC] = 3
1000000
[DOC] = 10
100000
ERICA value
1000
100
10
1
3
4
5
6
7
8
9
pH
U IV
100
10
[DOC] = 1
Kd l/kg
Kd l/kg
ERICA Onishi
sw pH 8
10000
[DOC] = 3
1
[DOC] = 10
ERICA value
sw pH 8
0.1
0.01
3
4
5
6
pH
7
8
9
Ni
Erica – sw value
100000
Kd l/kg
10000
1000
[DOC] 2
100
[DOC] 5
[DOC] 10
10
ERICA value (sw)
Cd
sw pH 8
1
3
4
5
6
7
8
100000
pH
9
10000
Kg l/kg
1000
[DOC] = 1
[DOC] = 3
[DOC] = 10
ERICA value (sw)
sw pH 8
100
10
1
Pb
3
4
5
6
pH
1000000
100000
Kd l/kg
10000
1000
[DOC] = 1
[DOC] = 3
100
[DOC] = 10
ERICA value (sw)
10
sw pH 8
1
3
4
5
6
pH
7
8
9
7
8
9
Changes with pH increase in
Wham
• rises – Cr, Zn, Eu, Cm, Pb (Fe III, Am)
• rise and fall – Mn, Co, Sr, UO2, Ni, Cd
• decrease – U IV (Th, Pu IV , PuO2)
Not possible to attribute differences systematically to only
one causal factor – this would be misleading
Effect of DOC conc on Kd in FW in
Wham IV
ratio 1 / 10 m g/l D O C
12.0
High values are all metal ions with have the
strongest binding to OM
10.0
So more DOC = more metal in solution
less DOC = less metal in soluton
6.0
4.0
2.0
u
E
m
C
m
A
h
T
2
uO
P
V
uI
P
IV
U
2
U
O
b
P
d
C
r
S
n
Z
i
N
o
C
II
eI
F
n
M
r
0.0
C
ratio o f K d
8.0
SW vs FW – Erica vs model
• FW much higher than Wham SW
– Am, Co, Mn, Sr, Th, PuIV, PuO2 (Ciffroy)
– Ni, Cd (sw values)
– UIV (Onishi)
• Similar – Pb (ERICA is sw)
• FW much lower than Wham SW
– UO2, Eu, Cm (Onishi)
FW vs SW– model
• Wham FW higher than Wham SW
– Cd, Mn, Sr, PuIV, PuO2 UIV (Co, Eu, Ni,)
• Similar
– Am, Cr, Cm, Fe III, Pb, Th, Zn
• FW lower than Wham SW
– UO2
Erica vs FW model
• Erica always higher than Wham
– Co, Mn, Th, PuIV, PuO2 (Ciffroy)
• Erica higher than Wham at low pH
– Am, Sr, Ni, Cd, Pb (sw values)
• Erica lower than Wham
– UO2, Eu, Cm (Onishi) – except at pH 4
• Similar at low pH, higher at high pH
– UIV (Onishi)
Conclusions
• ERICA AM values often high
• Model rarely predicts SW > FW, often FW
higher
• pH has large effect for many elements
• DOC important for Cr, Fe III, Pb, Am, Cm,
Eu
Does it matter
• Too High Kd values
– Will give low water conc – low whole body
conc – therefore NOT conservative but more
sensitive to error
– Will give high sediment conc – higher external
exposure - as >90% of most metals in
sediment – less sensitive to error
• Can we “do” something in ERICA to assist
user?