Supplementary information for Linking the chemical speciation of Ce to its
bioavailability in water for a freshwater alga
Philippe El-Akl†, Scott Smith‡, Kevin J. Wilkinson†*
†
Biophysical Environmental Chemistry Group, Department of Chemistry, University of
Montreal, C.P. 6128 Succursale Centre-ville, Montreal H3C 3J7, Canada
‡Department of Chemistry, Wilfrid Laurier University 75 University Avenue West,
Waterloo, Ontario, Canada N2L 3C5
*Corresponding author: Phone: +1-514 343 6741; fax: +1-514 343 7586; e-mail:
kj.wilkinson@umontreal.ca (KJW)
5x10-8
Ce filtrate concentration ()
4x10-8
3x10-8
2x10-8
10-8
0
0
1
2
3
4
5
6
7
Number of filtrations
Figure S1. Conditioning of the Amicon filter membranes by either 3.5x10-8 M cerium
(circles) or by 1.0x10-5 M lanthanum (triangles) at pH 5.0.
120
[Ce ]Cell/[Ce]Cell no washing
100
80
60
40
20
ED
TA
m
M
10
1
m
M
ED
TA
ED
TA
5m
M
0.
m
M
10
N
o
w
as
h
H
EP
ES
0
Washing condition
Figure S2. Wash efficiency of EDTA after a 1 h exposure of Ce to Chlamydomonas
reinhardtii at pH 7. N=3.
Percent of species concentration (%)
100
Ce(CO3)+
Ce3+
80
60
40
20
Ce(HCO3)2+
Ce(CO3)2-
0
4
5
6
7
8
pH
Figure S3. Speciation of cerium as a function of pH, as obtained from WHAM7 software.
The WHAM database was updated using constants from Hayes et al. [1] to take into
account the formation of Ce(OH)2+ and Ce(OH)3 (which were nonetheless negligible).
Modelling was performed using a total Ce concentration of 1x10-7 M, T= 20°C; pCO2 =
3.9x10-4 atm.
Table S1. Measured Ce concentrations for each of the pH conditions at the time of
preparation, after 24 hours of equilibration and in ultrafiltrates (3 kDa poresize). A nominal
Ce concentration of 3.5 x 10-8 M was added to the experimental media.
pH
4.0 ± 0.3
5.0 ± 0.3
6.0 ± 0.1
7.0 ± 0.1
8.0 ± 0.1
Ce concentration in
Ce concentration in
Ce concentration in
solution at t = 0 h
solution at t = 24 h
ultrafiltrate
(x10-8 M)
(x10-8 M)
(x10-8 M)
2.88
2.73
2.69
3.61
3.60
3.58
3.62
3.40
3.29
2.88
2.55
2.07
3.07
2.25
1.82
3.39
1.79
1.54
3.00
0.72
0.52
1.84
0.33
0.17
3.38
0.25
0.22
2.92
0.27
0.09
1.93
0.09
0.02
3.36
0.61
0.31
2.79
0.24
0.12
1.34
0.13
0.04
3.62
0.13
0.06
Table S2. Measured Ce concentrations for each of the pH conditions at the time of
preparation, after 24 hours of equilibration and in the ultrafilter retentates (3 kDa poresize).
A nominal Ce concentration of 1.0 x 10-7 M was added to the experimental media.
pH
4.0 ± 0.3
5.0 ± 0.3
6.0 ± 0.1
7.0 ± 0.1
8.0 ± 0.1
Ce concentration in
Ce concentration in
Ce concentration in
solution at t = 0 h
solution at t = 24 h
retentate
(x10-7 M)
(x10-7 M)
(x10-7 M)
1.13
1.00
0.07
1.11
1.00
0.07
1.10
1.01
0.06
1.11
1.05
0.14
1.10
1.03
0.15
1.12
1.03
0.16
1.10
1.02
0.17
1.11
1.02
0.21
1.10
1.01
0.24
1.10
0.48
0.30
1.10
0.32
0.24
1.12
0.12
0.10
1.10
0.46
0.42
1.18
0.45
0.47
1.14
0.50
0.49
Relative particulate concentration (%)
12
10
8
6
4
2
0
4
5
6
7
8
pH
Figure S4. Particulate Ce measured by SP-ICP-MS using a dwell time of 3 ms and 25000
reads (n=3).
The ICP-MS reads a number of counts per second (cps) of the analyte in solution. This
number of counts represents the intensity of the analytical signal I which is directly
proportional to the mass concentration of the analyte mc in mg L-1. In the case of a particle,
the mass concentration is related to the concentration in number of particles, Nc, by the
equation:
mc = NciVpi
where  is the particle density in g cm-3 and Vpi is the particle volume in cm3 .
(1)
pH5
0
100
200
300
400
500
600
265
260
255
250
245
240
235
230
270
Excitation wavelength (nm)
Excitation wavelength (nm)
270
265
260
255
pH7
0
20
40
60
80
100
250
245
240
235
230
300 320 340 360 380 400 420 440
Emission wavelength (nm)
300 320 340 360 380 400 420 440
Emission wavelength (nm)
Figure S5. Excitation-emission matrices for Ce at pH 5.0 and 7.0. The cerium
concentration was 5x10-5 M at an ionic strength of 0.01 M. The colors indicate the
measured fluorescence intensity.
3.0e-11
Internalised Ce (mol/cm2)
2.5e-11
2.0e-11
1.5e-11
1.0e-11
0.5e-12
0
0
20
40
Time (min)
60
Figure S6. Ce biouptake of Chlamydomonas reinhardtii as a function of time at pH 7.0 for
a nominal Ce concentration of 1x10-7 M. Linear regression parameters: a = 3.7x10-13 mol
cm-2 min-1 and b = 7.9x10-12 mol cm-2 with R2 = 0.992. Linear uptake was also observed at
pH 5.0. The importance of linear uptake, with respect to the respect of equilibrium
conditions, has been thoroughly discussed in Slaveykova and Wilkinson (2005) 2.
Table S3. Free Ce ion concentrations of the exposure media (replicate measurements) on data obtained at the start of uptake
experiments, with the measured average Ce uptake fluxes in Chlamydomonas reinhardti
Free Ce concentrationa (M)
pH
5.0
7.0
a.
2x10-10
9x10-10
1.40x10-8
3.60x10-8
8.00x10-8
5.94x10-8
2.32x10-7
4.08x10-7
8.40x10-7
4.50x10-6
1.0x10-9
6.1x10-9
9.3x10-9
2.69x10-8
1.18x10-7
2.52x10-6
1.0x10-9
3.4x10-9
1.16x10-8
3.50x10-8
5.44x10-8
7.20x10-8
2.20x10-7
3.83x10-7
7.83x10-7
4.30x10-6
1.2x10-9
7.4x10-9
1.01x10-8
1.18x10-8
1.18x10-7
3.03x10-6
9x10-10
2.8x10-9
1.20x10-8
2.80x10-8
5.10x10-8
7.70x10-8
4.50x10-7
7.58x10-7
4.55x10-6
2.4x10-9
1.26x10-8
1.85x10-7
2.61x10-6
1.20x10-8
2.70x10-8
5.00x10-8
8.20x10-7
4.55x10-6
Average
uptake flux
(mol cm-2 s-1)
3.9x10-16
1.1x10-15
3.8x10-15
9.6x10-15
1.1x10-14
1.4x10-14
2.3x10-14
2.3x10-14
2.4x10-14
2.7x10-14
1.3x10-15
6.8x10-15
1.3x10-14
6.4x10-14
3.8x10-14
8.1x10-14
Free ion concentration established by applying WHAMVII modeling to the measured concentration of ultrafiltered exposure media
Bibliography
[1]
Hayes SA, Yu P, O'Keefe TJ, O'Keefe MJ, Stoffer JO. 2002. The phase stability of
cerium species in aqueous systems - I. E-pH diagram for the Ce-HClO4-H2O system.
Journal of the Electrochemical Society 149: C623-C630.
2 Slaveykova VI, Wilkinson KJ. 2005. Predicting the bioavailability of metals and metal
complexes: critical review of the biotic ligand model. Environmental Chemistry 2:9-24.