Following retrieval, near-surface water samples (75 1) were promptly tiltered through membrane filters (0.45 pm) and uranium pre-concentrated
in 25 1 sub-samples by co-precipitation with Fe(OH)
3
for total dissolved
uranium determination. Measurement of colloidal uranium was carried
out on the remaining 50 1 of microfiltered water by tangential-flow ultrafiltration using polysulphone membrane cassettes with cut-offs corresponding to nominal molecular weight limits (NMWLs) of 10 kDa. Uranium was separated front the Fe(OH), co-predpitate and purified using
standard radiochemical techniques (León Vintró & Mitchell, 2000). Uranium sources were prepared by electrodeposition onto stainless-steel discs
and counted for periods of 10-20 days in a low-background alpha spectrometric system equipped with 24 passivated ion-implanted planar silicon (PlPS) detectors.
Results and discussion
The
238 U and 234 U concentrations at each of the sampling stations, together with the corresponding “
vt U/ - *U activity ratios, are given in the table.
The dissolved
i18 U concentration for the Garonne river (Stn. 13), at 0.63
± 0.()6 dpm T' (±2(5) is consistent with the value of 0.49 dpm 1 -1 reported
by Martin et d (1978) for the same river, and with the range of various
world-wide riverine ‘end-members’ reported by Carroll & Moore (1994).
This value, which can be taken as representative of the zero salinity ‘endmember’, is four times lower than that measured at the mouth of the estuaty
(Sta 10); the latter, at 2.6 ±0.2 dpm T 1 (±2o) is typical of open-ocean water
concentrations (Ku etd, 1977) and, thus, defines the seawater end-member.
234 U,
238 U concentrations (±2o) in filtered water sampled along the salinity gradient of the Gironde
estuary (Swamgir-1 expedition, 21st-29th June 1999).
Station
Latitude
(N)
Longitude
(W)
Salinity
(%o)
2MU
(dpm H)
234U
(dpm H)
234U / 238U
13
44-39.123'
0-21.016'
0
(1.63 ±0.06
0.67 + 0.06
1.07 + 0.08
16
45-1 1.220'
0-43.156'
1.4
0.4410.03
0.49 + 0.03
1.12 + 0.06
15
45” 11.179'
0-43.156’
1.8
0.53 ± 0.04
0.58 + 0.04
1.08 + 0.06
17
45-11.220'
0-43.156'
2.2
0.50 ±0.03
0.57 + 0.04
1.14 + 0.06
14
45-11.179'
0-43.156’
4.0
0.61 ±0.04
(1.72 + 0.04
1.14 + 0.06
18
45-11.179'
0-43.156'
4.(1
0.6310.04
0.70 + 0.04
1.14±n.04
07
45-19.886'
0-46.993'
7.7
0.8310.05
0.91 ±0.06
1.10 + 0.06
12
45-21.861’
0-45.071'
8.5
0.81 ±0.06
0.90 + 0.06
1.11 +0.04
11
45-21.342’
0-47.820'
9.5
0.9510.06
1.07 + 0.06
1.13 + 0.06
08
45-24.980’
0-51.475'
11.6
0.93 + 0.06
1.10 + 0.08
1.18 + 0.06
03
45-30.502'
0-59.169’
14.5
1.2810.10
1.45 + 0.12
1.13 + 0.06
04
45-32.264'
1-01.300'
16.0
1.3310.12
1.57 + 0.14
1.18 + 0.06
06
45-33.455'
1-02.038'
19.0
1.771(1.14
2.02 + 0.16
1.14 + 0.04
(ll
45-33.049'
1-01.006'
20.6
1.92 + 0.12
2.18 + 0.14
1.14 + 0.04
(P
45-34.413'
1-04.612'
22.0
1.92 + 0.16
2.17 + 0.18
1.13 + 0.04
05
45-33.938'
1-06.224'
25.3
1.8 ±0.2
2.1 ±0.2
1.17 + 0.06
09
45-38.830'
1-117.717'
27.9
2.05 + 0.10
2.26 + 0.12
1.11+0.04
10
45-38.471’
1-20.106’
34.0
2.6 ±0.2
3.0 ±0.3
1.15 + 0.04
299
in 25 1 sub-samples by co-precipitation with Fe(OH)
3
for total dissolved
uranium determination. Measurement of colloidal uranium was carried
out on the remaining 50 1 of microfiltered water by tangential-flow ultrafiltration using polysulphone membrane cassettes with cut-offs corresponding to nominal molecular weight limits (NMWLs) of 10 kDa. Uranium was separated front the Fe(OH), co-predpitate and purified using
standard radiochemical techniques (León Vintró & Mitchell, 2000). Uranium sources were prepared by electrodeposition onto stainless-steel discs
and counted for periods of 10-20 days in a low-background alpha spectrometric system equipped with 24 passivated ion-implanted planar silicon (PlPS) detectors.
Results and discussion
The
238 U and 234 U concentrations at each of the sampling stations, together with the corresponding “
vt U/ - *U activity ratios, are given in the table.
The dissolved
i18 U concentration for the Garonne river (Stn. 13), at 0.63
± 0.()6 dpm T' (±2(5) is consistent with the value of 0.49 dpm 1 -1 reported
by Martin et d (1978) for the same river, and with the range of various
world-wide riverine ‘end-members’ reported by Carroll & Moore (1994).
This value, which can be taken as representative of the zero salinity ‘endmember’, is four times lower than that measured at the mouth of the estuaty
(Sta 10); the latter, at 2.6 ±0.2 dpm T 1 (±2o) is typical of open-ocean water
concentrations (Ku etd, 1977) and, thus, defines the seawater end-member.
234 U,
238 U concentrations (±2o) in filtered water sampled along the salinity gradient of the Gironde
estuary (Swamgir-1 expedition, 21st-29th June 1999).
Station
Latitude
(N)
Longitude
(W)
Salinity
(%o)
2MU
(dpm H)
234U
(dpm H)
234U / 238U
13
44-39.123'
0-21.016'
0
(1.63 ±0.06
0.67 + 0.06
1.07 + 0.08
16
45-1 1.220'
0-43.156'
1.4
0.4410.03
0.49 + 0.03
1.12 + 0.06
15
45” 11.179'
0-43.156’
1.8
0.53 ± 0.04
0.58 + 0.04
1.08 + 0.06
17
45-11.220'
0-43.156'
2.2
0.50 ±0.03
0.57 + 0.04
1.14 + 0.06
14
45-11.179'
0-43.156’
4.0
0.61 ±0.04
(1.72 + 0.04
1.14 + 0.06
18
45-11.179'
0-43.156'
4.(1
0.6310.04
0.70 + 0.04
1.14±n.04
07
45-19.886'
0-46.993'
7.7
0.8310.05
0.91 ±0.06
1.10 + 0.06
12
45-21.861’
0-45.071'
8.5
0.81 ±0.06
0.90 + 0.06
1.11 +0.04
11
45-21.342’
0-47.820'
9.5
0.9510.06
1.07 + 0.06
1.13 + 0.06
08
45-24.980’
0-51.475'
11.6
0.93 + 0.06
1.10 + 0.08
1.18 + 0.06
03
45-30.502'
0-59.169’
14.5
1.2810.10
1.45 + 0.12
1.13 + 0.06
04
45-32.264'
1-01.300'
16.0
1.3310.12
1.57 + 0.14
1.18 + 0.06
06
45-33.455'
1-02.038'
19.0
1.771(1.14
2.02 + 0.16
1.14 + 0.04
(ll
45-33.049'
1-01.006'
20.6
1.92 + 0.12
2.18 + 0.14
1.14 + 0.04
(P
45-34.413'
1-04.612'
22.0
1.92 + 0.16
2.17 + 0.18
1.13 + 0.04
05
45-33.938'
1-06.224'
25.3
1.8 ±0.2
2.1 ±0.2
1.17 + 0.06
09
45-38.830'
1-117.717'
27.9
2.05 + 0.10
2.26 + 0.12
1.11+0.04
10
45-38.471’
1-20.106’
34.0
2.6 ±0.2
3.0 ±0.3
1.15 + 0.04
299