Zn isotopes in the suspended load of the Seine River, France: Isotopic variations and source determination

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Geochimica et Cosmochimica Acta 73 (2009) 4060–4076 www.elsevier.com/locate/gca

Zn isotopes in the suspended load of the Seine River, France: Isotopic variations and source determination JiuBin Chen a,*, Je´roˆme Gaillardet a, Pascale Louvat a, Sylvain Huon b a

Equipe Ge´ochimie et Cosmochimie, Institut de Physique du Globe de Paris, Universite´ Paris-Diderot, UMR CNRS 7154, 4 place Jussieu, 75252 Paris, France b UMR 7618 Bioemco (Bioge´ochimie et Ecologie des milieux Continentaux), Universite´ Pierre & Marie Curie, Case 120, 4 place Jussieu, 75252 Paris, France Received 29 October 2008; accepted in revised form 22 April 2009; available online 3 May 2009

Abstract We report Zn isotopic ratios (d66Zn) of river suspended particulate matter (SPM) and floodplain deposits (FD) from the Seine basin, France, with a precision 60.05&. A decrease in d66Zn from 0.30& to 0.08& is observed in SPM from the upstream to downstream parts of the fluvial system, associated with an increase in Zn concentration from 100 ppm to 400 ppm. The Zn/Al of SPM at the river mouth is up to five times greater than the Zn/Al of the natural background, and by normalizing to the later value we define a Zn enrichment factor. Suspended sediments from a temporal series of samples collected in Paris display a similar variation in d66Zn of between 0.08& and 0.26&, while showing an inverse relationship between the Zn enrichment factor and d66Zn. The amount of Zn transported as suspended load varies from 10% to 90%, as a function of increasing discharge. The d66Zn of SPM and the dissolved load are correlated, suggesting that adsorption processes are probably not the dominant process by which the Zn enrichment of SPM takes place. Instead, we interpret our data as reflecting the mixture of two main populations of suspended particles with distinct d66Zn. The first is characteristic of natural silicate particles transported by erosion processes to the river, while the second likely represents anthropogenic particles derived from wastewater treatment plants or combined sewer overflows. Based on isotopic ratios, we calculate that 70% of Zn in SPM of the Seine River in Paris is of anthropogenic origin. Ó 2009 Elsevier Ltd. All rights reserved.

1. INTRODUCTION River suspended particulate materials (SPM) can contain a record of weathering processes at the drainage basin scale and thus provide constraint on the cycling of elements at the Earth’s surface (Goldstein et al., 1984; Allegre et al., 1996; Gaillardet et al., 1999; Roy et al., 1999; Millot et al., 2004). They are essential carriers of nutrients, metals and organic pollutants, and are responsible for riverine turbidity and so play an important role in photosynthesis and food availability of the aquatic system (Meybeck et al., *

Corresponding author. Present address: Department of Chemistry, Trent University, 1600 West Bank Drive, Peterborough, Ont., Canada K9J7B8. E-mail address: [email protected] (J.-B. Chen). 0016-7037/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.gca.2009.04.017

1998; Seidl et al., 1998b; Even et al., 2004; Gaillardet et al., 2005; Bibby and Webster-Brown, 2006; Thevenot et al., 2007). In populated and industrialized regions, river sediments integrate the impact of human activities. In addition, SPM play a central role in the regulation of trace metals in river waters, which through exchange can influence the composition of the dissolved load. In the context of understanding the increasing impact of human activities on the aqueous environment, isotopes of metal pollutants may be powerful tracers of anthropogenic contaminations. Little data has been reported for Zn isotopic composition of suspended sediments in rivers. One of the limiting factors is probably sampling difficulties due to the low SPM contents of most river waters. This paper is the first to systematically investigate the controls on the d66Zn of riverine SPM in an anthropogenically disturbed Seine River system,

Zn isotopes in suspended sediments of the Seine River

and to examine the link between these materials and dissolved constituents (Chen et al., 2008). The Seine basin displays two important characteristics: a relatively simple carbonate-dominated lithology and an increasing anthropogenic impact from the headland towards the estuary. The Seine River that crosses the Paris conurbation is one of the biggest rivers in Europe and has been recognized as a polluted river with respect to metal contamination (Roy, 1991; Meybeck et al., 1998). The long-term average suspended sediment concentration of the Seine River is estimated to be 44 mg/L, which is low in comparison to the world average of 100 mg/L (Roy et al., 1999). In summer, suspended sediment concentrations decrease, but can reach >100 mg/L during floods. The main source of SPM in the Seine River is from the sedimentary terranes of Jurassic and Tertiary age that outcrop in the drainage basin (Roy et al., 1999). The geochemistry of SPM shows high degrees of chemical depletion for the most soluble elements (i.e. Na, K and Mg) and suggests that they are derived from materials that have undergone one or more cycles of weathering and deposition. The major element chemical composition of the Seine SPM is thus typical of platform shales (Roy et al., 1999). Here, we report d66Zn measurements on SPM from the Seine River. In contrast to major elements, Zn concentrations of the Seine River sediments are much greater than the natural background. We show that this excess of Zn is not primarily due to adsorption processes, but rather reflects anthropogenic inputs that can be traced using Zn isotopes. 2. ANALYTICAL METHODS The sampling process and the three sample series (temporal samples in Paris between 2004 and 2007, geographical transect samples from headwaters to estuary, rain and anthropogenic waters) have been described in detail in Chen et al. (2008). Samples were collected on a transect from the spring to the estuary during two sampling cruises and monthly or bimonthly in Paris for 3 years (Fig. 1). Fifteen liters of water were collected in a clean plastic container with an aim to obtain the required mass of SPM for isotopic and chemical analyses (>50 mg). The particulate phases were isolated by collecting SPM both deposited on polysulfone ether filters (142 mm, 0.2 lm) and settled at the bottom of the container. We ensured that the recovery of SPM was close to 100% by comparing the collected particulate mass to the quantity obtained from independently filtering waters (250 ml to 1 L) with a smaller filtration unit (47 mm filter diameter). Nine floodplain deposits (FD) were collected on the banks of the Seine River (Fontaine-le-Port and Paris) and the Marne River (Noisy-le-Grand) shortly after flood events. Complementary samples include basin headland bedrocks of granite (in Morvan region) and chalk (at Provins), and anthropogenic samples: sludges from the wastewater treatment plant (WWTP) in Ache`res (SIAAP) and urban waters (roof and road streaming waters during rainfall). All Zn isotopic compositions were measured at the Institut de Physique du Globe de Paris (IPGP). For elemental

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concentrations, a set of samples with SPM mass >250 mg were analyzed in Service d’Analyse des Roches et des Mine´raux at Nancy, France (SARM), others measured at IPGP. SPM samples were dried at 60 °C and crushed in a mortar. Approximately 30 mg of powdered SPM were dissolved in 0.5 ml distilled 16 N HNO3 mixed with 0.5 ml distilled 27 N HF for 12 h at 120 °C. After evaporation at 90 °C, the residue was digested two times, with first 1 ml 16 N HNO3 and then 0.6 ml 0.9 N H3BO3 mixed with 0.15 ml 16 N HNO3. The final residue was dissolved in 2 ml distilled 6 N HCl for chemical purification and an aliquot dissolved in 2% HNO3 for concentration measurement. This procedure resulted in clear solutions for most samples. Gels or black precipitates that formed in some cases were separated by centrifugation. Major elements were measured by ICP-AES. Concentrations of trace elements were measured on ICP-MS. Analytical quality was controlled by internal standard addition (In and Re) and regular international geo-standard (i.e. SLRS4) measurements. The precision for trace element concentrations was generally better than 5%. After carbonate removal, the content of particulate organic carbon (POC) was measured, when sufficient SPM was available, by EA (Carlo-Erba NA-1500NC) at the Laboratoire de Bioge´ochimie et Ecologie des Milieux Continentaux (Universite´ Pierre & Marie Curie), according to the previous reported methods (Huon et al., 2002; Galy et al., 2007). The mineralogy of the Seine River SPM was investigated by XRD and SEM. Zn was extracted by anion exchange chromatography according to a new procedure based on the method developed by Marechal et al. (1999), which was the first attempt capable of separating Zn, Cu and Fe from the sample matrix. This method has been successfully used after modification to remedy premature Cu elution and reduce the total elution volume and thus the procedural blank (Archer and Vance, 2004; Pokrovsky et al., 2005; Chapman et al., 2006; Borrok et al., 2007; John et al., 2007a,b). In this study, 6 N HCl was used as the introduction solution rather than 7 N HCl. This modification not only lessens problems with evaporation due to concentrated hydrochloric acid use (P7 N), but also reduces the quantity of cobalt present in the Cu fraction (Borrok et al., 2007), since the Co partition coefficient in 6 N HCl is almost 10 times smaller than in 7 N. Digested samples (in 1 ml 6 N HCl) were loaded onto the column filled with 1.6 ml AG MP-1 resin. After the matrix elution with 10 ml 6 N HCl, Cu, Fe and Zn were collected in 20 ml 6 N HCl, 10 ml 2 N HCl and 10 ml 0.5 N HNO3, respectively. The final Zn fraction was evaporated and conditioned for MC-ICP-MS measurement (dissolution in 0.05 N HNO3 and Cu addition) (Chen et al., 2009). This procedure led to Zn yields close to 100% for most samples, checked by comparison with Zn concentrations measured previously by ICP-MS. The total Zn procedural blank was about 19 ± 2 ng. This blank contribution had no significant influence on Zn isotopic measurements considering a typical sample size of 1 lg (Chen et al., 2009). The technique for Zn isotopic measurement was described in detail in Chen et al. (2009). Briefly, all samples

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J.-B Chen et al. / Geochimica et Cosmochimica Acta 73 (2009) 4060–4076

LE HAVRE

Aisne

39

Se

ine

37

Marne

36 40, FD5-9

PTWW2

ACHERES

SW1, PTWW1

31

FD2

32 TROYES

Yonne

g

Loin

0°

ne

ne 33

Sei 34

Au

be

35, FD1

ar

RF5 RD2 FD3,4

PARIS

M

1-27 41- 48 63- 65

N

REIMS

O

Eure

38

is e

ROUEN

30

50°

29 in

Se e

Cur e

28

100 km

ne

Yon

AN RV

O

M

Fig. 1. Map of the Seine basin and sampling locations. RF, RD and FD denote roof runoff, roadway runoff and fresh floodplain deposit, respectively. Untreated sewage water SW1 and plant-treated wastewater PTWW1 were collected in SIAAP wastewater treatment plant in Noisy-le-Grand, and PTWW2 in Ache`res.

and standards were diluted to 200 ppb of Zn in 0.05 N HNO3. Zn isotopic analyses were performed at IPGP on the Neptune multiple-collector-ICP-MS (Thermo Finnigan, Germany), using the Apex HF as introduction system. The instrumental mass bias was corrected using the developed ‘‘empirical external normalization” method by adding CuSRM976 in both Zn sample and standard solutions as internal standard with Zn/Cu = 2. All Zn isotopic results in this study are expressed as d66Zn (in &): h i d66 Zn ¼ ð66 Zn=64 ZnÞsample =ð66 Zn=64 ZnÞJMC  1  1000 ð1Þ where JMC represents the JMC 3–0749L Zn isotopic standard solution (from Lyon, France). Only d66Zn values are discussed in this study, as all other Zn isotopic ratios are proportional, since they all follow the theoretical massdependent fractionation law. The international standard BCR-1 basalt (USGS, USA) has been measured in this study using the previously described chemical and analytical protocol. Our average value of 0.28 ± 0.02& (2r) is consistent with those reported in other studies (0.20–0.32&) (Archer and Vance, 2004; Chapman et al., 2006; Viers et al., 2007; Cloquet et al., 2008).

3. RESULTS 3.1. Zn concentrations and enrichment factors in suspended particulate matter Zn concentrations were measured in the 48 river waters that contained sufficient quantities of suspended materials for analysis (P50 mg). Generally, these samples were collected during the high water period both in Paris and along the geographical transect, while some low water samples in Paris were also analyzed (Table 1). Zn concentrations in river SPM of the whole Seine basin collected during the February 2006 flood period range from 94 ppm (or mg/kg, pristine Seine sample S29) to 323 ppm (the Seine River before the estuary, S38). A linear increase in Zn concentration in SPM is observed with distance from the Seine spring to its estuary (Fig. 2a). The Seine River samples in Paris have generally higher particulate Zn concentrations (130–452 ppm) compared to the transect samples (94–323 ppm), in particular during the low water stages (water discharge lower than 350 m3/s, Table 1). Zn concentrations in these temporal samples decrease with the water discharge (Fig. 2b). During high water stages in Paris, Zn concentrations are lower and close to those mea-

Table 1 Enrichment factors, isotopic compositions of Zn and element concentrations in rivers of the Seine basin. Discharge (m3/s)

Al (ppm)

Ca (ppm)

Cr (ppm)

Cu (ppm)

Zn (ppm)

La (ppm)

Th (ppm)

0.22 ± 0.01 0.15 ± 0.04 nd 0.22 ± 0.04 nd nd nd nd 0.20 ± 0.04 nd nd 0.18 ± 0.04 nd 0.18 ± 0.03 0.14 ± 0.02 0.14 ± 0.05 nd 0.12 ± 0.03 0.08 ± 0.03 0.16 ± 0.03 0.15 ± 0.05 nd 0.14 ± 0.02 0.11 ± 0.03 0.19 ± 0.04 nd 0.21 ± 0.05 nd 0.20 ± 0.04 0.24 ± 0.03 0.18 ± 0.04 0.20 ± 0.05 nd 0.15 ± 0.02 nd nd 0.26 ± 0.03 0.18 ± 0.05

nd nd nd 57 nd nd nd nd 42 nd nd nd nd nd nd nd nd 58 59 58 nd nd nd 71 71 nd 48 nd nd 36 nd nd nd nd nd nd 41 64

51266 55000 54378 60026 64712 59824 51049 63522 50213 45546 42886 41264 49816 45707 49220 48610 nd 51890 48116 45524 44470 nd 43032 55403 46554 nd 61459 nd 55302 53639 46982 49837 nd 42261 nd nd 61154 38370

156206 135659 122066 102880 91698 104843 128200 101857 131187 144367 151806 124729 120752 127082 129299 123377 nd 137903 138351 129463 122045 nd 117831 99341 105349 nd 101879 nd 127664 nd 140257 126900 nd 130945 nd nd 119269 118235

74 79 77 81 87 80 74 89 74 68 70 66 75 72 75 97 89 96 91 87 83 nd 81 91 76 74 85 92 86 83 74 76 73 76 nd 87 96 63

53 58 40 35 43 42 56 34 34 32 44 68 61 71 68 84 128 122 98 102 93 nd 116 70 58 105 42 41 38 30 33 40 33 65 nd 75 39 85

235 244 193 171 205 197 222 156 135 130 153 235 229 248 251 378 444 452 403 358 356 nd 415 330 290 430 243 245 223 195 181 217 213 299 nd 291 244 290

26 25 26 29 32 28 26 31 27 24 26 22 26 25 27 27 29 30 27 27 26 nd 24 26 24 24 31 32 30 30 24 28 26 24 nd 30 33 21

8.4 8.2 8.2 9.0 9.7 8.7 8.2 9.3 8.0 7.5 7.8 6.7 7.7 7.3 7.9 7.6 8.0 8.6 7.7 7.2 7.0 nd 6.8 7.9 6.9 6.7 9.2 9.6 8.9 8.8 7.5 8.3 7.7 7.4 nd 8.1 10.4 7.0

Geographical transect samples of the whole Seine basin: the sampling cruise of 22 February 2006 S28 Seine@Sring S29 Seine@Buncey 1.8 25.5 17.2 0.20 ± 0.04 56 S30 Seine@Bar 2.3 67.2 31.8 0.14 ± 0.04 75

28048 28906

nd 220300

58 62

14 37

94 123

Samples of temporal series in Paris (December 2004–March 2007) S1 23/12/04 2.5 413 53.6 S2 21/01/05 2.4 336 6.3 S3 25/01/05 1.9 535 69.2 S4 27/01/05 1.6 436 81.4 S5 29/01/05 1.7 404 45.4 S6 31/01/05 1.8 311 44.7 S7 14/02/05 2.4 486 30.9 S8 17/02/05 1.4 543 83.0 S9 20/02/05 1.5 542 73.4 S10 22/02/05 1.6 483 60.0 S11 24/02/05 2.0 461 43.3 S12 08/04/05 3.1 251 8.9 S13 29/04/05 2.5 316 8.1 S14 19/05/05 3.0 222 10.6 S15 25/05/05 2.8 180 5.5 S16 23/06/05 4.3 100 1.8 S17 11/07/05 179 21.0 S18 25/07/05 4.8 119 14.0 S19 26/08/05 4.6 143 13.9 S20 17/09/05 4.3 183 10.8 S21 03/10/05 4.4 167 3.9 S22 09/11/05 118 3.8 S23 29/11/05 5.3 122 3.2 S24 22/12/05 3.3 125 4.4 S25 24/01/06 3.4 226 6.6 S26 17/02/06 368 24.4 S27 20/02/06 2.2 601 150.8 S41 01/03/06 321 32.8 S42 10/03/06 2.2 785 110.4 S43 14/03/06 2.0 1013 108.4 S44 20/03/06 2.1 730 36.0 S45 31/03/06 2.4 775 46.4 S46 11/04/06 503 18.0 S47 15/05/06 3.9 379 11.0 S48 21/06/06 104 3.7 S63 13/10/06 nd 294 33.8 S64 07/03/07 2.7 800 82.8 S65 10/05/04 4.2 372 30.2

22 5.5 17 4.8 (continued on next page)

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POC (mg/g)

SPM (mg/L)

Zn isotopes in suspended sediments of the Seine River

d66Zn (&)

E.F. (Zn)

4064

Table 1 (continued) Discharge (m3/s)

SPM (mg/L)

d66Zn (&)

POC (mg/g)

Al (ppm)

Ca (ppm)

Cr (ppm)

Cu (ppm)

Zn (ppm)

La (ppm)

Th (ppm)

1.1 1.5 1.3 1.9 1.8 2.3 2.4 2.9

49 31.7 96 257 400 203 701 807 27.1 157

86.0 63.0 101.6 109.2 105.8 258.8 122.0 56.8 47.6 115.6

0.27 ± 0.01 0.19 ± 0.04 0.20 ± 0.04 nd 0.22 ± 0.02 nd 0.17 ± 0.01 0.12 ± 0.02 nd nd

27 35 30 nd 45 nd 42 50 nd nd

57256 60152 64239 68723 68273 50215 59792 61145 nd 51898

149764 141357 140093 85057 96000 87693 92100 nd nd 136221

81 88 93 103 98 98 102 99 89 83

18 28 21 36 33 34 47 71 56 37

116 168 152 236 227 207 263 323 330 162

27 26 28 37 35 27 32 29 30 33

8.5 8.4 8.8 11.3 10.8 8.1 9.4 8.4 8.6 8.4

Anthropogenic samples in Paris mega-city (February 2005–July 2006) RF5 Roof streaming 72.6 RD2 Road streaming nd SW1 Noisy-le-Grand nd 336 PTWW1 Noisy-le-Grand nd 49 PTWW2 Ache`res 81.3 28 Sludge Ache`res 24.0

0.15 ± 0.02 0.13 ± 0.04 nd 0.19 ± 0.04 0.08 ± 0.04 0.31 ± 0.02

113 235 nd 263 195 nd

36218 nd nd nd 3300 27603

13642 nd nd nd 19557 43467

125 111 nd 22 28 79

154 361 nd 642 115 491

4778 1153 nd 581 488 1204

23 19 nd 2 2 2

6.2 5.3 nd 0.5 0.4 0.9

Fresh floodplain deposits FD1 Fontaine FD2 Orly FD3 Paris FD4 Paris FD5 Noisy-le-Grand FD6 Noisy-le-Grand FD7 Noisy-le-Grand FD8 Noisy-le-Grand FD9 Noisy-le-Grand

nd 0.18 ± 0.04 0.20 ± 0.00 0.21 ± 0.01 0.20 ± 0.01 0.21 ± 0.01 0.24 ± 0.01 0.22 ± 0.02 0.30 ± 0.01

42 26 nd nd nd 22 25 nd 8

46350 17455 18942 15495 27401 35566 31258 17191 6430

177336 82290 123572 105589 130067 137610 122459 148793 145271

75 32 43 39 52 67 56 34 18

25 18 24 26 30 33 29 19 10

151 70 112 95 103 119 108 72 42

22 13 17 17 24 28 26 18 9

6.6 3.9 6.1 6.1 7.3 8.5 7.6 5.1 2.2

0.33 ± 0.06 0.88 ± 0.10

nd nd

77138 1533

1269 241766

5.4 0.9

5 6

69 8

17 5

17.8 0.1

S31 S32 S33 S34 S35 S36 S37 S38 S39 S40

Aube Seine@Chaˆtres Seine@Noyen Yonne Seine@Fontaine Oise Seine@Meulan Seine@laBouille Eure Marne

1.7

1.8 2.2 3.3 3.4 2.1 1.8 1.9 2.3 3.6

Headland bedrocks of the Seine basin Granite Morvan 0.5 Chalk Provin 3.0

Zn isotope analytical uncertainties are 2 external standard deviations (2r). SPM, suspended particulate matter; E.F. (Zn), enrichment factor of Zn (see details in text); POC, particulate organic carbon; RF, roof runoff collected in Paris mega-city; RD, road runoff in Paris mega-city; FD, fresh floodplain deposit; SW, sewage wastewater; PTWW, plant-treated wastewaters in SIAAP system; nd, not determined.

J.-B Chen et al. / Geochimica et Cosmochimica Acta 73 (2009) 4060–4076

E.F. (Zn)

Zn isotopes in suspended sediments of the Seine River Zn (ppm)

δ66Zn of transect SPM

δ Zn of Paris flood SPM

δ66Zn of Paris low water SPM

66

0.30

organic matter, and allows for better comparison of the relative Zn concentrations in the different samples. Here, we use Al concentrations to calculate Zn enrichment factor (EF): . EF ¼ ðZn=AlÞsample ðZn=AlÞBG ð2Þ

350

a S31

300

250

S29

0.20 S32

0.15

200

S30

Zn (ppm)

δ66Zn (‰)

0.25

150 S38

0.10

100 The Seine basin

0.05

50 0

100

200

300

400

500

600

700

Distance from the Seine spring (km) 0.30

500

b

0.25

300 0.15

Zn (ppm)

δ66Zn (‰)

400 0.20

200 0.10 The Seine in Paris

0.05 0

200

400

600

800

1 000

4065

100 1 200

Water discharge (m3/s)

Fig. 2. Zn concentrations (squares) and d66Zn in SPM as a function of (a) the distance from the Seine River spring for the transect samples of the whole Seine basin, and (b) the water discharge for the temporal samples in Paris. We observed inverse relationships between Zn concentration and d66Zn. SPM Zn concentrations increase downstream from the Seine spring to its estuary. Apart from the headwaters (S29, S30 and S32), for which a local metal-pipe contamination is suspected, d66Zn (circled cross) decrease with the distance to the Seine spring (a). In Paris (b), SPM Zn concentration decreases with increasing water discharge, but d66Zn of flood sediments (black circles) are significantly higher than those of low water SPM (red circles). Very similar relationships were observed for the dissolved loads of the same samples (Chen et al., 2008). (For interpretation of color mentioned in this figure caption the reader is referred to the web version of the article.)

sured in the geographical transect samples from the pristine headland areas. Zn concentrations of the Seine River samples can also be quantified in terms of an enrichment factor. The normalization of Zn concentration to that of an element mainly derived from natural sources (Al, Th, etc.) can be used as an index of Zn enrichment relative to the ‘‘natural background”. This normalization also cancels any dilution effect caused by natural composites such as carbonate, quartz, or

where BG denotes the natural background. We estimate that (Zn/Al)BG = 0.0018 (Al/Zn of 550) for the Seine basin, using the average concentrations of Zn and Al in uncontaminated forest water sediments and pre-historical deposits (Zn = 60 ppm and Al = 33000 ppm) (Thevenot et al., 2007). This value is close to the average ratio for suspended sediments from the Amazon River (considered as a nonpolluted river) (Al/Zn = 750, Bouchez et al., 2007), but differ from the Upper Continental Crust (UCC) composition (Al/Zn = 1132, Taylor and McLennan, 1985) and the Morvan granite analyzed in this study (Zn = 69 ppm, Al/ Zn = 1100). This discrepancy can be explained by considering that the SPM are derived from sedimentary rocks of the Paris basin that have experienced previous weathering and sedimentation cycles which have resulted in a greater loss of Zn relative to Al during these processes. The use of Th instead of Al in the definition of EF would result in similar conclusions since Al and Th in SPM of the Seine River are well correlated (Table 1). The EF calculation shows that almost all river SPM from the Seine basin are characterized by a Zn enrichment, from slight enrichments with EF close to 1 in the Seine headwaters (with Zn concentrations close to the natural level) to higher EF (up to 5.3 in Paris during low water stages) and downstream Paris (Table 1). For the geographical series samples collected during the February 2006 flood, a gradual 3-fold increase of EF is observed from the spring to the mouth of the Seine River, showing that the SPM become increasingly Zn-enriched when moving downstream. For the temporal sample series collected in Paris, a clear inverse relationship is observed between the EF and water discharge or SPM concentration (which themselves are correlated). High EF (>3) are associated with a water discharge lower than 400 m3/s (or SPM concentrations lower than 40 mg/L). At high water level, the samples from the Seine in Paris display low EF (1.4–3), similar to that of the largest tributaries of the Seine River upstream of Paris, collected during the flood period of February 2006. Finally, the floodplain deposits, deposited soon after the flood peak, show similar Zn enrichment (EF) as those of the corresponding flood samples in the Seine River. Flood deposits have lower Zn concentrations (43–150 ppm) than river SPM, which probably reflects dilution by carbonate minerals (Table 1). The high EF of the Seine River SPM suggests the presence of non-natural Zn in these samples. Using Al concentrations (assumed to be only natural) and a (Zn/ Al)BG = 0.0018 for the Seine basin geological background (Thevenot et al., 2007), we calculated that Zn excess in the Seine SPM in Paris varies from 30% at high water stage, up to 80% at low water discharge.

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3.2. Zn isotope ratios in the Seine River SPM and flood deposits d66Zn ranges from 0.08& to 0.30& for all SPM and flood deposits of the Seine River basin (Table 1). In the Seine basin, headwater samples generally have higher d66Zn. The highest d66Zn value (0.27&) is found in sediments of the Aube River (S31) and not for the spring (S29) and headwaters (S30 and S32) of the Seine River (0.14–0.20&, Table 1). This agrees with observations from the dissolved load, where lower d66Zn of the Seine headwaters (S30 and S32) were attributed to a local source of contamination by canalization pipes (Chen et al., 2008). Here the SPM d66Zn values for S29, S30 and S32 are also suspected to be influenced by local contaminations. After mixing with the Aube River, d66Zn of the Seine SPM decreases downstream. The pre-estuary sample, S38, has the lowest d66Zn = 0.12& (Fig. 2a). The dissolved loads of basin transect samples, which had a larger range in d66Zn (0.09– 0.58&), showed the similar variation (Chen et al., 2008, Fig. 2). For temporal samples in Paris, the range of SPM d66Zn (0.08–0.26&) is similar to that measured in the whole basin. SPM d66Zn increases gradually with water discharge (and with SPM concentration) (Fig. 2b): high water samples display significantly higher d66Zn (mean value of 0.20&) than low water samples (0.15&). The dissolved load of samples in Paris, whose d66Zn varied between 0.07& and 0.30&,

Flood samples in Paris Low water samples in Paris Basin transect samples Flood-plain deposit

Plant-treated wastewater Roof stream Basement granite

0.35 Nat

ura

l so

urce

S31

0.25

An

0.20 S32

ni ge po ce ro r th sou

δ66Zn (‰)

0.30

S29

c

0.15 S30

0.10 0.05 0

1

2

3

4

5

EF Fig. 3. d66Zn of suspended sediments versus Zn enrichment factor EF (sample Zn/Al ratio normalized to the natural background Zn/ Al ratio). In such a diagram, a mixing between two end-members is represented by a hyperbola. Data points for SPM of temporal samples in Paris (black and red circles), geographical transect samples (circled cross) and floodplain deposits (triangles) all plot in a mixing area between the defined natural source (represented by basement granite) and the anthropogenic source, close to that of the plant-treated wastewater (helix) and roof runoff (square). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this paper.)

displayed similar variations for Zn isotopic composition and concentration as a function of the water discharge (Chen et al., 2008). Floodplain deposits show relatively narrow d66Zn variation (0.18–0.24&), with the exception of FD9 (0.30&), similar to that of SPM collected during the high water stage. This isotopic similarity contrasts with their differences in Zn concentration, with 42–151 ppm in the floodplain deposits and 130–300 ppm in flood SPM in Paris, respectively. A negative correlation is observed between d66Zn and Zn enrichment factor in Paris temporal and basin geographical sample series and the floodplain deposits (Fig. 3). The most Zn-contaminated sediments (higher EF) generally have the lowest Zn isotopic compositions. Observing this relationship, which would be the most important result of this study, is reliant on recording the good quality of Zn isotopic measurements (2r of 0.01– 0.05&, Table 1) (Chen et al., 2009). 3.3. Zn isotopic ratios and concentrations in geological and anthropogenic samples Bedrocks from the Seine basin were analyzed in order to constrain the isotopic compositions of the natural Zn source. The granite sampled in the Southern basement of the basin has a d66Zn of 0.33& while the headland chalk (at Provins) shows a d66Zn of 0.88&. These d66Zn values are in agreement with those reported for other geological materials (Luck et al., 1999; Viers et al., 2007; Cloquet et al., 2008). It is beyond the scope of this paper to interpret these contrasted d66Zn values in geological samples, but these differences do indicate that strong Zn isotope variations may occur during the natural geochemical cycle of Zn. All anthropogenic samples show high Zn concentrations (up to 4800 ppm) and very large enrichment factors (up to 82). The suspended sediments of plant-treated wastewaters (PTWW1 and PTWW2) delivered by WWTP display high Zn concentrations (581 and 488 ppm, respectively) and very high organic content (20–30%, Table 1). However, these two samples have different d66Zn of 0.19& for PTWW1 and 0.08& for PTWW2. In Paris, almost all urban waters (roof and road runoff, domestic and industrial wastewaters) are collected in the sewer system (SIAAP), with the exception of waters from combined sewer overflow (CSO) during storms and some direct input of non-treated industrial waters. As discussed by Chen et al. (2008) for the dissolved load, the higher d66Zn of PTWW1 collected during dry summer weather may represent the d66Zn signature of domestic wastewaters. The roof runoff sample collected in Paris (where roofs are mainly made of Zn) has lower d66Zn value (0.10&) and probably does not influence the d66Zn of these domestic wastewaters (Chen et al., 2008). Before treatment, the settled sludge from the treatment plant has a high concentration (1200 ppm) and relatively high d66Zn value (0.30&). However, the most Zn-concentrated samples are the suspended materials recovered from road and roof runoff waters, with Zn concentrations of 1200 ppm and 4800 ppm, respectively. These samples show lower Zn isotopic ratios (0.13–0.15&), in

Zn isotopes in suspended sediments of the Seine River

agreement with that of the SPM from the PTWW2. These low d66Zn values are close to those of typical anthropogenic sources of dissolved Zn of between 0.10& and 0.08& (Chen et al., 2008).

4. DISCUSSION 4.1. Carbonate dilution and grain-size effects on Zn enrichment The mineralogy and grain size of SPM may control the nature of reactive surface areas of sediment grains and thus influence the Zn elemental and isotopic composition. Here we investigate how these factors are linked to Zn enrichment. The Al/Ca ratio provides an index of the relative abundance of clay minerals compared to carbonates (coarse minerals). The plot of Zn/Ca as a function of Al/Ca (Fig. 4) shows two trends. The first, a coupled increase in Zn/Ca and Al/Ca, is observed in floodplain deposits (coarse and carbonate-enriched), the SPM of high water stages in Paris and the SPM from the geographical transect. This is probably a ‘‘carbonate-dilution” line, representing the dilution of Al and Zn by addition of carbonate minerals. This line defines a mean Al/Zn ratio of 300 ± 50, which is much lower than that reported for the basin headland granite (1 1 0 0) or for the Amazon River SPM (considered to transport pristine sediments, Al/Zn = 750), suggesting it is not a natural trend of dilution of silicate minerals by carbonates. By contrast, SPM samples from low water stage

Low water samples in Paris

Flood samples in Paris

Flood-plain deposits

Basin transect samples

3.0

(Zn×1000)/Ca

n

Low wate r trend

4.0

3.4. Mineralogy, POC content and granulometry of SPM The flood sediments are composed of calcite (20–30%), feldspars and clays (essentially kaolinite, 25–40%), quartz and other minerals (20–40%) and organic matter (3–7%). Suspended sediments of the Seine River are characterized by high carbonate contents. These carbonates can be either detrital, derived mainly in the headwaters of the basin, or secondary, in downstream samples. The floodplain deposits clearly show the presence of carbonate shells. The content of organic carbon in SPM varies from 8 to 75 mg/g for samples of the Seine basin, with floodplain deposits occupying the lower end of this range (8–42 mg/ g). Basin transect samples show an increase in POC content with distance from the Seine spring, except for two headwater samples (S29 and S31). In Paris, POC concentration of SPM decreases with water discharge (Table 1): during low water stages, the POC content is much more important, probably due to the presence of micro-algaes such as diatoms. Anthropogenic samples generally have higher POC contents (from 113 mg/g to 263 mg/g). The granulometric mode of SPM is another parameter to describe the mineralogical nature of suspended particles and depends upon the hydrodynamics of the river. Where determined, the granulometric mode for the Seine River SPM is 50 lm (mainly from high water stage). Floodplain deposits are generally coarser, with granulometric modes ranging from 50 lm to 250 lm. In general, river sediments with finer grain particles have lower carbonate contents (i.e. lower Ca/Al ratio).

4067

tio lu di e t d na en bo tr

r

Ca

2.0

end

ral tr

1.0

Natu S31 FD9

S30 Headland chalk

0.0 0.0

0.2

0.4

0.6

0.8

1.0

Al/Ca Fig. 4. Zn/Ca versus Al/Ca diagram. Most of the Seine River suspended sediments during flood (black circles and circled cross) and floodplain deposits (triangles) define a linear relationship that can be related to their carbonate content and interpreted as a ‘‘carbonate dilution” of the SPM chemical composition. The Al/Ca ratio is supposed to be an index of the relative abundance of natural origin silicates compared to carbonates. However, this ‘‘carbonate-dilution” line has a different Zn/Al ratio from that of uncontaminated river sediments (calculated from averages of unpolluted forest water sediments and pre-historical sedimentary deposits). SPM samples from the low water stage in Paris (red circles), with a Zn/Al ratio even higher, clearly plot above the previous dilution line, emphasizing the metal pollution effect especially at low water stages. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this paper.)

in Paris do not follow this carbonate dilution line and instead define a different trend (Fig. 4), with a Al/Zn slope of 100–200. This low-water trend intercepts the previously defined carbonate dilution line at Al/Ca = 0.35 and Zn/ Ca = 1.5. Low water stage samples are characterized, at a given carbonate content (or Al/Ca ratio), by much higher Zn enrichment compared to the high water stage sediments. This attests a particular Zn contribution to the Seine River during low water stages. Similar trends to those observed between Al/Ca and Zn/ Ca (Fig. 4) are also found by plotting Cu/Ca, Pb/Ca, Cd/ Ca or Mo/Ca as a function of Al/Ca. In contrast, elements such as Sc, Cr, Th and Rare Earth Elements (REE) define a unique trend in element/Ca versus Al/Ca diagrams. Elements such as Ni, Co, Fe and Mn show an intermediate behavior: the low water stage samples define only a slightly different trend compared to the main dilution trend. The different relationships for these various trace elements results either from their different chemical behaviors in the Seine River or from different source inputs. In these three-element diagrams, floodplain deposits always plot at the lower end of the correlation defined by the high water stage samples. This strongly suggests that floodplain deposits and flood SPM have a common carbonate rich source.

J.-B Chen et al. / Geochimica et Cosmochimica Acta 73 (2009) 4060–4076

It can be seen, from investigating elemental ratios, which despite a grain size and carbonate content control on Zn concentration, Zn is clearly more enriched in the Seine SPM during low water stages (Fig. 4). Even though floodplain deposits are enriched in carbonate in comparison to SPM of high water stage samples in Paris, both have similar d66Zn values of 0.20&, higher than that of low water samples in Paris (0.15&, Table 1). In addition to the grain-size effect on Zn enrichment in SPM, the negative correlations between d66Zn and Zn concentration (Fig. 2) and between d66Zn and EF (Fig. 3) suggest other processes, such as biological complexation, adsorption of Zn onto SPM and/or mixing between two end-members with distinct composition may control these variables. We will discuss separately these processes.

500 Flood samples in Paris Low water samples in Paris Flood-plain deposit

400

Zn (ppm)

4068

300

200

100

a 0 0

10

20

30

40

50

60

70

80

90

POC (mg/g)

4.2. Effects of in situ biological process on Zn concentration and isotopic composition

0.35 0.30

R–COO þ Zn2þ () R–COOZnþ

ð3Þ

The equilibrium constant of this reaction was about 104.8. Assuming that bacteria complex Zn in a similar manner as diatom species, and that they contain 150 lmol of carboxylic groups per gram of humid cells (Gelabert et al., 2006), the removal of dissolved Zn by bacterial biomass with a typical content of 70 lgC/L (108 lg of dry cells/L = 1080 lg of humid cells/L) would represent 6  104 lmol of Zn per liter of water. This is a negligible fraction of the dissolved Zn typically present in the Seine

0.25

δ66Zn‰

Our results show that Seine SPM has higher Zn concentrations at low water stages than during floods. One possible explanation could be that, during low water stages, organic biomass development within the river produces organic-rich suspended sediments enriched in Zn and other metals that have affinity for organic matter (Meybeck et al., 1998). This pool of newly formed particles would settle and eventually be resuspended during rainy events. The observed trend in Fig. 3 would then result from the mixing between natural materials and Zn-enriched particles associated with in situ biological activities. Low water stage SPM are indeed enriched in organic carbon (Table 1) and a correlation between Zn and POC concentrations in Paris support this hypothesis (Fig. 5a). Many authors have studied the biological activity of the Seine River in summer, and in particular the influence of combined sewer overflows (CSO), which discharge organic-rich waters directly into the Seine during storms. High Zn concentrations in organic-rich layers (2000 ppm) and biofilms (200 ppm) have been reported in the sewer deposits (Rocher et al., 2004), suggesting a high affinity of Zn for these organic materials. The average content of bacterial biomass in the Seine River is about 70 lgC/L in Paris (Seidl et al., 1998a). This can increase to 200–300 lgC/L after CSO events as a result of the biomass input (mainly large bacteria) and riverine bacteria development. Recently, based on experiments on freshwater diatoms, Gelabert et al. (2006) quantified the affinity of Zn for cells and showed that the carboxylic groups are responsible for the Zn complexation, according to the reaction:

0.20 0.15 0.10 0.05

b 0.00 0

10

20

30

40

50

60

70

80

90

POC (mg/g) Fig. 5. Zn concentrations (a) and d66Zn (b) as a function of particulate organic carbon (POC) content for temporal samples collected in Paris (black and red circles) and floodplain deposits (triangles). Zn concentrations increase with POC contents (a), while d66Zn values decrease (b). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this paper.)

River (0.06 lmol/L) and shows Zn complexation by bacteria has a negligible effect on the dissolved load. Alternatively, one can consider that bacterial Zn removal would lead to a Zn concentration of 400 ppm in the bacterial organic phase, which is lower than that of the organic layer (up to 2000 ppm) in sewers (Rocher et al., 2004). In addition to bacteria, the Seine River is characterized by algal development in spring and summer (Meybeck et al., 1998; Seidl et al., 1998a). At lower water stage, a decrease in nitrate, Ca and HCO3 concentrations can be attributed to the increased activity of riverine biomass (phytoplankton and chlorophytes), and to the associated precipitation of carbonate and Fe oxides (Garban et al., 1996; Meybeck et al., 1998; Roy et al., 1999; Thevenot et al., 2007; Cloquet et al., 2008). Since organic matter and oxides have strong affinities for metals (Pokrovsky and Schott, 2002), these precipitates would incorporate Zn and thus lead to higher Zn concentrations in the SPM. The typical biomass development can result in up to 5 mgC/L during

Zn isotopes in suspended sediments of the Seine River 0.90

Kd=1000

60

40

20

0.70

nd

Natural source

Ba sin

80

δ66Zn (‰) in dissolved phase

100000

Proportion of particulate Zn (%)

Kd=10000

re

Flood samples in Paris Low water samples in Paris Basin transect samples Plant-treated wastewater

tt

Transect samples

ec

Low water samples in Paris

100

tra ns

Flood samples in Paris

4069

0.50 Paris

0.30

oral

temp

trend

(7)

0.10

(6) (5) (4)

(3)

(2)

(1)

Anthropogenic source

Kd=100

-0.10

0

0.05

0

50

100

150

200

250

300

SPM (mg/l) Fig. 6. Proportion of Zn transported in particulate form versus SPM content in the Seine River waters. The proportion of Zn in SPM (compared to total Zn amount in dissolved and suspended loads) increases with the SPM concentration. During low water stages, Zn in the dissolved load can represent more than 80% of the total Zn amount. The different lines represent predicted curves assuming variable partition coefficient Kd of Zn (Zn concentration ratio between the suspended and dissolved loads, in L/kg). Almost all Seine samples plot in a zone defined by Kd between 10,000 and 100,000. These Kd are higher than most published values of contaminated soils (Sauve et al., 2000).

phytoplankton blooms (Garnier et al., 1995). This is about 100 times the bacterial biomass content measured in the Seine during a CSO event. Using the same calculation as that used for bacteria, we conclude that the concentration of fixed Zn derived from dissolved load should be 0.06 lmol/L. This is the same order of magnitude as the dissolved Zn concentration and so Zn removal by these processes should be accompanied by a drastic decrease in dissolved Zn during low water stages in summer. This is contrary to observations (Chen et al., 2008). The Zn concentration expected in the pure organic fraction would then be about 550 ppm. The in situ biomass effect discussed above should be considered a maximum, because the POC in the Seine River is probably not completely of autochthonous origin. If we suppose that the typical content is 10% for POC derived totally from the biomass blooming with Zn concentration of 550 ppm, and 90% for inorganic sediment with a typical Zn concentration of 90 ppm, the calculated Zn concentration in SPM would be about 150 ppm, much lower than those observed in the Seine River at low water stage (up to 450 ppm, Table 1). We conclude that in situ biological processes may lead to high Zn concentrations of the SPM during low water stage. However, the above calculations are not in agreement with the measured Zn concentrations in dissolved and suspended loads. Moreover, the fact that dissolved Zn concentration displays a good correlation (r2 = 0.87) with the concentration of the conservative element Na but not with those of biogenic elements (Ca, NO3) confirms that Zn is not a limiting factor of biomass development (Chen et al., 2008).

0.10

0.15

0.20

0.25

0.30

0.35

δ66Zn (‰) in SPM Fig. 7. d66Zn of the Seine River dissolved load versus d66Zn in suspended sediments. Both basin transect samples (circled cross) and samples of the temporal series in Paris (black and red circles) show linear relationships: dissolved d66Zn increase with increasing SPM d66Zn. These relationships are explained by mixing of sources: two major sources of SPM Zn (natural and anthropogenic) and three sources of dissolved Zn (natural, domestic and metalderived). Dotted lines (numbered 1–7) represent the adsorption modeling results (see Section 4.3.2) with different Kd (5, 8, 8, 8, 8, 8 and 10  104) and D (dissolved to SPM isotopic fractionation factor) values (0.20, 0.10, 0.05, 0.05, 0.10, 0.15, and 0.20, respectively). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this paper.)

Isotopically, Zn isotopic fractionation due to biological processes has been poorly studied. Laboratory experiments on fresh water biomass and marine diatoms suggest that extra-cellular adsorption generally results in the preferential uptake of heavy Zn isotopes onto the cell surface, and negative isotopic fractionation may occur during Zn incorporation in a ‘‘clean” environment (Gelabert et al., 2006; John et al., 2007a). Considering these different fractionation results and other possible fractionation effects (i.e. Rayleigh effect), it is difficult to predict the in situ Zn isotopic fractionation resulting from Zn removal (adsorption, complexation, incorporation, etc.) by POC-enriched sediments in the Seine River. In this study, analogous results of d66Zn data from the sewage samples (PTWW2 and sludge from Ache`res) may provide relevant constraints. The high POC concentration in PTWW (20 to 30%) implies an important biological Zn-complexation. The dissolved Zn from PTWW2 displays a relatively low d66Zn value of 0.03& (Chen et al., 2008), compared to that of SPM from the same sample (0.08&). The sludge from the same wastewater treatment plant has an even higher d66Zn = 0.31&. Moreover, a d66Zn variation of 0.20& in dissolved load has been determined between untreated wastewater (0.28&, SW1) and treated wastewater (0.08&, PTWW1) from the same treatment plant (Chen et al., 2008), suggesting that the treatment processes (mainly organic matter coagulation and sedimentation) lead to a 64Zn enrichment in the dissolved load. This supports the observation that heavy isotopes are preferentially complexed during bio-processes

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(Gelabert et al., 2006; John et al., 2007a). However, this is not consistent with observations from the Seine River, where SPM samples show a d66Zn decrease with increasing POC content (Fig. 5b). All these arguments suggest that in situ scavenging of Zn by biological process is not the major mechanism to produce Zn-enriched SPM with low d66Zn during low water stage in summer. 4.3. Relationships between dissolved and suspended loads and adsorption effects 4.3.1. Zn partition between dissolved and suspended loads Dissolved Zn concentrations and isotopic compositions of the Seine River samples analyzed here have been published in a previous paper (Chen et al., 2008). The proportion of Zn transported in the suspended load (P, in %) can be calculated using the following relationship: P¼

SPM  C p ðZnÞ  100 SPM  C p ðZnÞ þ C w ðZnÞ

ð4Þ

where SPM, Cp(Zn) and Cw(Zn) are the concentration of SPM (in g/L), concentrations of Zn in the suspended phase (ppm) and in the dissolved load (lg/L), respectively. This proportion ranges from 10% during lower water stages (in summer) to 95% when SPM concentrations are high (Fig. 6). Zn in the dissolved load behaves as a soluble element in a similar manner to Na, K or Cl (Chen et al., 2008), which means that dissolved Zn concentration decreases with increasing water discharge. At low water stage, high dissolved Zn concentration and low SPM content result in a preferential transport of Zn in the dissolved load. Based on mean Zn concentrations in dissolved (2 lg/L) and suspended (200 ppm) loads, and average SPM concentration of 60 mg/L, we calculate that 85% of Zn is transported in SPM by the Seine River. Using the Kd notation (Kd is the partition coefficient defined as the Zn concentration ratio between the solid and liquid phases, in L/kg), the above Eq. (4) can be written as: P¼

SPM  Kd  100 SPM  Kd þ 1

ð5Þ

this partition coefficient here is calculated using the bulk Zn concentration in SPM, that actually includes a constitutive pool. In the Seine River, the calculated log Kd ranges from 4.9 to 5.3. These values are in the upper range of the solidsolution partition coefficients of Zn in contaminated soils (Zn concentration 500 ppm) at pH P 8 (Sauve et al., 2000). 4.3.2. Adsorption effects on isotopic relationships between dissolved and suspended loads Although the range of d66Zn in the dissolved load (0.07– 0.58&) is much larger than that of the suspended load (0.08–0.30&) and the enrichment factor of Zn in the dissolved load is much more variable (from 1 to 300) (Chen et al., 2008), the relationship between d66Zn and EF for the suspended sediments (Fig. 3) is remarkably similar to that reported for the dissolved load (Chen et al., 2008). In both cases, d66Zn values decrease with an increase in EF. In Paris, both dissolved and suspended d66Zn values increase with the water discharge, associated with relatively

restricted variation in d66Zn of 0.23& and 0.18& for the dissolved load (Chen et al., 2008) and for SPM, respectively (Fig. 2b). For the geographical transect, the particulate phases are relatively more depleted in heavy isotopes (0.12–0.27&) compared to the associated dissolved loads (up to 0.58&), that also show larger temporal variations (Chen et al., 2008). Two different relationships are observed for samples of the whole Seine basin (transect and temporal samples) when d66Zn in the dissolved loads are plotted as a function of the d66Zn of SPM (Fig. 7). The geographical samples of the February 2006 flood event and several temporal samples in Paris define a linear relationship between dissolved d66Zn and SPM d66Zn, with a slope of about 2. The other samples, essentially collected during the 2 years monitoring of the Seine River in Paris lie on the second linear trend with a slope of 1. In Paris, the Zn isotopic signatures of the dissolved and suspended phases are similar, within analytical error. The correlation between dissolved d66Zn and the d66Zn of SPM (Fig. 7) may result from exchange processes between these phases. The observation that the highest Zn concentrations are found in both dissolved and suspended loads during low water stages in summer supports this conceptual view. This exchange hypothesis is tested below. Chen et al. (2008) have observed an inverse relationship between d66Zn and Zn concentrations in the dissolved load of the Seine River. This was attributed to an increasing relative contribution of anthropogenic Zn during low water stages (Chen et al., 2008). Assuming the exchange equilibrium is reached rapidly, Zn concentration in the SPM can be predicted according to the exchange coefficient K: K¼

C exch p ðZnÞ C w ðZnÞ

ð6Þ

where C exch p ðZnÞ and Cw(Zn) are the exchangeable Zn and dissolved Zn concentrations, respectively. The isotopic composition of the exchangeable Zn pool then can be defined: d66 Znexch ¼ d66 Znw þ D

ð7Þ

where D stands for the isotope fractionation factor between suspended and dissolved loads, d66Znexch and d66Znw denote the Zn isotopic compositions of the exchangeable and dissolved pools, respectively. Based on the empirical relationship between d66Znw and Cw(Zn) (d66Znw = 0.04Cw(Zn) + 0.31) reported by Chen et al. (2008), the isotopic composition of the bulk SPM can be then calculated as the sum of the exchangeable and constitutive (natural) fractions: d66 ZnSPM ¼ fnat d66 Znnat þ ð1  fnat Þðd66 Znw þ DÞ

ð8Þ

where fnat is the fraction of Zn in SPM derived from a natural source: fnat ¼

C nat ðZnÞ C w ðZnÞ  K þ C nat ðZnÞ

ð9Þ

and the relationship between dissolved and SPM isotopic compositions thus can be predicted. We fixed the natural d66Zn to 0.35&. Using an Al/Zn ratio of 550 and Al concentration varying from 45,000 ppm to 65,000 ppm, the

Zn isotopes in suspended sediments of the Seine River

calculated corresponding Zn concentration of the natural source ranges from 80 to 120 ppm. According to the calculation, the K value should be close to 80,000 (104.9) in order to explain the excess particulate Zn (from 130 ppm to 490 ppm in SPM) by exchange processes. The only way to explain the 1:1 relationship between dissolved and SPM d66Zn (Fig. 7) is by setting D = 0.10&. This negative value shows that light isotopes should be preferentially fixed onto SPM during the exchange process. Experimental studies do not support this hypothesis, showing that adsorption favors the heaver Zn isotopes on solid surfaces (Pokrovsky et al., 2005; Gelabert et al., 2006; Balistrieri et al., 2008; Juillot et al., 2008). While exchange processes in the Seine River might be more complex than adsorption processes, the isotopic data suggest that in situ exchange between suspended and dissolved loads is not the dominant process controlling d66Zn in the Seine River sediments. In order to support this conclusion, Zn distribution in the suspended particles has been investigated by leaching the Seine River sediments. The leaching experiments were carried out on SPM of four samples (S3-6), using first Milli-Q water (three times), then acetic acid (1 M) and finally a mixture of concentrated HNO3, HCl and HF. Zn concentrations were measured in each leaching fraction, and the proportions of Zn calculated. Water leached Zn represents only 5.5–8.6% of the total Zn content, suggesting that Zn adsorption onto SPM is minor. Acetic-acid leached Zn proportions vary from 26 to 39%, higher than the proportions expected from the carbonate content in SPM (30–40% of carbonate with a Zn concentration of 48 ppm). Complementarily, the high Zn proportions (56–69%) found in the third mixed acid leachate cannot only be due to silicate phase dissolution, as this phase has a Zn concentration of 90 ppm (Thevenot et al., 2007). Based on Zn concentrations in materials of the natural background and the above proportions, the calculated integrated Zn concentration in SPM would be about 100 ppm, reaching only 50% of bulk Zn concentrations (171–205 ppm) found actually in these samples. These leach experiments show that another phase that would be leached with concentrated acids is present. It is likely that such phases are organic material, oxyhydroxides or sulfides. Leaching procedures and isotopic doping techniques applied to the contaminated sediments of the Lot River (France) also lead to the conclusion that the exchangeable Zn proportion is not higher than 10% (Sivry, 2008). Based on the above discussions (Sections 4.2 and 4.3), we can conclude that the in situ biological processes and the adsorption cannot easily explain our data and the observed relationships (Figs. 2, 3, 5 and 7). The alternative interpretation is to invoke a mixture of sources. We decipher here the possible end-members.

4071

(Chen et al., 2008). Indeed, the mineralogical nature of the sediments transported by the Seine River during high water stages (transect series of February 2006 and flood samples in Paris) possibly indicates a dominant natural origin for these sediments. Major and trace elements of SPM in the Seine River that are not influenced by human activities (such as REE and Th) have a similar composition to those of sediments from the Congo River (Gaillardet et al., 1999), and display similar distribution patterns as those of the average Upper Continental Crust (UCC) (Roy et al., 1999). However, Seine SPM were found to be depleted in more soluble elements (such as Na, K and Mg) compared to the UCC. The same result is obtained in this study. Rare earth elements analyzed here are comparable to the REE relative abundances (i.e. La/Th = 3) reported for the UCC (Taylor and McLennan, 1985) and for French loess of the Seine basin (Gallet et al., 1998; Sterckeman et al., 2006). This re-enforces the notion that SPM in the Seine is of natural origin and is derived from sedimentary bedrocks that have experienced previous weathering cycles during their geological history (Gaillardet et al., 1999). This result is consistent with the geological nature of the Seine basin. From headland to Paris, the Seine River drains tablelands of Jurassic (mainly limestone), Lower Cretaceous (mainly phosphatic sands and marls), Upper Cretaceous (chalk) and Tertiary (argillaceous limestones and marls) formations (Roy et al., 1999). The potential natural sources of the Seine River sediments are thus materials derived from the weathering of elastic sedimentary rocks during Jurassic and Tertiary periods and from superficial eolian and fluvial deposits formed during Quaternary period (loess and ‘‘limons des plateaux”). No or very little d66Zn data are available for loess or uncontaminated sediments from the Seine basin. However, our study shows that the analysis of the granite from the basement region (d66Zn = 0.33&) is consistent with the extrapolation (to EF = 1, natural background) of the mixing hyperbola (Fig. 3). This suggests that d66Zn of the natural end-member is between 0.30& and 0.40&, similar to the reported mean integrated value of 0.30& for terrestrial Zn (igneous and sedimentary rocks, dust, loess, etc.) transported to the ocean (Cloquet et al., 2008). No correlation exists between Ca concentration and both the Zn enrichment factor and d66Zn in river SPM and floodplain sediments. This indicates that, except for the dilution effect, carbonate does not influence the Zn content of this natural end-member, nor its d66Zn signature. Based on Zn concentrations and d66Zn of the headland carbonate (Zn 8 ppm, d66Zn 0.88&) and of the typical uncontaminated silicate rock (Zn 90 ppm, d66Zn 0.35&) analysis (Table 1), a mass budget calculation confirms this conclusion.

4.4. Natural sources of Zn in the Seine River sediments 4.5. The anthropogenic end-members The negative correlation between d66Zn and Zn concentration (Fig. 2) and between d66Zn and EF (Fig. 3) probably suggest a mixing process between two end-members with distinct composition. In such a mixing scenario, one of the end-members could be the ‘‘natural background”

If mixing is controlling the Zn elemental and isotopic composition in the Seine River (Fig. 3), then a second end-member with high Zn enrichment factor and low d66Zn is necessary to explain the data. This second end-

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member should have a d66Zn lower than that of the most contaminated samples collected during low water stages in Paris (0.10&), as constrained geometrically from a mixing hyperbola (Fig. 3). This value is consistent with the d66Zn values (0.08–0.15 &) determined in the SPM released from the Ache`res wastewater treatment plant (PTWW2) and in the roof and road runoff samples in Paris (RF5 and RD2, Fig. 3). d66Zn of dissolved loads from the PTWW and roof/road runoff are slightly lower (0.10& to 0.08&) than those of the SPM. This probably results in the strong contribution of Zn leached from the Parisian roofs (d66Zn = 0.10&) to the dissolved phase (Chen et al., 2008). There are numerous potential SPM sources in the Seine basin and in the Paris conurbation that are consistent with the geochemistry of this required end-member (high EF and low d66Zn), such as the atmosphere, punctual industrial wastes, treated or untreated wastewaters and the mixture of domestic and urban runoff waters (Estebe et al., 1997). Here we will discuss successively the possible contribution of allochthonous sources. 4.5.1. Combined sewer overflow Previous studies have reported that combined sewer overflows (CSO) are a significant source of anthropogenic particles to the Seine River (Estebe et al., 1998; Meybeck et al., 1998; Seidl et al., 1998a,b). In general, the urban wastewaters of Paris (domestic wastewaters and street runoff) are collected and treated in treatment plants. However, during (or after) storm events, the sewage system is saturated and the surplus waters are discharged directly into the Seine by devoted outlets, disseminated along the course of the river in the Paris conurbation. These CSO are composed of urban runoff, loaded with surface pollution (atmospheric particles, roof and street runoff waters), urban wastewaters stored in the sewer system and of re-suspended deposits, that were accumulated in the sewage system during previous storm episodes (Buzier et al., 2006). In Paris, the CSO discharge 2  108 m3/yr of water to the Seine River, twice that of plant-treated waters delivered by the WWTP (1  108 m3/yr, Estebe et al., 1998; Meybeck et al., 1998). As Zn concentration in CSO waters can reach 6700 ppm (Estebe et al., 1998; Meybeck et al., 1998), a significant increase in SPM Zn concentration would result from CSO events. Estebe et al. (1998) estimated that under certain climatic conditions, the amount of suspended Pb and Zn discharged by the CSO can be as high as the fluxes discharged by the Ache`res treatment plant (treating 80% of Parisian wastewaters). However, most of the SPM present in the CSO waters settle rapidly once they reach the river due to the decrease of flow velocity and only finer particles remain in suspension. Particles can be re-suspended by boat navigation along the Seine, resulting in long-term pollution. In this study, we were not able to directly analyze the Zn isotopic composition of CSO waters, but their d66Zn should be intermediate between those of the SPM transported in roof and road runoff (0.13–0.15&) and delivered by WWTP during flood period (0.08&). An extensive study of hydrocarbons and heavy metals in sewer deposits in the small Seine tributary catchment of ‘‘Le

Marais” (in the historical Paris center) reported Zn concentrations ranging from 200 ppm in biofilms, to 2000 ppm in the organic layer deposits and gross bed sediments (Rocher et al., 2004). Zn was identified as the most abundant metal (among Pb, Cu and Cd), reaching 70% of the total metal content in the organic matter layer and biofilms. Using the organic matter chemical composition of these SPM, Rocher et al. (2004) showed that suspended solids issued from domestic activities were the major component of organic layers and biofilms and that urban (road and roof) runoff and street cleaning were the major processes leading to the contamination of bedload sediments. Sulfides with stabilized metals were also mentioned as a possible source for suspended particles of urban runoff (Meybeck et al., 1998). This discussion shows that Zn can be scavenged into both organic matters and sediments in the sewer deposits. These materials, which contain large amounts of Zn and other metals, are flushed to the Seine River during CSO events and could provide an important contribution to SPM in the Seine River. Their supposed d66Zn signature (around 0.10&) is coherent with the second end-member of a mixing trend defined by the SPM (Fig. 3). 4.5.2. Plant-treated wastewaters The input by WWTP is the other dominant source of Zn-enriched SPM in most large villages and cities of the Seine basin. Wastewaters collected in the sewers have relatively high SPM concentrations (up to 200 mg/L). In the WWTP, most of the organic rich particles are removed by sedimentation and coagulation. Finest particles and colloids that are not scavenged by the WWTP are released to the Seine River. The mean SPM concentration of the WWTP outlet waters is between 28 and 49 mg/L (Estebe et al., 1998; Meybeck et al., 1998; Thevenot et al., 2007). These SPM have high POC contents (up to 34%), as determined in this study for PTWW1 (26%) and PTWW2 (19%). The PTWW waters thereby introduce Zn into the Seine River in a relatively stable incorporated form. Zn origin in these waters can be from a combination of domestic sources, re-suspension of organic particles that scavenged metals in the sewer network, roof and road runoff, and street cleaning (Buzier et al., 2006). Although the comparison between inlet and outlet metal fluxes for the Ache`res Plant conducted by Buzier et al. (2006) did not report Zn data, it showed that the metal removal yields were very high for Pb and Cu. According to the mass budgets of Thevenot et al. (2007), more than 30% of the total Zn entering the WWTP is discharged into the Seine River (90t/yr). Our results show that the SPM discharged by the Ache`res WWTP are highly enriched in Zn with low isotopic ratio (0.08&) and could be the second end-member that is necessary to explain the isotopic mixing trend in Fig. 3. 4.5.3. Contribution from atmosphere and agricultural composting The atmosphere and agricultural compost represent two other possible sources of Zn-enriched particles. Rainwater is usually enriched in Zn (Chen et al., 2008) and a Zn concentration as high as 2330 ppm has been reported in highway aerosols (Garnaud et al., 1999). A

Zn isotopes in suspended sediments of the Seine River

significant atmospheric dust fallout flux of about 15 kg/ km2/yr (comprising wet and dry deposition) was determined for the Seine basin (Azimi et al., 2003). The fate of atmospheric particulate Zn is expected to be very different between urban and rural areas. A recent study of grain-size effect on Zn isotopic composition of urban aerosols has shown that finer particles are enriched in light isotopes compared to coarse ones (Gioia et al., 2008). In cities, these fine atmospheric particles are finally collected in the sewers and are easily delivered into the river by the CSO or through the sewage system, ultimately becoming a net source of particulate Zn. The residence time of particulate Zn is thus likely to be short in urban areas. In rural regions, weathering and Zn incorporation in newly formed particles or minerals at the soil surface may complicate their transport to the river system. Indeed, in rural areas of the Seine basin, the contribution of dissolved Zn from rainwater (d66Zn = 0.20&) is not detected in the Seine River (d66Zn>0.40&), probably because of Zn adsorption onto the clays and oxide minerals due to high rock–water ratio in soils (Chen et al., 2008). Fertilizers and the sludge from the WWTP are used as agricultural composts in the Seine basin. Chen et al. (2008) have found that rural samples of the region most impacted by agricultural inputs display higher d66Zn values (>0.40&) than that of fertilizers (0.19–0.42&). This indicates that fertilizers are not a direct source of dissolved Zn in river water, though they have high Zn concentration (0.2–2.6 ppm). Mean Zn concentrations of 1200 ppm are also found in sludge from the Ache`res WWTP (Table 1), leading to a Zn input of about 83 t/yr for the Seine basin (Thevenot et al., 2007). However, our data do not imply a direct contribution of the sludge with high d66Zn (0.31&) and high EF (Fig. 3). Recent studies have reported the rapid re-distribution of Zn derived from sewage sludge composting in soils and the possible isotopic fractionation of atmospheric (and agricultural) Zn (Weiss et al., 2005; Cloquet et al., 2008; Torri and Lavado, 2008). As a consequence, a strong retention of Zn probably exists in the topsoil profiles in rural areas. 4.6. Main mixing process aspect According to the above discussion of possible sources (Sections 4.4 and 4.5), we can conclude here that mixing is the best scenario to explain the relationships between dissolved and suspended loads (Fig. 7). The linear trends in Fig. 7 are thereby indicative of mixtures between reservoirs with different isotopic signatures. The natural source is quite obvious. The d66Zn of the natural silicate end-member is 0.35&, which implies graphically a d66Zn value for the associated dissolved Zn of 0.90& (Chen et al., 2008). This value is close to the d66Zn of headland chalk of the Seine basin (0.88&, Table 1) and the previously reported values of carbonates (Luck et al., 1999; Marechal et al., 2000). The dissolution of limestone (that can contribute almost entirely to the dissolved load) and the erosion of soil materials (mainly for the SPM) thus dominate the natural end-member. The possibility that the natural silicate materials might undergo partial

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dissolution and release dissolved Zn remains unconstrained. However, results here and published elsewhere (Chen et al., 2008) suggest that if it exists, this fraction is likely to be minor. It is interesting to highlight that the described natural source of Zn in the Seine River gives different d66Zn for SPM (0.35&) and dissolved loads (0.90&). This exemplifies in a remarkable way the carbonate/silicate weathering mechanisms of the Seine River pristine headlands: the dissolved load is mainly characterized by carbonate weathering, and the SPM by residual silicates. The second end-member can be attributed to anthropogenic pollution through WWTP and CSO discharges. Chen et al. (2008) have reported low dissolved isotopic ratios (between 0.10& and 0.08&) for Zn derived from PTWW or from roof and road runoff in Paris conurbation. The d66Zn values of the associated suspended particles are close to 0.10&, as inferred from the above discussion. The slight difference between dissolved and SPM anthropogenic d66Zn values either results from isotopic fractionation between dissolved and suspended Zn occurred during collection, transport and treatment of wastewaters (or CSO), or more likely, the contribution of dissolved Zn from the leaching of Parisian roof materials with a d66Zn of 0.10& (Chen et al., 2008). A few samples deviate from the inferred mixing line between the natural and anthropogenic end-members and define a straight line with a slope of 1 (Fig. 7). These samples correspond to Paris temporal samples. The flood samples have the lowest particulate enrichment factors and the SPM d66Zn values close to the natural end-member, but relatively low dissolved d66Zn compared to the natural value (0.90&). As shown by Chen et al. (2008), the dissolved Zn isotopic composition of these samples is much influenced by the domestic wastewaters in the rural regions upstream Paris with d66Zn much higher (0.35&) than that of Parisian wastewaters (0.10& to 0.08&). The main difference between Parisian and upstream rural wastewaters are due to the contribution of Zn-covered roofs (metallic Zn). We infer that the two different trends between dissolved and SPM d66Zn (Fig. 7) are a consequence of the variability of the isotopic signature of anthropogenic Zn in the dissolved load between domestic and metal-derived Zn. The deviation of some samples from the mixing line between the natural and anthropogenic sources therefore reflect the existence of two major sources of SPM Zn (natural and anthropogenic) contrasting with three sources of dissolved Zn (natural, domestic and metallic Zn) in the Seine basin. 4.7. Proportions of natural and anthropogenic Zn in the Seine sediments Using Zn normalized chemical ratios X/Zn and d66Zn values, equations of a binary mixing can be written to calculate the proportions of Zn derived from the natural and anthropogenic end-members: d66 Znriv ¼ d66 Znnat xnat þ d66 Znanth xanth and       X X X ¼ xnat þ xanth Zn riv Zn nat Zn anth

ð10Þ

ð11Þ

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where xnat and xanth are the proportion of particulate Zn derived from the natural and anthropogenic sources, respectively. The following condition must be satisfied: 1 ¼ xnat þ xanth

size the strong anthropogenic impact on rivers draining highly populated regions and confirm that Zn isotopic composition is a powerful tracer of the anthropogenic contamination.

ð12Þ 66

For the natural source, we chose the d Zn value of 0.35& (Section 4.4) and element ratios that correspond to those of the background of the Seine basin (Meybeck et al., 1998; Thevenot et al., 2007), this implies an Al/Zn ratio close to 550, Cr/Zn of 0.7, Ni/Zn of 0.3, Ba/Zn of 3, Th/ Zn of 0.15, etc. The anthropogenic end-member is much more enriched in Zn. We can reasonably assume that this end-member has d66Zn value of 0.10& (Section 4.5) and element ratios (Al/Zn of 10, Cr/Zn of 0.05, Ni/Zn of 0.03, Ba/Zn of 0.2, Th/Zn of 0.001, etc.) close to the mean value of SPM from the anthropogenic sources (PTWW, roof and road runoff). Using these values, the contribution of both sources was calculated for each water sample. In rural areas even for samples having the highest d66Zn (i.e. S31, the Aube River), the proportion of Zn from the natural source does not exceed 70%. As expected, the anthropogenic proportion increases downstream, with a basin average value of 62% and the highest value for the pre-estuary sample S38 with 86%. If the output flux of particulate Zn from the Seine River is 315 t/yr (Thevenot et al., 2007), the contribution of particulate Zn from natural basin bedrocks represents 44 t/yr, in good agreement with the previous result of 42 t/yr obtained from a monitoring study of the Seine River basin (Thevenot et al., 2007). For the temporal sample series in Paris, the average natural contribution is only about 28%, and the anthropogenic contribution of particulate Zn varies from 40% (S64) to about 100% (S19, S24), increasing with a decrease in water discharge. 5. CONCLUSIONS The d66Zn of the SPM transported by the Seine River decrease from the headwaters to the estuary, while Zn concentrations increase. When compared to a natural background by normalizing Zn concentration to Al, SPM within and downstream of Paris are up to five times enriched in Zn. In Paris, enrichment factor and isotopic composition strongly vary as a function of water discharge (or time): particularly strong Zn enrichments, associated with low d66Zn values, are observed during low water periods. We interpret these observations as the result of mixing processes between natural and anthropogenic sources, rather than adsorption of Zn from dissolved load. Our main argument is that for typical Zn partition coefficient, the isotopic fractionation between dissolved and SPM Zn required to explain the observed d66Zn variation, is not compatible with literature results on Zn adsorption. Our data indicate that SPM in the Seine River result from mixing of natural particles mobilized by erosion processes and of anthropogenic particles that are depleted in heavy isotopes. Our study suggests that wastewater treatment plants (WWTP) and combined sewer overflows (CSO) are the main contributors of anthropogenic particles. Considering our previous work on the dissolved load (Chen et al., 2008), we empha-

ACKNOWLEDGMENTS We thank J. Bouchez, J.L. Birck, M. Benedetti and A. Gelabert from IPGP and Universite´ Paris Diderot (Paris VII), O. Beyssac and N. Findling from Ecole Normale Supe´rieure for analytical assistance and constructive discussions. Thanks are extended to R. Hilton for English correction. The authors acknowledge the associated editor M. Rehka¨mper and reviewers D. Vance, S. John and W. Abouchami who greatly improved the quality of the manuscript. SIAAP supplied PTWW samples. JiuBin Chen was granted from the Region Ile-de-France. This is IPGP Contribution No. 2484.

REFERENCES Allegre C. J., Dupre B., Negrel P. and Gaillardet J. (1996) Sr–Nd– Pb isotope systematics in Amazon and Congo River systems: constraints about erosion processes. Chem. Geol. 131, 93–112. Archer C. and Vance D. (2004) Mass discrimination correction in multiple-collector plasma source mass spectrometry: an example using Cu and Zn isotopes. J. Anal. Atom. Spectrom. 19, 656– 665. Azimi S., Ludwig A., Thevenot D. R. and Colin J.-L. (2003) Trace metal determination in total atmospheric deposition in rural and urban areas. Sci. Total Environ. 308, 247–256. Balistrieri L. S., Borrok D. M., Wanty R. B. and Ridley W. I. (2008) Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: experimental mixing of acid rock drainage and ambient river water. Geochim. Cosmochim. Acta 72, 311–328. Bibby R. L. and Webster-Brown J. G. (2006) Trace metal adsorption onto urban stream suspended particulate matter (Auckland region, New Zealand). Appl. Geochem. 21, 1135– 1151. Borrok D. M., Wanty R. B., Ridley W. I., Wolf R., Lamothe P. J. and Adams M. (2007) Separation of copper, iron, and zinc from complex aqueous solutions for isotopic measurement. Chem. Geol. 242, 400–414. Bouchez J., Gaillardet J., France-lanord C., Galy V. and MauriceBourgoin L. (2007) Weathering over a large range of erosion solid products: insights from Amazon River depth-samplings, Goldschmidt Abstracts 2007 – B. Geochim. Cosmochim. Acta 71, A48–A138. Buzier R., Tusseau-Vuillemin M.-H., Martin dit Meriadec C., Rousselot O. and Mouchel J.-M. (2006) Trace metal speciation and fluxes within a major French wastewater treatment plant: impact of the successive treatments stages. Chemosphere 65, 2419–2426. Chapman J. B., Mason T. F. D., Weiss D. J., Coles B. J. and Wilinson J. J. (2006) Chemical separation and isotopic variations of Cu and Zn from five geological reference materials. Geostand. Geoanal. Res. 30, 5–16. Chen J.-B., Gaillardet J. and Louvat P. (2008) Zinc isotopes in the Seine River water, France: a probe of anthropogenic contamination. Environ. Sci. Technol. 40, 6494–6501. Chen J.-B., Louvat P., Gaillardet J. and Birck J. L. (2009) Direct separation of Zn from dilute natural waters for isotopic measurements using multi-collector ICP-MS. Chem. Geol. 259, 120–130.

Zn isotopes in suspended sediments of the Seine River Cloquet C., Carignan J., Lehmann M. and Vanhaecke F. (2008) Variation in the isotopic composition of zinc in the natural environment and the use of zinc isotopes in biogeosciences: a review. Anal. Bioanal. Chem. 390, 451–463. Estebe A., Boudries H., Mouchel J.-M. and Thevenot D. R. (1997) Urban runoff impacts on particulate metal and hydrocarbon concentrations in river seine: suspended solid and sediment transport. Water Sci. Technol. 36, 185–193. Estebe A., Mouchel J.-M. and Thevenot D. R. (1998) Urban runoff impacts on particulate metal concentrations in River Seine. Water Air Soil Pollut. 108, 83–105. Even S., Poulin M., Mouchel J.-M., Seidl M. and Servais P. (2004) Modelling oxygen deficits in the Seine River downstream of combined sewer overflows. Ecol. Modell. 173, 177–196. Gaillardet J., Dupre´ B. and Allegre C. J. (1999) Geochemistry of large river suspended sediments: silicate weathering or recycling tracer? Geochim. Cosmochim. Acta 63, 4037–4051. Gaillardet J., Viers J. and Dupre B. (2005) Trace element in river waters. In Treatise on Geochemistry. Surface and Ground Water Weathering and Soils, vol. 5 (eds. J. J. Drever, H. D. Holland and K. K. Turekian). Elsevier, New York, pp. 225– 272. Gallet S., Jahn B.-M., Van Vliet Lanoe B., Dia A. and Rossello E. (1998) Loess geochemistry and its implications for particle origin and composition of the upper continental crust. Earth Planet. Sci. Lett. 156, 157–172. Galy V., Bouchez J. and France-Lanord C. (2007) Determination of total carbon content and d13C in carbonate-rich detrital sediments. Geostand. Geoanal. Res. 31, 199–207. Garban B., Ollivon D., Carru A. M. and Chesterikov A. (1996) Origin, retention and release of trace metals from sediments of the river Seine. Water Air Soil Pollut. 87, 363–381. Garnaud S., Mouchel J.-M., Chebbo G. and Thevenot D. R. (1999) Heavy metal concentrations in dry and wet atmospheric deposits in Paris district: comparison with urban runoff. Sci. Total Environ. 235, 235–245. Garnier J., Billen G. and Coste M. (1995) Seasonal succession of diatoms and Chlorophyceae in the drainage network of the river Seine: observations and modelling. Limnol. Oceanogr. 40, 750– 765. Gelabert A., Pokrovsky O. S., Viers J., Schott J., Boudou A. and Feurtet-Mazel A. (2006) Interaction between zinc and freshwater and marine diatom species: surface complexation and Zn isotope fractionation. Geochim. Cosmochim. Acta 70, 839–857. Gioia S., Weiss D., Coles B., Arnold T. and Babinski M. (2008) Accurate and precise zinc isotope ratio measurements in urban aerosols. Anal. Chem. 80, 9776–9780. Goldstein S. L., O’Nions R. K. and Hamilton P. J. (1984) A Sm– Nd isotopic study of atmospheric dusts and particulates from major river systems. Earth Planet. Sci. Lett. 70, 221–236. Huon S., Grousset F. E., Burdloff D., Bardoux G. and Mariotti A. (2002) Sources of fine-sized organic matter in North Atlantic Heinrich Layers: d13C and d15N tracers. Geochim. Cosmochim. Acta 66, 223–239. John S. G., Geis R. W., Saito M. A. and Boyle E. A. (2007a) Zinc isotope fractionation during high-affinity and low-affinity zinc transport by the marine diatom Thalassiosira oceanica. Limnol. Oceanogr. 52, 2710–2714. John S. G., Genevieve Park J., Zhang Z. and Boyle E. A. (2007b) The isotopic composition of some common forms of anthropogenic zinc. Chem. Geol. 245, 61–69. Juillot F., Marechal C., Ponthieu M., Cacaly C., Morin G., Benedetti M., Hazemann J. L., Proux O. and Guyot F. (2008) Zn isotopic fractionation caused by sorption on goethite and 2lines ferrihydrite. Geochim. Cosmochim. Acta 72, 4886–4900.

4075

Luck J. M., Ben Othman D., Albarede F. and Telouk P. (1999) Pb, Zn and Cu isotopic variations and trace elements in rain. Geochem. Earth’s Surf. Armannsson, 199–203. Marechal C., Nicolas E., Douchet C. and Albarede F. (2000) Abundance of zinc isotopes as a marine biogeochemical tracer. Geochem. Geophys. Geosyst. 1 (1999GC000029). Marechal C., Telouk P. and Albarede F. (1999) Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry. Chem. Geol. 156, 251–273. Meybeck M., de Marsily G. and Fustec E. (1998) La Seine en son bassin: Fonctionnement e´cologique d’un syste`me fluvial anthropise´. Elsevier, 749 pp.. Millot R., Allegre C.-J., Gaillardet J. and Roy S. (2004) Lead isotopic systematics of major river sediments: a new estimate of the Pb isotopic composition of the Upper Continental Crust. Chem. Geol. 203, 75–90. Pokrovsky O. S. and Schott J. (2002) Iron colloids/organic matter associated transport of major and trace elements in small boreal rivers and their estuaries (NW Russia). Chem. Geol. 190, 141– 179. Pokrovsky O. S., Viers J. and Freydier R. (2005) Zinc stable isotope fractionation during its adsorption on oxides and hydroxides. J. Colloid Interface Sci. 291, 192–200. Rocher V., Azimi S., Moilleron R. and Chebbo G. (2004) Hydrocarbons and heavy metals in the different sewer deposits in the ‘Le Marais’ catchment (Paris, France): stocks, distributions and origins. Sci. Total Environ. 323, 107–122. Roy S. (1991), Utilisation des isotopes du Pb et du Sr comme traceurs des apports anthropiques et naturels dans les pre´cipitations et les rivie`res du basin de Paris. Ph.D. thesis, University of Paris, France. Roy S., Gaillardet J. and Allegre C. J. (1999) Geochemistry of dissolved and suspended loads of the Seine River, France: anthropogenic impact, carbonate and silicate weathering. Geochim. Cosmochim. Acta 63, 1277–1292. SARM, Service d’Analyse des Roches et des Mine´raux. http:// helium.crpg.cnrs-nancy.fr/SARM/. Sauve S., Hendershot W. and Allen H. E. (2000) Solid–solution partitioning for metals in contaminated soils: dependence on pH, total metal burden, and organic matter. Environ. Sci. Technol. 34, 1125–1131. Seidl M., Huang V. and Mouchel J. M. (1998a) Toxicity of combined sewer overflows on river phytoplankton: the role of heavy metals. Environ. Pollut. 101, 107–116. Seidl M., Servais P. and Mouchel J. M. (1998b) Organic matter transport and degradation in the river Seine (France) after a combined sewer overflow. Water Res. 32, 3569–3580. SIAAP, Syndicat Interde´partemental pour Assainissement de l’Agglome´ration Parisienne. http://w1.siaap.fr/. Sivry Y. (2008) Utilisation des isotopes stables pour quantifier le compartiment e´changeable des e´le´ments trace me´talliques et pour tracer les pollutions polyme´talliques (66Zn). Ph.D. thesis, University of Toulouse III-Paul Sabatier, France. Sterckeman T., Douay F., Baize D., Fourrier H., Proix N., Schvartz C. and Carignan J. (2006) Trace element distributions in soils developed in loess deposits from northern France. Eur. J. Soil Sci. 57, 392–410. Taylor S. R. and McLennan S. M. (1985). In The Continental Crust: Its Composition and Evolution, an Examination of the Geochemical Record Preserved in Sedimentary Rocks. Blackwell Scientific Publications, Oxford, London, p. 312. Thevenot D. R., Moilleron R., Lestel L., Gromaire M.-C., Rocher V., Cambier P., Bonte P., Colin J.-L., de Ponteves C. and Meybeck M. (2007) Critical budget of metal sources and pathways in the Seine River basin (1994–2003) for Cd,

4076

J.-B Chen et al. / Geochimica et Cosmochimica Acta 73 (2009) 4060–4076

Cr, Cu, Hg, Ni, Pb and Zn. Sci. Total Environ. 375, 180–203. Torri S. I. and Lavado R. (2008) Zinc distribution in soils amended with different kinds of sewage sludge. J. Environ. Manage. 88, 1571–1579. Viers J., Oliva P., Nonell A., Gelabert A., Sonke J. E., Freydier R., Gainville R. and Dupre B. (2007) Evidence of Zn isotopic fractionation in a soil–plant system of a pristine tropical

watershed (Nsimi, Cameroon). Chem. Geol. 239, 124– 137. Weiss D. J., Mason T. F. D., Zhao F. J., Kirk G. J. D., Ciles B. J. and Horstwood M. S. A. (2005) Isotopic discrimination of zinc in higher plants. New Phytol. 165, 703–710. Associate editor: Mark Rehkamper