Zinc isotopes in the Seine River water, France: a probe of. anthropogenic contamination

Transcription

1 Zinc isotopes in the Seine River water, France: a probe of anthropogenic contamination Jiubin Chen*, Jérôme Gaillardet and Pascale Louvat Equipe Géochimie et Cosmochimie, Institut de Physique du Globe de Paris, Université Paris- Diderot, UMR CNRS 7154, 4 place Jussieu, Paris, France. Number of pages : 7 Number of tables : 1 Number of appendix : 4 * Corresponding author: Phone: Fax: chen@ipgp.jussieu.fr.

2 TABLE 1. Enrichment Factor, Concentrations and Isotopic Compositions of Zn in Samples of the Seine Basin ph Discharge SPM E.F.(Zn) Cl Na Ca Zn Cu Th (m 3 /s) (mg/l) ( mol/l) ( mol/l) ( mol/l) (nmol/l) (nmol/l) (nmol/l) ( ) First temporal sampling series in Paris (May.2004 Mar.2007) S1 23/12/ ±0.02 S2 21/01/ ±0.01 S3 25/01/ nd S4 27/01/ nd S5 29/01/ nd S6 31/01/ nd S7 14/02/ nd S8 17/02/ nd S9 20/02/ nd S10 22/02/ nd S11 24/02/ nd S12 08/04/ ±0.05 S13 29/04/ nd S14 19/05/ nd S15 25/05/ ±0.05 S16 23/06/ ±0.03 S17 11/07/ nd S18 25/07/ ±0.06 S19 26/08/ ±0.01 S20 17/09/ ±0.02 S21 03/10/ ±0.03 S22 09/11/ nd S23 29/11/ ±0.02 S24 22/12/ ±0.02 S25 24/01/ ±0.04 S26 17/02/ nd S27 20/02/ ±0.02 S1 66 Zn

3 TABLE 1. (Continued) Enrichment Factor. Concentrations and Isotopic Compositions of Zn in Rivers of the Seine Basin ph Discharge SPM E.F.(Zn) Cl Na Ca Zn Cu Th (m 3 /s) (mg/l) ( mol/l) ( mol/l) ( mol/l) (nmol/l) (nmol/l) (nmol/l) ( ) S41 01/03/ ±0.02 S42 10/03/ nd S43 14/03/ ±0.02 S44 20/03/ ±0.01 S45 31/03/ ±0.03 S46 11/04/ ±0.04 S47 15/05/ nd S48 21/06/ ±0.01 S63 13/10/ ±0.04 S64 07/03/ ±0.03 S65 10/05/ nd Second geographical transect series on the whole Seine basin: the flood sampling cruise of 22 Feb S28 Seine@Sring ±0.05 S29 Seine@Buncey nd S30 Seine@Bar <lod <lod 0.18±0.01 S31 Aube ±0.05 S32 Seine@Châtres ±0.05 S33 Seine@Noyen ±0.03 S34 Yonne nd S35 Seine@Fontaine ±0.02 S36 Oise ±0.01 S37 Seine@Meulan ±0.02 S38 Seine@laBouille ±0.04 S39 Eure ±0.02 S40 Marne ±0.03 Second geographical transect series on the whole Seine basin: the low water sampling cruise of 31 Jul S49 Seine@Sring ±0.04 S50 Seine@Buncey nd S2 66 Zn

4 TABLE 1. (Continued) Enrichment Factor. Concentrations and Isotopic Compositions of Zn in Rivers of the Seine Basin ph Discharge SPM E.F.(Zn) Cl Na Ca Zn Cu Th (m 3 /s) (mg/l) ( mol/l) ( mol/l) ( mol/l) (nmol/l) (nmol/l) (nmol/l) ( ) S51 Seine@Bar nd S52 Aube ±0.01 S53 Seine@Châtres nd S54 Yonne nd S55 Loing ±0.03 S56 Seine@Fontaine nd S57 Marne nd S58 Seine@Paris ±0.02 S59 Oise nd S60 Seine@Meulan nd S61 Eure nd S62 Seine@laBouille nd Third sampling series of rain waters and anthropogenic samples in Paris conurbation (Feb Jul. 2006) RW1 Rainwater@Paris nd RW2 Rainwater@Paris ±0.02 RW3 Rainwater@Paris ±0.08 RW4 Rainwater@Paris nd RW5 Rainwater@Paris ±0.04 RW6 Rainwater@Morvan nd 69 nd ±0.01 RF1 Roof streaming ±0.04 RF2 Roof streaming nd RF3 Roof streaming nd RF4 Roof streaming nd ±0.04 RF5 Roof streaming nd ±0.05 RD1 Road streaming nd RD2 Road streaming nd ±0.01 SW1 Noisy-le-Grand ± Zn S3

5 TABLE 1. (Continued) Enrichment Factor. Concentrations and Isotopic Compositions of Zn in Rivers of the Seine Basin ph Discharge SPM E.F.(Zn) Cl Na Ca Zn Cu Th (m 3 /s) (mg/l) ( mol/l) ( mol/l) ( mol/l) (nmol/l) (nmol/l) (nmol/l) ( ) PTWW1 Noisy-le-Grand ±0.06 PTWW2 Achères ±0.04 Complementary samples N-fertilizer 4 nd ±0.01 P-fertilizer (DAP) 3 nd ±0.02 K-fertilizer nd Leached sample of zinc roof nd nd nd nd nd nd -0.10±0.01 Chalk of the Seine headland* 1 nd ±0.10 Granite of the Seine headland* 0.1 nd ±0.06 Suspended load of S31* nd ±0.01 Suspended load of PTWW2* 22 nd ±0.04 Reused WWTP sludge* 22 nd ±0.02 Zn isotope analytical uncertainties are 2 external standard deviations (2 ). SPM, suspended particulate matter; E.F.(Zn), enrichment factor of Zn (see details in text); RW, rain water; RF, roof runoff samples collected in Paris conurbation; RD1.2. road runoff waters in Paris conurbation; SW, sewage wastewater; PTWW, plant-treated wastewaters in SIAAP system; nd, not determined; <lod, inferior to the limit of determination (0.002nmol/l for Th) * element concentrations in mg/kg solid; Zn isotope compositions reported in Chen et al (29). 66 Zn S4

6 Appendix A.1 Analytical techniques The main difficulty with analysis of Zn isotopes in river water is the relatively low concentrations. Our newly developed separation procedure allows introducing large volumes of filtered natural water samples (typically 500 ml) directly onto the first ion exchange column (0.5 ml of Chelex 100 resin), avoiding evaporation and acid digestion steps which are particularly susceptible to Zn contamination. Elimination of ionic matrix and cleaning are made using 20 ml ammonium acetate buffer and 14 ml HNO 3 solutions. Zn is removed from the resin using 10 ml dilute HNO 3. After evaporation and re-dissolution in HCl, the Zn sample is further purified on a second column containing 0.1mL of AG1-X4 resin. The Zn fraction is eluted in 0.5N HNO 3, ready to be analyzed by MC-ICP-MS after appropriate dilution to a Zn concentration of 1.54 μmol/l. This second procedure allows Ni separation. Recovery yield of the chromatographic procedure was 100±1%. Reproducibility of the procedure was tested by analysis of numerous replicates of synthetic solutions and river waters. No isotopic fractionation occurred (total 66 Zn/ 64 Zn variation of 6ppm) (27) and no significant interferences were found during Zn isotopic measurement. Field filtration, sample storage and chemical separation led to an average blank of 12 ng (approx. 1.4% of the total sample Zn). Zn isotopic analyses were performed on a Neptune MC-ICP-MS (Thermo Finnigan, Germany) at IPGP, using the APEX HF desolvator (from ESI) with a 50μl/min microconcentric nebuliser as the sample introduction system. All samples and standards were measured in 0.05M HNO 3, with SRM916 Cu added as an internal standard (Zn/Cu = 2) (11,29). One measurement lasted for 13 minutes (on-peak baseline, peak center, and 5 blocks of 20 cycles). The Cu-spiked Zn standard was measured every 3 to 4 samples, and each sample measurement was repeated three times during a measurement session and at least 3 other times another day. Simultaneous measurement of Zn and Cu isotopes allows correction of instrumental mass bias on Zn according to the empirical external normalization method (11, 27). Error bars given in this paper are all 2 standard deviation external uncertainties. S5

7 A.2 Zn isotopic fractionation due to adsorption effect. Let us consider a liter of river water in which Zn-free suspended particulate matter is added. [Zn] 0 denote concentrations of Zn in the initial solution. After equilibration, [Zn] AD and [Zn] D denote concentrations of Zn adsorbed onto SPM and in dissolved load, respectively. The final concentration of sediments is denoted [SPM] (g/l). The mass budget for concentration and isotopic ratios R (i.e., 66 Zn/ 64 Zn) implies that: [ Zn] 0 = [ SPM] [ Zn] AD + [ Zn] D (1) [ Zn] 0 R 0 = [ Zn] AD [ SPM] R AD + [ Zn] D R D (2) where R 0, R AD ad R D are the isotopic ratios of Zn in the initial solution, adsorbed on SPM and in the dissolved phase at equilibrium. Introducing the partition coefficient Kd of Zn (expressed in liter of water per kg of sediment) and isotopic fractionation factor a: Kd = [ Zn] AD [ Zn] D (3) = R AD /R D (4) then the isotopic shift (in ) from the initial isotopic composition of the solution is [ ] 1+ Kd [ SPM] 1000(1 ) Kd SPM ( ) = (5) A.3 Mass budget calculation for mixing between the main Seine channel and its tributaries In the absence of adsorption of Zn onto SPM, the isotopic composition of the mixture M between two tributaries A and B can be calculated using the equation: 66 Zn M = 66 Zn A A + 66 Zn B (1) where 66 Zn A, 66 Zn B, 66 Zn M denote the Zn isotope composition of end-members A and B, and the mixture respectively. The mixing proportions A and B are related to water discharges Q and Zn concentrations [Zn] according to: A = ( [ Zn] Q A A ) ([ Zn] M Q M ) (2) S6

8 and B = ( [ Zn] Q B B ) ([ Zn] M Q M ) (3) This mass budget calculation was carried out for flood samples S31 (Aube), S32 (Seine River at Châtres) and S33 (Seine River at Noyen), collected before and after the mixing of these two rivers (Table 1, Fig. 1). The mass budget calculation reveals that 49% of Zn in sample S33 (just after the confluence) is derived from S31 (Aube River) and 51% is derived from S32 (Seine River before mixing). According to 66 Zn values of S31 (0.58 ) and S32 (0.35 ), these mixing proportions give a 66 Zn of 0.46 for S33, consistent with the measured value 0.47 (±0.03 ). This conclusion shows that mixing is the dominant mechanism controlling 66 Zn variation in the Seine River and Zn isotopes can be used as a proxy of different sources. A.4 Zn adsorption in soil In a volume V of soil having a mass of M, the proportion P AD of Zn adsorbed onto surfaces can be calculated as follows: P AD = M.[Zn] AD M.[Zn] AD + W [Zn] D (1) where W is the amount of water in the soil, [Zn] AD and [Zn] D are concentrations of adsorbed and dissolved Zn, respectively. Introducing partition coefficient of Zn: P AD = Kd Kd +, the water rock ratio W/M, and Kd, the (2) For typical porosity values of 10-20% for agricultural soils and Kd of 10,000, we calculate values between 0.1 and Then, typical P AD values are close to 99%. S7