Vanadium distribution in the Seine Estuary

Ouddane B.¹, Skiker M.^1,2, Fischer J.C.¹ and Wartel M.¹

¹ Université des Sciences et Technologies de Lille ELICO UPRESA CNRS 8013

Laboratoire de Chimie Analytique et Marine Bât. C8 (2ème étage)

59655 Villeneuve d’Ascq Cedex, France

(E-mail : ouddane@univ-lille1.fr)

² Université Mohamed Premier, Faculte des sciences Oujda (Morocco)

ABSTRACT

The distribution of dissolved and particulate vanadium was investigated in the Seine estuary during several surveys between 1993 and 1998. The results obtained indicated an apparent contamination of the estuary by this metal. This can be do to anthropogenic inputs. There are many industrial discharges in the region and particularly the manufacture of TiO₂, which is situated in the lower part of the estuary, has a daily contribution of about 870 Kg of vanadium. The behavior of vanadium observed in the Seine estuary at the different surveys realized was non conservative. The dissolved vanadium speciation revealed that the predominant species was the H₂VO₄^-. The distribution of the chemical forms was pH-dependent. In the particulate phase, the determination of vanadium distribution was conducted by sequential extraction corresponding to four fractions (carbonate, oxy-hydroxide, organic and residual).

INTRODUCTION

Vanadium is considered as a potential marine pollutant and is toxic to a variety of organisms (Miramand and Fowler, 1998). Its solution chemistry in natural environments is influenced by anthropogenic inputs. In oxygenated natural waters, vanadium is essentially under five oxidization state as vanadate anions. However, depending on the source of vanadium, its chemical form may vary. In the chemical conditions of redox potential and of pH found in the Seine estuary waters, vanadium is found predominantly in its anionic form H₂VO₄^-. In order to extend our knowledge of the estuarine behavior of vanadium, various surveys were conducted in the Seine estuary.

The Seine estuary is known to be highly contaminated by waste derived from industrial sources (30 % of the French industrial activity is located in the Seine Basin), from agricultural operations (40 % of the french agriculture is located in this area) and finally from sewage inputs, since 30 % of the whole French population lives in the Seine Basin (75 000 km² area). The hydro-sedimentological processes in the Seine estuary are very complex. They are enhanced by a macrotidal regime which controls suspended material transport, deposition and erosion, as discussed by Avoine (1986). The average water discharge is 450 m³ s^-1, with an average interannual variation from 200 to 650 m³ s^-1. The minimum discharge recorded has been 60 m³ s^-1 and the highest one has been more than 2200 m³ s^-1. The salinity intrusion may extend up to 50 km upstream of Le Havre during periods of low river discharge, and up to 20 km during flood conditions. The limit of tide variations can be observed 100 km upstream of Le Havre. The estuary is characterized by a high turbidity zone (up to several g l^-1).

A total of five surveys were carried out during the period 1993-1998 in different conditions (spring or neap tide, high or low flow, along the estuary or at a fixed station). The 1995 survey was realized in specific conditions of high discharge (2019-2079 m³ s^-1) under spring tide. In 1996 two surveys were carried, the first under spring tide conditions at a fixed station during a tide cycle on February. The second one was realized under neap tide conditions and during a period of low discharge (201 m³ s^-1) on May. Field sampling was performed essentially throughout the estuarine mixing zone in approximate coincidence with the local high water. Sampling positions were chosen to cover of the full salinity range and sometimes around industrial inputs.

Methods

The water samples were collected from a boat, at a depth of 1 m below the water surface (surface samples) and at ~1 m above the bottom (deep samples) using a Teflon pumping system. Approximately 2 l of unfiltered water were collected for the determination of total suspended particulate matter (SPM). Each vanadium sample (~ 10 l) was filtered directly on site through 0.4 µm cleaned Nuclepore filters (diameter: 147 mm) under a horizontal laminar flow hood. A portion of filtered water (500 ml) was collected in special centrifugation Nalgene flasks (high density polyethylene) for the analysis of trace metals after a preconcentration procedure. The gallium coprecipitation method was used and adapted to the estuarine waters by Ouddane et al. (1997) and vanadium was measured by inductivity coupled plasma atomic emission spectrometry (VARIAN Axial Liberty Series II). Three replicates were determined for each sample and the relative standard deviations were below 5%.

Particulate total metals were determined by means of ICP-AES after total acid digestion with a mixture of boiling concentrated acids (HCl + HNO₃ + HF) in PTFE flasks. For the validation of the digestion procedure and the analytical method, MESS-1, BCSS-1 and PACS-1 Sediment standards Reference Material for metals supplied by the National Research Council of Canada have been used. Chemical speciation was determined by sequential extraction procedures. Four fractions were identified, carbonates, easily reducible phases (Mn oxide or hydroxide, amorphous Fe oxide), organic-bound and residual. The reagents used for each fraction are the same as used in Tessier et al. (1979).

Determinations of pH, temperature and salinity were made on site in unfiltered samples. Measurements of pH were performed with an Orion pH meter. Salinity and temperature were measured with a WTW apparatus Model LF191.

RESULTS AND DISCUSION

The results of dissolved vanadium for the different cruises are plotted as a function of salinity in Fig. 1. Except for the May 1996 survey, the profiles indicate a significant non-conservative behavior of dissolved vanadium in the Seine estuary with a maximum at the medium salinities. Contrary to our results, Yeats (1992) had noticed a linear variation of the vanadium in a very extended salinity range (0 to 35) in the Saint Laurent estuary. This conservative behavior of vanadium was also observed by Van der Sloot et al. (1985) in the Rhine and the Schelde estuaries. A non-conservative behavior has been shown by Prange and Kremling (1985) in the Baltic, which was attributed to scavenging of vanadium by terrigenous and/or by biogenic particulate material.

Relatively low dissolved vanadium concentration were observed in May 1996 survey compared to other surveys. This depletion was most probably caused by the high biological activity during this period (spring phytoplankton blooms) which contributed in the uptake of vanadium by the biological material. Miramand et al. (1993) have reported a significant removal of dissolved vanadium from the solution by a number of phytoplankton cells in the Seine bay. The evidence of spring phytoplankton blooms during this cruise was indicated by the low dissolved silicon concentrations observed then, in contrast to other surveys periods when silicon concentrations were generally clearly decreasing with salinity (Ouddane et al., 1999). Shiller and Boyle (1987) have observed the same phenomenon in the Mississippi and Amazon rivers, they explain the depletions of dissolved vanadium by the biological (diatom bloom) uptake.

Figure 1: Dissolved vanadium concentrations (µg/l) as function of salinity

Figure 2: vanadium concentrations as function of the distance

(kilometer points, distance from Paris)

In the river part of the Seine estuary (at low salinities), the V concentrations (~ 1 µg/l) were very similar to those reported by Shiller and Boyle (1987) in the major world rivers (0.75 µg/l). Yeats (1992) has measured 0.9 to 1.2 µg/l in the Saint Laurent river and 0.3 µg/l in the Sagueney fjord. In the Mid of the Seine estuary, vanadium concentrations were rather superior to the world average and concentrations greater than 6 µg/l were measured. These high concentrations can be due, either to the dissolution of particulate vanadium in the mixing zone, or to surface sediments remobilization, or to industrial inputs. The largest industrial contribution is situated in the region of Le Havre (Millenium factory, production of TiO₂) in the lower part of the estuary: the daily discharge is about 870 Kg of vanadium, although the factory aims at reducting its inputs this last years. For the February 1996 transect, the maximum vanadium concentration was situated between the salinity 5 and 15. A discrepancy between vanadium concentrations in surface and bottom layers was noticeable when vanadium concentrations were plotted as function of the distance (fig 2.). This result confirmed that the high concentration, particularly in the bottom layers may be of antropogenic origin and may come from the lower estuary.

The particulate suspended vanadium distributions in the estuarine zone were showed little variation. Except the samples collected in the marine zone (near the industrial input), the average particulate vanadium content in 85 samples was 96 ± 10 ppm. This value is smaller compared to the Shale (130 ppm). For the samples collected near the source of contamination the particulate vanadium concentrations reached 500 ppm. Under these conditions, removal from or release into solution was therefore not reflected in observable change in particulate vanadium concentrations. In order to identify the extent of contamination by vanadium in comparison to other metals, we have normalized all metal concentrations to aluminum. Aluminum was used because of its conservativity and to reduce grain size effect. Its concentration is usually unaltered by contaminant input. The range of values observed in the Seine estuary, the Seine bay and the sampling stations closed to industrial input are compared in Table 1.

	Shales	Seine estuary	Seine bay	Stations close to industrial input
Fe/Al	0.59	0.67 ± 0.02	0.67 ± 0.06	1.34 ± 0.06
Ti/Al	0.056	0.068 ± 0.004	0.078 ± 0.007	0.433 ± 0.021
Cr/Al * 10^3	1.12	2.36 ± 0.17	2.71 ± 0.21	10.90 ± 0.50
Zn/Al * 10^3	1.19	4.94 ± 0.57	4.36 ± 0.07	4.94 ± 0.57
Mn/Al * 10^3	10.62	12.42 ± 1.23	11.31 ± 0.37	9.33 ± 0.02
Cu/Al * 10^3	1.12	1.24 ± 1.23	0.97 ± 0.06	0.99 ± 0.05
V/Al * 10^3	1.63	2.06 ± 0.09	2.06 ± 0.09	20.67 ± 0.91

Table 1 : comparison between suspended particulate metal/Al rations(overages)

Except for copper, the data in Table 1 suggest a metal enrichment in the Seine estuary and bay in comparison to the Shales data. The influences of industrial discharge were consistently higher at the stations situated around the industrial input. This is particularly noticeable for Cr, Ti and V which have an enrichment factor of 4, 5, 10 respectively. These results confirmed that the antropogenic inputs may affect the particle composition in this estuary paticularly for vanadium. The chemical fractionation confirmed that the major form of vanadium was in the residual fraction. The difference was explicit only near the industrial discharge. At these stations the oxy-hydroxide becomes the major fraction.

References

Avoine J, Boust D, Guillaud JF (1986), Rapp. P-v. Réun. Cons. Perm. Inter. Explor. Mer, 186: 392-411.

Miramand P, Fowler SW (1998), In: Vanadium in the Environment, Pt.1, Chemistry and Biochemistry. ( J. Nriagu, Editor), Chichester, Wiley-Interscience.

Miraman P, Bentely D, Guary JC, Brylinski JM (1993). Oceanologica Acta, 16 :5-6, 625-632.

Ouddane B, Skiker M, Fischer JC, Wartel M (1997), Analusis, 25 : 308-313

Ouddane B, Skiker M, Fischer JC, Wartel M (1999), J. of Environ. Monitoring, 1 : 489-496.

Prange A, Kremling K (1985), Mar. Chem., 16 : 259-274.

Shiller A., Boyle E. A. (1987), Earth and Planetary Science Letters, 86 : 214-224.

Tessier A, Campbell PGC, Bisson M (1979), Anal. Chem., 51: 844-851.

Van der Sloot HA, Hoede D, Wijkstra J, Duinker JC, Nolting RF (1985), Estuar. Coast. and Shelf Sci., 21 : 633-651.

Yeats PA (1992), Estuar. Coast. and Shelf Sci. 34 : 85-93.