Article pubs.acs.org/est
Zinc Speciation in the Suspended Particulate Matter of an Urban River (Orge, France): Influence of Seasonality and Urbanization Gradient Pierre Le Pape,*,†,‡,∇ Cécile Quantin,† Guillaume Morin,∥ Delphine Jouvin,† Isabelle Kieffer,⊥ Olivier Proux,⊥ Jaafar Ghanbaja,# and Sophie Ayrault‡ †
Geosciences Paris Sud (GEOPS), UMR 8148 UPS-CNRS, Campus universitaire d'Orsay Bâtiment 504, Rue du belvédère, 91405 Orsay Cedex, France ‡ Laboratoire des Sciences du Climat et de l'Environnement (LSCE), UMR 8212 CEA-CNRS-UVSQ, Bât. 12 Av. de la Terrasse,91198 Gif-sur-Yvette Cedex, France ∥ Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR 7590 CNRS-UPMC/Paris VI-IRD, 75252 Paris, France ⊥ Observatoire des Sciences de l’Univers de Grenoble (OSUG), UMS 832 CNRS-UJF, BP 53, 38041 Grenoble, Cedex 9, France # Institut Jean Lamour, UMR 7198 CNRS-Université de Lorraine, 34 Cours Léopold, 54000 Nancy, France S Supporting Information *
ABSTRACT: Among trace metal pollutants, zinc is the major one in the rivers from the Paris urban area, such as the Orge River, where Zn concentration in the suspended particulate matter (SPM) can reach 2000 mg/kg in the most urbanized areas. In order to better understand Zn cycling in such urban rivers, we have determined Zn speciation in SPM as a function of both the seasonal water flow variations and the urbanization gradient along the Orge River. Using TEM/ SEM-EDX and linear combination fitting (LCF) of EXAFS data at the Zn Kedge, we show that Zn mainly occurs as tetrahedrally coordinated Zn2+ sorbed to ferrihydrite (37−46%), calcite (0−37%), amorphous SiO2 (0−21%), and organicP (0−30%) and as octahedrally coordinated Zn2+ in the octahedral layer of phyllosilicates (18−25%). Moreover, the Zn speciation pattern depends on the river flow rate. At low water flow, Zn speciation changes along the urbanization gradient: geogenic forms of Zn inherited from soil erosion decrease relative to Zn bound to organic−phosphates and amorphous SiO2. At high water flow, Zn speciation is dominated by soil-borne forms of Zn regardless the degree of urbanization, indicating that erosion of Zn-bearing minerals dominates the Zn contribution to SPM under such conditions.
■
phases as a function of the physicochemical conditions20 as well as a function of the nature of the colloidal and solid phases.21 Except in the specific case of acidic waters, Zn is mainly associated with the particulate phase in riverine systems, that is, with the suspended particulate matter (SPM).22,23 During the last few decades, Zn speciation has been extensively studied in terrestrial environments, such as in natural13,24 and contaminated soils8−13,25−28 and, to a lesser extent, in sediments.29,30 These studies have highlighted recurrent Zn species in these media, including Zn2+ structurally incorporated in layered minerals, such as layered double hydroxides12,24,25,28−30 and phyllosilicates,8−10,24−31 as well as Zn2+ associated with iron oxides,12,24,29,32 organic matter12,13,24
INTRODUCTION Zinc is one of the most abundant trace metals on the Earth’s surface, with an average crustal abundance of 70 mg.kg−1.1 It is an essential element for living organisms; however, it has been recognized to have phytotoxic properties2−4 and to induce modifications in both the structure and activity of natural microbial communities when present at high concentrations in soils.5−7 For the last few centuries, large amounts of Zn have been released into the environment from smelting activities8−14 and waste combustion.15,16 Substantial Zn has also been deposited on cultivated soils due to the application of sewage, pig slurry, and other biosolids.17 Zn speciation refers to Zn valence state and chemical status as a sorbed/complexed cation or as a constituting/substituting cation in mineral structures at the molecular/atomic level. Consequently, this parameter largely determines the mobility and bioavailability of Zn in aquatic environments.18,19 In surface waters, trace metals are partitioned between the dissolved, colloidal and particulate © XXXX American Chemical Society
Received: February 11, 2014 Revised: September 10, 2014 Accepted: September 16, 2014
A
dx.doi.org/10.1021/es500680x | Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Article
(average flow rate ∼2 m3.s−1 at the “V” site), while campaigns 2 and 3, performed in September 2010 and January 2011, respectively, corresponded to high water flow periods (average flow rate ∼3−4 m3.s−1 at the “V” site).45 Sampling Procedure. At each site, both water and SPM were collected using PVC buckets previously soaked in 2N HNO3 and rinsed three times with river water before sampling. SPM were recovered by filtration through 0.45 μm cellulose filters under a N2 atmosphere.35 After filtration, SPM were kept under a N2 atmosphere to avoid the oxidation of the redox sensitive species. In addition, bottom sediments were collected at the “E” site during another sampling campaign. Sediments were sampled in the first 30 cm under the surface using a spade and stored in a PVC bucket, keeping water on the top to avoid direct exposure to air. An aliquot was then quickly freeze-dried and stored in the glovebox until analysis. Selection of SPM Samples. Of a total of 28 SPM samples collected from the Orge River during the four sampling campaigns described above, nine samples were selected as representative of the ranges in (i) Zn concentration and partition between the particulate and the dissolved compartments (SI Figure S2), (ii) urbanization gradient along the river (SI Figure S1) and (iii) seasonal variations in water flow conditions. Thus, following the urbanization gradient from upstream to downstream in the watershed, samples D1, E1, E2, E3, E4, V1, V2, V3, and V4 are representative of the Orge River SPM in terms of Zn contamination, covering a Zn concentration range from 200 to 2000 mg/kg.45,46 Among those selected SPM samples, D1, E1, V1, E4, and V4 are representative of low water flow conditions, whereas E2, V2, E3, and V3 are representative of high water flow conditions.45,46 Additional details concerning the geochemical composition of these samples, including dissolved Zn concentration and Zn partition between SPM and the dissolved compartment (
