Environ. Sci. Technol. 2009 43, 9314–9320
Use of Reflectance Infrared Spectroscopy for Monitoring the Metal Content of the Estuarine Sediments of the Nerbioi-Ibaizabal River (Metropolitan Bilbao, Bay of Biscay, Basque Country) JAVIER MOROS,† SILVIA FDEZ-ORTIZ DE VALLEJUELO,‡ AINARA GREDILLA,‡ ALBERTO DE DIEGO,‡ JUAN MANUEL MADARIAGA,‡ SALVADOR GARRIGUES,† AND M I G U E L D E L A G U A R D I A * ,† Department of Analytical Chemistry, University of Valencia, 50 Dr. Moliner Street, 46100 Burjassot, Valencia, Spain, and Department of Analytical Chemistry, University of the Basque Country, P.O. Box 644, 48080 Bilbao, Basque Country, Spain
Received July 17, 2009. Revised manuscript received October 20, 2009. Accepted October 28, 2009.
Multivariate partial least-squares (PLS) calibration models have been developed for the spatial and seasonal simultaneous monitoring of 14 trace elements (Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V, and Zn) in sediments from 117 samples taken in the estuary of the Nerbioi-Ibaizabal River. Models were based on the chemometric treatment of diffuse reflectance near-infrared (NIR) and attenuated total reflectance (ATR) mid infrared (MIR) spectra, obtained from samples previously lyophilized and sieved with a particle size lower than 63 µm. Vibrational spectra were scanned in both, NIR and MIR regions. Developed PLS models, based on the interaction between trace elements and organic mater provide good screening tools for the prediction of trace elements concentration in sediments.
Introduction Estuaries pollution is due to anthropogenic activity that influences the physical and chemical characteristics of the system (1). The contamination of estuarine environments by trace metals raises special interest because metals cannot be eliminated and tend to accumulate, thus representing a serious risk to the human health (2). Potentially toxic elements can be involved in chemical and biological reactions as well as to interact with sediment components as minerals, humic substances, metal oxides, microorganisms, and/or ligands, depending on physical-chemical and biological conditions in the estuary. Moreover, biogeochemical processes can affect the fate and bioavailability of metals and metalloids in sediments (3). Due to the dynamic character of estuaries, they must be regularly monitored to evaluate seasonal and * Corresponding author phone: +34 96 354 4838; fax: +34 96 354 4845; e-mail:
[email protected]. † University of Valencia. ‡ University of the Basque Country. 9314
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 24, 2009
geographical chemical and physical variations of surface sediments (4). For trace element determination conventional methods are based on wet digestion with hot concentrated acids followed by inductively coupled plasma (ICP) or atomic absorption spectrometry (AAS) (5), being in general complex, tedious, expensive, and highly time-consuming (6). So, for monitoring programs requiring the determination of several parameters in a high number of samples, fast and well validated methods are required. However vibrational spectroscopy provides unique tools for the direct determination of different parameters in untreated solid samples, thus offering a green analytical alternative (7). Vibrational measurements have been applied to determine metals in soils and sediments (8-16) based on the interaction of the organic matter bands with trace elements (see Supporting Information (SI) Table S1), and it can be seen that only in two works, sediment samples were analyzed. Moreover, it must be noticed that, in our knowledge, there is only one precedent based on the use of MIR measurements to determine metals in soils (10). So, the aim of this work has been the development of fast, accurate and reagent free analytical methods for the simultaneous evaluation of 14 elements (Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V, and Zn) in estuarine sediments from the Nerbioi-Ibaizabal River (Metropolitan Bilbao, Bay of Biscay, Basque Country) using measurements in both, NIR and MIR domains, and multivariate calibration.
Experimental Section Apparatus and Reagents. Two Bruker Fourier transform spectrometers were employed for spectra acquisition: (i) a near-infrared (NIR) model multipurpose analyzer (MPA) equipped with an integrating sphere as measurement accessory, and (ii) a Fourier transform middle infrared (FT-IR) model Tensor 27 equipped with a KBr beamspliter, a DLaTGS detector and a three-reflection diamond/ZnSe composite DuraSamplIR accessory. Instrumental and measurement control, data acquisition, spectra treatment, and data manipulation were carried out using OPUS program Version 4.2 from Bruker Gmbh (Bremen, Germany). Reference trace element concentrations used for building the prediction models were obtained by inductively coupled plasma/mass spectrometry (ICP/MS) made with an Elan 9000 ICP/MS spectrometer (Perkin-Elmer, Ontario, Canada), with Ryton cross-flow nebulizer, Scott-type double pass spray chamber and standard nickel cones. Preparation of calibrations and analysis of samples was done inside a clean room (class 100). Nitric acid (69%, Tracepur) and hydrochloric acid (36%, Tracepur) were purchased from Merck (Darmstadt, Germany). Milli-Q (Millipore, Billerica, MA) quality water with a conductivity lower than 0.05 µS · cm-1 was used for samples and standards dilutions. Multielemental standard solutions of the analytes were prepared by weight in 1% HNO3 from individual commercial stock solutions of Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V, and Zn (1000 mg · L-1 in 5% HNO3, Specpure from Alfa Aesar, War Hill, MA). Be9, Sc45, In115, and Bi209 from stock standard solutions (1000 mg · L-1 in 5% HNO3, Specpure), were added to blank, standard and sample solutions as internal standard to yield 10 µg · L-1. Argon (99.999%, Praxair, Spain) was used as plasmogen and carrier gas. A certified reference material NIST-SRM 1646a (estuarine sediment from the National Institute of Standards and Technology, Gaithersburg, MD) was used to validate the accuracy of the whole procedure. 10.1021/es9005898 CCC: $40.75
2009 American Chemical Society
Published on Web 11/10/2009
FIGURE 1. Geographical location of the Nerbioi-Ibaizabal estuary (Metropolitan Bilbao) and spatial distribution of the different sampling stations: 1. Alde Zaharra (AZ), 2. Zorroza (ZO), 3. Kadagua (KA), 4. Asua (AS), 5. Galindo (GA), 6. Udondo (UD), 7. Gobela (GO), and 8. Arriluze (AR). Lead concentration profile as the average total concentration of AZ, ZO, and KA sampling stations among the 15 sampling campaigns. Samples and Measurements. 117 sediment samples were collected from the estuary of the Nerbioi-Ibaizabal River, located on the continental shelf of the Cantabrian coastline in the southeastern part of the Bay of Biscay. Approximately 500 g of surface sediment samples (∼2 cm depth) were collected at low tide, from eight stations distributed with an average distance of 11 km (see Figure 1). Two sampling points (Nos. 1, 2) are located in the main channel, four (Nos. 3, 4, 5, 7) in the main tributary rivers, another one (No. 8) in the mouth of the estuary, and one (No. 6) in a semiclosed dock. Sediments were sampled every three months (15 sampling campaigns from January 2005 to October 2008), using plastic sampling utensils and latex gloves to avoid sample contamination. Samples were set inside cleaned plastic bags and transported to the laboratory at 4 °C to reduce the microbiological activity (17). Sediment samples were frozen at -20 °C, lyophilized at 150 mTorr and -52 °C in a Cryodos apparatus (Telstar, Spain) for 48 h and then sieved until a maximum particle size of 63 µm and kept in the refrigerator at 4 °C. Trace elements were determined in the fine fraction (
