Article pubs.acs.org/est
Screening of Lake Sediments for Emerging Contaminants by Liquid Chromatography Atmospheric Pressure Photoionization and Electrospray Ionization Coupled to High Resolution Mass Spectrometry Aurea C. Chiaia-Hernandez,†,‡ Martin Krauss,§ and Juliane Hollender*,†,‡ †
Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092 Zürich, Switzerland § Helmholtz Centre for Environmental Research (UFZ), Permoserstraße 15, 04318 Leipzig, Germany ‡
S Supporting Information *
ABSTRACT: We developed a multiresidue method for the target and suspect screening of more than 180 pharmaceuticals, personal care products, pesticides, biocides, additives, corrosion inhibitors, musk fragrances, UV light stabilizers, and industrial chemicals in sediments. Sediment samples were freeze-dried, extracted by pressurized liquid extraction, and cleaned up by liquid−liquid partitioning. The quantification and identification of target compounds with a broad range of physicochemical properties (log Kow 0−12) was carried out by liquid chromatography followed by electrospray ionization (ESI) and atmospheric pressure photoionization (APPI) coupled to high resolution Orbitrap mass spectrometry (HRMS/MS). The overall method average recoveries and precision are 103% and 9% (RSD), respectively. The method detection limits range from 0.010 to 4 ng/gdw, while limits of quantification range from 0.030 to 14 ng/gdw. The use of APPI as an alternative ionization source helped to distinguish two isomeric musk fragrances by means of different ionization behavior. The method was demonstrated on sediment cores from Lake Greifensee located in northeastern Switzerland. The results show that biocides, musk fragrances, and other personal care products were the most frequently detected compounds with concentrations ranging from pg/gdw to ng/gdw, whereas none of the targeted pharmaceuticals were found. The concentrations of many urban contaminants originating from wastewater correlate with the highest phosphorus input into the lake as a proxy for treatment efficiency. HRMS enabled a retrospective analysis of the full-scan data acquisition allowing the detection of suspected compounds like quaternary ammonium surfactants, the biocide triclocarban, and the tentative identification of further compounds without reference standards, among others transformation products of triclosan and triclocarban.
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INTRODUCTION
household chemicals, or pesticides is not well explored. One example for the suitability of sediments for the study of less lipophilic compounds is nonylphenol, for which the dynamic of sediment loads could be clearly correlated to the restriction of their use in Switzerland at the end of the 1980s. Lara-Martin et al.5 studied the distribution of surfactants in sediment cores and detected degradation intermediates in deeper sediment layers and partly in pore water. Undisturbed cores are a prerequisite for construction of historic records. River sediments are usually not suitable because of turbulences and stronger influences of sampling locations as have been shown for human and veterinary antibiotics.6
Today, approximately 300 million tons of synthetic compounds are used annually in industrial and consumer products.1 These compounds can enter natural waters via wastewater treatment plant effluents, urban and industrial sewage, erosional runoff, and leaching from agricultural areas. Once in natural waters, these compounds may sorb to sediments depending on their physical chemical properties. Sediments are excellent archives of environmental contaminants if the chemicals persist over time, since they can act as integrators of many inputs within a catchment. This is particularly true for hydrophobic organic compounds, which rapidly sorb to sediments and suspended particles.2 Until recently, such records have been mainly used to characterize the contamination by legacy compounds with highly lipophilic characteristics such as polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAH).3,4 The long-term contamination of sediments with medium polar contaminants such as pharmaceuticals, personal care products, © 2012 American Chemical Society
Received: Revised: Accepted: Published: 976
September 25, 2012 November 26, 2012 December 7, 2012 December 7, 2012 dx.doi.org/10.1021/es303888v | Environ. Sci. Technol. 2013, 47, 976−986
Environmental Science & Technology
Article
screening of organic contaminants and was analyzed in great detail, while the second core was used for confirmation. Core samples were extracted by free fall gravity corer and stored vertically in the dark at 4 °C. Individual cores were dissected into approximately 2 cm slices and transferred to glass jars, closed airtight, and stored in the dark at −20 °C. Total phosphorus and nitrogen concentrations for each sediment layer were measured using peroxodisulfate oxidation, as described by Ebina et al.17 Dating of Lake Greifensee sediment cores was performed by counting yearly laminations (varves) because the oxic and anoxic color composition of the lake can be easily identified. The results were compared with sedimentation rates and with another study that characterized lake Greifensee using 137Cs signals.18 Extraction of Sediments. Previously frozen, individual sediment layers were freeze-dried, homogenized with a mortar and pestle, weighed, and transferred to stainless steel cells prepared with a 27 mm glass fiber filter and a 16.2 mm cellulose filter (Dionex, Olten, Switzerland). The final amount of sediment delivered to the cell was between 4 to 6 g. In addition, 250 mg of diatomaceous earth was added to each extraction cell to increase solvent channeling (Hydromatrix, Resteck, Bellefonte, PA). The cells were then extracted by pressurized liquid extraction (PLE) using an ASE 350 system (Dionex, Sunnyvale, U.S.A.) at 80 °C using a mixture of the two polar aprotic solvents ethyl acetate and acetone with intermediate dielectric constants and polarity at a ratio of 70:30 (% v/v). Details on temperature and solvent ratio selection are provided in the Supporting Information (SI). Extracts of approximately 23 mL were spiked with 60 μL of 2.5 ng/μL internal standard mixture with an absolute amount of 150 ng of each compound. Afterward, the extracts were gently evaporated to 100 μL with an automated evaporator system at a temperature of 30 °C (EZ-2 evaporation system from Genevac, Gardiner, U.S.A.). After evaporation, extracts were diluted to 2.5 mL with HPLC water. Clean-up and Enrichment of Sediment Extracts. The removal of matrix from the sediment extracts was based on a modification of the multiresidue method “QuEChERS” (quick, easy, cheap, effective, rugged, and safe) developed by Anastassiades et al. for the determination of polar pesticide residues in fruits and vegetables19 and has been previously applied in river sediments.20 5 mL of acetonitrile was added to the extracts, followed by 1.6 g of MgSO4 to promote partitioning of less-polar analytes into the acetonitrile phase and 0.4 g NH4Cl to initiate and influence liquid−liquid partitioning, thereby improving the recoveries of polar compounds. The addition of dispersive solid phase extraction material (dSPE) containing primary secondary amine (PSA) was tested additionally to remove matrix interferences such as humic acids through anion exchange interactions. Since the use of d-SPE decreased recoveries for the more hydrophobic compounds up to 65%, similar to that described for steroids and drugs in soil,21 it was omitted from the final method. The mixture was vortexed and centrifuged for 10 min at 3500 rpm (1920 × g) (Megafuge 1.0R, Kendro laboratories, Langenselbold, Germany). After separation, the acetonitrile phase was transferred to a graduated centrifuge tube, evaporated to 50 μL, and brought to a volume of 500 μL by adding methanol. The final extract was filtered into 2 mL autosample vials using 0.2 μm PTFE filters (BGB analytics, Boeckten, Switzerland).
In the past decade, detection and quantification of polar to medium polar organic contaminants in the environment has typically been achieved by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Until recently, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) were the most commonly used ionization technologies. Atmospheric pressure photo ionization (APPI) is a newer type of ionization technique for the analysis of poorly ionizable, less polar compounds. The suitability and universality of APPI has been demonstrated by the analysis of drugs,7,8 PCBs and PAHs,9,10 perfluorinated compounds,11,12 steroids,13,14 and fullerenes.12 Therefore, the combination of ESI and APPI as complementary ionization techniques for the analysis of environmental samples could significantly expand the detection and quantification of a wide range of compounds in a single study. In addition to the difficulty in the ionization and detection of organic contaminants, there are additional challenges to be addressed such as the lack of reference standards for potential contaminants and especially transformation products. Triple quadruple (QqQ) instruments have shown to be highly selective and sensitive and have a strong potential for quantitative analysis when operating in selected ion monitoring (SIM) or selected reaction monitoring (SRM), but QqQ instruments can only measure nominal masses, and when they are operated in the full scan mode, the sensitivity is low, restraining the analysis to a given number of analytes. The use of high resolution mass spectrometry (HRMS) can overcome these challenges by studying parent compounds, metabolites, and transformation products with and without reference standards based on accurate mass acquisition and fragmentation patterns.15 The most common HRMS instruments have a resolving power of 10−20 000, while the new technologies reach values of 100 000 (Orbitrap) and up to 1 000 000 (FTICR), with high mass accuracy (
