Geochemical Journal, Vol. 44, pp. 161 to 166, 2010
Possible precursor of perylene in sediments of Lake Biwa elucidated by stable carbon isotope composition NOBUYASU ITOH* and NOBUYASU HANARI National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Umezono, Tsukuba, Ibaraki 305-8563, Japan (Received March 25, 2009; Accepted August 17, 2009) We determined the stable carbon isotope compositions (δ 13C values) of perylene and compounds coexisting with it to elucidate the precursor of perylene in sediments of Lake Biwa. Although we found a high amount of friedelin (6.5 µ g g–1) in extracts, originating mainly from C3 angiosperms, its δ13C value (–30.8‰ ± 0.1‰) was different from that of perylene (–27.8‰ ± 0.3‰). The δ13C values of friedelin and perylene lay within the ranges for Japanese angiosperms (C3, –37.5‰ to –28.6‰) and gymnosperms (C 3, –28.3‰ to –26.0‰), respectively. Since these values were clearly more negative than those of Japanese aquatic plants (C3, –16.5‰ to –14.6‰), it can be considered that the perylene originated from the land, principally from gymnosperms. Keywords: Lake Biwa, perylene, stable carbon isotopic composition, sediment
transformed into perylene by removal of oxygen and aromatization under anaerobic conditions (Ishiwatari and Matsushita, 1986; Jiang et al., 2000). Sato and Kumada extracted perylenequinone from podzolic soils and showed that it can be reduced with zinc dust (Sato and Kumada, 1967; Sato, 1976c). Ishiwatari and Matsushita (1986) showed that the amount of perylene in sediment samples increased significantly as a result of reduction of perylenequinone with zinc dust. These results suggest that the precursor of perylene has a terrestrial origin, including both plants and parasitic fungi (Aizenshtat, 1973; Ishiwatari et al., 1980; Jiang et al., 2000; Bechtel et al., 2007; Jiang and Liu, 2008). However, Wakeham et al. (1979) detected abundant perylene in the Namibian Shelf (0.17–0.82 µg g–1), where the input of terrigenous material is negligible, and precursors such as perylenequinone might not be associated with terrigenous material. Compound-specific stable carbon isotope ratios (δ13C) of PAHs in environmental samples have been used to elucidate the origins of PAHs, because these values do not change during transport and preservation (Okuda et al., 2002; Stark et al., 2003; Walker et al., 2005). Although the formulae of perylenequinone (C 20 H 10 O 4 ) and binaphthyl (C 20 H 14 O 4 ) differ from that of perylene (C20H12), the number of carbons is the same (Fig. 1). Thus, if perylenequinone and binaphthyl are precursors of perylene, the δ 13C value of perylene in sediments should indicate that. Lake Biwa is the largest lake in Japan, and its physical, chemical, and biological characteristics have been well studied (e.g., Sohrin et al., 1996; Yoshida et al., 2001;
INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs), some of which are carcinogenic (Luch, 2004), are formed through incomplete combustion in anthropogenic processes, such as burning of fossil fuels, and in natural processes, such as forest fires (Finlayson-Pitts and Pitts, 2000). Because they are not only transported over long distances, but are also well preserved, they have been found in most flux and sediment samples throughout the world (e.g., Fernández et al., 1999; Tamamura et al., 2009). Perylene (C20H12) is commonly found with other PAHs (Ishiwatari and Hanya, 1975; Gschwend et al., 1983; Venkatesan, 1988; Soma et al., 1996; Jiang et al., 2000; Silliman et al., 2001) in the natural environment, but its vertical distribution in sediment cores differs from those of other PAHs that originate from combustion (Venkatesan, 1988; Jiang et al., 2000; Silliman et al., 2001). Although the source and mechanism of formation of perylene are not clearly understood, many studies suggest that it has an origin other than combustion, such as in terrestrial or other biota, and that it arises from precursor components under anaerobic conditions (Venkatesan, 1988; Silliman et al., 2001). The most plausible hypothesis is that perylenequinone (4,9-dihydroxyperylene-3,10quinone) and binaphthyl (Fig. 1) are produced by fungi and insects (Sato, 1976b; Jiang et al., 2000) and are then *Corresponding author (e-mail:
[email protected]) Copyright © 2010 by The Geochemical Society of Japan.
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(a)
(b) OH
(c) O
OH
N OH
Lake Biwa
Northern basin
OH
O
OH
OH
Japan
Fig. 1. Chemical structures of (a) perylene, (b) perylenequinone, and (c) binaphthyl. Sampling point Southern basin
Hayakawa, 2004; Nakano et al., 2008). Ishiwatari and Hanya (1975) reported high amounts of perylene (0.86 µg g –1 on average) and a low organic carbon content (10 mg g –1 on average) throughout a 200-m core collected from Lake Biwa. Lake Biwa sediments typically contain abundant perylene (Ishiwatari et al., 1980; Gschwend et al., 1983; Venkatesan, 1988; Soma et al., 1996; Jiang et al., 2000; Silliman et al., 2001), and thus its sediment should be suitable for elucidating the origin of the perylene. Here we examined δ 13 C values of perylene and friedelin in Lake Biwa sediment to elucidate the origin of the perylene. We discuss the reasons for the notable accumulation of perylene in this lake. EXPERIMENTAL Lake Biwa Lake Biwa, in central Japan (Fig. 2), is the largest lake in Japan. It is surrounded by mountains and comprises a large northern basin (surface area, 614 km2; mean depth, 43 m; water volume, 27.3 km 3) and a smaller southern basin (surface area, 56 km 2; mean depth, 4 m; water volume, 0.2 km 3). More than 100 rivers flow into the lake, and its catchment area is more than 3000 km2. Inputs of compounds and sediment into the lake depend strongly on the rivers (Nakano et al., 2008). Most of them flow into the northern basin, whereas water drains from the lake via only one river (the Seta River) at the southern end of the southern basin. Thus, the aquatic environment of the southern basin is strongly controlled by that of the northern basin, which is in turn controlled by its tributary rivers. Sample and reagents The sample used was the matrix-type certified reference material for PAH analysis (NMIJ CRM 7307-a) obtained from the National Metrology Institute of Japan (NMIJ). It had been prepared from sediments collected
162 N. Itoh and N. Hanari
Seta river
Fig. 2. Map of Lake Biwa and location of the sampling point.
from the southern basin of Lake Biwa (35°01′ N, 135°05′ E) in 2001 (100 kg dry wt, surface sediment to a depth of 10 m from the lake bed). The 100-kg sample was air-dried, pulverized, sieved to remove particles larger than 106 µm, homogenized, and subsampled into 60-g portions to form 1000 bottles. The subsamples were bottled, sterilized by γ-irradiation with 60Co, and stored at 4°C (Itoh et al., 2009). Perylene was obtained from Wako Pure Chemicals (Osaka, Japan). Crystalline d12-perylene (C 20D 12) was obtained from Cambridge Isotope Laboratories (Andover, MA, USA) and was used as an internal standard. Friedelin was obtained from Aldrich (St. Louis, MO, USA). These chemicals were used for identification and quantification of compounds in the extracts. Acetone, dichloromethane (DCM), hexane, and anhydrous Na2SO4 were of pesticide analysis and PCB analysis grade (Kanto Chemical, Tokyo, Japan). Activated Cu powder was obtained from Kishida Chemical (Osaka, Japan).
δ13C values and organic carbon content of sediment The δ13C value of the bulk sediment was analyzed with an isotope ratio mass spectrometer (Delta V-Conflo III on-line system, ThermoFisher Scientific, San Jose, CA, USA) and an elemental analyzer (Flash EA1112, ThermoFisher Scientific). The parameters were set as follows: He carrier gas at 100 mL min–1, oxidation temperature 1000°C, reduction temperature 680°C, and column temperature 45°C. We used 5-mg samples of sediment without treatment and treated to remove carbonate (Itoh et al., 2003) to obtain the δ13C values for total carbon (organic + inorganic) and for organic carbon, respectively. The δ13C values were
calculated from a reference CO2 gas calibrated with the IAEA-CH-6 standard, and the whole system was calibrated with L-alanine (Nakarai, Kyoto, Japan), which had been calibrated with the NBS 19 standard. All δ13C values were calculated relative to the PDB (Peedee Belemnite) standard. Aliquots of sediment sample (100 mg) treated to remove carbonate (Itoh et al., 2003) were analyzed with an elemental analyzer (Flash EA1112, Thermo Fisher Scientific) to determine total organic carbon (TOC) content. The TOC content of bottled sample was 1.07 ± 0.01 wt% (n = 4). Pressurized liquid extraction (PLE) PLE was performed with a Dionex (Sunnyvale, CA, USA) ASE 200 system equipped with stainless steel extraction cells (11 mL), as reported previously (Itoh et al., 2008), with some modification. A glass fiber filter was placed at the bottom of the cell, and 5 g of sediment and a few grams of anhydrous Na2SO4 were added. After addition of d12-perylene as an internal standard, the samples were extracted with DCM under static conditions at 130°C, 15 MPa, for 10 min (two cycles). The extract was transferred to a glass vial, and a small amount of activated Cu powder was added to remove any elemental sulfur. After filtration through a polytetrafluoroethylene (PTFE) membrane filter (0.1-µm pores), the extract was concentrated to 1 mL in a rotary evaporator under a gentle stream of N2 at room temperature, and the concentrate was filtered again through a PTFE membrane filter. Gas chromatography-mass spectrometry (GC-MS) GC-MS used an Agilent Technologies (Palo Alto, CA, USA) 6890/5975 system equipped with a DB-17MS column (30 m × 0.25 mm i.d., 0.25 µm film thickness; J&W Scientific, Folsom, CA, USA) (Itoh et al., 2008). The GC system was operated in splitless mode, and 1-µ L aliquots of the extracts were injected using an autosampler. Both the injection liner and the transfer line were maintained at 300°C. The oven temperature program was 50°C (2 min hold) to 240°C at 10°C min–1 to 300°C (10 min hold) at 1.25°C min –1. Helium was used as the carrier gas at 1.0 mL min–1 in constant flow mode. The electron ionization energy was 70 eV. Data were obtained in full scan mode (m/z 50–500) for identifying GC-detectable compounds in the extract and in selected ion monitoring (SIM) mode for quantification (m/z 252.2 for perylene, 264.2 for d12-perylene, and 426.5 for friedelin). Determination of compound-specific δ13C values To avoid interference with the perylene and friedelin peaks in the GC chromatograms by unknown compounds, we obtained extracts for the determination of compound-
specific δ13C values by using PLE with toluene (150°C, 15 MPa, 10 min, two cycles), and passed the extract through a silica gel cartridge (500 mg/3 mL; Isolute Silica, International Sorbent Technology, Hengoed, UK) with a Zymark (Hopkinton, MA, USA) RapidTrace automation system. The extract was eluted with 3 mL hexane for the perylene fraction, 9 mL DCM/hexane (5/95 v/v) for the alcohol fraction, and 6 mL hexane/acetone (1/1 v/v) for the friedelin fraction. The friedelin fraction was cleaned up in a silica gel solid-phase extraction cartridge and eluted with 1 mL hexane/acetone (1/1 v/v). The perylene fraction and the cleaned-up friedelin fraction were combined for measurement of δ 13C values with a gas chromatograph (Trace Ultra GC, Thermo Fisher Scientific) equipped with an isotope-ratio mass spectrometer (Delta V Plus, Thermo Fisher Scientific) via a combustion interface (GC/C/TC, Thermo Fisher Scientific). Separation was performed in an HP-5MS column (60 m × 0.25 mm i.d., 0.25 µ m film thickness, Agilent Technologies). The GC system was operated in splitless mode, and 1-µ L aliquots were injected by an autosampler. The injection liner was maintained at 280°C and the oven temperature program was 50°C (2 min hold) to 300°C (30 min hold) at 10°C min–1. Helium was used as the carrier gas at 1.4 mL min –1 in constant flow mode. The oxidation reactor of the interface was set at 1050°C under 160-kPa He. The δ13C values were calculated relative to the PDB standard via reference CO2 gas, and the whole system was calibrated with n-alkanes (Indiana University, Bloomington, IN, USA), which had been calibrated with NBS 19 and L-SVEC standards. RESULTS AND DISCUSSION GC-detectable compounds in extract The sediment sample was mixed surface sediments collected to 10-m depth (see Experimental section). Thus, most of the precursors in the sample should have been converted to perylene, since the sedimentation rate in Lake Biwa is low (
