Environment International 32 (2006) 28 – 33 www.elsevier.com/locate/envint
Composition, sources, and potential toxicological significance of PAHs in the surface sediments of the Meiliang Bay, Taihu Lake, China Min Qiao, Chunxia Wang*, Shengbiao Huang, Donghong Wang, Zijian Wang State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Shuangqing Road 18, Haidian District, Beijing 100085, PR China Received 16 November 2004; accepted 5 April 2005 Available online 5 July 2005
Abstract Twenty-five surface sediment samples were collected from Meiliang Bay, Taihu Lake, China, in 2003. The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs), identified as priority pollutants by the USEPA, were determined by gas chromatography equipped with a mass spectrometry detector (GC-MS). Total concentrations of the PAHs ranged from 1207 to 4754 ng/g dry weight. Sediment samples with the highest PAH concentrations were from the northern site of the bay, which is in proximity to the incoming PAH source; the PAH levels in the southern part were relatively low. The observed PAH levels were higher than those in river sediments in China but were lower than those found in sediments of urban areas and harbors. According to the observed molecular indices, PAHs originated largely from the high-temperature pyrolytic process, whereas the petrogenic process was more commonly responsible for PAH contamination in harbors. A good correlation existed between the benzo[a]pyrene level and the total PAH concentration (r = 0.97), making benzo[a]pyrene a potential molecular marker for PAH pollution. According to the numerical effect-based sediment quality guideline (SQGs) of the United States, the levels of PAHs at most studied sites in Meiliang Bay, except some sites in the northern part of the bay, should not exert adverse biological effects. In the northern part of the bay, the PAH levels at sites 21 and 22 exceed the effects range low (ERL) and could thus cause acute biological impairments, in comparison with the sediment quality guidelines. The total PAH levels were expressed as the B[a]P toxicity equivalents (TEQscarc) and compared to the contaminated sediments from Guba Pechenga, Barents Sea, Russia. D 2005 Elsevier Ltd. All rights reserved. Keywords: PAHs; Origin indices; Sediment quality guidelines; TEQscarc
1. Introduction Polycyclic aromatic hydrocarbons (PAHs) with two or more fused rings form a large group of organic pollutants. They are formed as incomplete combustion products of coal, oil and gas, garbage, or other organic substances like tobacco or charbroiled meat (Nadal et al., 2004). Apart from the combustion source, another common anthropogenic source of PAHs is the accidental spillage of fossil fuels, including crude oils and refined oil products (e.g., petrol). The solubility of PAHs in water is generally low; it decreases with increasing molecular weight among the congeners. PAHs are generally highly lipophilic. Several PAHs may * Corresponding author. Tel.: +86 10 6232 7173; fax: +86 10 6292 3543. E-mail address: [email protected]
(C. Wang). 0160-4120/$ - see front matter D 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2005.04.005
induce a number of adverse effects, such as immunotoxicity, genotoxicity, carcinogenicity, and reproductive toxicity (Sverdrup et al., 2002). Under this consideration, the United States Environmental Protection Agency (USEPA) has placed 16 of these PAHs in the priority-pollutant list. In the environment, PAHs may associate with particulates and dissolved organic matter and deposit onto sediments, the latter being a huge sink for air and waterborne contaminants that reflect the inputs for an ecosystem. In general, PAHs come mainly from two sources: petrogenic and pyrogenic. PAHs with four to six rings are derived generally from pyrogenic origin (Sanders et al., 2002; Dahle et al., 2003). Molecular indices based on the ratios of individual PAH levels in sediment can be used to assess the origin of PAHs. For example, phenanthrene/anthracene (Phe/An) and fluoranthene/pyrene (Flu/Pyr) congener ratios
M. Qiao et al. / Environment International 32 (2006) 28 – 33
are examples that are widely used to distinguish between PAHs from diverse origins (Guinan et al., 2001). Taihu Lake is situated in the south of the Yangtze Delta, China among 30-55V– 31-33VN and 119-55V– 120-36VE with a land area of 2338 km2 and an average water depth of 1.9 m. It is one of the five largest freshwater lakes in China. Taihu Lake Basin has almost the highest population density in one of the most heavily industrialized areas in China. Meiliang Bay, in the northern part of the Taihu Lake, serving as the main water supply for Wuxi, an industrial city with a population of 1 million located approximately 2 km northeast of Taihu Lake. However, with rapid population rise, as well as industrial and agricultural developments near the lake, the water quality in Taihu Lake has deteriorated. In recent years, the water contamination of the lake has threatened water supply and recreation. Significant levels of organochlorine pesticide residues have been found in this region (Feng et al., 2003). The primary objective of this study is to investigate PAH contamination in the area, identify possible PAH sources, and evaluate potential toxicological impacts.
2. Materials and methods
phenanthrene (Phe), anthracene (An), fluoranthene (Flu), pyrene (Pyr), benzo[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (Inp), dibenzo[a,h]anthracene (DBA), and benzo[ghi]perylene (BgP) ] in a mixture solution of 2000 Ag/ml were purchased from Supelco (USA). Neutral silica gel (60 – 200 mesh) and alumina (50 – 200 mesh) were purchased from Acros Organics (USA). Sodium sulfate was baked at 450 -C and stored in sealed containers. All organic solvents of pesticide analytical grade were obtained from Fisher Co. (USA). 2.2. Sample extraction and fractionation Sediment samples were freeze-dried (Mai et al., 2003), meshed, and extracted with a Soxhlet apparatus. Each sample (20 g) was spiked with a surrogate standard, phenanthrene-d 10, then extracted with 200 ml of methylene chloride/acetone (vol/ vol = 1:1) for 72 h, to which activated copper was added for desulphurization. The extract was pre-concentrated to 2 ml by a rotary evaporator (Bu¨chi Vac V-800, Switzerland) and solventexchanged to hexane. The hexane extract was fractionated and cleaned up by an alumina/silica gel column. Sodium sulfate (1 cm) was added to the top of the alumina. The column was eluted with 70 ml of methylene chloride/hexane (vol/vol = 3:7) to obtain PAH. The PAH fraction was finally concentrated to 1 ml under a gentle stream of nitrogen.
2.1. Sample collection and materials 2.3. Analytical procedure Twenty-five surface sediment samples were collected from the Meiliang Bay, Taihu Lake, in July 2003, using a stainless steel grab sampler. Sampling locations in the Meiliang Bay are shown in Fig. 1. The sampling stations were distributed radially from a point, from where the local waterworks draw off the source water. The surface sediment samples (upper 20 – 30 cm) were scooped into aluminum jars, which have been pre-washed with methylene chloride, and then cooled with ice during transportation to the laboratory where they were stored at 20 -C until further analyses. Standards of 16 USEPA priority PAHs [naphthalene (Naph), acenaphthylene (Aceph), acenaphthene (Ace), fluorine (Fl), N W
3 1 4 6
Fig. 1. Map of the study area and sampling sites.
The concentrations of PAH in the extracts were determined by an Agilent 6890 GC equipped with 5973 mass selective detector (MSD) under the selected ion monitoring mode (SIM). A HP-5 silica fused capillary column (60 m 0.25 mm inner diameter 0.25 Am film thickness) was used with helium as the carrier gas at a constant flow rate of 1 ml/min. Splitless injection of 1 Al of the sample was conducted with an autosampler. The GC oven temperature was programmed from 50 -C (2 min) to 200 -C (2 min) at 20 -C/min, then to 240 -C (2 min) at 5 -C/min before reaching 290 -C at 3 -C/min and held for 15 min. The injector and detector temperatures were 280 -C and 300 -C, respectively. Mass spectra were acquired at the electron ionization (EI) mode with an electron multiplier voltage of 906 eV. Before sample analyses, the instrument was tuned daily with decafluorotriphenyphosphine (DFTPP). PAHs in the samples were identified by the retention time and the abundance of quantification ions/ confirmation ions with respect to authentic PAH standards. Automated library searching was performed using the National Institute of Standards and Technology (NIST) Mass Spectral Database. Quantization was performed using the five-point calibration curve for individual components. Detection limits were 1.7 – 4.9 ng/g dry weight for PAHs. All the results were expressed on a dry weight basis. 2.4. Quality assurance and quality control Laboratory quality control procedures include analyses of method blanks (solvent), spiked blanks (standards spiked into solvent), matrix spikes/matrix spike duplicates, and sample duplicates. Instrument stability and response were checked using NIST standard solutions. The instruments were calibrated daily
M. Qiao et al. / Environment International 32 (2006) 28 – 33 0.00
with calibration standards and the relative percent differences between the five-point calibration and the daily calibrations were < 20% for all of the target analyses. The recoveries for surrogate standards fell within a fairly narrow range and, for individual PAHs, between 58.7 T 7.4% and 96.3 T 5.8%.
3. Results and discussion
5+ 6ri ng
3.1. PAH concentrations 0.75
The total PAH concentrations (sum of the 16 EPA priority pollutants) in sediments of Meiliang Bay ranged from 1207 to 4754 ng/g dry weight with the mean value of 2563 ng/g dry weight. Maximum PAH levels were found in site 22 (4754 ng/g), the next highest in site 21 (4097 ng/g) and site 25 (3959 ng/g). These sites are all at the northern part of the bay. Some work has been done on PAHs levels in aquatic sediments in China. Concentration levels of total 16 PAHs in surface sediments from different locations in Meiliang Bay, Taihu Lake, were close to those found at the Bohai Sea and Yellow Sea in China (877 – 5730 ng/g) (Table 1) (Ma et al., 2001) and higher than those found in sediments of some rivers in China, such as Yalujiang River (68 – 1500 ng/g) (Wu et al., 2003) and Minjiang River Estuary (112 – 877 ng/g) (Zhang et al., 2004a,b). However, the levels were lower than those reported in urbanized and industrialized areas, such as Pearl River (1434 – 10,811 ng/g) (Mai et al., 2002), the Macao Harbor (294 – 12,714 ng/g) (Mai et al., 2002), the Kiel Harbor (3 – 30,000 ng/g) (Baumard et al., ´ zmit Bay, Turkey (250 – 25,000 ng/g) (Tolun et 1999), and the Y al., 2001). 3.2. Composition and source identification of PAHs According to the number of aromatic rings, the 16 PAH compounds were divided into three groups, representing two-, and three-, four-, and five-, and six-ring PAHs. Higher proportions of PAH species with four rings (27.6 – 43.8%) and five to six rings (37.7 – 64.3%) were detected. Compositions and relative abun-
Table 1 Comparison of PAH concentrations (ng/g dry weight) in surface sediments of different regions Locations
Average Maximum References PAH PAH
Guba Pechenga, Barents Sea, Russia Todos Santos Bay
Savinov et al., 2003
290 409 433 560 877
1500 726 887 1006 5734
Macias-Zamora et al., 2002 Wu et al., 2003 Zhang et al., 2004a Zhang et al., 2004b Mai et al., 2002 Ma et al., 2001
Yalujiang River, China Deep Bay, China Minjiang River Estuary, China Lingding Bay, China Bohai Sea, the Yellow Sea, China Zhujiang River, China I˙zmit Bay, Turkey Kiel Harbor Meilang Bay, Taihu Lake a
NA, not available.
2432 NAa 8000 2563
10,811 25,000 30,000 4754
Mai et al., 2002 Tolun et al., 2001 Baumard et al., 1999 This work
2+3ring Fig. 2. Triangular diagram of percentage concentration for the 16 PAHs in sediments.
dance of individual PAH in sediments of the Meiliang Bay were quite similar (Fig. 2), except for site 4, where the four-ring PAH was predominant. The result suggests that the PAH contamination in Meiliang Bay comes essentially from an identical source and is indicative of a pyrolytic origin. Among all 16 PAHs, benzo[b]fluoranthene and indeno[1,2,3cd]pyrene were predominant species and accounted approximately for 14% and 17% of total PAHs, respectively. In addition, fluoranthene, pyrene, benzo[a]pyrene, and benzo[ghi]perylene were prevalent in samples from most of the sites. Generally, biomass combustion process and release of uncombusted petroleum products are the two main sources of anthropogenic PAHs found in the environment. In present study, three typical pyrogenic PAHs (i.e., pyrene, chrysene, and benzo[a]pyrene) were present at high concentrations. Furthermore, in all samples, level of fluoranthene was higher than pyrene and that of indeno[1,2,3cd]pyrene was higher than benzo[ghi]perylene. The PAH congener distribution varies with the production source as well as the composition and combustion temperature of the organic matter. Molecular indices based on ratios of selected PAH concentrations may be used to differentiate PAHs from pyrogenic and petrogenic origins. Six specific PAH ratios were calculated for the studied samples: Phe/An, Flu/Pyr, Chr/BaA, Flu/ (Flu + Pyr), InP/(InP + BgP), and Pyr/BaP. To estimate the origin of the PAHs in the Meiliang Bay sediment samples, the LMW/HMW ratio (the sum of the low molecular weight PAH concentrations to the sum of higher molecular weight PAH concentrations; i.e., Naph + Aceph + Ace + Fl + Phe + An / Flu + Pyr + BaA + Chr + BbF + BkF + BaP + Inp + DBA + BgP) was determined. The choice of this index for source identification was based on the fact that the PAHs from a petrogenic origin consist predominantly of those with lower molecular weights (three to four rings), while the PAHs from a pyrogenic origin generally have higher molecular weights (Soclo et al., 1999). The above molecular indices were used recently by others to assess and determine the origin of PAHs observed in various environments (Woodhead et al., 1999; Luca et al., 2004). The Phe/An index reflects that phenanthrene (Phe) is more thermodynamically stable than anthracene (An). Because of their different physico-chemical properties, they might behave differ-
M. Qiao et al. / Environment International 32 (2006) 28 – 33 500 450 400
350 300 250 200 150 100 150
Flu (ng/g) 4500 4000
ently in the environment with characteristic Phe/An values for the identification of the PAH origin. Generally, a Phe/An ratio <10 and Flu/Pyr ratio > 1 indicates that the contamination by PAHs results from a combustion process (Soclo et al., 1999). Similarly, fluoranthene (Flu) is less thermodynamically stable than pyrene (Pyr); they are often associated with each other in natural matrices and a predominance of Flu over Pyr is characteristic of a pyrolytic process, while in petroleum-derived PAHs, pyrene is more abundant than fluoranthene. Some typical values of these indices are given in Table 2. Results from present study showed that Phe/An ratio is < 7 for all sites and Flu/Pyr ratio is > 1 in most sites. The relationship between levels of fluoranthene and pyrene was shown to be significantly correlated (r = 0.97, p < 0.0001) (Fig. 3), which indicated that PAHs in Meiliang Bay had presumably undergone similar environmental processes independent of the sampling sites. The Flu/(Flu + Pyr) ratios were from 0.48 to 0.56 and could be indicative of pyrolytic origin, or coal combustion. The pyrolytic PAH inputs at Meiliang Bay are also confirmed by the Chry/BaA ratios being lower than 1. Data in Table 2 showed that for the majority of samples, the LMW/HMW ratios were relatively low (0.05 – 0.23) to support the pyrolytic origin (Soclo et al., 1999). Furthermore, BaP as a marker for some combustion-derived PAHs has been investigated in the past few years (Magi et al., 2002), based on the fact that its level in petroleum is usually negligible. The present finding of a significant correlation between BaP and (~16 PAHs – BaP) (r = 0.97, p < 0.0001; Fig. 3) confirmed the view of a general pyrolytic origin for PAHs in Meiliang Bay, whereas the petrogenic origin is more commonly found for PAHs in harbors (Muniz et al., 2004).
3500 3000 2500 2000 1500 1000 0
3.3. Assessment of sediment quality using biological thresholds The effects range low (ERL) and the effects range median (ERM) values were used for assessment of aquatic sediment with a ranking of low to high impact values (Long et al., 1995). The measured concentrations of PAHs were compared with the ERL and ERM values. Table 3 listed the thresholds for sediments from Meiliang Bay. Results showed that the total PAH concentrations at all sites were below the ERL except for sites 21 and 22; the latter showed values above ERL but below ERM. For most sites, individual PAH did not exceed ERM; however, there was at least one PAH in a site that exceeded ERL. These findings indicated that the sediments in all sites, especially those in the northern part of Meiliang Bay, should have potential biological impact, but should have no impairment. No samples contained PAHs whose concen-
Table 2 Characteristic values of selected molecular ratios for pyrolytic and petrogenic origins of PAHs Pyrolytic Petrogenic This study References origin origin Phe/An Chr/BaA Flu/Pyr Flu/(Flu + Pyr) LMW/HMW
<10 <1 >1 >0.5 Low
>15 >1 <1 <0.5 High
Abbreviations are as stated in the text. a NA, not available.
2.97 – 6.39 NAa – 0.93 0.94 – 1.22 0.48 – 0.56 0.05 – 0.23
Baumard et al., 1998 Soclo et al., 1999 Baumard et al., 1998 Budzinski et al., 1997 Budzinski et al., 1997
Fig. 3. Correlation analysis between levels of Flu and Pyr (above) and BaP and (~16 PAHs – BaP) (below).
trations exceed ERM or frequently pose biological impairments. The PAHs with potential impacts were fluorene, benzo[a]anthracene, and dibenzo[a,h]anthracene, respectively. Table 3 Standard pollution criteria of PAH components for sediment matrix (ng/g) Compound
Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo[a]anthracene Chrysene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Indeno[1,2,3-cd]pyrene Dibenzo[a,h]anthracene Benzo[ghi]perylene Total
160 44 16 19 240 853 600 665 261 384 NAa NA 430 NA 63.4 NA 4000
2100 640 500 540 1500 1100 5100 2600 1600 2800 NA NA 1600 NA 260 NA 44,792
NA, not available.
This study Average
24.7 5.1 5.5 25.7 101.9 24.4 281.1 255.1 197.4 138.3 422.4 125.1 256.1 389.9 63.9 294.8 2611
72.1 14.5 18.6 83.4 212.7 47.7 460.8 450.9 371.0 233.5 749.3 231.1 537.2 718.4 129.9 583.9 4918
M. Qiao et al. / Environment International 32 (2006) 28 – 33
3.4. Assessment of sediment toxicity based on the total concentration of CPAH Some PAHs and especially their metabolic products are of great concern due to their documented carcinogenicity. Total concentrations of potentially carcinogenic PAHs (CPAH), including benzo[a ]anthracene, benzofluoranthene, benzo[a ]pyrene, indeno[1,2,3-cd]pyrene, and dibenzo[a,h]anthracene (Savinov et al., 2003), varied from 621 to 2737 ng/g dry weight, with the average of 1418 ng/g dry weight, and accounted for 48 – 60% of total PAHs in sediments from Meiliang Bay, Taihu Lake. Benzo[a]pyrene is the only PAH for which toxicological data are sufficient for derivation of a carcinogenic potency factor among all known potentially carcinogenic PAHs (Peters et al., 1999). The toxic equivalency factors (TEFscarc) were used to quantify the carcinogenicity of other PAHs relative to benzo[a]pyrene and to estimate benzo[a]pyrene-equivalent doses (BaPeq dose) (Nadal et al., 2004). Calculated TEFs for benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, indeno[1,2,3cd]pyrene, dibenzi[a,h]anthracene, and chrysene are 0.1, 1, 0.1, 0.01, 0.1, 1, and 0.001, respectively, according to the USEPA. In this study, we converted the above mentioned seven PAH concentrations into one toxic concentration for each site using the corresponding TEFcarc. The total toxic benzo[a]pyrene equivalent (TEQcarc) for all PAHs was calculated as:
Ci TEFcarc i :
Total TEQcarc values calculated for samples varied from 94 ng/g TEQcarc to 856 ng/g dry weight TEQcarc, with an average of 407 ng/g dry weight TEQcarc. The maximum total TEQcarc value was found at the northern site 22. In comparison with other studies, TEQscarc values were higher in sediments of Meiliang Bay than those of other literature-reported sites, such as the bottom sediments from Guba Pechenga, Barents Sea, Russia (Savinov et al., 2003). Among different PAHs, contribution to the total TEQcarc decreased in the order: BaP (60.38%) > DBA (15.06%) > BbF (10.37%) > Inp (9.19%) > BaA (4.66%) > BkF (0.31%) > Chr (0.03%).
4. Conclusions Analyses of 25 surface sediment samples from Meiliang Bay, Taihu Lake, showed that the levels for 16 PAHs ranged from 1207 to 4754 ng/g dry weight, with the mean value of 2563 ng/g dry weight. The levels of PAHs ranged from a relatively low to a moderately high PAH pollution compared to other urbanized coastal areas worldwide. The highest levels of PAHs were found in the northern part of the Meiliang Bay, which was closer to the industrial area in Wuxi City, indicating a strong influence of the anthropogenic activity on the level of PAHs in large lakes. Four- to six-ring PAHs were predominant in Meiliang Bay sediments. By fingerprinting analysis, PAHs in the sediment were mostly pyrogenic origin, due probably to the high combustion inputs and urban runoffs from the urbanized areas. To assess the ecological impairment, most of the sediment samples could be classified to ERL or potential
impacts. When the potentially carcinogenic PAHs were normalized by multiplying by respective TEFcarc, the maximum total toxic benzo[a]pyrene equivalent (TEQcarc) was also found at the northern part of the bay, with a value higher than those of literature-reported areas. In conclusion, our analysis indicated that the PAH levels in most of the Meiliang Bay sediments would only rarely cause acute toxic effects to benthic organisms in the region, but manifested carcinogenic potential.
Acknowledgements This work was supported by the National Natural Science Foundation of China (40273046), the High-Technology Research and Development Program of China (2002AA601000-03-02), and the Chinese Academy of Sciences (KZCX3-SW-431).
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