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Characteristics of sedimentary polycyclic aromatic hydrocarbons (PAHs) in the subtropical Feitsui Reservoir, Taiwan
Journal of Hydrology 391 (2010) 217–222
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Characteristics of sedimentary polycyclic aromatic hydrocarbons (PAHs) in the subtropical Feitsui Reservoir, Taiwan Cheng-Wei Fan a,*, Tien-Nan Yang b, Shuh-Ji Kao c a
Department of Earth and Environmental Sciences, National Chung Cheng University, Chia-Yi 621, Taiwan Institute of Earth Sciences, Academia Sinica, Taipei 115, Taiwan c Research Center for Environmental Changes, Academia Sinica, Taipei 115, Taiwan b
a r t i c l e
i n f o
Article history: Received 2 November 2009 Received in revised form 27 May 2010 Accepted 19 July 2010 This manuscript was handled by L. Charlet, Editor-in-Chief, with the assistance of E. Silvester, Associate Editor Keywords: PAHs Sediment Reservoir Fluvial Subtropical
s u m m a r y Polycyclic aromatic hydrocarbons (PAHs) are usually loaded through atmospheric deposition into a water body and eventually into sediments. We study the PAHs from a 22-cm sediment core collected from the subtropical Feitsui Reservoir in Taiwan, and find the PAHs deposition characteristics in the reservoir, the man-made water body, is different from those in natural water bodies. The surficial sedimentary PAH fluxes are significantly higher than those in the European high altitude mountain lakes and those in the northeastern USA urban/industrial lakes. However, the catchment-corrected PAH fluxes normalized by the ratios of the catchment area to the water surface area are comparable to those of remote lakes in Europe and USA, suggesting the sedimentary PAHs in the reservoir is fluvial dominated, i.e., the reservoir system concentrated the atmospheric PAHs from the catchment area into the sediments. PAHs distribution found in the Feitsui Reservoir indicates both biogenic and anthropogenic origins. We also find the vehicular transport upstream of the reservoir is likely one of the PAHs sources to this reservoir. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are members of a class of organic chemicals consisting of two or more fused benzene rings in linear, angular, and cluster like arrangements. They are pollutants of significant concern due to their carcinogenic nature. PAHs are found ubiquitously in aquatic environments, even in remote areas (Broman et al., 1991). In addition to natural sources such as forest fires, volcanic eruption, and organic matter diagenesis, anthropogenic sources such as by-products of the incomplete combustion of fossil fuels from urban and industrial sources contribute primarily to the increase of PAH loading in the environment. It has been reported that the atmosphere is the major pathway for loading of anthropogenic PAHs to many water bodies (Sanders et al., 1996; Fernandez et al., 1999; Lima et al., 2003). Once deposited into a water body, PAHs are rapidly associated with a variety of physical, chemical, and biological interactions, including volatilization, partitioning, bioaccumulation, trophic transfer, degradation, and sedimentation (Baker et al., 1991; Dachs et al., 1999; Gevao et al., 2000; Gigliotti et al., 2002; Fan and Reinfelder, 2003; Meijer et al., 2006, 2009; Berrojalbiz et al., 2009). Sediments are usually the final * Corresponding author. Tel.: +886 5 2720411x66213; fax: +886 5 2720807. E-mail address: [email protected] (C.-W. Fan). 0022-1694/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhydrol.2010.07.020
depositional sink for PAHs and they serves as a good record of PAH loading as a result of historical activities (Simcik et al., 1996; Fernandez et al., 2000; Van Metre et al., 2000; Rose and Rippery, 2002; Donahue et al., 2006). Furthermore, the analysis of PAHs in sediments provides an excellent tool for evaluating and reconstructing of modern day events and even the paleoenvironment (Meyers and Ishiwatari, 1993; Meyers, 2003; Das et al., 2008). It is generally assumed the PAHs transport paths are similar in all water body systems. However, there should be some characteristics differences between natural lakes and man-made reservoirs. River sediment and sediment-reactive chemicals, such as PCBs, DDT, and PAHs, have been reported to sink and trap to the bottom of the reservoir (Van Metre et al., 1997, 2000). The aim of this study is to quantify the concentration of various PAHs, and to characterize the surfacial PAH fluxes in a sedimentary reservoir system in Taiwan by comparing these data to those reported in areas in USA and Europe. The source of PAHs to this reservoir is also investigated. The study area is the Feitsui Reservoir which locates in northern Taiwan in a subtropical zone. The Feitsui Reservoir is a dam structure which was completed in 1987. The major function of the Feitsui Reservoir is to supply water to the Taipei metropolitan area, where the area has the highest population density in Taiwan. Studies on the water quality and hydrodynamic aspect of this res-
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service in June 2006, cross through the catchment area of Feitsui Reservoir.
ervoir were found in a few reports. The seasonal rainfall-induced hydrodynamics, such as winter density currents and summer/autumn storm-induced turbidity currents result in variations of dissolved oxygen, phosphorus content, and concentrations of suspended solids (Chang and Wen, 1997; Chang and Chuang, 2001; Chen and Wu, 2003; Kuo et al., 2003; Chen et al., 2006; Fan and Kao, 2008). In this paper, we report: (1) PAH concentrations in sediments from the Feitsui Reservoir, and the comparison with those in the lakes in Europe and USA; (2) the role of catchment in PAHs loading into the subtropical reservoir; and (3) the correlation of phenanthrene and the nearby traffic conditions.
2.2. Sampling of core sediments A 22-cm sediment core was collected by inserting a plastic tube directly into the sediments in the middle of the reservoir in August 2002. It was observed that the end section of the sediment core has a noticeable different layer, which contains some root-like debris, indicating the end of the sediment core reached the bottom of the reservoir. Since the operation of this reservoir started in 1987, this 22-cm sediment core was evidently deposited during 1987–2002, a duration of 15 years. The sediment core was divided into sections of 1–2 cm slices, freeze-dried, and stored in solvent pre-rinsed glassware bottles until further treatment in the laboratory.
2. Materials and methods 2.1. Study area The study area is the Feitsui Reservoir in Taiwan (latitude 25°270 N, longitude 121°330 E) as shown in Fig. 1. The reservoir has a surface area of 10.24 km2, mean depth of 39.6 m with a maximum depth of 113.5 m, full capacity of 406 million m3, and a total watershed of 303 km2. The reservoir is sited downstream of three major tributaries, the Kingkwa Creek, Diyu Creek, and the Peishih Creek, and is about 30 km from the city of Taipei (Chang and Wen, 1997; Chen and Wu, 2003; Kuo et al., 2003; Chen et al., 2006). The local provincial PeiYi highway and a national PeiYi Freeway No. 5, which was constructed in 1996 and opened for full
2.3. PAH analysis Freeze-dried sediments (5–10 g) were spiked with deuterated naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysened12, and perylene-d12 (Merck) as surrogate standards and extracted by sonication with dichloromethane for 20 min. The extraction was repeated three times. The extracts were concentrated and reduced in volume to approximately 1 ml. The concentrated extract was fractionated and cleaned up on a column of silica gel. The PAH
China Reservoir Site
23°5' N
Tropic of Cancer
Taiwan
121 E
Provincial PeiYi highway
National freeway No. 5
Peishih Creek
Sediment sampling site
Diyu Creek
Kingkwa Creek
islets Dam Site 0
1
2
3 kilometers
Fig. 1. Location of the Feitsui Reservoir and the sediment sampling site.
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fraction was eluted with 2:1 dichloromethane: hexane, and concentrated to 0.1–0.2 ml. An internal standard (benzo(a)anthracene-d10, Merck) was added to the samples prior to instrumental analysis. All the samples were analysed on a Hewlett–Packard 6890 gas chromatograph coupled to a Hewlett–Packard 5973 flame ionization detector. A HP-5MS column was used (30 m 0.25 mm i.d. with 5% phenyl and 95% methylpolysilarylene). Surface section sediment samples were also analysed on a Varian CP-3800 gas chromatograph coupled to a Satum 2200 mass selective detector. A VF-5MS column was used (60 m 0.25 mm i.d. with 5% phenyl and 95% methylpolysilarylene). The identity and subsequent retention time of each PAH was confirmed by using of calibration standards which contained known concentrations of surrogate standards, internal standard, and all of the PAHs of interest in this study. A total of 17 PAHs were analysed, including perylene and the 16 listed as priority pollutants by the United Stated Environmental Protection Agency. Surrogate standard recoveries for the entire pretreatment averaged naphthalene-d8 57 ± 21%, acenaphthene-d10 95 ± 13%, phenanthrene-d10 92 ± 9%, chrysene-d12 102 ± 18%, and perylene-d12 83 ± 30% (n = 13). The concentrations reported in this study were corrected by the surrogate recoveries. 3. Results and discussion 3.1. Surficial PAH concentrations Out of the 17 PAHs analysed, 15 PAHs were detected in surface sediment and further quantified. Naphthalene measured was not included in this study due to high analytical uncertainties. The PAHs concentrations in surficial sediment, sedimentary fluxes, and the catchment-corrected fluxes for individual PAH are shown in Table 1. Among the different PAHs quantified, perylene and phenanthrene had the highest concentrations, presenting 41% and 17%, respectively. Perylene measured in the sediments has much higher level compared to other PAHs, implying perylene may originate mainly from biogenic rather than anthropogenic sources (Simcik et al., 1996; Fernandez et al., 2000; Lima et al., 2003). Perylene can be simply considered as originated from the diagenetic processes whenever its content is higher than 10% of the whole PAHs, where the whole PAHs is denoted PAHtotal in Table 1 (Tolosa et al., 1996). Besides perylene, phenanthrene is also
abundant in the sediments, followed by benz[b + k]fluoranthenes, fluoranthene, and pyrene (Table 1). Phenanthrene is one of the most abundant PAHs found in the environment as a result of human activities such as fossil fuel combustion, and it contributes about 29% of PAHpp15 in this reservoir. PAHpp15 denotes the sum of the 16 priority pollutants excluding naphthalene, as shown Table 1. PAH distribution found in the Feitsui Reservoir therefore indicates both natural (biogenic) and anthropogenic origins. A similar PAHs distribution pattern obtained from another sediment core collected 5 km downstream apart from the core sampling site of this study was observed, in which the PAHs is dominated by 60% perylene, and 13% phenanthrene of total PAHs (Ku, 2007). The results indicate the PAHs distribution pattern in this reservoir may not have a significant variation at different sites. PAH concentrations in the Feitsui Reservoir surface sediment are compared with those measured in other aquatic systems to understand the relative PAH contamination at this reservoir. Table 2 shows the concentrations and sedimentary fluxes of PAHs at various locations. The concentrations of PAHpp15 and phenanthrene as a specific compound are used for comparison. The concentration of PAHpp15 and phenanthrene in the reservoir sediment are 236 ng/g and 68 ng/g, respectively. These PAH concentrations at this study site are comparable to those measured in remote areas (less polluted) such as Lake Arrejoen in the Arctic (Fernandez et al., 1999), 210 ng/g and 28 ng/g, respectively. The results indicate that the surficial sediment in this study site is not severely polluted. 3.2. Sedimentation rate and surficial PAH sedimentary fluxes In addition to PAH concentrations, which can imply the PAH pristine status found in the reservoir sediment, the PAH sedimentary fluxes or burial rates can be used to evaluate the PAH loading from the anthropogenic pollution to Feitsui Reservoir. The PAH sedimentary fluxes were calculated by multiplying the PAH concentrations with the sedimentation rate in the Feitsui Reservoir. The sedimentation rate in this reservoir was estimated to be 1.76 g cm2 y1 by assuming the bulk density was 1.2 g cm3, and the 22-cm sediment core was deposited during the reservoir operation duration of 15 years (1987–2002), i.e., 1.47 cm per year. The sedimentary rate of 1.76 g cm2 y1 in this reservoir is roughly in the same order of those measured in the other reservoirs across
Table 1 Surficial sediment concentrations, sedimentary fluxes, and catchment-corrected fluxes for individual PAHs.
a b c d e f
Compound
Abbreviation
Concentration (ng/g)
Sedimentary fluxesa (lg m2 y1)
Catchment corrected fluxesb (lg m2 y1)
Fluorine Phenanthrene Anthracene Fluoranthrene Pyrene Benz[a]anthracene Chrysene Benzo[k + b]-fluoranthrene Benzo[a]pyrene Perylene Indeno[1,2,3-cd]-pyrene Dibenz[ah]-anthracene Benzo[ghi]perylene PAHtotalc PAHpp15d Phen%e Pery%f
Flu Phen Anthr Fl Pyr Baa Chry Bkf + Bbf Bap Pery Ind Dba Bghip
11.1 68 7.6 18.6 17.5 8.4 24.9 37.9 7.6 164 14 5 15.7 400 236 17 41
195 1197 134 327 308 148 438 667 134 2886 246 88 276 7040 4154 17 41
6 39 4 11 10 5 14 22 4 93 8 3 9 227 134 17 41
PAHs sedimentary fluxes are the products of the individual PAHs concentration and the mass accumulation rate of 1.76 g cm2 y1. PAHs catchment-corrected fluxes are calculated by dividing the PAHs sedimentary fluxes by the ratio of catchment area to the area of reservoir (a ratio of 31). Sum of all PAHs compounds. Sum of the 16 priority pollutants excluding naphthalene. Phenanthrene percentage of all PAHs compounds. Perylene percentage of all PAHs compounds.
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Table 2 PAHs surficial sediment concentrations and sedimentary fluxes. Location
Feitsui (Taiwan) Schwarsee ob Solden (Austria) Starolesnianske (Slovakia) Arrejoen (Norway) Lake Michigan (USA) Wabamun lake (Canada) Lac Ste. Ame (Canada) Pigeon (Canada) Loch Coire nan Arr. (Scotland) a
Concentrations
Sedimentary fluxes a
Phenanthrene (ng/g)
PAHpp15
68 48 590 28 154–366
236 730 16,000 210 3000–4000 2756 771 895 700
35
(ng/g)
References 2
Phenanthrene (lg m
1
y
)
1197 2.3 51 1.1 30–80 50 30 20
PAHpp15
a
4154 40 1700 6.9 500–800 900 350 160
2
(lg m
y
1
) This study Fernandez et al. (1999) Fernandez et al. (1999) Fernandez et al. (1999) Simcik et al. (1996) Donahue et al. (2006) Donahue et al. (2006) Donahue et al. (2006) Rose and Rippery (2002)
PAHpp15: sum of the 16 priority pollutants excluding naphthalene.
the United States, ranging from 0.11 to 1.95 g cm2 y1 (Van Metre et al., 2000). However, the sedimentary rate in Feitsui Reservoir is 1–3 orders of magnitude higher than those of natural lakes in Europe, where the sedimentary rates in these lakes range from 0.0023 g cm2 y1 at Lake Arresjoen to 0.0325 g cm2 y1 at Lake Cimera (Fernandez et al., 1999). Our result agrees with the earlier reports that sedimentations are greater in the reservoirs than in natural lakes (Van Metre et al., 1997 and references therein). With the sedimentary rate of 1.76 g cm2 y1, the estimated total flux for sedimentary PAHpp15 and phenanthrene fluxes at Feitsui Reservoir are 4154 lg m2 y1 and 1197 lg m2 y1, respectively. In European high altitude mountain lakes (Fernandez et al., 1999), the PAH fluxes ranges from 6.9 lg m2 y1 at Lake Arresjoen in Norway, to 1700 lg m2 y1 at Lake Starolesnianske in Slovakia. These data as well as the PAH fluxes in northeastern USA urban/ industrial lakes are shown in Table 2. The PAHpp15 sedimentary fluxes of 4154 lg m2 y1 obtained from the Feitsui Reservoir is significantly higher than those in the lakes of the most polluted sites in Europe and USA, as shown in Table 2. The Feitsui Reservoir is one of the most monitored reservoirs in Taiwan and agricultural and urbanized activities in the drainage area are restricted. Therefore, the high PAH loading rate found in Feitsui Reservoir is unlikely to be the result of the regional atmospheric PAH pollution. As described in the last section, this study site can be considered as non-severely polluted, evident from the PAHs concentration in the sediment. The high sedimentary fluxes therefore suggest fluvial dominated PAH inputs. 3.3. Catchment-corrected PAH fluxes and atmospheric PAH input The atmosphere is the major pathway for PAH input to many water bodies. The same applies to the Feitsui Reservoir and its catchment. PAHs input from atmospheric deposition (dry/wet deposition) into the catchment area that is subsequently transported as surface runoff by precipitation, and eventually to the Feitsui Reservoir sediments. Therefore, the PAH sedimentary fluxes mentioned above are not representative for evaluating the atmospheric PAH loading and regional air pollution in the Feitsui Reservoir, but should correlate with the catchment area. Airborne mercuric accumulation rates from sediment cores of several remote lake sediments were reported to have a linear relationship with respect to the catchment area, and can be used to estimate the atmospheric mercuric deposition (Swain et al., 1992). With the same approach, we estimated catchment-corrected PAH fluxes by dividing the PAH fluxes by the ratio of catchment area to reservoir area (a ratio of 31) to reflect the atmospheric PAH deposition in the Feitsui Reservoir (Table 1). The catchmentcorrected PAHpp15 and phenanthrene fluxes of 134 lg m2 y1 and 39 lg m2 y1, respectively, are found to be comparable to the remote lakes in Europe and the USA (Fernandez et al., 1999).
It may be questioned that the atmospheric PAH deposition is underestimated because a burial efficiency should not be 100%, since some deposited PAHs are retained in the catchment compartment. However, the subtropical characteristic climate in Taiwan, with typhoon seasons in summer and autumn coming with heavy precipitation and strong wind, would decrease the detention amount of deposited PAHs to the catchment, even if the PAHs are contained in soils. It is therefore reasonable to assume that a high proportion of deposited PAHs to the catchment can be exported to this subtropical reservoir by the transport mechanisms caused by extreme climate events such as typhoons and summer storms. It is likely that a certain amount of PAHs in the sediments come from soils in the catchment area. Some PAHs might be degraded in the water column, while the degradation shall not change PAHs pattern observed in this study since the residence time in the water column is relatively short. Once deposited in the sediment, however, PAHs are subjected to degradation. Our study suggests that the catchment plays an important role in determining the PAH loading into the sediment of a subtropical reservoir. Our finding is consistent with the earlier studies on the dominance of fluvial inputs of organic pollutants, such as PCBs, total DDT and PAHs in a reservoir system (Van Metre et al., 1997, 2000). 3.4. The PAH source There are various sources of the atmospheric PAH deposition, including vehicular emission and industrial or municipal combustion. For a well-protected water resource such as the Feitsui Reservoir, industrial and agricultural activities are limited to the drainage area. In addition to PAHs transported from urban and industrial areas in the catchment, one of the major processes resulting in a continuous supply of PAH loading in the Feitsui Reservoir appears to be vehicular emission from the local provincial PeiYi highway situated upstream of the Feitsui Reservoir catchment. The location of the PeiYi highway is shown in Fig. 1. In order to get an idea of the correlation of the vehicular emission and the sedimentary PAHs in Feitsui Reservoir, the traffic flows in the PeiYi highway is used to compare with the phenanthrene profile in the sediment core, as phenanthrene is the most dominant PAH. The average daily traffic flows as 1000 vehicles per day along the highway from 1987 to 2002 are shown as the triangle dots in Fig. 2. The data were retrieved from the annual report of the Institute of Transportation from the Ministry of Transportation and Communications of Taiwan. The phenanthrene catchment-corrected fluxes at various depths in the sediment core are shown as the circle dots in Fig. 2. The dating of the core was approximated by assuming a linear relationship between depth increment of the 22-cm core sediment and the corresponding sedimentation duration of 15 years. The phenanthrene catchment-corrected fluxes and the
C.-W. Fan et al. / Journal of Hydrology 391 (2010) 217–222
is excluded). The result suggests that vehicular PAH emission is likely one of the major PAHs sources in the Feitsui Reservoir.
-2 -1
Phenanthrene catchment corrected fluxes, µg m y 0
0
10
20
30
40
221
2002
phenanthrene
4. Conclusions 2000
5
1996
10
1994 15
Age, AD
Depth, cm
1998
1992 1990
20 1988
Daily traffic
1986
25 0
20
40
60
Thousand vehicles
Acknowledgements
Fig. 2. The phenanthrene catchment-corrected fluxes at various depths in the Feitsui Reservoir, and the average daily traffic flows in the provincial PeiYi highway during 1986–2002.
Phenanthrene catchment corrected fluxes, µg m-2y-1
daily traffic flow show similar variations pattern, as shown in Fig. 2. Two points (daily traffic flows of 1999 and 2000) are deviated from the curve of the traffic flow, while the deviation is not shown on the curve of the phenanthrene fluxes. It is possible the value of the phenanthrene flux obtained from each section of the sediment core does not accurately correspond to a specific year but represents the average value of sediments from 2 to 3 years, since it is well known that the surface of the sediment is constantly disturbed, thus each part of the sediment inevitably contains a mixture of the deposited particles generated within a range of times. The phenanthrene catchment-corrected fluxes and their corresponding daily traffic flows as shown in Fig. 2 are plotted in Fig. 3 to further understand their relationship. With the sample number n = 13, a linear relation is observed in Fig. 3, which has a r2 = 0.938 where r is the correlation coefficient (one outlier point
40
30
20
10
0 0
10
20
30
We studied the characteristics of sedimentary PAHs in a subtropical reservoir in Taiwan. The sedimentary PAH fluxes are significantly higher than those in European high altitude mountain lakes and in northeastern USA lakes. However, the catchment-corrected PAH fluxes are comparable to those of remote lakes in Europe and USA. The sedimentary PAHs in this reservoir is fluvial dominated, i.e., the reservoir system concentrates the atmospheric PAHs from the catchment area into the sediments. PAH distribution found in the Feitsui Reservoir indicates both biogenic and anthropogenic origins. The downcore phenanthrene profile was found to be correlated with the vehicular traffic flow in a nearby major provincial highway in upstream Feitsui Reservoir, indicating vehicular PAH emission is likely one of the major PAHs sources to this reservoir.
40
50
60
70
Daily traffic in thousands of vechiles Fig. 3. Phenanthrene catchment-corrected fluxes versus daily traffic flow in the Feitsui Reservoir area.
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Characteristics of sedimentary polycyclic aromatic hydrocarbons (PAHs) in the subtropical Feitsui Reservoir, Taiwan Cheng-Wei Fan a,*, Tien-Nan Yang b, Shuh-Ji Kao c a
Department of Earth and Environmental Sciences, National Chung Cheng University, Chia-Yi 621, Taiwan Institute of Earth Sciences, Academia Sinica, Taipei 115, Taiwan c Research Center for Environmental Changes, Academia Sinica, Taipei 115, Taiwan b
a r t i c l e
i n f o
Article history: Received 2 November 2009 Received in revised form 27 May 2010 Accepted 19 July 2010 This manuscript was handled by L. Charlet, Editor-in-Chief, with the assistance of E. Silvester, Associate Editor Keywords: PAHs Sediment Reservoir Fluvial Subtropical
s u m m a r y Polycyclic aromatic hydrocarbons (PAHs) are usually loaded through atmospheric deposition into a water body and eventually into sediments. We study the PAHs from a 22-cm sediment core collected from the subtropical Feitsui Reservoir in Taiwan, and find the PAHs deposition characteristics in the reservoir, the man-made water body, is different from those in natural water bodies. The surficial sedimentary PAH fluxes are significantly higher than those in the European high altitude mountain lakes and those in the northeastern USA urban/industrial lakes. However, the catchment-corrected PAH fluxes normalized by the ratios of the catchment area to the water surface area are comparable to those of remote lakes in Europe and USA, suggesting the sedimentary PAHs in the reservoir is fluvial dominated, i.e., the reservoir system concentrated the atmospheric PAHs from the catchment area into the sediments. PAHs distribution found in the Feitsui Reservoir indicates both biogenic and anthropogenic origins. We also find the vehicular transport upstream of the reservoir is likely one of the PAHs sources to this reservoir. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are members of a class of organic chemicals consisting of two or more fused benzene rings in linear, angular, and cluster like arrangements. They are pollutants of significant concern due to their carcinogenic nature. PAHs are found ubiquitously in aquatic environments, even in remote areas (Broman et al., 1991). In addition to natural sources such as forest fires, volcanic eruption, and organic matter diagenesis, anthropogenic sources such as by-products of the incomplete combustion of fossil fuels from urban and industrial sources contribute primarily to the increase of PAH loading in the environment. It has been reported that the atmosphere is the major pathway for loading of anthropogenic PAHs to many water bodies (Sanders et al., 1996; Fernandez et al., 1999; Lima et al., 2003). Once deposited into a water body, PAHs are rapidly associated with a variety of physical, chemical, and biological interactions, including volatilization, partitioning, bioaccumulation, trophic transfer, degradation, and sedimentation (Baker et al., 1991; Dachs et al., 1999; Gevao et al., 2000; Gigliotti et al., 2002; Fan and Reinfelder, 2003; Meijer et al., 2006, 2009; Berrojalbiz et al., 2009). Sediments are usually the final * Corresponding author. Tel.: +886 5 2720411x66213; fax: +886 5 2720807. E-mail address: [email protected] (C.-W. Fan). 0022-1694/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhydrol.2010.07.020
depositional sink for PAHs and they serves as a good record of PAH loading as a result of historical activities (Simcik et al., 1996; Fernandez et al., 2000; Van Metre et al., 2000; Rose and Rippery, 2002; Donahue et al., 2006). Furthermore, the analysis of PAHs in sediments provides an excellent tool for evaluating and reconstructing of modern day events and even the paleoenvironment (Meyers and Ishiwatari, 1993; Meyers, 2003; Das et al., 2008). It is generally assumed the PAHs transport paths are similar in all water body systems. However, there should be some characteristics differences between natural lakes and man-made reservoirs. River sediment and sediment-reactive chemicals, such as PCBs, DDT, and PAHs, have been reported to sink and trap to the bottom of the reservoir (Van Metre et al., 1997, 2000). The aim of this study is to quantify the concentration of various PAHs, and to characterize the surfacial PAH fluxes in a sedimentary reservoir system in Taiwan by comparing these data to those reported in areas in USA and Europe. The source of PAHs to this reservoir is also investigated. The study area is the Feitsui Reservoir which locates in northern Taiwan in a subtropical zone. The Feitsui Reservoir is a dam structure which was completed in 1987. The major function of the Feitsui Reservoir is to supply water to the Taipei metropolitan area, where the area has the highest population density in Taiwan. Studies on the water quality and hydrodynamic aspect of this res-
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service in June 2006, cross through the catchment area of Feitsui Reservoir.
ervoir were found in a few reports. The seasonal rainfall-induced hydrodynamics, such as winter density currents and summer/autumn storm-induced turbidity currents result in variations of dissolved oxygen, phosphorus content, and concentrations of suspended solids (Chang and Wen, 1997; Chang and Chuang, 2001; Chen and Wu, 2003; Kuo et al., 2003; Chen et al., 2006; Fan and Kao, 2008). In this paper, we report: (1) PAH concentrations in sediments from the Feitsui Reservoir, and the comparison with those in the lakes in Europe and USA; (2) the role of catchment in PAHs loading into the subtropical reservoir; and (3) the correlation of phenanthrene and the nearby traffic conditions.
2.2. Sampling of core sediments A 22-cm sediment core was collected by inserting a plastic tube directly into the sediments in the middle of the reservoir in August 2002. It was observed that the end section of the sediment core has a noticeable different layer, which contains some root-like debris, indicating the end of the sediment core reached the bottom of the reservoir. Since the operation of this reservoir started in 1987, this 22-cm sediment core was evidently deposited during 1987–2002, a duration of 15 years. The sediment core was divided into sections of 1–2 cm slices, freeze-dried, and stored in solvent pre-rinsed glassware bottles until further treatment in the laboratory.
2. Materials and methods 2.1. Study area The study area is the Feitsui Reservoir in Taiwan (latitude 25°270 N, longitude 121°330 E) as shown in Fig. 1. The reservoir has a surface area of 10.24 km2, mean depth of 39.6 m with a maximum depth of 113.5 m, full capacity of 406 million m3, and a total watershed of 303 km2. The reservoir is sited downstream of three major tributaries, the Kingkwa Creek, Diyu Creek, and the Peishih Creek, and is about 30 km from the city of Taipei (Chang and Wen, 1997; Chen and Wu, 2003; Kuo et al., 2003; Chen et al., 2006). The local provincial PeiYi highway and a national PeiYi Freeway No. 5, which was constructed in 1996 and opened for full
2.3. PAH analysis Freeze-dried sediments (5–10 g) were spiked with deuterated naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysened12, and perylene-d12 (Merck) as surrogate standards and extracted by sonication with dichloromethane for 20 min. The extraction was repeated three times. The extracts were concentrated and reduced in volume to approximately 1 ml. The concentrated extract was fractionated and cleaned up on a column of silica gel. The PAH
China Reservoir Site
23°5' N
Tropic of Cancer
Taiwan
121 E
Provincial PeiYi highway
National freeway No. 5
Peishih Creek
Sediment sampling site
Diyu Creek
Kingkwa Creek
islets Dam Site 0
1
2
3 kilometers
Fig. 1. Location of the Feitsui Reservoir and the sediment sampling site.
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fraction was eluted with 2:1 dichloromethane: hexane, and concentrated to 0.1–0.2 ml. An internal standard (benzo(a)anthracene-d10, Merck) was added to the samples prior to instrumental analysis. All the samples were analysed on a Hewlett–Packard 6890 gas chromatograph coupled to a Hewlett–Packard 5973 flame ionization detector. A HP-5MS column was used (30 m 0.25 mm i.d. with 5% phenyl and 95% methylpolysilarylene). Surface section sediment samples were also analysed on a Varian CP-3800 gas chromatograph coupled to a Satum 2200 mass selective detector. A VF-5MS column was used (60 m 0.25 mm i.d. with 5% phenyl and 95% methylpolysilarylene). The identity and subsequent retention time of each PAH was confirmed by using of calibration standards which contained known concentrations of surrogate standards, internal standard, and all of the PAHs of interest in this study. A total of 17 PAHs were analysed, including perylene and the 16 listed as priority pollutants by the United Stated Environmental Protection Agency. Surrogate standard recoveries for the entire pretreatment averaged naphthalene-d8 57 ± 21%, acenaphthene-d10 95 ± 13%, phenanthrene-d10 92 ± 9%, chrysene-d12 102 ± 18%, and perylene-d12 83 ± 30% (n = 13). The concentrations reported in this study were corrected by the surrogate recoveries. 3. Results and discussion 3.1. Surficial PAH concentrations Out of the 17 PAHs analysed, 15 PAHs were detected in surface sediment and further quantified. Naphthalene measured was not included in this study due to high analytical uncertainties. The PAHs concentrations in surficial sediment, sedimentary fluxes, and the catchment-corrected fluxes for individual PAH are shown in Table 1. Among the different PAHs quantified, perylene and phenanthrene had the highest concentrations, presenting 41% and 17%, respectively. Perylene measured in the sediments has much higher level compared to other PAHs, implying perylene may originate mainly from biogenic rather than anthropogenic sources (Simcik et al., 1996; Fernandez et al., 2000; Lima et al., 2003). Perylene can be simply considered as originated from the diagenetic processes whenever its content is higher than 10% of the whole PAHs, where the whole PAHs is denoted PAHtotal in Table 1 (Tolosa et al., 1996). Besides perylene, phenanthrene is also
abundant in the sediments, followed by benz[b + k]fluoranthenes, fluoranthene, and pyrene (Table 1). Phenanthrene is one of the most abundant PAHs found in the environment as a result of human activities such as fossil fuel combustion, and it contributes about 29% of PAHpp15 in this reservoir. PAHpp15 denotes the sum of the 16 priority pollutants excluding naphthalene, as shown Table 1. PAH distribution found in the Feitsui Reservoir therefore indicates both natural (biogenic) and anthropogenic origins. A similar PAHs distribution pattern obtained from another sediment core collected 5 km downstream apart from the core sampling site of this study was observed, in which the PAHs is dominated by 60% perylene, and 13% phenanthrene of total PAHs (Ku, 2007). The results indicate the PAHs distribution pattern in this reservoir may not have a significant variation at different sites. PAH concentrations in the Feitsui Reservoir surface sediment are compared with those measured in other aquatic systems to understand the relative PAH contamination at this reservoir. Table 2 shows the concentrations and sedimentary fluxes of PAHs at various locations. The concentrations of PAHpp15 and phenanthrene as a specific compound are used for comparison. The concentration of PAHpp15 and phenanthrene in the reservoir sediment are 236 ng/g and 68 ng/g, respectively. These PAH concentrations at this study site are comparable to those measured in remote areas (less polluted) such as Lake Arrejoen in the Arctic (Fernandez et al., 1999), 210 ng/g and 28 ng/g, respectively. The results indicate that the surficial sediment in this study site is not severely polluted. 3.2. Sedimentation rate and surficial PAH sedimentary fluxes In addition to PAH concentrations, which can imply the PAH pristine status found in the reservoir sediment, the PAH sedimentary fluxes or burial rates can be used to evaluate the PAH loading from the anthropogenic pollution to Feitsui Reservoir. The PAH sedimentary fluxes were calculated by multiplying the PAH concentrations with the sedimentation rate in the Feitsui Reservoir. The sedimentation rate in this reservoir was estimated to be 1.76 g cm2 y1 by assuming the bulk density was 1.2 g cm3, and the 22-cm sediment core was deposited during the reservoir operation duration of 15 years (1987–2002), i.e., 1.47 cm per year. The sedimentary rate of 1.76 g cm2 y1 in this reservoir is roughly in the same order of those measured in the other reservoirs across
Table 1 Surficial sediment concentrations, sedimentary fluxes, and catchment-corrected fluxes for individual PAHs.
a b c d e f
Compound
Abbreviation
Concentration (ng/g)
Sedimentary fluxesa (lg m2 y1)
Catchment corrected fluxesb (lg m2 y1)
Fluorine Phenanthrene Anthracene Fluoranthrene Pyrene Benz[a]anthracene Chrysene Benzo[k + b]-fluoranthrene Benzo[a]pyrene Perylene Indeno[1,2,3-cd]-pyrene Dibenz[ah]-anthracene Benzo[ghi]perylene PAHtotalc PAHpp15d Phen%e Pery%f
Flu Phen Anthr Fl Pyr Baa Chry Bkf + Bbf Bap Pery Ind Dba Bghip
11.1 68 7.6 18.6 17.5 8.4 24.9 37.9 7.6 164 14 5 15.7 400 236 17 41
195 1197 134 327 308 148 438 667 134 2886 246 88 276 7040 4154 17 41
6 39 4 11 10 5 14 22 4 93 8 3 9 227 134 17 41
PAHs sedimentary fluxes are the products of the individual PAHs concentration and the mass accumulation rate of 1.76 g cm2 y1. PAHs catchment-corrected fluxes are calculated by dividing the PAHs sedimentary fluxes by the ratio of catchment area to the area of reservoir (a ratio of 31). Sum of all PAHs compounds. Sum of the 16 priority pollutants excluding naphthalene. Phenanthrene percentage of all PAHs compounds. Perylene percentage of all PAHs compounds.
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Table 2 PAHs surficial sediment concentrations and sedimentary fluxes. Location
Feitsui (Taiwan) Schwarsee ob Solden (Austria) Starolesnianske (Slovakia) Arrejoen (Norway) Lake Michigan (USA) Wabamun lake (Canada) Lac Ste. Ame (Canada) Pigeon (Canada) Loch Coire nan Arr. (Scotland) a
Concentrations
Sedimentary fluxes a
Phenanthrene (ng/g)
PAHpp15
68 48 590 28 154–366
236 730 16,000 210 3000–4000 2756 771 895 700
35
(ng/g)
References 2
Phenanthrene (lg m
1
y
)
1197 2.3 51 1.1 30–80 50 30 20
PAHpp15
a
4154 40 1700 6.9 500–800 900 350 160
2
(lg m
y
1
) This study Fernandez et al. (1999) Fernandez et al. (1999) Fernandez et al. (1999) Simcik et al. (1996) Donahue et al. (2006) Donahue et al. (2006) Donahue et al. (2006) Rose and Rippery (2002)
PAHpp15: sum of the 16 priority pollutants excluding naphthalene.
the United States, ranging from 0.11 to 1.95 g cm2 y1 (Van Metre et al., 2000). However, the sedimentary rate in Feitsui Reservoir is 1–3 orders of magnitude higher than those of natural lakes in Europe, where the sedimentary rates in these lakes range from 0.0023 g cm2 y1 at Lake Arresjoen to 0.0325 g cm2 y1 at Lake Cimera (Fernandez et al., 1999). Our result agrees with the earlier reports that sedimentations are greater in the reservoirs than in natural lakes (Van Metre et al., 1997 and references therein). With the sedimentary rate of 1.76 g cm2 y1, the estimated total flux for sedimentary PAHpp15 and phenanthrene fluxes at Feitsui Reservoir are 4154 lg m2 y1 and 1197 lg m2 y1, respectively. In European high altitude mountain lakes (Fernandez et al., 1999), the PAH fluxes ranges from 6.9 lg m2 y1 at Lake Arresjoen in Norway, to 1700 lg m2 y1 at Lake Starolesnianske in Slovakia. These data as well as the PAH fluxes in northeastern USA urban/ industrial lakes are shown in Table 2. The PAHpp15 sedimentary fluxes of 4154 lg m2 y1 obtained from the Feitsui Reservoir is significantly higher than those in the lakes of the most polluted sites in Europe and USA, as shown in Table 2. The Feitsui Reservoir is one of the most monitored reservoirs in Taiwan and agricultural and urbanized activities in the drainage area are restricted. Therefore, the high PAH loading rate found in Feitsui Reservoir is unlikely to be the result of the regional atmospheric PAH pollution. As described in the last section, this study site can be considered as non-severely polluted, evident from the PAHs concentration in the sediment. The high sedimentary fluxes therefore suggest fluvial dominated PAH inputs. 3.3. Catchment-corrected PAH fluxes and atmospheric PAH input The atmosphere is the major pathway for PAH input to many water bodies. The same applies to the Feitsui Reservoir and its catchment. PAHs input from atmospheric deposition (dry/wet deposition) into the catchment area that is subsequently transported as surface runoff by precipitation, and eventually to the Feitsui Reservoir sediments. Therefore, the PAH sedimentary fluxes mentioned above are not representative for evaluating the atmospheric PAH loading and regional air pollution in the Feitsui Reservoir, but should correlate with the catchment area. Airborne mercuric accumulation rates from sediment cores of several remote lake sediments were reported to have a linear relationship with respect to the catchment area, and can be used to estimate the atmospheric mercuric deposition (Swain et al., 1992). With the same approach, we estimated catchment-corrected PAH fluxes by dividing the PAH fluxes by the ratio of catchment area to reservoir area (a ratio of 31) to reflect the atmospheric PAH deposition in the Feitsui Reservoir (Table 1). The catchmentcorrected PAHpp15 and phenanthrene fluxes of 134 lg m2 y1 and 39 lg m2 y1, respectively, are found to be comparable to the remote lakes in Europe and the USA (Fernandez et al., 1999).
It may be questioned that the atmospheric PAH deposition is underestimated because a burial efficiency should not be 100%, since some deposited PAHs are retained in the catchment compartment. However, the subtropical characteristic climate in Taiwan, with typhoon seasons in summer and autumn coming with heavy precipitation and strong wind, would decrease the detention amount of deposited PAHs to the catchment, even if the PAHs are contained in soils. It is therefore reasonable to assume that a high proportion of deposited PAHs to the catchment can be exported to this subtropical reservoir by the transport mechanisms caused by extreme climate events such as typhoons and summer storms. It is likely that a certain amount of PAHs in the sediments come from soils in the catchment area. Some PAHs might be degraded in the water column, while the degradation shall not change PAHs pattern observed in this study since the residence time in the water column is relatively short. Once deposited in the sediment, however, PAHs are subjected to degradation. Our study suggests that the catchment plays an important role in determining the PAH loading into the sediment of a subtropical reservoir. Our finding is consistent with the earlier studies on the dominance of fluvial inputs of organic pollutants, such as PCBs, total DDT and PAHs in a reservoir system (Van Metre et al., 1997, 2000). 3.4. The PAH source There are various sources of the atmospheric PAH deposition, including vehicular emission and industrial or municipal combustion. For a well-protected water resource such as the Feitsui Reservoir, industrial and agricultural activities are limited to the drainage area. In addition to PAHs transported from urban and industrial areas in the catchment, one of the major processes resulting in a continuous supply of PAH loading in the Feitsui Reservoir appears to be vehicular emission from the local provincial PeiYi highway situated upstream of the Feitsui Reservoir catchment. The location of the PeiYi highway is shown in Fig. 1. In order to get an idea of the correlation of the vehicular emission and the sedimentary PAHs in Feitsui Reservoir, the traffic flows in the PeiYi highway is used to compare with the phenanthrene profile in the sediment core, as phenanthrene is the most dominant PAH. The average daily traffic flows as 1000 vehicles per day along the highway from 1987 to 2002 are shown as the triangle dots in Fig. 2. The data were retrieved from the annual report of the Institute of Transportation from the Ministry of Transportation and Communications of Taiwan. The phenanthrene catchment-corrected fluxes at various depths in the sediment core are shown as the circle dots in Fig. 2. The dating of the core was approximated by assuming a linear relationship between depth increment of the 22-cm core sediment and the corresponding sedimentation duration of 15 years. The phenanthrene catchment-corrected fluxes and the
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is excluded). The result suggests that vehicular PAH emission is likely one of the major PAHs sources in the Feitsui Reservoir.
-2 -1
Phenanthrene catchment corrected fluxes, µg m y 0
0
10
20
30
40
221
2002
phenanthrene
4. Conclusions 2000
5
1996
10
1994 15
Age, AD
Depth, cm
1998
1992 1990
20 1988
Daily traffic
1986
25 0
20
40
60
Thousand vehicles
Acknowledgements
Fig. 2. The phenanthrene catchment-corrected fluxes at various depths in the Feitsui Reservoir, and the average daily traffic flows in the provincial PeiYi highway during 1986–2002.
Phenanthrene catchment corrected fluxes, µg m-2y-1
daily traffic flow show similar variations pattern, as shown in Fig. 2. Two points (daily traffic flows of 1999 and 2000) are deviated from the curve of the traffic flow, while the deviation is not shown on the curve of the phenanthrene fluxes. It is possible the value of the phenanthrene flux obtained from each section of the sediment core does not accurately correspond to a specific year but represents the average value of sediments from 2 to 3 years, since it is well known that the surface of the sediment is constantly disturbed, thus each part of the sediment inevitably contains a mixture of the deposited particles generated within a range of times. The phenanthrene catchment-corrected fluxes and their corresponding daily traffic flows as shown in Fig. 2 are plotted in Fig. 3 to further understand their relationship. With the sample number n = 13, a linear relation is observed in Fig. 3, which has a r2 = 0.938 where r is the correlation coefficient (one outlier point
40
30
20
10
0 0
10
20
30
We studied the characteristics of sedimentary PAHs in a subtropical reservoir in Taiwan. The sedimentary PAH fluxes are significantly higher than those in European high altitude mountain lakes and in northeastern USA lakes. However, the catchment-corrected PAH fluxes are comparable to those of remote lakes in Europe and USA. The sedimentary PAHs in this reservoir is fluvial dominated, i.e., the reservoir system concentrates the atmospheric PAHs from the catchment area into the sediments. PAH distribution found in the Feitsui Reservoir indicates both biogenic and anthropogenic origins. The downcore phenanthrene profile was found to be correlated with the vehicular traffic flow in a nearby major provincial highway in upstream Feitsui Reservoir, indicating vehicular PAH emission is likely one of the major PAHs sources to this reservoir.
40
50
60
70
Daily traffic in thousands of vechiles Fig. 3. Phenanthrene catchment-corrected fluxes versus daily traffic flow in the Feitsui Reservoir area.
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