Fate of Polycyclic Aromatic Hydrocarbons in Seawater from the

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Fate of Polycyclic Aromatic Hydrocarbons in Seawater from the Western Pacific to the Southern Ocean (17.5°N to 69.2°S) and Their Inventories on the Antarctic Shelf Minggang Cai,*,†,‡,§ Mengyang Liu,§ Qingquan Hong,§ Jing Lin,§,⊥ Peng Huang,§ Jiajun Hong,¶ Jun Wang,§ Wenlu Zhao,§ Meng Chen,*,¶ Minghong Cai,# and Jun Ye§ †

State Key Laboratory of Marine Environmental Science, ‡Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, §College of Ocean and Earth Science, and ¶College of the Environment and Ecology, Xiamen University, Xiamen 361102, P.R. China ⊥ Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, P.R. China # SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136, P.R. China S Supporting Information *

ABSTRACT: Semivolatile organic compounds such as polycyclic aromatic hydrocarbons (PAHs) have the potential to reach pristine environments through long-range transport. To investigate the longrange transport of the PAHs and their fate in Antarctic seawater, dissolved PAHs in the surface waters from the western Pacific to the Southern Ocean (17.5°N to 69.2°S), as well as down to 3500 m PAH profiles in Prydz Bay and the adjacent Southern Ocean, were observed during the 27th Chinese National Antarctic Research Expedition in 2010. The concentrations of Σ9PAH in the surface seawater ranged from not detected (ND) to 21 ng L−1, with a mean of 4.3 ng L−1; and three-ring PAHs were the most abundant compounds. Samples close to the Australian mainland displayed the highest levels across the cruise. PAHs originated mainly from pyrogenic sources, such as grass, wood, and coal combustion. Vertical profiles of PAHs in Prydz Bay showed a maximum at a depth of 50 m and less variance with depth. In general, we inferred that the water masses as well as the phytoplankton were possible influencing factors on PAH surface-enrichment depth-depletion distribution. Inventory estimation highlighted the contribution of intermediate and deep seawater on storing PAHs in seawater from Prydz Bay, and suggested that climate change rarely shows the rapid release of the PAHs currently stored in the major reservoirs (intermediate and deep seawater).

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INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous hydrophobic organic compounds in the environment, with semivolatile and bioaccumulative characteristics.1−3 Many PAHs, known for their high toxicity, carcinogenicity, and/or mutagenicity, pose a serious threat to the health and well-being of humans and other animals and affect the environment.4,5 Anthropogenic sources, such as the incomplete combustion and pyrolysis of fossil fuels or wood and the release of petroleum products, contribute more to the occurrence of PAHs compared to natural processes.6,7 PAHs can be subdivided into petrogenic and pyrogenic types and have different levels of mutagenicity, with the former being particularly toxic.8 The global distribution and fate of PAHs have been studied both in field measurements and numerical models.9−14 Longrange transport (LRT) is suggested as an important pathway for PAHs or other persistent organic pollutants (POPs) to reach pristine areas in high latitudes.15−19 The dominant input of PAHs to the surface oceans comes from the atmosphere, and © XXXX American Chemical Society

in particular, diffusive air−water exchange is the main process driving the exchange of the 2−4-ring PAHs in marine samples.20−23 In addition, ocean currents provide significant transfer routes to the polar region, as is observed in the Ross Sea.24−26 The biological pump drives accumulation of POPs in phytoplanktonic organic matter and its subsequent downward settling.2 Especially, low-MW (LMW) soluble PAHs are effectively more available to dissolved phase-organic carbon partition, more efficiently scavenged by organic-rich particles such as phytoplankton and fecal pellets and prone to eventually sink to deep waters and sediments.21,27,28 This surface−deep ocean transfer has the potential to deplete concentrations of the dissolved POPs, enhance air−water disequilibria, and influence atmospheric transport.29,30 Not only the surface recycling but Received: June 2, 2016 Revised: August 9, 2016 Accepted: August 10, 2016

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DOI: 10.1021/acs.est.6b02766 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

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Environmental Science & Technology also settling fluxes in the water column also represent a final sink.30,31 Global change with different temperatures and organic matter stocks will influence the reservoirs of POPs especially in the polar region because of the coupling of climatic and biogeochemical controls.32 Prydz Bay (Figure S1) is located in the Indian sector of the Southern Ocean, East Antarctic Margin. The southernmost part of the bay is in contact with the Amery Ice Shelf while the northernmost part extends to the continental shelf edge, and this semiclosed bay is influenced profoundly by glacier ablation and melt from the Amery Ice shelf in conjunction with dominant winds.33 Even though once considered as a final sink for POPs, several studies have shown evidence that historical burdens of POPs are currently remobilized from retreating glaciers/ice cover in the Arctic and Antarctica.34−36 On the other hand, recent climatic changes have increased primary production globally, which would strengthen the role of the biological pump in sequestering atmospheric POPs in high-latitude oceanic regions.37,38 Considering the ongoing release of PAHs and climate change, the redistribution and fate of contaminants in the polar area are currently uncertain and need much investigations.32,34 Limited investigations report the presence of PAHs in the atmosphere, seawater, soils and sediments, ice or snow, and organisms in Antarctica, even though its remote location provide an excellent opportunity to investigate the LRT of PAHs on large spatial scales.17,25,39−41 These studies focus mostly on the South Atlantic and Antarctic Peninsula sectors of the Southern Ocean, while little is known about PAHs in the Indian−Pacific sector. In our study, PAHs from surface seawater samples on a large latitudinal scale, as well as from deep water columns (up to 3500 m) in Prydz Bay, are reported. The objectives of the study were to (1) reveal the meridional distribution and potential sources of dissolved PAHs in the surface seawater from the western Pacific to the Southern Ocean; (2) obtain full depth profiles of dissolved PAHs in Prydz Bay and their possible influencing factors; (3) estimate the inventory of PAHs in Prydz Bay and its proportion among various water masses and environmental medias; and (4) examine the overall response of PAHs in Antarctic seawater to the climate change.

surrogate internal standards (acenaphthylene-d10, phenanthrene-d10, chrysene-d12, and pyrene-d12), the filtrates were passed through C18 SPE cartridges (ENVI 18, SUPELCO, USA) at a flow rate of 6 mL/min using a peristaltic pump for enrichment. All samples were wrapped with precombusted aluminum foil, labeled with their basic parameters, and stored at −20 °C until laboratory analysis. Sampling information for the surface stations is listed in Table S1, and those for the depth stations in Prydz Bay in Table S2. Treatment and Instrument Analysis. Each C18 column had 8−9 g of anhydrous sodium sulfate, which had been precleaned with 5 mL of ethyl acetate, as its top. Next, the analytes were eluted with 15 mL of ethyl acetate, and the eluents collected were condensed to 0.5 mL in a rotary evaporator. The concentrated eluents were solvent-exchanged to hexane and further condensed to 150 μL under a gentle nitrogen stream. Finally, 50 μL of 100 ppb internal standard pyrene-d10 obtained from Accustandard Inc. (New Haven, CT, USA) was added prior to instrumental analysis. All samples were analyzed for 15 PAHs in this study, and the analysis of PAHs was performed using a gas chromatograph coupled with a mass spectrometer (Shimadzu, GC−MSQP2010 Plus, Japan) (page S2, Supporting Information). However, to provide valuable data with good quality and reliability, only the following nine PAHs are reported here, namely, acenaphthylene (Acpy), acenaphthene (Acp), fluorene (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (FluA), pyrene (Pyr), benzo[a]anthracene (BaA), and chrysene (Chr). QA/QC. GFFs were baked at 450 °C for 4 h prior to use. C18 columns were initially precleaned with dichloromethane (35 mL), acetone (20 mL), and n-hexane (35 mL) in sequence before the sampling campaign, and were preconditioned with 5 mL of methanol and 5 mL of Milli-Q water before the enrichment. All glassware, aluminum foil, and anhydrous sodium sulfate were baked at 450 °C for 4 h prior to use. The instrumental detection limits (IDLs) and ions monitored are shown in Table S3. Three field blanks and three laboratory blanks were analyzed (Table S4). Every field blank was performed using 4 L of distilled water and shared the same treatment from storage in an amber glass bottle and filtration to the final instrumental analysis. Average field blanks of PAH congeners ranged from below the IDL to 0.88 ng L−1 (Phe), and were subtracted from sample masses. The laboratory blanks were performed on the cleaned C18 columns in the same manner as samples in the laboratory. Average laboratory blanks of PAH congeners ranged from below the IDL to 0.95 ng (Acp) per column, and were not subtracted from the sample masses. Method detection limits were derived from average field blanks plus three times the standard deviation (Table S4). In addition, four perdeuterated PAHs were added to samples prior to extraction on the expedition, and the average recoveries of acenaphthylene-d10, phenanthrene-d10, chrysene-d12, and pyrlene-d12 were 82 ± 14, 72 ± 12, 62 ± 15, and 76 ± 26%, respectively. Standard checks were analyzed every 12 samples to monitor instrument performance. The concentrations reported were corrected for their relative response factors, which were calculated as the ratios of the peak area for each PAH congener to that of the internal standard Pyr-d10. Ocean Data View 4.5.6 and Grapher 10.1.640 were used for Figures 1 and 2, and the Kriging interpolation method and Surfer 10.7.972 were used for Figure 3. Inventory calculation was performed using Microsoft Excel.

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MATERIALS AND METHODS Sampling. Surface seawater samples were collected from the western Pacific to the Southern Ocean during the 27th Chinese National Antarctic Research Expedition from November 2010 to March 2011, onboard the R/V Xuelong (Snow Dragon). Sampling covered a latitudinal transect from 17.5°N to 69.2°S, by way of the South China Sea, Sulu Sea, Celebes Sea, Makassar Strait, Indian Ocean, and Prydz Bay. In addition, samples were collected from 15 water columns in Prydz Bay. Surface seawater samples were taken using the vessel’s intake system (stainless steel pipe line) along the cruise, and seawater samples at different depths were collected in Prydz Bay using a conductivity, temperature, and depth sampler (CTD) with Niskin bottles.42 In addition, the vertical profile of temperature, salinity, and chlorophyll data for the sampling area were obtained from the CTD system. On average, 4 L of seawater samples were transferred into amber glass bottles which had been rinsed with dichloromethane before use, and then were filtered in situ through glass fiber filters (GFF) of 0.7 μm pore size and 47 mm diameter. After being spiked with 100 ng of B


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obvious for PAHs.49 The Southern Ocean is away from direct terrestrial influence and affected mostly by LRT. Field measurements revealed a net input from the atmosphere to the ocean for most PAHs, and for three- to four-ring PAHs, the air−water diffusive fluxes were up to 3 orders of magnitude greater than the dry deposition fluxes in all oceans.46 Meanwhile, a variety of different factors interact in the overall transport dynamics, such as photodegradation with OH radicals during their atmospheric transport, and temperature-dependent biological activities as well as air−water exchange.50 As shown in Figure 2, for surface seawater samples from Prydz Bay, the concentrations of PAHs were relatively low,

RESULTS AND DISCUSSION Surface Distribution of PAHs along the Cruise. LMW PAHs were the predominant compounds, and three-ring PAHs accounted for 95% of the ∑9PAH, while 83% of PAH congeners with five rings or six rings were not detected. The concentrations of dissolved ∑9PAH in all surface water samples are shown in Figure 1 and Table S5, ranging from ND to 21 ng

Figure 1. Concentrations of dissolved PAHs (ng L−1) in the surface seawater along the cruise path.

L−1, with a mean value of 4.3 ng L−1. The concentrations reported here were higher than those in a transect of the eastern Atlantic Ocean (58−1070 pg L−1),43 close to the levels found in the Japan Sea (4.8−6.5 ng L−1, mean 5.6 ng L−1),44 and significantly lower than those in the Pearl River Estuary, South China Sea (13−182 ng L−1).45 As to individual PAHs, Phe displayed on average the highest concentration (1.7 ng L−1), contributing 40% to Σ9PAH, followed by Flu (1.4 ng L−1, 33%). Such an abundance trend was the same as that for global seawater reported previously, although their average concentrations for Phe (0.4 ng L−1) and Flu (0.3 ng L−1) were lower.46 The spatial distribution of dissolved PAHs in surface water illustrated a generally increasing trend in the PAHs with increase in the southern latitude from 17°N to 32°S (D01− D36). Concentrations of seawater from coastal stations D31− D36 which were within 50 km of the West Australia coast, all exceeded 10 ng L−1. The Leeuwin Current (Figure S1), which is along the Australia coast, is the only poleward-flowing and nonupwelling eastern boundary current globally.47 The greatest concentration (21 ng L−1) was observed at station D36, which was within 5 km of Fremantle Harbor, Perth, Western Australia, where the vessel berthed at this harbor for 3 days during the expedition. The accumulation by the surficial Leeuwin Current and access to continental discharges were suggested to be responsible for the high concentrations of PAHs observed here. The ∑9PAH in the open ocean (40−60°S) decreased to 2.4 ng L−1 on average, and three-ring PAHs showed a southward decreasing trend (Figure S2) while no significant latitudinal trend was shown for four-ring PAHs. The continuous eastwardflowing Antarctic Circumpolar Current (ACC) is considered as the northern border of the Southern Ocean, and links the ocean basins of the Atlantic, Indian, and Pacific Oceans.48 Thus, the waters carried in the ACC contain a mix of waters originating in different parts of the world, and the ∑9PAH (2.4 ng L−1) of the surface seawater from 40 to 60°S was close to the average for the global ocean (1.4 ng L−1). In addition, several main fronts inside the ACC result in large meridional gradients for many oceanographic parameters, although such gradients were not

Figure 2. Concentrations of dissolved PAHs (ng L−1) in surface seawater from Prydz Bay.

ranging from ND to 6.3 ng L−1, with a mean value of 2.0 ng L−1. ∑9PAH values in Prydz Bay were comparable to those found in the South Atlantic (mean 1.8 ng L−1),46 the Ross Sea (1.2−4.0 ng L−1),40 and the Gerlache Inlet, Antarctica (2.1−2.9 ng L−1).41 Owing to the geological and topographical conditions acting like a “bottleneck”, the seawater in Prydz Bay has weak interchangeability and thus maintains long-term accumulation. Part of the Antarctic coastal current flowing through the bay is captured by the Prydz Bay Gyre and recirculated into the bay. The cyclonic gyre is centered on the midpart to western part of the bay, and fed by inflow of relatively warm and salty waters of the circumpolar deep water (CDW).33,51 PAH concentrations in the Amery Basin were relatively low (0.7 ng L−1 in IS-01 and 0.4 ng L−1 in IS-09) with the exception of IS-02 (6.3 ng L−1). Glacier ice from the Lambert Glacier-Amery Ice Shelf system flows into the Amery Basin, and this high level in IS-02 might reflect the additional PAH load carried by melting ice as shown in the surface sediments.52 The concentrations of PAH in the Fram Bank and the Four Ladies Bank both fluctuated and did not show a significant difference. Vertical Distribution of PAHs in Prydz Bay and Their Possible Influencing Factors. Up to a 3500 m depth vertical profile of dissolved PAHs in Prydz Bay water columns was obtained, which generally showed a surface-enrichment depthdepletion distribution (Figure 3 and Supporting Information, Figure S3). ∑9PAH in the Prydz Bay columns ranged from ND to 14 ng L−1, with a mean value of 2.9 ng L−1 (Table S6). The maximum concentration was found at 50 m at station P2-14 which was situated at the edge of Fram Bank, while the minimum concentration was found at 707 m at station IS-11 near the Amery Ice Shelf. Vertically, PAH concentrations showed a decreasing trend from the surface (mean 3.2 ng L−1) to the 25 m depth (mean 1.6 ng L−1), then reached the C


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Figure 3. Vertical profile (0−500 m depth) of dissolved Σ9PAH (ng L−1) (a), dissolved oxygen (mg L−1) (b), and chlorophyll (arbitrary unit) (c) in seawater columns from Prydz Bay. We used dissolved oxygen and chlorophyll to represent the physical property variations (such as water masses or air−water diffusion) and biological productivity, respectively.

maximum (mean 5.2 ng L−1) at 50 m, and finally were reduced to a steady level (mean 1.9 ng L−1) at depths deeper than 500 m. Two factors that might have contributed to the distribution patterns were biological processes and water masses. First, the role of biogeochemical cycles in influencing the vertical distribution of dissolved PAHs was significant in water columns above the 50 m depth. From the surface to the 25 m depth, where phytoplankton were abundant, PAHs exhibited a depletion profile. A biological pump for semivolatile hydrophobic chemicals has been referred to, which reduces the dissolved-phase concentrations due to uptake by phytoplankton, enhances the export of POPs toward the hypolimnion and sediments during the bloom and postbloom phase, and as a result of the rapid growth dilution, reduces biota concentration.22 As the same time, along the 73°E section (Figure S4), PAHs and phytoplankton shared the same trend with topographical change, decreasing from the edge of Fram Bank to the open sea, but increasing at station P3-06. As one impact of the biological pump, concentrations of dissolved PAHs decreased in the euphotic layer in Prydz Bay, while the relatively deeper waters (50−100 m depth) contained higher PAH concentrations (3.7 ng L−1 for ∑9PAH). This was possibly related to enhanced release and export, as well as partial transfer of PAHs from the particulate phase to the dissolved phase during the settling process.22,44 The characteristic vertical PAH profiles (surface enrichment and depth depletion) were in agreement with the introduction of contaminants into the surface water, uptake by phytoplankton and their degradation, or depletion along the water column.53,54 Water masses especially in the upper layers may also influence the vertical distribution and diffusion of PAHs. Figure S6 shows the different potential temperature-salinity profiles among stations, and the major water masses in Prydz Bay and the adjacent regions. The variable summer surface water (SSW), whose thickness ranges from 5 to 30 m in Prydz Bay, is formed by ice melting or direct solar warming and constitutes a low-density cap over the water column.55 Cooler and denser winter water (WW), which is beneath the SSW, is formed by winter convection.55 The water mass has distinct modal and core properties with temperatures below −1.5 °C and salinity in the range of 34.2 to 34.56 psu. In Figure 3, higher PAH levels existed at a depth of 50−75 m, where temperature ranged from −1.94 to −1.47 °C and the salinity

from 34.11 to 34.43 psu. In other words, high levels of PAHs occurred beneath the seasonal thermocline and in the WW. This seasonal thermocline increased the stratified stability and weakened vertical diffusion, and thus the WW layer may have reflected the water characteristics of the previous winter. In addition, three stations were selected to represent the PAH, salinity, and temperature variance in water columns from the continental shelf (A1-04) via the continental slope (P3-11) to the open sea (P3-08) (Figure 4). From the continental shelf to the open sea, Σ9PAH roughly declined from 5 to 1 ng L−1, and the depth of the halocline varied from 50 to 500 m northward. At station A1-04, the vertical mixing was relatively enhanced and no significant thermocline was observed, while a double-thermocline existed at the 100 and 500 m depth at stations P3-11 and P3-08. Under thermally stratified conditions, the PAH concentrations rose in the second thermocline at station P3-11, and conversely, it slumped in the second thermocline at station P3-08. Moreover, although CDW and Antarctic bottom water (AABW) were observed at station P308, no obvious fluctuation of PAH concentrations in the deeper layer was found, as in the Ross Sea.25,40 PAHs declined from the continental shelf while temperature showed an increasing trend. Since temperature controls semivolatile organic compounds dynamics in gas, the higher is the surface temperature, the stronger the air-sea exchange processes occur.56 Thus, a different process may occasionally produce a similar distribution of PAHs, and so particular care must be taken when low concentrations have to be interpreted. PAH Sources. Different production sources and their combustion temperature result in various PAH congener distributions. Therefore, molecular indices based on ratios of selected PAH concentrations can be applied to differentiate PAHs from pyrogenic and petrogenic origins.52 Two specific PAH ratios were calculated from samples studied here: Flu/ (Flu+Pyr) and Ant/(Ant+Phe). The petroleum boundary ratio appears closer to 0.4 for Flu/(Flu+Pyr), and ratios between 0.4 and 0.5 are more characteristic of petroleum combustion, whereas ratios greater than 0.5 are characteristic of grass, wood, or coal combustion.6 For Ant/(Ant+Phe), a ratio less than 0.1 infers the petroleum source, and a ratio more than 0.5 infers a combustion source (pyrogenic source).6,57 As shown in Figure 5a, within 95% of the surface samples the ratios of Flu/(Flu +Pyr) were more than 0.5, indicating a combustion source. D


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Figure 4. Vertical profiles of Σ9PAH (ng L−1), salinity (psu), and temperature (°C) at stations A1-04 (on the continental shelf), P3-11 (on the continental slope), and P3-08 (on the open sea).

Figure 5. Diagnostic ratios of Flu/(Flu+Pyr) and Ant/(Ant+Phe) in the surface seawater (a) and Prydz Bay water columns (b).

However, for 69% of the surface samples, the ratios of Ant/ (Ant+Phe) were less than 0.1, suggesting a petrogenic source.

The remainder of the surface samples, which were mostly located in the Southern Ocean, had ratios greater than 0.1, E


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ments and in long-term could help better understand the influence of climate change on the fate of PAHs or other POPs. In conclusion, this study provided the distribution of dissolved PAHs in the surface waters from the western Pacific to the Southern Ocean (17.5°N to 69.2°S), as well as the down to 3500 m PAH profiles in Prydz Bay and its adjacent Southern Ocean. Three-ring PAHs, which were the most abundant compounds, showed a southward decreasing trend in the open ocean (40− 60°S), while there was no significant latitudinal trend for the four-ring PAHs. The surface-enrichment depthdepletion distribution reflected the influence of water masses and phytoplankton on the PAH vertical profiles. Inventory estimation for PAHs in the Prydz Bay highlighted the role of intermediate and deep seawater as a major reservoir for PAHs in seawater. Beyond the complication of ongoing emissions and properties of the PAHs, further developments should address more deeply the coupling climate change and biogeochemical change in the polar regions.

indicating a pyrogenic source. PAHs may undergo photodegradation reaction with OH radicals during atmospheric LRT, thus, the diagnostic ratios would have a deviation because of direct or indirect photolysis and should be used with caution. PAH congener ratios fluctuated in Prydz Bay, implying differences of PAH sources from those in the open ocean. As shown in Figure 5b, for 75% of the column samples, the ratios of Flu/(Flu+Pyr) were more than 0.5, thus indicating a combustion source. Approximately half of the Ant/(Ant+Phe) ratios exceeded 0.1, suggesting a pyrogenic source. Zhongshan Station is situated at the southeast of Prydz Bay, research and basic daily activities might have inevitably brought about PAHs. Several high PAH levels were observed in Prydz Bay (IS-02 Σ9PAH 6.3 ng L−1, and P3-07 Σ9PAH 5.2 ng L−1), implying the existence of possible local sources. The larger pyrogenic proportion and a decreasing gradient of PAHs from nearshore areas to the open ocean were consistent with local source emissions. Considering the sensitive and fragile environment in Antarctica, local sources of PAHs in the Antarctic should be regulated to reduce the environment risk.58 Mass Inventory of PAHs in Prydz Bay. The mass inventories (I, tons) of PAHs in Prydz Bay were estimated based on the concentrations in seawater (dissolved phase) measured here, PAHs in the atmosphere (gas and aerosol), and surface sediments as outlined in the literature (Table S7).46,52 Furthermore, the water masses in Prydz Bay were divided into the compartments SSW (0−50 m), WW (50−200 m), and shelf water (SW) (200−500 m) to calculate their individual contribution.51 Because of the lack of data of PAHs in the particulate phase from seawater−water, the contribution of seawater storing PAHs might be underestimated. Considering the limited sampling sites and nonhomogeneous distribution of PAHs in Prydz Bay, there was inevitable resulting bias. A detailed description and the results of the calculation are shown in the Supporting Information text and Table S8. The mass inventory of Σ9PAH was estimated to be 180 t in Prydz Bay. This PAH mass inventory might be compared with a global emission estimate, and is equivalent to global atmospheric emission for 3 h.59 Among the compartments, seawater was the largest reservoir of PAHs, and represented approximately 83.5% of the total inventory, as much as 51.4% stored in shelf water (Figure S7). In addition, the dissolved PAH inventory proportions in the Southern Ocean were roughly estimated based on the stratified water column P3-08, where SSW, WW, CDW, and AABW exist.51,55 CDW was the major reservoir of PAHs (57%), followed by AABW (39%), and WW (4%). In conclusion, middle-deep water masses hold most of the PAHs in Prydz Bay even in the Southern Ocean. Besides PAHs, the presence of numerous POPs such as polychlorinated biphenyls, organochlorine pesticides, and polybrominated diphenyl ethers in deeper water also highlights the important role of deep ocean as an oceanic sink storing POPs.60 To forecast the influence of climate change on the reservoirs of PAHs in the Prydz Bay, the air−water exchange gradients were calculated according to the measured values and gas concentrations in literature.46 The results (SI, Text 3) showed net input into the seawater for most PAHs in the Prydz Bay except Acpy and Flu (Table S9). Combined with the current high net input from the atmosphere to the global ocean for most PAHs,46 we suggested that PAHs stored in the major compartments will not show a rapid response for climate change. Additional work, ideally both in multimedia environ-

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.6b02766. Details on sampling information, GC−MS analysis, QA/ QC, measured PAH concentrations, inventory calculations, and distribution figures (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*M. Cai: Phone: +86 592 2886188; email: [email protected]. *M. Chen: Phone: +86 592 2183127; email: mengchen@xmu. edu.cn. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We wish to express our gratitude to all the members of the 27th Chinese National Antarctic Research Expedition. This research was financially supported by the National Natural Science Foundation of China (41076133 and 41576180), Chinese Polar Environment Comprehensive Investigation and Assessment Programs, the Natural Science Foundation of Fujian Province, China (2014J06014), the Program for New Century Excellent Talents in University and the Basal Research Fund of Xiamen University (2072010507). We are also grateful to Prof. John Hodgkiss for his assistance with English.

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