Atmospheric DDTs over the North Pacific Ocean and the adjacent Arctic region: Spatial distribution, congener patterns and source implication

Atmospheric Environment 43 (2009) 4319–4326

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Atmospheric DDTs over the North Pacific Ocean and the adjacent Arctic region: Spatial distribution, congener patterns and source implication Xiang Ding a, c, Xin-Ming Wang a, *, Qiao-Yun Wang a, d, Zhou-Qing Xie b, Cai-Hong Xiang a, Bi-Xian Mai a, Li-Guang Sun b a

State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China Pearl River Delta Research Center of Environmental Pollution and Control, Chinese Academy of Sciences, Guangzhou 510640, China d Graduate University of Chinese Academy of Sciences, Beijing 100049, China b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 23 December 2008 Received in revised form 30 May 2009 Accepted 1 June 2009

During the 2003 Chinese Arctic Research Expedition (CHINARE 2003) from Bohai Sea to the high Arctic P (37 N–80 N), air samples were collected and analyzed for DDTs. DDTs (sum of six congeners) ranged 3 3 from 0.52 to 265 pg m with an average of 13.1 pg m . Higher DDT concentrations were observed in Bohai Sea and near eastern Russia. The congener patterns were obviously different between the Far East Asia and the higher latitudinal regions that p,p’-DDT and o,p’-DDT were dominated in the former; while o,p’-DDT and o,p’-DDE were dominated in the latter. The source contributions of technical DDT and dicofol type DDT were estimated. Results showed that technical DDT was the dominant source (>94%) which was fresher in the Far East Asia compared to the North Pacific Ocean and the Arctic. For dicofol type DDT, the estimated contribution was minor. The ‘‘new’’ o,p’-DDT observed should have relatively more contribution from dicofol type DDT in the North Pacific Ocean and the Arctic. Ó 2009 Elsevier Ltd. All rights reserved.

Keywords: DDTs Far East Asia North Pacific ocean Arctic

1. Introduction DDTs are a group of chlorinated pesticides (Table 1) that have long been a great concern due to their susceptibility to atmospheric transport, persistence in the environment, bio-accumulative potential and harmful effects especially on wildlife (Stokstad, 2007). Technical DDT, containing w85% p,p’-DDT and w15% o,p’DDT, was heavily used in agriculture as well as in the control the spread of vector-born human diseases, like malaria, since 1940s (Metcalf, 1973; Qiu et al., 2004). Although technical DDT was banned worldwide for agricultural use from 1970s, restricted usage in disease vector control continues to this day in certain parts of the world, especially in Africa (Lubick, 2007). DDT can be degraded into DDE via oxidative dehydrochlorination and into DDD via reductive dechlorination. After the ban of agricultural use, ambient concentration of p,p’-DDT was decreasing gradually (Bignert et al., 1998). Its major metabolites, p,p’-DDE and p,p’-DDD, became increasingly dominant in the environment (Hung et al., 2002; Mai et al., 2002). Unfortunately, these metabolites are also highly persistent and toxic to wildlife. DDE, for example, was found to induce eggshell thinning in birds by disrupting calcium absorption (Lundholm,

* Corresponding author. Tel.: þ86 20 85290180; fax: þ86 20 85290706. E-mail address: [email protected] (X.-M. Wang). 1352-2310/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.06.003

1997). Despite its obvious toxicity to animal, DDT is still a controversial issue in its effects on human health. DDT is classified as ‘‘moderately hazardous’’ by WHO (2005) and has no significant correlation with cancer (Lo´pez-Cervantes et al., 2004; Brody et al., 2007). Since DDT was banned mainly for ecological reasons (Rogan and Chen, 2005), considering its low cost, high effectiveness, persistence and low acute toxicity to human beings, WHO even announced that it supported the return of DDT in the fight against malaria on 16 September 2006 (Lubick, 2007). In addition, ‘‘new’’ o,p’-DDT input recently reported in the environment made the situation more complicated. High concentration of o,p’-DDT was observed in the air across Asia (Qiu et al., 2004; Jaward et al., 2005). Dicofol, containing high contents of o,p’DDT congeners as impurities, is regarded as a main contributor to ambient o,p’-DDT (Gillespie et al., 1994; Qiu et al., 2004). This pesticide is used to protect cotton, fruit trees, and vegetables from mites (Qiu et al., 2005) and was temporarily banned in United States and England until DDT contents were reduced (Rasenberg and van de Plassche, 2003). The successive input of o,p’-DDT would lead to the variation of DDT composition in ambient sample. In the Arctic, an increasing temporal trend of o,p’-DDT was observed during a five-year observation (Hung et al., 2002). Considering source inputs, transport, degradation and exchanges between various media, the congener patterns and spatial distribution of DDTs in the environment would be very complex.

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Table 1 Information of DDT congeners. Abbreviations

CAS-Numbers

IUPAC Names

Structure

Cl Cl p,p’-DDT

50-29-3

Cl

1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene

Cl

Cl

Cl

p,p’-DDE

72-55-9

Cl

1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethenyl]benzene

Cl

Cl

Cl

p,p’-DDD

72-54-8

Cl

1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethyl]benzene

Cl

Cl

Cl Cl

o,p’-DDT

789-02-6

Cl

Cl

1-chloro-2-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene

Cl

Cl

Cl

Cl

o,p’-DDE

3424-82-6

1-chloro-2-[2,2-dichloro-1-(4-chlorophenyl)ethenyl]benzene

Cl

Cl

Cl

Cl o,p’-DDD

53-19-0

1-chloro-2-[2,2-dichloro-1-(4-chlorophenyl)ethyl]benzene

Cl

To get a better understanding of the fate of DDTs, large-scale surveys are necessary to gain the information of source areas, compositional characteristics and long-range atmospheric transport (LRAT). In a previous cruise during 1989–1990 Iwata et al. (1993) first revealed the global distribution of DDTs in the ocean air. Simonich and Hites (1995) later also made a survey of DDT levels around the world based upon tree bark samples. Compared to other

places (Oehme et al., 1996; Hung et al., 2002; Jaward et al., 2004a; Shen et al., 2005), Asia is one of the hot spots of DDTs where multiple sources of DDT can be found, including dicofol usage for cotton protection (Qiu et al., 2004), and technical DDT usage for disease control (Sharma, 2003), antifouling paints for fishing ships (Li et al., 2007), and even illegal agriculture purpose (Jaward et al., 2005). Previous studies showed that LRAT of persistent toxic

X. Ding et al. / Atmospheric Environment 43 (2009) 4319–4326

compounds from Eurasia had deep influence on the Arctic atmosphere (Halsall et al., 1997; Halsall, 2004). However, there is no large-scale observation of atmospheric DDTs in ocean air from the North Pacific to the Arctic, except the global cruise in 1989–1990 (Iwata et al., 1993). During July to September 2003, air samples were collected along a cruise from Bohai Sea to the North Pole Area (37 N–80 N) aboard the icebreaker ‘‘Xuelong’’. Taking advantage of this opportunity, spatial distribution, source identification and long-range transport have been investigated for polybrominated diphenyl ethers (Wang et al., 2005), hexachlorocyclohexanes (Ding et al., 2007a) and polycyclic aromatic hydrocarbons (Ding et al., 2007b). In the current study, we focus on DDT congeners and the purposes are (1) to reveal the spatial distribution and compositional patterns of DDTs over a large latitudinal range; (2) to provide information for the sources as well as potential source areas of DDTs in the western of the North Pacific Ocean and the adjacent Arctic region. 2. Materials and methods 2.1. Sampling A total of 49 particle samples were taken from July 11 to September 21, 2003, between Bohai Sea (37.78 N, 123.12 E) and the Arctic (80.22 N, 146.75 W), among which 30 vapor samples were collected simultaneously. A high volume air sampler (Tianhong Intelligent Instrument Plant of Wuhan, China) was placed windward on the upper-most deck of the ship. The air volumes ranged from 1215 to 3030 m3 (at 0  C and 1 atm) at a flow rate of w1.0 m3 min1. Air was aspirated through a quartz fiber filter (QFF) (Whatman QM-A, 20.3  25.4 cm, UK) to collect total suspended particles (TSP) from the air stream, and the gas-phase compounds were trapped on a polyurethane foam plug (PUF, 6.5 cm diameter  8 cm height) contained in an aluminum cylinder. In order to remove possible organic impurities, before field use, the QFFs were heated at 450  C for 4 h, and the PUFs were Soxhlet extracted for 24 h, with methanol (Merk, Germany) and dichloromethane (DCM, redistilled), respectively. Exposed QFFs and PUFs were wrapped in aluminum foil and zipped in Teflon bags and stored in freezers at 20  C until analysis. In addition, three blank samples were obtained by placing QFFs and PUFs in the sampler for 10 min with the pump off. Fig. 1 presents the whole sample route.

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calibration method with m/e ¼ 246 and 248 for DDEs and m/e ¼ 235 and 237 for DDTs and DDDs. Splitless injection of a 2 mL sample was performed with a five-minute solvent delay. The injection port temperature was maintained at 280  C during the entire GC run. The oven temperature was initiated at 80  C (held for 2 min), and increased to 290  C at 4  C min1 (held for 10 min). Previous study implied that degradation of DDT might occur in the GC injection system over a sequence of routine GC analyses (Foreman and Gates, 1997). To avoid such degradation, a DDT degradation check solution was analyzed daily to examine the needed degradation extent of DDT less than 15% before samples were taken to the analytical equipment. The method detection limits (MDLs) were 0.18, 0.16, 0.15, 0.15, 0.18 and 0.20 pg m3 for o,p’-DDE, p,p’-DDE, o,p’-DDD, p,p’-DDD, o,p’-DDT, and p,p’-DDT, respectively, when the average sampling volume (2051 m3) was calculated. Half of MDL was assigned to a value less than MDL when calculating total DDT amount. Many values were close to MDL, especially in the Arctic. To avoid the uncertainty caused by undetectable data, zero was assigned to values less than MDL when calculating congener ratios. In the present study, the concentrations of DDT congeners in particulate phase were less than MDLs. Thus only gaseous data are discussed in this study. Table 2 presents all the data during the expedition. 2.4. Quality assurance/quality control Three field blanks and six laboratory blanks were processed. These samples were extracted and analyzed in the same way as field samples. There was no target compound detected in the laboratory and field blanks. Surrogate recovery (n ¼ 97, including field and laboratory control samples) was 90.2  10.5% for PCB15. Recoveries for DDT congeners in spiked blank samples (DDT standards spiked into solvent with clean QFFs and PUFs n ¼ 6), matrix spiked samples (DDT standards spiked into pre-extracted QFFs and PUFs n ¼ 6) were ranged from 86 to 97% and 74–91% respectively. Thus the reported results were not adjusted using recovery rate. Before the field campaign, breakthrough was tested by sampling ambient air for 48 h in Guangzhou with one-and-a-half PUFs instead of one PUF installed in the high-volume sampler. DDT congeners were not detected in the backup half PUF, so for the relatively lower DDT levels over the oceans, breakthrough was not a problem in this study.

2.2. Chemical analysis

2.5. Back trajectories

Sample extraction was conducted based on an analytical procedure published elsewhere (Chen et al., 2006). Briefly, prior to 72 h Soxhlet extraction with DCM, PCB15 was added to all samples as a surrogate compound. The extracts were concentrated and solvent-exchanged to hexane (redistilled), and then purified using a 1:2 alumina/silica gel column. The first fraction was eluted with 15 mL of hexane and discarded. The second fraction, containing DDT congeners, was collected by eluting 70 mL of DCM/hexane (3:7 v/v), and then concentrated to a final volume of 50 mL under a gentle stream of nitrogen. 2, 4, 5, 6-Tetrachloro-m-xylene (TCmX) was added to the samples as internal standard before instrumental analysis.

Air mass origins were determined for the cruise samples using HYSPLIT transport and dispersion model from the NOAA Air Resources Laboratory (Draxler and Rolph, 2003). Two back trajectories (BTs) were performed, for the start and end of each sampling episode. BTs were traced for 5 days with 6 h steps at 100, 500, and 1000 m above sea level. Fig. 1 showed the general indication of direction of the air mass origins.

2.3. Instrumental analysis All samples were analyzed by an Agilent 6890 series gas chromatograph (GC)/5973 mass spectrometric detector (MSD) in the selective ion monitoring (SIM) mode with a 30 m HP-5 MS capillary column (i.d. 0.25 mm, 0.25 mm film thickness). Basing on authentic standards, DDT congeners were quantified using an internal

3. Results and discussions 3.1. Spatial distribution of DDT congeners P As Table 3 showed, DDTs (sum of six congeners) ranged from 3 0.52 to 265 pg m during this cruise. Although the component of P DDTs varied in different studies, our measurements were comparable to the data of global oceanic air with a range from undetected level to several hundred pg m3 (Iwata et al., 1993; Jaward et al., 2004b; Montone et al., 2005; Wurl et al., 2006). Fig. 2 P presents the spatial distribution of DDTs during the expedition. Highest concentration occurred near the Liaodong peninsula

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120°E

150°

180°

150°

120°W

90° Arctic Ocean

4245 4041 4749 39 43444648 29 35 38 27 28 32 26 30 24 33 36 37 23 25 22 31 34 20 21

Russia

60°

16 15

13

17

19 18

U.S.A.

Canada

14 10

China

11

12

8 9 7

2 1

30°

N

5

3

6

Pacific Ocean 4

Fig. 1. The sample route of CHINARE 2003 and broad origins of the air masses. Green means both QFF and PUF samples are collected (site1–3, 6, 8, 10, 12, 13, 15, 16, 19, 21, 23–35, 37– 39, 41, 45), blue means only QFF samples are collected (other sites).

(265 pg m3, site 1), and concentrations at three sites in the Arctic (site 25, 26 and 31) were below MDL (0.52 pg m3). A decreasing P spatial distribution was observed where mean levels of DDTs in Far East Asia (3448 N), North Pacific Ocean (4866 N) and the Arctic (>66.7 N) were 65.1, 6.49, and 1.59 pg m3, respectively. 3.1.1. o,p’-DDTs P o,p’-DDTs (sum of o,p’-DDE, o,p’-DDD and o,p’-DDT) varied between 0.26 and 108 pg m3. Fig. 3 shows the latitudinal variation P of o,p’-DDTs. The highest concentration was observed near P o,p’-DDTs Liaodong peninsula (108 pg m3). The levels of observed in the Far East Asia, the North Pacific Ocean, and the Arctic were 27.1  45.8, 4.65  5.25, and 0.94  0.51 pg m3, respectively. P Obviously, the concentrations of o,p’-DDTs raised in the North Pacific Ocean and peaked near eastern Russia (site 12 and 13) after a wane in the Far East Asia (Fig. 3). Table 3 showed the results from P different regions. In the Far East Asia, o,p’-DDTs in our study was comparable to those for China but about one order of magnitude higher than those for Japan and Korea (Jaward et al., 2005; Lammel et al., 2007). In 1990, o,p’-DDT were 8.3 (1.3–20) and 5.1 (0.9–17) pg m3 in the East China Sea and the North Pacific Ocean, respectively (Iwata et al., 1993). Our measurements were about double of the former but half of the latter. In the Arctic, Halsall et al. (1998) P reported o,p’-DDTs was 0.52  0.23 pg m3 during 1993–1994. An increasing temporal trend of o,p’-DDT was also observed at Alert, Arctic, from 1993 to 1997 (Hung et al., 2002). In the present P study, o,p’-DDTs and o,p’-DDT (0.49 pg m3) were both higher than these previous studies, probably indicating such an increasing trend of o,p’-DDT was still valid now. 3.1.2 p,p’-DDTs P p,p’-DDTs (sum of p,p’-DDE, p,p’-DDD and p,p’-DDT) varied between 0.26 and 157 pg m3 (Fig. 3). The highest concentration was also observed near Liaodong peninsula (157 pg m3). The levels P of p,p’-DDTs in the Far East Asia, the North Pacific Ocean, and the Arctic were 38.0  67.4, 1.84  1.84, and 0.65  0.89 pg m3, P respectively. Like o,p’-DDTs, relative higher concentration of P p,p’-DDTs was also observed near eastern Russia. As Table 3 P present, p,p’-DDTs in the Far East Asia during our cruise was comparable to those reported in the surrounding land (Jaward P et al., 2005; Lammel et al., 2007). And p,p’-DDTs concentrations

in the North Pacific Ocean and the Arctic were lower than (Iwata et al., 1993) and comparable with (Halsall et al., 1998; Hung et al., 2002) those reported in the corresponding regions in the previous studies. After the ban of technical DDT worldwide in 1970s, p,p’DDE became the dominant compound detected in the air. The level of p,p’-DDE appeared to remain constant in the Arctic (0.34  0.08 pg m3) (Hung et al., 2002). Compared with this previous study, our measurement of p,p’-DDE in the Arctic (0.23  0.25 pg m3) was a little lower. 3.2. Spatial variation of DDT composition 3.2.1. DDT ratios Since DDTs (p,p’-DDT and o,p’-DDT) will degrade into DDEs during LRAT, the ratio of DDT to DDE can be used to trace the degree of DDT decomposition and to distinguish the recent and historical input of DDTs (Tao et al., 2008). Generally, the ratio of DDT to DDE more than one can be regarded as the relative fresh application of DDTs (Harner et al., 2004). The ratios of o,p’-DDT/o,p’-DDE in the Far East Asia, North Pacific Ocean and Arctic were 1.74  1.83, 2.02  2.79, and 1.53  0.86, respectively, indicating o,p’-DDT was relatively fresh in the western of the North Pacific Ocean and the Arctic. The ratio of p,p’-DDT/p,p’-DDE was 1.61  0.99 in the Far East Asia but less than 1.0 in the higher latitude areas (0.79  0.72 and 0.90  0.95 in the North Pacific Ocean and Arctic, respectively). This suggested that p,p’-DDT was relatively fresh in the Far East Asia but ‘‘old’’ in the higher latitude regions. To show the relative contriP P butions of o,p’-DDTs and p,p’-DDTs to DDTs, the ratio of o,p’P P P DDTs to p,p’-DDTs ( o,p’-DDTs/ p,p’-DDTs) is also calculated. In P P the Far East Asia o,p’-DDTs/ p,p’-DDTs was near one with small variation (0.94  0.30); while such ratios were about thrice higher in North Pacific Ocean (2.82  1.69) and the Arctic (2.89  1.93). 3.2.2. Congener patterns As an indication of the occurrence of DDT congeners in the atmosphere of the North Pacific Ocean and the Arctic Ocean, Fig. 4A presents the percentages of these compounds whose concentrations were more than MDLs in the different regions. In the Far East Asia, all DDT congeners were detected in all samples except absence of o,p’-DDT in site 8. p,p’-DDT was dominant in this region, followed by o,p’-DDT (Fig. 4B). In the North Pacific Ocean, o,p’-DDT and p,p’-DDE

X. Ding et al. / Atmospheric Environment 43 (2009) 4319–4326

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Table 2 Air concentrations of DDT congeners during the cruise (pg m3). Sitea

Start date

Duration (hour)

Latitude ( N)b

Longitude ( E)b

Temp. ( C)

o,p’DDE

o,p’DDD

o,p’DDT 73.2 14.6 0.33 0.49

P o,p’DDTsc

p,p’DDE

p,p’DDD

p,p’DDT

P p,p’DDTsd

P

108 21.8 3.09 0.97 1.86

42.8 7.14 1.23 0.29 0.65

1.98 8.46 0.20 0.22 0.44

112 10.4 3.22 0.23 0.35

157 26.0 4.66 0.74 1.44

265 47.9 7.74 1.70 3.30

DDTse

1 2 3 6 8

2003-7-11 2003-7-13 2003-7-15 2003-7-17 2003-7-19

48 48 48 45 24

38.35 38.43 37.31 41.47 47.33

122.39 122.29 127.3 136.27 145.35

– – 20.72 15.51 8.74

26.3 3.38 2.60 0.33 1.15

8.10 3.87 0.16 0.15 0.62

Far East Asia 10 12 13 15 16g 19

2003-7-20 2003-7-21 2003-9-15 2003-7-25 2003-9-14 2003-7-29

20 46 48 45 24 24

49.77 50.94 56.56 58.23 61.7 66.08

152.27 160.69 165.94 176.05 174.2 168.82

14.99 10.38 9.26 10.34 9.24 10.60 3.58

6.75 1.74 0.86 7.63 0.62 0.81

2.58 0.22 0.69 0.28

17.7 0.86 6.05 6.15 0.62 0.65 0.38

27.1 2.82 7.60 14.1 1.33 1.53 0.55

10.4 0.33 1.38 1.91 0.40 0.25 0.29

2.26 0.15 0.08 0.30 0.25

25.3 0.37 2.50 2.23 0.25

38.0 0.86 3.97 4.43 0.90 0.43 0.47

65.1 3.68 11.6 18.5 2.23 1.96 1.02

8.90

1.96

0.24

2.45

4.65

0.76

0.16

0.93

1.84

6.49

1.18 1.34 0.23 2.30 0.10 3.30 1.90 2.81 0.78 3.48 2.18 0.34 0.36 1.15 0.50 3.35 1.96 1.19 3.28

0.36 0.51 0.35

0.29 0.17

1.21 0.37 0.44

1.11 0.46 0.19

0.31

3.00 0.20

0.17 0.37

0.32

0.15

0.27

0.72 0.31 0.27 0.34 0.47 0.27 0.19 0.68 1.14

1.65 1.17 0.95 0.26 0.26 1.05 1.55 1.41 0.80 0.26 1.16 0.61 0.56 0.68 0.95 0.69 0.36 1.57 1.89

4.19 0.98 0.37 0.26 0.26 0.47 0.92 0.36 0.51 0.26 0.54 0.46 0.26 0.37 0.26 0.26 0.26 0.74 0.56

5.83 2.15 1.32 0.52 0.52 1.52 2.46 1.78 1.31 0.52 1.70 1.07 0.82 1.05 1.21 0.95 0.62 2.32 2.46

1.00

0.34

0.49

0.94

0.23

0.65

1.59

North Pacific Ocean 21 23 24 25 26 27 28 29 30 31 32 33 34 35 37 38 39 41 45

2003-7-30 2003-8-8 2003-9-8 2003-7-31 2003-8-1 2003-8-9 2003-8-10 2003-9-6 2003-8-2 2003-8-6 2003-8-11 2003-8-3 2003-8-16 2003-8-18 2003-8-14 2003-8-19 2003-8-12 2003-8-20 2003-8-25

23 23 46 23 23 24 24 48 24 23 24 44 23 26 46 24 41 48 24

68.91 70.37 73.28 72.04 73.44 73.76 74.82 76.78 72.13 71.09 74.59 71.56 71.34 74.49 72.77 74.59 76.62 77.93 79.87

Arctic a b c d e f g

168.48 169.02 173.80 168.80 168.75 169.47 166.79 166.43 165.01 161.46 159.12 157.78 156.88 156.67 153.50 152.48 153.87 150.55 147.4

0.19 0.57 0.56 0.38

f

0.18

0.18

0.36 0.22 0.21 0.26 0.40 0.35 0.81 0.68 0.11

0.68 0.90 0.77 0.25

0.21 0.23 0.18

0.36 0.18

0.20 0.19

0.41 0.38

0.26

0.12

0.29

Sample sites are corresponding with Fig. 1. Mean location of the start and end of each sampling episode. P o,p’-DDTs: sum of o,p’-DDE, o,p’-DDD and o,p’-DDT. P p,p’-DDTs: sum of p,p’-DDE, p,p’-DDD and p,p’-DDT. P DDTs: sum of all congeners. Blank means the level is less than MDL. Half of MDL is assigned to this value when computing the sum of DDTs. Sample sits in longitude west after site 16.

occurred in all samples, followed by o,p’-DDE (Fig. 4A); and o,p’-DDT and o,p’-DDE were dominant compounds in this region (Fig. 4B). In the Arctic o,p’-DDT and o,p’-DDE showed not only higher frequencies of occurrence in the samples (>80%, Fig. 4A) but

also higher percentages among the six congeners (Fig. 4B). p,p’-DDT congeners had low frequencies of occurrence and low contributions in the Arctic. It is worthy noting that o,p’- and p,p’-DDD exhibited higher concentrations (Table 2) as well as higher contributions

Table 3 Data comparison for different regions. Location

Year

Far East Asia North Pacific Ocean Arctic Entire cruise Indian Ocean South Atlantic Ocean Atlantic and Antarctic oceans East China Sea North Pacific Ocean Chukchi Sea Bering Sea China Japan Korea Qingdao, China Gosan, Korea Arctic Alert, Arctic

2003 2003 2003 2003 2004–2005 2001 1995 1989–1990 1989–1990 1989–1990 1989–1990 2004 2004 2004 2003 2003 1993–1994 1993–1997

P o,p-DDTs

P

P

Reference

27.1 (0.97–108) 4.65 (0.55–14.1) 0.94 (0.26–1.89) 6.04 (0.26–108)

38.0 (0.74–157) 1.84 (0.43–4.43) 0.65 (0.26–4.19) 7.11 (0.26–157) 9.4 (<0.6–37.8) 22.2 (<3.7–52.4) 16.1 (3.7–102.6) 10.6 (1.6–23) 6.7 (1.1–22) 5.0 (3.5–6.6) 3.3 (1.2–5.7) 28.1 (0.95–256) 14.1 (<0.67–135) 2.93 (<0.67–5.89) 111 (35–205) 376 (194–519) 0.65 (0.07–15.0) 0.53 (0.04–11.3)

65.1 (1.70–265) 6.49 (1.02–18.5) 1.59 (0.52–5.83) 13.1 (0.52–265) 10.4 (2.5–33.2) 22.2 (<3.7–52.4) 16.1 (3.7–102.6) 19 (2.9–43) 12 (2–39) 5.8 (3.4–8.3) 3.6 (1.1–5.6) 57.1 (2.12–343) 15.7 (0.36–151) 3.07 (0.44–8.27) 164 (53–272) 389 (201–527) 1.16 (0.14–10.5) 0.94 (0.08–13.0)

This study This study This study This study Wurl et al., 2006 Jaward et al., 2004b Montone et al., 2005 Iwata et al., 1993 Iwata et al., 1993 Iwata et al., 1993 Iwata et al., 1993 Jaward et al., 2005 Jaward et al., 2005 Jaward et al., 2005 Lammel et al., 2007 Lammel et al., 2007 Halsall et al., 1998 Hung et al., 2002

8.3 (1.3–20) 5.10 (0.9–17) 0.9 (<0.3–1.7) 0.3 (<0.3–1.3) 29.4 (1.17–103) 3.77 (0.36–15.8) 1.49 (0.44–2.93) 53.3 (<76-140) 8.30 (6.60–10.0) 0.52 (0.03–8.35) 0.41 (0.04–3.20)

p,p-DDTs

DDTs

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120°E

150°

180°

150°

120°W

90° Arctic Ocean 265 pg m-3

U.S.A.

Russia

60°

Canada

China 4.0 pg m-3

Pacific Ocean

30°

N P DDTs (sum of six congeners) during this cruise.

(Fig. 4B) in the Far East Asia, compared to the higher latitudinal areas. DDDs can be formed via reductive dechlorination of DDTs in the anaerobic environment, such as soil (Guenzi and Beard, 1967), which means DDTs would not degrade to DDDs in the air (a typical aerobic environment). Thus, the relatively higher air levels of DDDs observed in the Far East Asia might not result from DDTs’ degradation in the air but probably from direct transport of DDDs from the adjacent continent where DDDs could be formed in the anaerobic media (such as soil) and envelope into atmosphere. BTs also support our explanation with air masses all originated from land in the Far East Asia. As shown in Fig. 4B, the congener profiles in the North Pacific Ocean and the Arctic shared the similar pattern, but were different from that in the Far East Asia: The contributions of o,p’-DDT and o,p’-DDE were dominant in the North Pacific Ocean and Arctic; while p,p’-DDT and o,p’-DDT had the similar contributions in the Far East Asia. The different DDT patterns observed between Far East Asia and higher latitudinal areas might reflect the differences in the DDT usage and air mass originations in the respective region. For example, the air masses in the Far East Asia were all originated from the adjacent lands which are considered as hot spots of DDTs; while the air masses were cycled in the Arctic Ocean where obviously has no primary emission. Moreover, meteorological condition may

account for the different patterns. In summer, the polar front is situated far north and creates a meteorological barrier weakening northward air penetration into the Arctic. According to Iversen (1996), summer only accounts for 20% of the annual south to north air transport into the Arctic. 100

A Pencentage of Conc. >MDL

Fig. 2. Spatial distribution of

80

60

40

20

0

60

100

B

40

an

0

ce O

tA

fic

as

Pa

ci

rE

Latitude (oN) P P Fig. 3. Spatial distribution of o,p’-DDTs and p,p’-DDTs during this cruise.

N

or

th

Fa

38.35 38.43 37.31 41.47 47.33 49.77 50.94 56.56 58.23 61.70 66.08 68.91 70.37 71.09 71.34 71.56 72.04 72.13 72.77 73.28 73.44 73.76 74.49 74.58 74.59 74.82 76.62 76.78 77.93 79.87

.1

A rc

1

tic

20

10

sia

Concentrations (pg m–3)

Σ o,p'-DDTs Σ p,p'-DDTs

Percentage ( )

1000

o,p'-DDE o,p'-DDD o,p'-DDT p,p'-DDE p,p'-DDD p,p'-DDT

Fig. 4. Frequencies of congeners more than MDLs in different regions (A); congener patterns of DDTs in different regions (B). Whiskers indicate one standard deviation for DDT congeners.

X. Ding et al. / Atmospheric Environment 43 (2009) 4319–4326

3.3. Source implication of DDTs There are two known sources of DDT: technical type and dicofol type with both containing o,p’-DDT and p,p’-DDT. Normally a higher proportion of o,p’-DDT than p,p’-DDT can be found in dicofol residues. The o,p’-DDT/p,p’-DDT ratio was reported to be 0.2w0.3 in technical DDT (Venkatesan et al., 1996) and w7.0 in dicofol products (Qiu et al., 2005). Thus the ratio of o,p’-DDT/p,p’-DDT can be used to distinguish technical DDT from dicofol-type DDT. Since DDTs are mostly used in the land, the evaporation from soil should be the major input pathway of DDTs in the air. Due to the difference in physical and chemical characters of DDT congeners, the fractionation of DDT isomers during soil-air exchange would lead to the changes in the ratios of o,p’-DDT/p,p’-DDT, resulting in a calculated ratio of 0.74–0.96 for technical DDT and w28 for dicofol-type DDT, respectively, in the air (Liu et al., 2009). Without considering any unknown source and the persistence difference between the two DDT congeners, the relative contribution of two sources can be calculated as equations (1) and (2):

Rairða=bÞ ¼ RS1ða=bÞ *X þ RS2ða=bÞ *Y

(1)

XþY ¼ 1

(2)

where a and b means o,p’-DDT and p,p’-DDT, respectively; Rair(a/b) is the observed value of o,p’-DDT/p,p’-DDT in the air, RS1(a/b) is the calculated gas-phase ratio of o,p’-DDT/p,p’-DDT from technical DDT; RS2(a/b) is the calculated gas-phase ratio of o,p’-DDT/p,p’-DDT from dicofol type DDT; X and Y means the relative contributions of technical DDT and dicofol type DDT in the air samples. Here we use 0.85 and 28 for RS1(a/b) and RS2(a/b) respectively to estimate the relative contributions of these two sources. Based on the o,p’DDT/p,p’-DDT ratios of 1.07  0.88, 2.49  0.20, and 1.69  0.95 in the Far East Asia, the North Pacific Ocean and the Arctic, respectively, the corresponding contributions of technical DDT were calculated to 99%, 94%, and 97%. Thus, technical DDT was the dominant source of DDTs in the oceanic air of western North Pacific Ocean and the Arctic. Liu et al. (2009) reported DDTs in the air of China cities and estimated technical DDT contributing w95% of DDTs in China based on the similar method, although the observed o,p’-DDT level was twice higher than p,p’-DDT. Lee et al. (2001) observed high concentrations of p,p’-DDT congeners in the sediments of Kyeonggi Bay, Korea; and the compositional pattern of DDT congeners suggested continuous usage of technical DDT in this region. BTs also showed most air masses in this region were originated from Eurasia during our expedition. The higher ratio of p,p’-DDT/p,p’-DDE (1.61) observed in the Far East Asia indicated much fresher input of technical DDT in this region when compared to the ratios of 0.79 and 0.90 in the North Pacific Ocean and the Arctic, respectively. For dicofol type DDT, our estimate implied minor contribution. However, the ratios of o,p’-DDT/o,p’DDE were all higher than 1.0, indicating the relatively ‘‘new’’ input of o,p’-DDT. As discussed above, technical DDT was relatively ‘‘old’’ in the higher latitudinal regions. Thus o,p’-DDT should have relatively more contribution from dicofol type DDT in the North Pacific Ocean and the Arctic. Acknowledgments The authors thank the financial support from the National Science Foundation of China (40673074), Chinese Academy of Sciences (KZCX3-SW-121) and Guangzhou Institute of Geochemistry (GIGCX-08-07). Without the technical assistance and convenience offered by the Chinese Antarctic and Arctic Administration and the crew of Xuelong, it would have been impossible for us to

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conduct the present study. The National Oceanic and Atmospheric Administration’s Air Resources Laboratory is also gratefully acknowledged for the provision of the HYSPLIT transport and dispersion model and the READY website (http://www.arl.noaa. gov/ready.html) used in this study. This is contribution No. IS1089 from GIGCAS.

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