Atmospheric Environment 41 (2007) 3889–3903 Organochlorine pesticides in the atmosphere of Guangzhou and Hong Kong: Regional sources and long-range atmospheric transport Jun Li a , Gan Zhang a, , Lingli Guo a , Weihai Xu a , Xiangdong Li b , Celine S.L. Lee b , Aijun Ding b , Tao Wang b a State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, No. 511, Kehua Street, Wushan, Guangzhou, Guangdong 510640, China b Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong Received 8 October 2006; received in revised form 27 December 2006; accepted 28 December 2006 Abstract Organochlorine pesticides (OCPs) were measured in the atmosphere over the period of December 2003–December 2004 at four sampling sites in Guangzhou and Hong Kong. Gas phase and particle phase concentrations of 8 OCP species, including trans-chlordane (t-CHL), cis-chlordane (c-CHL), p,p 0 -DDT, p,p 0 -DDE, o,p 0 -DDT, a-endosulfan, a- and g-hexachlorocyclohexane (HCH), were studied. OCPs were found predominantly in the gas phase in all seasons. t-CHL, c-CHL, o,p 0 -DDT, p,p 0 -DDT and a-endosulfan had significantly (po0.001) higher concentrations than other OCPs, with mean values (gas+particle) typically ranging from 103 to 1440 pg m 3 . In general, the concentrations of OCPs in summer were higher than that in winter, except for a-HCH which showed no clear seasonal pattern. Higher levels of g-HCH and o,p 0 -DDT found in Guangzhou could be attributed to the present usage of lindane and dicofol in the Pearl River Delta (PRD) region. The very high concentrations of p,p 0 -DDT and a-endosulfan were observed at all sampling sites. The results of 7 days air back trajectory analysis indicated that the unusual high p,p 0 -DDT levels in summer in both cities could be related to the seasonal usage of DDT containing antifouling paints for fishing ships in the upwind seaports of the region. The high concentrations of a-endosulfan in winter in the study area suggested an atmospheric transport by the winter monsoon from the East China, where endosulfan is being used as insecticide in cotton fields. The consistency of the seasonal variation of concentrations and isomeric ratios of DDTs and a-endosulfan with the alternation of winter monsoon and summer monsoon suggested that the Asian monsoon plays an important role in the long-range atmospheric transport of OCPs. r 2007 Elsevier Ltd. All rights reserved. Keywords: OCPs; HCH; DDT; Chlordane; Back trajectory; Hong Kong; Guangzhou; South China 1. Introduction Organochlorine pesticides (OCPs) are a group of persistent organic pollutants (POPs) which are to be eliminated or reduced on their release into the environment in many countries. Because of their ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2006.12.052 Corresponding author. Tel.: +86 20 85290178; fax: +86 20 85290706. E-mail address: [email protected] (G. Zhang).
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Atmospheric Environment 41 (2007) 3889–3903
www.elsevier.com/locate/atmosenv
Organochlorine pesticides in the atmosphere of Guangzhouand Hong Kong: Regional sources and long-range
atmospheric transport
Jun Lia, Gan Zhanga,�, Lingli Guoa, Weihai Xua, Xiangdong Lib,Celine S.L. Leeb, Aijun Dingb, Tao Wangb
aState Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, No. 511, Kehua Street,
Wushan, Guangzhou, Guangdong 510640, ChinabDepartment of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Received 8 October 2006; received in revised form 27 December 2006; accepted 28 December 2006
Abstract
Organochlorine pesticides (OCPs) were measured in the atmosphere over the period of December 2003–December 2004
at four sampling sites in Guangzhou and Hong Kong. Gas phase and particle phase concentrations of 8 OCP species,
including trans-chlordane (t-CHL), cis-chlordane (c-CHL), p,p0-DDT, p,p0-DDE, o,p0-DDT, a-endosulfan, a- and
g-hexachlorocyclohexane (HCH), were studied. OCPs were found predominantly in the gas phase in all seasons. t-CHL,
c-CHL, o,p0-DDT, p,p0-DDT and a-endosulfan had significantly (po0.001) higher concentrations than other OCPs, with
mean values (gas+particle) typically ranging from 103 to 1440 pgm�3. In general, the concentrations of OCPs in summer
were higher than that in winter, except for a-HCH which showed no clear seasonal pattern. Higher levels of g-HCH and
o,p0-DDT found in Guangzhou could be attributed to the present usage of lindane and dicofol in the Pearl River Delta
(PRD) region. The very high concentrations of p,p0-DDT and a-endosulfan were observed at all sampling sites. The results
of 7 days air back trajectory analysis indicated that the unusual high p,p0-DDT levels in summer in both cities could be
related to the seasonal usage of DDT containing antifouling paints for fishing ships in the upwind seaports of the region.
The high concentrations of a-endosulfan in winter in the study area suggested an atmospheric transport by the winter
monsoon from the East China, where endosulfan is being used as insecticide in cotton fields. The consistency of the
seasonal variation of concentrations and isomeric ratios of DDTs and a-endosulfan with the alternation of winter
monsoon and summer monsoon suggested that the Asian monsoon plays an important role in the long-range atmospheric
transport of OCPs.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: OCPs; HCH; DDT; Chlordane; Back trajectory; Hong Kong; Guangzhou; South China
e front matter r 2007 Elsevier Ltd. All rights reserved
Organochlorine pesticides (OCPs) are a group ofpersistent organic pollutants (POPs) which are to beeliminated or reduced on their release into theenvironment in many countries. Because of their
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persistence in the environment, and biologicalaccumulation through the food web, OCPs cancause environmental damage, and affect humanhealth (Colborn et al., 1996). Due to their volatilityand persistence in the air, OCPs are subjected tolong-range atmospheric transport (LRAT). There-fore, OCPs released in the tropical and subtropicalenvironments could be dispersed rapidly through airand water, and tend to be redistributed on a globalscale (Tanabe, 1991; Wania and Mackay, 1996).Many recent studies showed that the atmospherictransport from these regions across the PacificOcean was one of the major contributing sourcesfor OCPs in the Canadian west coast and arcticregions (Bailey et al., 2000; Harner et al., 2005). The
Fig. 1. Sampling
Asian monsoon was supposed to have been playingan important role in the long-range atmospherictransport of POPs (Tanabe, 1991; Iwata et al.,1994).
The Pearl River Delta (PRD), including HongKong and Macao, located in the south coast ofChina, and covering an area of about 42,794 km2, isone of the rapid developing regions in China overthe last three decades (Fig. 1). The region is understrong influence of the Asian monsoon system.A few investigations on OCPs in various environ-mental media of the PRD have been conductedrecently (Wong et al., 2002; Zhang et al., 2002;Monirith et al., 2003; Luo et al., 2004). Thesestudies not only detected higher concentrations of
locations.
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HCHs and DDTs in water, sediment, fish, andhuman breast milk in Guangzhou, the center of thePRD, but also found a similar problem in HongKong where no HCHs and DDTs were presently inuse. Studies on trace gases and ozone showed thatthe PRD was a receptor of many anthropogenicemissions from the Asian continent and SoutheastAsia (Chan et al., 1998), but there were only a verylimited number of reports about the behavior ofatmospheric OCPs in south China (Cheng et al.,2000; Louie and Sin, 2003).
In an effort to better characterize OCPs in the airof the PRD, and to study the potential influence ofthe Asian monsoon on the transport of OCPs overthis subtropical region, a year-round air samplingcampaign was conducted in Guangzhou and HongKong, the two major cities in the PRD. The presentwork aims to study the seasonal patterns and thespatial distribution of OCPs in the air, particularlyon the influences of Asian monsoon on thelong-range transport of these contaminants in thelow-latitude region.
2. Materials and methods
2.1. Sampling sites
The PRD has population of 38.7 millions and aland area of 42,794 km2 in 2000. Large cities,including Guangzhou, Hong Kong, Shenzhen,Fushan, Dongguang, Macao etc., form one of themost urbanized regions in South China. Publicconcerns arose when DDT concentrations in humanbreast milk in Guangzhou and Hong Kong werefound to be the second highest in the world (Wonget al., 2002). To observe POPs in the region, fouractive atmospheric sampling stations were set up in2003, including two urban sites, at the Hong KongPolytechnic University, Hong Kong (PU) and SunYet-sen (Zhongshan) University, Guangzhou (ZU);and two suburban sites, at Hok Tsui (CapeD’Aguilar), Hong Kong (HT), and Baiyun Moun-tain, Guangzhou (BY).
2.2. Sampling method
Sampling was conducted concurrently at the foursampling sites for a consecutive 24 h period on abiweekly basis from December 2003 to December2004. A total of 90 pairs of samples were collectedfrom four sampling sites. Air volumes of314–328m3 were drawn through quartz microfibre
filter (QFF) (Grade GF/A, 20.3� 25.4 cm, What-man, Maidstone, England), and subsequentlythrough 6.5 cm in diameter� 7.5 cm in thickness(a density of 0.030 g cm�3) polyurethane foam(PUF) plugs using a high-volume sampler (of theAnderson type) at a flow rate of 0.217–0.228m3min�1.Prior to sampling, QFFs were baked at 450 1C for12 h to remove any organic contaminant, and PUFplugs were Soxhlet extracted for 48 h with methanoland then acetone for 24 h, followed by two over-night extractions using dichloromethane (DCM).PUF plugs were dried overnight in a vacuumdesiccator and stored in solvent-rinsed glass jarswith Teflon lined lids before use. During the samplecollection, gloves were worn, and QFFs and PUFswere handled using acetone-rinsed stainless steeltongs. After sampling, loaded QFFs were wrappedwith pre-baked aluminum foils and sealed withdouble layers of polyethylene bags, and PUFs wereplaced in solvent rinsed glass jars with Teflon linedlids, and then transported to the laboratory andstored at �20 1C until extraction. Meteorologicaldata, such as temperature, relative humidity, windspeed/direction, and precipitation were recorded ateach sampling station.
2.3. Extraction and analysis
QFFs and PUFs were spiked with 20 ng of2,4,5,6-tetrachloro-m-xylene (TCmX) and deca-chlorobiphenyl (PCB209) as surrogates, and Soxh-let-extracted with dichloromethane (both DCM andhexane obtained from Merck & Co. Inc.) for 48 h.Activated copper granules were added to thecollection flask to remove elemental sulfur. Theextract was concentrated and solvent exchanged ton-hexane and purified on an 8mm i.d. alumina/silicacolumn packed, from the bottom to top, withneutral alumina (6 cm, 3% deactivated), neutralsilica gel (10 cm, 3% deactivated), 50% (on a weightbasis) sulfuric acid silica (10 cm), and anhydroussodium sulfate (1 cm). Before use, neutral alumina,neutral silica gel, and anhydrous sodium sulfatewere Soxhlet-extracted for 48 h with DCM, andthen baked for 12 h in 250, 180, and 450 1C,respectively. The column was eluted with 50ml ofdichloromethane/hexane (1:1) to yield the OCPsfraction. The fraction was reduced to a final volumeof 25 mL under a gentle stream of nitrogen andsolvent exchanged to 25 mL of dodecane containinga known quantity of pentachloronitrobenzene(PCNB) as an internal standard.
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GC–MS analysis was carried out on an Agilent-5975 GC-MSD system with a CP-Sil 8 CB capillarycolumn (50m length� 0.25mm i.d., 0.25 mm filmthickness), operating under selected ion monitoring(SIM) mode. The selected ion groups for mostOCPs have been listed by Yeo et al. (2004). Theoven temperature began at 60 1C for 1min andincreased to 290 1C (10min hold time) at a rate of4 1Cmin�1. Split/splitless injection of a 1 mL samplewas performed with a 12min solvent delay time.Injector temperature was at 250 1C. The inletdegradation of DDT was checked daily andcontrolled within 15%.
2.4. QA/QC
All analytical procedures were monitored usingstrict quality assurance and control measures.Laboratory and field blanks consisted of PUF andQFFs were extracted and analyzed in the same wayas samples. Four field blank samples (clean QFFand PUF) deployed at four sampling sites and sixlaboratory blanks were used. When the blanksamples were analyzed, OCPs were not detected inthe QFF and PUF blanks except CHLs in PUF fieldblank, which were detected at less than 2% of themass in the samples, and they were appropriatelysubtracted from the sample concentrations.
Method detection limits (MDLs) of individualOCPs were as follows: 1.1 pgm3 for a-HCH,1.5 pgm3 for g-HCH, 1.4 pgm–3 for t-CHL andc-CHL, 1.8 pgm–3 for p,p0-DDE, 2.5 pgm–3 for o,p0-DDT, 3.6 pgm–3 for p,p0-DDT, and 3.9 pgm–3 fora-endosulfan. Concentrations lower than MDLswere considered non-detectable for quantifiedOCPs.
Before the extraction, each media was fortifiedwith 20 ng of recovery standards TCmX andPCB209. Recoveries for TCmX and PCB209 were7579% and 80713%, respectively. Data shown inthis paper were corrected according to the recoveryrates of the standards.
2.5. Back-trajectory calculation
To investigate the possible sources of OCPs, airmass backward trajectories were calculated usingthe HYSPLIT model (HYbrid Single-ParticleLagrangian Integrated Trajectory, Version 4.7),a comprehensive modelling system developed bythe National Oceanic and Atmospheric Adminis-tration (NOAA) Air Resource Laboratory (Draxler
and Rolph, 2003). Because the synoptic atmosphericconditions at two locations in the same city (i.e. thePU and HT sites in Hong Kong, and the ZU andBY sites in Guangzhou) were quite similar, 7-dayback trajectories ending at Hong Kong andGuangzhou at 0600 UTC, i.e. 14:00 local time forall sampling dates, were calculated. For theclassification of air masses, these trajectories endedat the height of 500m AGL (above ground level), alevel of about half the height of the mean daytimeplanet boundary layer (PBL), to represent generaltransport conditions in the PBL.
3. Results and discussion
3.1. Concentrations of OCPs in air
The arithmetic mean concentrations with theirstandard errors, minimum and maximum valuesand median concentrations of the various analytesin both particle phase and gas phase in the airsamples collected at four sampling sites are given inTables 1–4, respectively. Due to the high atmo-spheric temperature in this subtropical area, theOCPs in this study were predominantly in gaseousphases. For a-HCH and g-HCH, the particle-phasefraction was less than 1% in all seasons except somesamples at the urban site in Guangzhou, where thefraction was less than 5% of the total. For t-CHLand c-CHL compounds, this fraction was less than5% in the non-winter seasons and less than 15%during the winter months, except one sampleattained to 32% at the urban site in Hong Kong.For a-endosulfan and the DDT compounds,the particle fraction was less than 20% in mostsamples; the fraction has occasionally reached ashigh as 75% in the winter season. Therefore, thesum of vapor phase and particulate phase was usedin the data analysis, except only gas-phase in theClausius–Clapeyron equation.
Among the analyzed compounds at the four sites,g-HCH, t-CHL, c-CHL, o,p0-DDT, p,p0-DDT anda-endosulfan had high concentrations with themaximum values of 2640, 2030, 4190, 3380, 4530,and 2500 pgm�3, respectively. a-HCH and p,p0-DDE showed similar ranges with the highestconcentrations of 313 and 526 pgm�3, respectively.The significantly high values of these compoundsmay imply the fresh inputs of those OCPs in thisregion. Chlordane was used as a termiticide ofwoods in many parts of the world, and was detectedin high levels where the technical chlordane was
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Table 2
Summary of air concentrations and Clausius–Clapeyron regression results of organochlorine pesticides in the suburban site (HT) of Hong
nd, not detected; ns, not statistically significant.
J. Li et al. / Atmospheric Environment 41 (2007) 3889–3903 3893
sprayed (Bidleman et al., 1998; Murayama et al.,2003). In China, technical chlordane is still beingextensively used against termites in buildings, withan estimated amount of over 200 t year�1 in recent
years (Xu et al., 2004). The PRD, located in thesubtropics, always suffers from termites in rainyseason, the high concentrations of t-CHL andc-CHL observed may be predominantly due to the
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Table 4
Summary of air concentrations and Clausius–Clapeyron regression results of organochlorine pesticides in the suburban site (BY) of
nd, not detected; ns, not statistically significant.
J. Li et al. / Atmospheric Environment 41 (2007) 3889–39033894
current usage of technical chlordane as a termiticidein this area. In the past, large quantities of technicalHCH and DDT had been used in China, and totalof 4.9 million tons (HCH) and 0.4 million tons(DDT) were produced until the production wasbanned in 1983 (Hua and Shan, 1996). After that, asthe substitutes, the purified g-HCH isomer (lindane)and DDT-type pesticide (dicofol) has been pro-duced in many factories (Qiu et al., 2004, 2005;Jaward et al., 2005). The extremely high values ofg-HCH and DDTs observed in this area wereconsistent with other research results, such as thehigh concentrations of HCHs and DDTs in water,sediment, fish, and human breast milk in the PRD(Wong et al., 2002; Zhang et al., 2002; Monirithet al., 2003; Luo et al., 2004). Endosulfan is anotherremaining OCPs registered in China for the controlof cotton bollworm (Helicoverpa armigera) andnative budworm (H. punctigera) in cotton crops,and regarded as a ‘‘soft’’ organochlorine because ofits chemical properties, degradation rate, andmetabolism in plants and animals (Gupta andGupta, 1979). The annual production of endosulfanwas about 2400 t in China. The eastern China plainis one of the major areas for cotton culture in thecountry, consisting of parts of the lower reaches ofthe Yellow River, Huaihe River, and the middle andlower reaches of the Yangtze River. No cotton isgrown in the PRD. The high levels of a-endosulfanmight be the outflow from the cotton productionfields in eastern China.
HCHs, CHLs, o,p0-DDT, and a-endosulfanshowed significant different concentrations betweenthe two cities. The concentrations of these com-pounds were significantly (po0.05) higher in the air
of Guangzhou than in Hong Kong. However,elevated concentrations of p,p0-DDE and p,p0-DDT at the HT site in Hong Kong were alsoobserved. Besides this, the distribution of OCPsmean and median concentrations in Guangzhouand Hong Kong showed different patterns. Forexample, Guangzhou had higher t-CHL and o,p0-DDT than c-CHL and p,p0-DDT, and HongKong showed slightly higher c-CHL and p,p0-DDTthan t-CHL and o,p0-DDT. While the concentrationdifferences between the two cities may indicate thatthe agricultural areas (mostly around Guangzhou inthe rural PRD) are a dominant source of mostOCPs in the air of PRD, the different patterns ofOCPs between the two cities may also suggest thatthere might be other types of emission sourcescoexistent in the region.
3.2. Comparison of OCPs with other countries
As shown in Table 5, atmospheric concentrationsof OCPs in several places were compared with thosein Guangzhou and Hong Kong. In India, which hasbeen known as a large point source of HCHs andDDTs, the concentrations of a-HCH, g-HCH, andp,p0-DDE were higher than that in the PRD. Thecomparable or higher concentrations of OCPs in thePRD than other places were observed in the currentstudy. For example, a-HCH in the PRD showedsimilar levels to that in Korea and Japan.a-endosulfan in Guangzhou showed as high levelsas in Seoul, where endosulfan is one of theremaining OCPs registered in Korea. The concen-tration of chlordane in Guangzhou and Hong Kongshowed much higher value than other countries,
Belize, Central Americaf 63722 34739 32742 4587127 5567356 145745
aQiu et al. (2004).bRajendran et al. (1999).cYeo et al. (2004).dMurayama et al. (2003).eBidleman et al. (1998).fAlegria et al. (2000).
J. Li et al. / Atmospheric Environment 41 (2007) 3889–3903 3895
although chlordane has been largely used to controltermites around homes in Japan and the UnitedStates. o,p0-DDT had similar high levels to that inTaihu Lake region, China, where high concentra-tion of o,p0-DDT was attributed to the dicofol usage(Qiu et al., 2004). Moreover, high concentrations ofp,p0-DDT were detected in both Guangzhou andHong Kong, which were higher than that in Indiaand central America where technical DDT is still inuse (Rajendran et al., 1999; Alegria et al., 2000). Allof above results might indicate that there were freshinputs of those OCPs in the PRD region.
3.3. Seasonal variation and sources
Generally, gas-phase concentrations of mostOCPs in many cities of the world were higher insummer with higher ambient temperature than inwinter with lower temperature (Murayama et al.,2003; Yeo et al., 2003, 2004; Gioia et al., 2005). Thispattern is consistent with the theory of liquid-vaporequilibrium described by the Clausius–Clapeyronequation (Hoff et al., 1992, 1998; Bidleman et al.,1998; Cortes et al., 1998; Wania et al., 1998; Carlsonand Hites, 2005):
ln P ¼ �DH=R� �
ð1=TÞ þ constant ¼ mð1=TÞ þ b,
(1)
where P is the SVOC partial pressure (Pa), DH is acharacteristic environmental phase-transition en-ergy of the compound (kJmol–1), R is the gasconstant, and T is the average atmospheric tem-
perature (K) during the sampling period. It issuggested that a negative slope in the Clausius–Cla-peyron plot indicates that gas-phase concentrationsincrease with increasing temperature. The slope of aline fitting to these data (m) multiplied by thenegative universal gas constant (�R) gives achemical’s phase-transition energy (DH). In adynamic environment, an increase in temperaturecan affect other processes that will lead to anincrease or decrease in atmospheric gas-phaseconcentrations of pesticides, such as transfer acrossthe air/water interface and partitioning from terres-trial surfaces. As a result, DH is useful to under-stand the environmental behavior of thesecompounds. The different DH values among thesites may reflect the different processes that controlthe concentrations of these compounds. Whilestrong temperature dependence is indicative ofpartitioning between surfaces and the atmosphere,and can be indicative of seasonal pesticide use, aweaker dependence may be due to processes thathave an opposite correlation with temperature, forexample, long-range transport or the direction oflocal winds. This means the atmosphere transportalso plays an important role in controlling theseasonal variations of OCPs in the air.
For a better insight on the controlling factors ofthe OCPs temporal trends, the plots of the 7-dayback trajectories ending at Hong Kong and Guangz-hou during the measurement period (December2003–December 2004) are presented in Figs. 6a–b.In general, three categories of air masses can beidentified during the annual cycle, (1) CI—air masses
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coming from the north or northeast that originatedfrom the continental inland areas of northern China,Mongolia, Central Asia and Siberia and reaching theSouth China region through the inland areas ofChina; (2) CT—air masses from the north ornortheast that originated from continental inlandareas of the northern China, reaching the SouthChina region through the Southeast China coast;(3) SS—air masses coming from the south, south-west, or east that originated mostly from the sea,including the South China Sea, the Indian Ocean andthe Pacific Ocean (Lee et al., 2007). The character-istics of the long-range transport pattern of theair masses arriving at the South China regionexhibited a clear seasonal pattern throughout theannual cycle. From December 2003 to March 2004,the whole South China region was generally domi-nated by the air masses CI and CT, due to theAsian winter monsoon. Since early April 2004, theregion had begun to be influenced by the marine airmasses SS, although sometimes the continental airmasses occasionally affected the study sites. At theend of the annual cycle, from mid August 2004 toDecember 2004, the air masses CI and CT were againdominant.
The Clausius–Clapeyron equation was appliedfor each gas-phase pesticide group at each samplingsite in this study, and the DH values and thelinear regression coefficient values (r2) are given inTables 1–4.
3.3.1. a-HCH and g-HCH
For a-HCH, the DH values and the linearregression coefficient values (r2) shown in Tables1–4 indicates that there is no significant correlationbetween a-HCH concentrations and temperature.Unlike a-HCH, g-HCH displayed significantlystronger temperature dependence (po0.05) at twosites in Guangzhou than those at two sampling sitesin Hong Kong. Many studies have shown that asteep slope indicates that air concentrations arecontrolled by re-volatilization from surfaces, while aflatter slope indicates that advection of air isgoverning atmospheric concentration levels (Corteset al., 1998; Yeo et al., 2003). The differences ofslopes in this study suggested that a-HCH levelsboth in Hong Kong and Guangzhou and g-HCH atHong Kong sites may be governed primarily bytransport, whereas the g-HCH levels in Guangzhouwere driven by temperature changes via evaporationfrom nearby terrestrial surfaces.
The similar levels of a-HCH as reported in otheradjacent countries (Table 5) and no obvious peakappeared in the whole year data at the foursampling sites may imply no current usage oftechnical HCHs in the PRD region, and the majorsources of a-HCH could be the residue of previouslyused technical HCHs or might be due to possiblephototransformation of g-HCH to a-HCH (Pacynaand Oehme, 1988; Barrie et al., 1992). Previousstudies showed that in the areas where lindane wasused or in the nearby areas, high concentrations ofg-HCH, ranging from several hundred to severalthousand pgm�3 can be detected (Granier andChevreuil, 1997; Haugen et al., 1998). Highconcentrations of g-HCH in the center of the PRDindicated that lindane was still used in this region.The average of the a/g ratio observed in the airduring the sampling period was 2.8 for Guangzhouand 1.6 for Hong Kong, also suggesting a currentinput of lindane in the study area (Fig. 2).
3.3.2. Chlordane
Gas-phase t-CHL were significantly correlatedwith 1/T (po0.05) among all sampling sites in thePRD, with relatively lower r2 values ranging from0.203 to 0.306, whereas gas-phase c-CHL had nocorrelation with 1/T for all sampling sites except atthe suburban site in Hong Kong with also lower r2
values of 0.302. This result indicated that theconcentrations of those compounds were notstrongly correlated with ambient temperature.Fig. 3 shows the seasonal variations of chlordaneand the ratios of t-CHL/c-CHL. In Hong Kong,clearly seasonal patterns were observed, and thehigh concentration and relative uniform t-CHL/c-CHL ratios of about 1 were recorded in summerand autumn, and the opposite results were noted inwinter and spring. Whereas, in Guangzhou, therewas no clear seasonal variation, and the ratios of t-CHL/c-CHL varied from 0.27 to 1.44 throughoutthe whole year.
In the international market, technical chlordane isa mixture of over 140 different components, themost abundant of components are trans-chlordane(t-CHL, 13%), cis-chlordane (c-CHL, 11%), hepta-chlor (5%) and trans-nonachlor (5%), and theratios of t-CHL/c-CHL in technical chlordaneare 1.2:1.0 (Bidleman et al., 2002). In this study,the t-CHL/c-CHL ratios were 0.7870.33 and0.9570.18 in Guangzhou and Hong Kong, respec-tively. These values were significantly (po0.001)different with that of technical chlordane. The lower
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Fig. 2. The back trajectories of air masses in (a) Hong Kong and (b) Guangzhou. Air mass categories: CI—continental inland areas; CT—
coastal areas; SS—marine sources.
J. Li et al. / Atmospheric Environment 41 (2007) 3889–3903 3897
t-CHL/c-CHL ratios in Guangzhou were similar tothose in the pine needles in Beijing (Xu et al., 2004),and were likely attributed to the different values ofhalf-life of t-CHL and c-CHL or the different
compositions of t-CHL and c-CHL in the mixtureof technical chlordane used in China. Fig. 4 displaysthe t-CHL/c-CHL ratios with the logarithm of thesum of the concentrations of t-CHL and c-CHL in
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Fig. 3. Seasonal variations of chlordane concentration and ratio of T-CHL/CC in urban and suburban areas of Hong Kong and
Guangzhou, South China.
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Fig. 4. The logarithm of the sum of T-CHL and CC concentrations correlated with the T-CHL/CC ratios.
J. Li et al. / Atmospheric Environment 41 (2007) 3889–39033898
the two studied cities. In Hong Kong, high values oft-CHL/c-CHL, similar to technical chlordane,accompanied with high t-CHL+c-CHL concentra-
tions were observed. In Guangzhou, the oppositewas held with lower t-CHL/c-CHL ratios at highert-CHL+c-CHL concentrations. We analyzed the
ARTICLE IN PRESSJ. Li et al. / Atmospheric Environment 41 (2007) 3889–3903 3899
commercially available technical chlordane inGuangzhou market, and found a t-CHL/c-CHLratio of 0.76. Compared with this ratio, there wasno significant (p ¼ 0.383) difference from thatobserved in Guangzhou (0.7870.33). However, thisvalues was significantly (po0.001) lower than that(0.9570.18) in Hong Kong. Therefore, the differentpatterns of t-CHL and c-CHL at two cities might beattributed to potentially different sources of com-mercially available technical chlordane in Guangz-hou and Hong Kong.
3.3.3. DDT isomers
Correlations between ln p vs. 1/T the DDTs werestatistically significant at the four sampling sites(po0.01). DH estimated for o,p0-DDT at Guangz-hou and Hong Kong were similar. Hok Tsui site(suburban of Hong Kong) had the highest value ofp,p0-DDT and p,p0-DDE. Values found for DH ofp,p0-DDT were significantly higher than those forother DDT isomers, and the linear regressioncoefficient values (r2) for p,p0-DDT was also higherthan other compounds. The strong relationshipbetween temperature and gas-phase concentrationand higher DH values in the PRD suggest significantpartitioning of DDTs between air and the surface.Considering the generally higher DDTs concentra-tions in this region, the PRD are close to theatmospheric sources of DDT.
The ratios of DDT isomers have been used toidentify the possible DDT sources. A small value ofDDT/(DDE+DDD) ratio is indicative of aged(microbially degraded) DDT, and a value muchgreater than 1 indicates fresh application. More o,p0-DDT than p,p0-DDT in the environment candemonstrate the dicofol-type DDT usage (Qiu et al.,2004). The DDT isomer concentrations and ratiosof o,p0-DDT/p,p0-DDT and p,p0-DDE/p,p0-DDT atthe four monitoring sites (PU, HT, ZU and BY)over the 1-year period are plotted as a time series inFigs. 5a–d. Distinguished seasonal patterns werefound in the DDT isomer concentrations at the foursampling sites. The consistence of the seasonalvariation of concentrations and isomeric ratios ofDDTs with the alteration of winter monsoon andsummer monsoon was also observed. During theAsian winter monsoon season (from December 2003to March 2004), relatively lower concentrations oftotal DDTs with more o,p0-DDT than p,p0-DDT inGuangzhou and Hong Kong were recorded. This isin consistency with the compositional characteristicsof DDTs in the Taihu Lake region, as well as East
China Sea (Iwata et al., 1993; Qiu et al., 2004),suggesting the usage of dicofol in the PRD. Whereasduring the summer monsoon season (from earlyApril 2004 to mid-August 2004), especially frommid-June 2004 to mid-August 2004, the unusuallyhigh levels of p,p0-DDT were observed at allsampling sites (Fig. 2). The compositions of DDTschanged to more p,p0-DDT than o,p0-DDT, similarto that of technical DDT. This change might be dueto the usage of technical DDT or/and inputs fromDDT-containing products. The production andusage of technical DDT in the PRD and in HongKong was banned in 1983 and 1988, respectively(Wong et al., 2002). The potential sources of DDTduring this season might come from DDT contain-ing anti-fouling paints used on fishing boats in thePRD region, and DDTs transported by the Asianmonsoon from other areas. Anti-fouling paints aremainly used to prevent the adhesion of seaorganisms like barnacles. According to the recentinvestigation, the average annual production ofDDT was 4519 t during 2000–2003 in China, andthere was no DDT import from other countries.About 4% of total DDT production was used as theadditive for the production of anti-fouling paint forfishing ships. The coastal area of Guangdongprovince has ca. 60,000 fishing ships, which isabove 1/5 of the total number in China. It can beestimated that about 30–60 t of DDT may beintroduced to the coastal environment of Guang-dong, including the PRD.
In 1995, fisheries administrations suspended fish-ing activities during the summer months on the EastChina, Yellow, and Bohai Seas in order to protectmarine resources. In 1999, the protected area wasexpanded to include the South China Sea (from 1June 1 to 1 August). During the suspension season,many boats were in the maintenance (i.e. painting),and large quantities of DDT accompanied withanti-fouling paints usage were introduced into theenvironment. Moreover, with the prevailing south-easterly or southwesterly wind (Fig. 2), the PRDwas suffering from those high concentrations ofDDT from the upwind South China Sea wheremany fishing boats anchored for maintenance inseaports during this period. Several types ofantifouling paints in PRD market was analyzed(unpublished data by the research group), the mostremarkable one had p,p0-DDT, o,p0-DDT, and p,p0-DDE concentrations of 368, 151, and 6 mg g�1,respectively. The compositions of more p,p0-DDTthan o,p0-DDT in anti-fouling paint was consistent
ARTICLE IN PRESSJ. Li et al. / Atmospheric Environment 41 (2007) 3889–3903 3901
with the fact observed in the PRD atmosphereduring the summer monsoon season. From midAugust 2004 to December 2004, the Asian wintermonsoon were again dominant, the concentrationof p,p0-DDT significantly decreased, and the com-positions of DDT changed to more o,p0-DDT thanp,p0-DDT characteristic among all sampling sitesexcept at Hok Tsui (suburban of Hong Kong) site.Hok Tsui (Cape D’Aguilar) is located in thesoutheastern tip of Hong Kong Island (221130N,1141150E, with an elevation of 60m above sea level).The site is in a relatively clean area of Hong Kong,situated on a cliff with 2401 of ocean view stretchingfrom northeast to southwest. The air masses passedthrough the east part of the South China coastbefore arriving at the Hok Tsui under the east-northeast (E–NE) flow in the winter monsoonseason. The high concentrations of p,p0-DDT atthis station might be due to the air/water exchangeor pollutant flow-in from upwind position, such asXiamen, where highest p,p0-DDT was observed bypassive air sampling from September 2004 toNovember 2004 (Jaward et al., 2005). Furtherinvestigation is needed to verify the potential longrange transport of OCPs at the sampling site.
3.3.4. a-Endosulfan
a-Endosulfan showed no significant (p40.05) orweak (r2 ¼ 0.207, p ¼ 0.032) correlation with tem-perature at all sampling sites. The seasonal variationof a-endosulfan was different from the variation oftemperature (Fig. 6), whereas, the maximum valueswere obtained in late August and September 2004.In general, high concentrations of a-endosulfanwere observed was in the Asian winter monsoon
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Fig. 6. a-Endosulfan concentrations and the ambient temperature in u
China.
season with predominantly northeast wind direc-tion. The results of back-trajectory analysis showedthe continental air masses passed through the cottonculture region in eastern China where endosulfanwas widely used for the control of caterpillar. Thecoincidence of high levels in both cities might beattributed to alien source carried by the Asianwinter monsoon.
4. Conclusions
Elevated concentrations of OCPs (especially g-HCH, t-CHL, c-CHL o,p0-DDT, and p,p0-DDT)were found in the center of the PRD (Guangzhou)of the low-latitude subtropical region, showingsignificant local pollution. The potential sources ofthose pollutants might be the local usage of lindane,chlordane, dicofol and DDT containing anti-foulingpaints. Distinct seasonal trends were found in OCPsconcentrations in both Hong Kong and Guangz-hou, with high concentrations of DDTs during thesummer period, and low concentrations during thewinter time, while opposite seasonal variability wasobserved with a-endosulfan concentrations in thePRD. The high levels of those OCPs could beattributed to the seasonal usage of pesticides and thelong range atmospheric transport driven by theAsian monsoon. The very high p,p0-DDT levels insummer at both cities were probably related to theseasonal usage of DDT containing antifoulingpaints for fishing boats. The high concentrationsof a-endosulfan in winter in the study areasuggested an atmospheric transport by the wintermonsoon from the East China, where endosulfan isbeing used as insecticide in cotton fields.
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Acknowledgments
This work was supported by NSFC (Nos.40590391 and 40518002), and the Research GrantsCouncil (RGC) of the Hong Kong SAR Govern-ment (PolyU 5147/03E and N_PolyU535/05). Wewould like to thank Dr. Liu Guoqing, Ms. ZhangY.Y., Mr. Li K.C. and Mr. Guan Y.K. for samplingassistance. Special thanks are devoted to Dr. ChanC. Y. in PolyU for his help and comments. And wethank the two anonymous reviewers for theirvaluable comments/suggestions for improving themanuscript.
