Science of the Total Environment 497–498 (2014) 499–507

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Science of the Total Environment

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Maldives: An archipelago that burns. A first survey of PCDD/Fs andDL-PCBs from human activities

Andrea Colombo a,⁎, Roberta Bettinetti b, Giovanni Strona c, Felice Cambria a, Roberto Fanelli a,Zameer Zubair d, Paolo Galli b,e

a Department of Environmental Health Sciences, IRCCS — Istituto di Ricerche Farmacologiche “Mario Negri”, Milano, Italyb Department of Theoretical and Applied Sciences, University of Insubria, via Dunant 3, Varese, VA, Italyc European Commission, Joint Research Centre, Institute for Environment & Sustainability, Via Enrico Fermi 1, I-21020 Ispra, VA, Italyd CDE Consulting, Orchidmaage, Ameeru Ahmed Magu, 20095 Malé, Maldivese MaRHE Center (Marine Research and High Education Centre), Magoodhoo Island, Faafu Atoll, Maldives

H I G H L I G H T S

• PCDD/F concentrations were higher in the proximity local waste combustion sources.• DL-PCB concentrations are markedly lower than PCDD/Fs.• PCDD/F and DL-PCB concentrations are well correlated.• PCDD/F concentration decrease with the distance from local sources.• PCA identified the PCDD/F pollution source in the most contaminated locations.

⁎ Corresponding author. Tel.: +39 02390514536; fax:E-mail address: andrea.colombo@marionegri.it (A. Col

http://dx.doi.org/10.1016/j.scitotenv.2014.08.0130048-9697/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 29 May 2014Received in revised form 4 August 2014Accepted 4 August 2014Available online xxxx

Editor: Damia Barcelo

Keywords:PCDDsPCDFsPCBsMaldivesPCA

Due to its geographical peculiarities, the Republic of Maldives represents a case study of great interest for theinvestigation of persistent organic pollutants, from both a socio-economic and an ecological perspective. Thus,we conducted a first survey to assess the current status of polychlorinated dibenzo-p-dioxin (PCDD),polychlorinated dibenzofuran (PCDF) and dioxin-like polychlorinated biphenyl (DL-PCB) concentrations inMaldivian soils.The range for PCDD/F and DL-PCB soil concentrations was 0.01–49.3 pg WHO2005-TEQ g−1 and 0.01–3.69 pgWHO2005-TEQ g−1 dw respectively. PCDD/F concentrations exceeding several international soil guidelineswere found in samples from locations in the proximity of local waste combustion sources. DL-PCB concentrationswere lower than PCDD/Fs and comparable to those in previous reports from background areas and in areas withdeveloping industrial and agricultural activities. PCDD/F and DL-PCB levels (expressed asWHO2005-TEQ) in soilswere strongly correlated (r = 0.89), which suggests that, in most of the sites, they are originated from the sameemission sources. Results indicate that PCDD/F soil concentrations (expressed asWHO2005-TEQ) tend to decreasewith the distance from the local pollution sources.Principal component analysis (PCA) showed that PCDD/Fs in themost polluted locations aremainly generated bywaste combustion. Thesefindings highlight the need for immediate changes inwastemanagement policies in theArchipelago, in order to reduce the release of Persistent Organic Pollutants (POPs) in the fragile localenvironment.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinateddibenzo-p-furans (PCDFs) and polychlorinated biphenyls (PCBs) aretwo families of persistent organic pollutants (POPs) which may be

+39 0239014735.ombo).

unintentionally formed and released into the environment by severalanthropogenic activities.

Among the possible congeners of 419 PCDD/Fs and PCBs, only 172,3,7,8-chlorine substituted PCDD/Fs and 12 PCBs (DL-PCBs) areconsidered dioxin-like pollutants (Van den Berg et al., 1998, 2006).They are of great concern due to their high toxicity and tendency tobioaccumulate through the food chain. They are a class of ubiquitous pol-lutants with high chemical stability and extremely poor water solubility

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(Birnbaum, 1995; De Vito and Birnbaum, 1995; Haws et al., 2006;Schecter et al., 2006). Once these pollutants are released, they accumu-late in environmental sinks such as soils and sediments, with a longhalf-life (Sinkkonen and Paasivirta, 2000).

One of the aims of the Stockholm convention, adopted in 2001, is toprotect human health and the environment from these chemicals thatremain intact in the environment for long periods, become widelydistributed, accumulate in the fatty tissue of humans and wildlife, andhave adverse effects onhumanhealth or the environment (UNEP, 2001).

Althoughmany studies have investigated levels and sources of thesePOPs in populated areas (Caserini et al., 2004; Colombo et al., 2009,2011, 2013; Fiedler et al., 1996; Ogura et al., 2001; Rotard et al., 1994;Shen et al., 2009; Turrio-Baldassarri et al., 2007), there is little informa-tion on the presence and the distribution of PCDD/Fs in tropical regions.Dioxin-like compounds in tropical countries have not only a localimpact, but are also a point source of contamination even for distantareas, as they are transported through the atmosphere towards coldregions (UNEP, 1999, 2001). In this context, the Republic of Maldives,that is facing severe environmental issues due to its rapid economicgrowth, represents an area of high interest. To plan new sustainabledevelopment policies, the country needs to collect sufficient reliableenvironmental data for decision-making. Currently there are no base-line data on dioxin concentrations in the archipelago, though someinformation can be inferred from indirect indicators (Zubair et al.,2011).

Garbage incinerators, fossil fuel power plants and home generators,motorcycles and cars/taxis (only in Malé), motorized vessels (Changet al., 1999; Goodwin et al., 2000; Laroo et al., 2011; Pirard et al.,2005; UNEP, 1999) are some of the potential emission sources ofPCDD/F and DL-PCB.

Inmost inhabited islands, localwastes are burnt at low temperaturesin sites that are typically uncontrolled, usually located along vegetationlines or shorelines. Waste management in the resort islands is moreadvanced, based onminimizing, segregating and treating (making com-post) garbage. Each resort is required by law to have an incinerator forleaves, paper, packaging and cardboard. The average amount of wasteproduced in resort islands is 2.5–7.5 kg/person/day according to arecent report of the Asian Development Bank (Zubair et al., 2011). Onuninhabited islands, small amounts of waste from tourist picnics areoften burnt on beaches.

More specific information is available for Malé wastes, which areshipped to Thilafushi island, which is entirely used as a landfill. InMalé, the average rate of solid waste generation ranges between 0.8and 1.0 kg/person/day (Asian Development Bank, 2007) and 2.48 kg/person/day (JICA, 1999). According to the Municipality Waste Manage-ment Section in Malé, municipal solid waste is typically composed ofpaper and cardboard (33%), kitchen waste (15%), and constructionwaste (industrial/scraps) (52%). About 15% of the construction wasteis wood. Average daily solid waste generation in Malé is 140 tons, andbiodegradable waste is about 25 tons/day. The solid waste is sortedbefore shipment to the island of Thilafushi, where biodegradable andcombustible materials (i.e., organic) are dumped in the pits. Thecombustible materials are burnt first, then the ashes (plus unburntmatter) are dumped into the pit. The area has been used as a landfillfor more than ten years.

In the present study soils collected in Maldives were analyzed todetermine their PCDD/F and DL-PCB contents. Soils were chosen dueto their high capacity of acting as reservoirs for organic pollutantssuch as PCDD/Fs and DL-PCBs (Sinkkonen and Paasivirta, 2000). Abaseline information on concentrations of these contaminants insoils could help to fully understand the present environmental quality,and whether the area is at environmental risk.

Samples were collected from developed and urbanized sites, andfrom locations classified as unpolluted or pristine. Our aim was tomake an overall view of pollution in Maldivian soils, as a preliminarysurvey of the current status of PCDD/F and DL-PCB concentrations and

to investigate the potential emission sources of PCDD/Fs affecting theirsoil concentrations.

We used principal component analysis (PCA) to compare the“fingerprint” of the environmental data obtained from our sampleswith known data, in order to establish the origin of contamination.PCA is a powerful statistical technique widely used in this field(Wenning et al., 1993, 1994), for investigating large sets of data usingthe smallest number of variables while preserving the greatest amountof information.

2. Materials and methods

2.1. Sampling

The Republic of Maldives consists of 1190 tiny islands in the IndianOcean, and is the flattest country on earth (Khan et al., 2002). Accordingto the census conducted by theMinistry of Planning andNational Devel-opment, the total population of the Maldives was 300,000 in 2006, andwas growing at a rate of 1.96% per year. The entire population is distrib-uted among 200 inhabited islands. Malé is the urban center and thecapital of theMaldives, and hostsmore than a quarter of the population;in addition to these 200 inhabited islands, 100 islands serve exclusivelyas tourist resorts (www.cde.com.mv, 2007).

As regards land use, the islands of the Maldives can be divided intofour categories: islands inhabited by local populations (roughly 200islands); islands used exclusively as tourist resorts (100 islands);uninhabited islands; and the Capital, known as Malé Island (about2 km2 wide).

During 2012, a sampling campaignwas conducted in two areas withdifferent levels of urbanization: (1) a developed area on Malé Atoll(Fig. 1) and (2) an undeveloped area on Faafu Atoll (Fig. 2).

The developed area includes Malé, with approximately 100,000residents, 37,500 motorcycles, 12,500 cars/taxis and 600 anchoredvessels (Asian Development Bank, 2007), and Thilafushi island, whichis amanmade island of 1.4 km2, located 6.85 kmwest ofMalé. Thilafushihosts the big Maldivian Dump, currently used for the disposal of wastefrom the Capital and the surrounding islands.

The undeveloped area on Faafu Atoll is roughly 130 km far from theurbanized area. This area is characterized by a low population density,and by the presence of very few cars and vessels.

Top composite soil samples (0–30 cm) were collected at 25 points(Figs. 1 and 2). The sampling strategy was to collect each compositesoil from five sites on each island: north, south, east, west, and center.The shape of Thilafushi Island prevented us to collect a sample in thecenter. In addition, for security reasons, at the international airport,we were only allowed to collect one composite sample (site 15). Wecollected only one sample also on the uninhabited island, due to itsvery small size (about 150 meters long).

At each sampling site ten individual samples (100 g each) werecollected from a 10 × 10 m area, equally distributed on the two crossingdiagonals. Soil samples were cleaned by removing litter/grass layer (ifpresent). Soil sampleswerepreserved and stored at−20 °Cuntil analysis.

2.2. Analytical method

A 34-mL pressurized liquid extractor (Dionex ASE 300) cells werepacked with 3 g of anhydrous Na2SO4, 1 g of powdered copper and25 g of dried soil sample mixed with 2 g of copper. The sample wasspiked with known amounts of 13C12-labeled internal standards of 152,3,7,8-chlorosubstituted PCDD/Fs, 4 non-ortho PCBs (77, 81, 126 and169 named following the IUPAC nomenclature) and 8 mono-orthoPCBs (105, 114, 118, 123, 156, 157, 167 and 189 named following theIUPAC nomenclature) and extracted with a mixture of pesticide-gradeacetone/n-hexane (80/20) (Carlo Erba, Milano, Italy) (Fattore et al.,1997, 2003; Vives et al., 2008) at 100 °C, 10 MPa, 5-min static time,and 3 cycles for a total time of 1 h.

Fig. 1. Map of the developed area of Malé Atoll, showing the soil sampling locations. In the figure are shown 30-year mean percent frequency wind direction 1964–2000 for April–November (black lines) and December–March (gray lines) based on data from the Hulule climate station at Male atoll (Kench and Brander, 2006).

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The extract was concentrated to 1 mL and treated with 15 mL ofsulfuric acid (98%) for 2 h and transferred onto an Extrelut column(70–230 mesh; Merck; Darmstadt, Germany) and later eluted with200 mL of n-hexane. The eluate was concentrated by evaporation toapproximately 1mL and a further purificationwas obtained using a neu-tral alumina columns (Merck) activated at 400 °C before use. The alumi-na column was eluted first with n-hexane (9 mL) to remove interferingchemical contaminants, then with carbon tetrachloride (6 mL) to elutemono-ortho DL-PCBs, and finally with dichloromethane (7 mL) to elutePCDDs, PCDFs and non-ortho DL-PCB congeners (Vigh et al., 2013). Thecarbon tetrachloride and dichloromethane were collected, evaporatednear to dryness and reconstituted with 20 μL of 13C12-PCB-70 + 13C12-PCB-111 + 13C12-PCB-138 + 13C12-PCB-170 recovery standard and10 μL of 13C12-1,2,3,4-TCDD+ 13C12-1,2,3,7,8,9-HxCDD one, respectively.

The quantitative determinationwas performed by a TRACE GC 2000,ThermoFinnigan (ThermoFisher Scientific), coupledwith a high resolu-tion Mat 95 XP Mass Spectrometer, operating in the electron impactionization (EI+) mode at 48 eV with a resolution N10,000 and atemperature source of 280 °C.

The GCwas equipped with a BPX-DXN (60m× 0.20mm× 0.25 μm)(SGE, Analytical Science, Melbourne, Australia) capillary column and a

CTC PAL auto-sampler. 2 μL of each sample was injected in splitlessmode, with a splitless time of 1 min, a split flow of 100 mL min−1 at atemperature of 280 °C. Helium was used as carrier gas. The PCDD/Ftemperature program for analysis was 160 °C for 1 min, 2.5 °C/minincrease up to 300 °C, 300 °C maintained for 6 min. The PCB programwas 125 °C for 2 min, 7.5 °C/min increase up to 190 °C, 2.5 °C/minincrease up to 280 °C, 280 °C maintained for 7 min.

The ions monitored were M+ and M + 2 for tetra-chlorinatedcongeners and M + 2 and M + 4 for penta-, hexa-, hepta- and octa-chlorinated congeners. Peaks were accepted if the isotopic ratio waswithin 15% of the corresponding internal standard (IS) ratio.

A complete quantitative calibration was conducted annually, andrandomly selected single calibration points were checked before, inthe middle, and at the end of the analysis of each series of samples.The stability of the instrument was tested by quantifying if the relativeresponse factors and the coefficient of variation for each relativeresponse factor of a single standard was in the range of ±15%. PCDD/Fand PCB calibration standard complies with 1613 and 1668 US EPAmethods respectively (US EPA, 1994, 1999).

Limits of detection (LOD) were calculated individually for eachsample on the basis of a 3:1 signal-to-noise ratio. The LOD for PCDD/Fs

Fig. 2. Map of the undeveloped area of Faafu Atoll, showing the soil sampling locations. Arrows show the main directions of the winds. In the figure are shown 30-year mean percentfrequencywind direction 1964–2000 for April–November (black lines) and December–March (gray lines) based on data from theHulule climate station atMalé atoll (Kench and Brander,2006).

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varied from0.003 to 0.14 pg g−1 dw, and for the PCBs the correspondingvalues were 0.006–0.2 pg g−1 dw.

Limits of quantification (LOQ) were calculated for each sample onthe basis of a 10:1 signal-to-noise ratio. The LOQ for PCDD/Fs variedfrom 0.01 to 0.45 pg g−1 dw, and for the PCBs the corresponding valueswere 0.02–0.5 pg g−1 dw.

Blank spike duplicates and analytical blank and Certified ReferenceMaterial (CRM) CIL-EDF-5183 covering the whole analytical procedurewere replicated every 5 samples. Blank PCDD/F samples were belowthe detection limit and blank PCB samples gave negligible peaks. Therecovery of 13C12-labeled PCDD/Fs and DL-PCBs varied between 60and 95% and between 55 and 90% respectively. CMR served as qualitycontrol sample to validate the long determination process, resulting inan uncertainty between 5% and 25%, on the basis of the recovery ofthe IS and the coefficient of variation for concentrations on the certifiedmaterial. Our laboratory has regularly participated successfully ininterlaboratory comparison studies on PCDD/Fs and PCBs in biologicaland environmental samples, organized by the National Agency of theEuropean Standardization Committee (Unichim).

2.3. Data analysis

PCDD/F and DL-PCB concentrations were also expressed using themore recent toxic equivalent factors (TEFs) re-evaluated by the WorldHealth Organization (WHO) in 2005 (WHO2005-TEQ) (Van den Berget al., 2006). For the TEQ calculations, concentrations below the LODwere considered as half the limit (mediumbound determination level)(EC Commission Directive, 2002).

The relationship between PCDD/F and DL-PCB concentrations wastested using Pearson's correlation coefficient (r).

PCDD/F samples related to known emission sources to include in thePCA matrix were selected on the basis of knowledge of the potentialsources in the area. Data on these samples and those obtained in thepresent study were organized into a matrix with n objects (samples)and p variables (PCDD/F homologues). PCDD/F data were normalizedto the total concentration of PCDD/F by expressing each homologue asa percentage of the sum of the total PCDD/F before PCA. The Simca-P8.0 package (Umetrics AB, Umea, Sweden) was used for the analysis.

3. Results and discussion

3.1. PCDD/F and DL-PCB concentrations in soils

Table 1 summarizes PCDD/F and DL-PCB soil concentrations. Asshown PCDD/F soil concentrations in samples from the developed areaof the archipelago ranged from 1.09 to 49.3 pg WHO2005-TEQ g−1 dw(142 to 6820 pg g−1 dw as ∑PCDD/Fs) at Thilafushi (Island I) with amean of 23.0 ± 25.0 pg WHO2005-TEQ g−1 dw (2740 ± 3160 pgg−1 dw as∑PCDD/Fs). The range of concentrations at Vilinghi (IslandII) was from 0.06 to 3.01 pgWHO2005-TEQ g−1 dw (6 to 504 pg g−1 dwas ∑PCDD/Fs) with a mean of 1.64 ± 1.43 pg WHO2005-TEQ g−1 dw(176 ± 199 pg g−1 dw as∑PCDD/Fs). The range of concentrations atMalé (Island III) was from 0.17 to 0.94 pg WHO2005-TEQ g−1 dw (35to 142 pg g−1 dw as ∑PCDD/Fs) with a mean of 0.59 ± 0.33 pgWHO2005-TEQ g−1 dw (105 ± 44 pg g−1 dw as ∑PCDD/Fs). PCDD/Fsoil concentration in sample collected at the International Airport Island

Table 1PCDD/F and DL-PCB (pg g−1 dw) concentrations in soils.

Island SitePCDD/Fs PCB

WHO2005-TEQ ∑PCDD/Fs WHO2005-TEQ ∑DL-PCBs

Developed areaThilafushi (I) 1 2.23 341 0.03 156

2 1.09 142 0.52 8853 49.3 6820 2.44 2534 39.3 3670 3.69 311

Mean ± S.D. 23.0 ± 24.0 2740 ± 3160 1.67 ± 1.70 401 ± 329

Vilinghi (II) 5 2.33 160 0.02 156 2.67 181 0.02 127 0.06 6 0.01 18 3.01 504 1.61 2589 0.12 28 0.03 11

Mean ± S.D. 1.64 ± 1.43 176 ± 199 0.34 ± 0.71 59 ± 111

Malé (III) 10 0.92 142 0.05 3211 0.44 88 0.02 8712 0.17 35 0.04 8413 0.94 138 0.03 4714 0.50 120 0.06 110

Mean ± S.D. 0.59 ± 0.33 105 ± 44 0.04 ± 0.02 72 ± 33

InternationalAirport (IV)

15 0.20 65 0.20 562

Undeveloped areaResort

Filitheyo (V)16 15.8 1290 1.54 6017 0.24 90 0.01 218 0.04 2 0.01 219 0.03 1 0.01 3

Mean ± S.D. 4.02 ± 7.84 346 ± 631 0.39 ± 0.76 17 ± 29

Adanga (VI) 20 0.05 9 0.01 b0.20

Magoodhoo (VII) 21 0.40 9 0.01 1422 0.29 44 0.02 323 0.62 223 0.01 224 0.02 1 0.01 1925 0.02 3 0.01 1

Mean ± S.D. 0.27 ± 0.26 56 ± 95 0.01 ± 0.003 8 ± 8

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(Island IV) was 0.20 pg WHO2005-TEQ g−1 dw (65 pg g−1 dw as∑PCDD/Fs).

The PCDD/F concentrations were highest in samples from Island I,where wastes are burnt directly in the open air. The concentrationsshowed a clear decrease from here through Islands II and III, towardsIsland IV, a distance of 7 km. Island II, next to Island I, is almost exclu-sively affected by the incinerator, while in the other islands othersources could be present.

PCDD/F concentrationsmay be affected by local weather conditions,and particularly to the wind direction (Cleverly et al., 2007; Lee et al.,1999; Lohmann and Jones, 1998; Oh et al., 2006). In Maldives windsblow mainly towards northwest during the Hulhangu monsoon seasonand towards northeast during the Iruvai monsoon season (Kench andBrander, 2006). Generally higher PCDD/F concentrations were insamples collected downwind from the PCDD/F sources, with lowerconcentrations in samples collected upwind.

Island III is probably affected by the combustion from Island I, at sites10 and 13 in particular, which are oriented towards the incineratorisland. Concentrations can also be boosted by local activities such asvehicle emissions, diesel combustion emissions from the State ElectricCompany, diesel combustion and dust emission from constructionwork.

The sample from in Island IV had low concentrations, indicating littledirect impact of aircraft engines on the area,which support the idea thatthe combustion of aviation fuel does not lead to significant releases ofPCDD/Fs (UNEP, 2005).

In the undeveloped area of the archipelago, the PCDD/F soil concen-trations in samples from Resort Island (Island V), used entirely byforeign tourists, ranged from 0.03 to 15.8 WHO2005-TEQ g−1 dw (1 to

1290 pg g−1 dw as ∑PCDD/Fs). Potential emission source is wastecombustion from one small-scale facility on the island. The PCDD/Fsoil concentration was highest in sample from site 16, the closest tothe incinerator.

On the island inhabited by Maldivians (Island VII), PCDD/F soilconcentrations ranged from 0.02 to 0.62 WHO2005-TEQ g−1 dw (1 to223 pg g−1 dw as ∑PCDD/Fs). On this island wastes are burnt at lowtemperatures in typically uncontrolled sites, and consequently PCDD/Fs might be released into the environment (Xu et al., 2009).

The uninhabited island (Island VI) can be considered the unpollutedreference area in the archipelago, with a PCDD/F soil concentration of0.05 pg WHO2005-TEQ g−1 dw (9 pg g−1 dw as∑PCDD/Fs).

Currently the Maldives have no environmental guidelinesestablished for PCDD/Fs. Compared to Canadian guidelines, a conserva-tive example, PCDD/F concentrations in soils from sites 3, 4, and 16exceed the limit of 4 pg-TEQ g−1 (CCME, 2002). These concentrationsalso exceed soil quality guidelines adopted in several European coun-tries, including Germany (5 pg-TEQ g−1) (BUNR, 1992), Sweden(5 pg-TEQ g−1) (UNEP, 1999), Netherlands (1–10 pg-TEQ g−1)(UNEP, 1999) and UK (8 pg-TEQ g−1) (Environment Agency, 2009),but lower than the guidelines in Japan (1000 pg-TEQ g−1) (MOEJapan, Ministry of the Environment, 2003). PCDD/F soil concentrationsdetected at the other sites in the archipelago are at levels found inremote areas of Slovakia (0.38–0.71 pg-TEQ g−1) (Dömötörová et al.,2012), Australia (0.21–0.98 pg-TEQ g−1) (Müller et al., 2004) andreported by the U.S. EPA (U.S. EPA, 2007) where the mean PCDD/Fconcentrations ranged from 0.4 to 2.8 pg-TEQ g−1 in pristine areas ofNorth America and Canada, with no potential industrial emission.

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Fig. 3 shows the average PCDD/F contribution and standard devia-tion of each PCDD/F homologue group to the total PCDD/F concentrationof soil samples collected in the developed and undeveloped area.Octachlorodibenzo-p-dioxin (OCDD) accounted for 70% and 80% of thehomologues in samples from Islands IV and VI, these are typical “back-ground patterns” (Lohmann and Jones, 1998). The profiles of samplesfrom Islands II, III, V and VII showed a higher fraction of furans althoughOCDD remained dominant, while profile samples from Island I seemeddifferent from those collected in the other islands. The differences areprobably due more to the presence of close combustion sources thanlong-range transport of these pollutants, which usually producesenrichment of the higher chlorinated congeners.

The DL-PCB concentrations were markedly lower than PCDD/Fs.Nevertheless in this case too, the highest DL-PCB concentrations werehighest on Island I, from 0.03 to 3.69 pg WHO2005-TEQ g−1 dw (156 to885 pg g−1 dw as∑PCB). DL-PCB concentrations in soils from the de-veloped area ranged from 0.01 to 1.61 pg WHO2005-TEQ g−1 dw (1 to258 pg g−1 dw as ∑PCBs) on Island II, from 0.02 to 0.06 pgWHO2005-TEQ g−1 dw (32 to 110 pg g−1 dw as ∑PCBs) on Island IIIand 0.20 pg WHO2005-TEQ g−1 dw (562 pg g−1 dw as ∑PCBs) on Is-land IV.

In undeveloped areas of the archipelago DL-PCB concentrationsranged from 0.01 to 1.54 pg WHO2005-TEQ g−1 dw (2 to 60 pg g−1 dwas ∑PCBs) on Island V and from 0.01 to 0.02 pg WHO2005-TEQg−1 dw (1 to 19 pg g−1 as∑PCBs) on Island VII. All DL-PCB congenerconcentrations from Island VI were below the LOD.

The few DL-PCB data reported in the literature make comparisondifficult, but the concentrations found are comparable to those reportedby previous studies in background areas and in areas affected by devel-opment industrial and agricultural activities in Australia, with concen-trations ranging from LOD to 1.8 pg TEQ g−1 (Müller et al., 2004). Soilsamples collected in the vicinity of a ferrous metal producer and non-ferrous one in central South Africa showed concentrations ranging

Fig. 3. Average PCDD/F contribution and standard deviation of each PCDD/F homologuegroup to the total PCDD/F concentration of soil samples collected in the developed andundeveloped area.

from 0.04 to 4.4 pg WHO2005-TEQ g−1 dw (Nieuwoudt et al., 2009). Ina background area of Slovakia where no significant industrial sourcesare present DL-PCB concentrations in soils ranged 0.08 to 0.17 pgWHO1998-TEQ g−1 dw (Dömötörová et al., 2012).

Fig. 4 shows the average DL-PCB contribution and standarddeviation of each DL-PCB congener to the total DL-PCB concentrationof soil samples collected in the developed and undeveloped area. PCBcongener specific patterns across Islands I, III and V were dominatedby PCB-118, PCB-156, PCB-105 and PCB-77, and are similar to thosereported in previous studies (Dömötörová et al., 2012; Chi et al.,2007). PCB-118, PCB-156 and PCB-105 were also the most abundantcongener in samples from Islands II and VII, although a large variabilityof PCB-77 values was observed, while samples from Island IV weredominated by PCB 118 and PCB 105.

3.2. PCDD/F and DL-PCB source

PCDD/F and DL-PCB soil concentration expressed as WHO2005-TEQare well correlated (r = 0.89). The good correlation between PCDD/Fsand DL-PCBs indicates that most of the sites are exposed to the similarmixture of these pollutants originated from the same type of source.

Many studies have assessed the origin of PCDD/F contamination(Deister and Pommer, 1991; Jimenez et al., 1996; Schuhmacher et al.,1997, 1999, 2000, 2002; Domingo et al., 2000, 2001; Caserini et al.,2004; Park et al., 2004; Colombo et al., 2009, 2011, 2013). One methodfor identifying the source of PCDD/F contamination is to compare thelevels of PCDD/Fs at different distances. If PCDD/F levels tend to

Fig. 4. Average DL-PCB contribution and standard deviation of each DL-PCB congener tothe total DL-PCB concentration of soil samples collected in the developed and undevel-oped area.

Fig. 5. PCDD/F concentrations in soils at different distances from local waste incinerationfacilities.

Fig. 6. Principal component analysis (PCA) score plot on the PCDD/F homologue groups ofsoil samples collected.

Fig. 7. Principal component analysis (PCA) score plot on the PCDD/F homologue groups ofsoil samples collected on Islands I (○), II (Δ), III (◊), IV (+), V (□), VI (X) and VII (-), andsamples related to known emission sources: (♦) municipal solid waste incinerator(MSWI); (●) air from road traffic tunnel; (■) steel plant.

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decrease with the distance from a site, then the site can be considered asource (Oh et al., 2006). For the developed and the undeveloped areasPCDD/F concentrations decreasedwith distance from the local waste in-cineration facilities on Islands I and V (Fig. 5). This is in agreement withOh et al. (2006), which reported the trend of decreasing PCDD/F levelswith increasing the distance from a municipal waste incinerator(MSWI) as reliable, regardless of whether the source was dispersion offly ash or stack emission.

Moreover it is possible to indicate the origin of the contamination bycomparing the PCDD/F fingerprints of different sources with the pat-terns obtained in environmental samples (Colombo et al., 2009, 2013;Fattore et al., 1997, 2003). We therefore did a PCA to see which sourcewas responsible for PCDD/F in soil. Themethod investigates the originaldatamatrix using the smallest number of variableswhile preserving thegreatest possible amount of information (Colombo et al., 2009, 2011,2013). We used data from MSWI (Colombo et al., 2009) a steel plant(Colombo et al., 2009), air samples from a road traffic tunnel (Oehmeet al., 1991) and soil samples.

As the PCA loadingplot shows (Fig. 6), thefirst component takes intoaccount 35% of the variability of the dataset, and is mainly influencedpositively by PCDFs and negatively by PCDDs, distinguishing sampleson the basis of their PCDD/PCDF ratio. Profiles with higher PCDFs willbe located at higher values of the first component in the right part ofthe score plot, while profiles higher in PCDDs will be located at lowervalues of the first component in the left part of the score plot. The sec-ond component accounts for 30% of the variability of the data set andwas mainly influenced positively by high chlorinated PCDD/Fs such asheptachlorodibenzo-p-dioxin (HpCDD), heptachlorodibenzofurans(HpCDF), octachlorodibenzofuran (OCDF) and OCDD. Consequently

samples in which these homologues are dominant will be located athigher values of the second component in the upper part of the scoreplot, while samples with a higher content of low chlorinated PCDD/Fswill be located at lower values of the second component in the lowerpart of the score plot.

As the PCA score plot shows (Fig. 7), the samples related to emissionform three clusters: cluster A comprises samples of emissions from theMSWI (♦); cluster B includes samples of emissions from the steel plant(■) and cluster C, air samples from a road traffic tunnel (●).

Soil samples collected on Island I (○), the most polluted amongthose investigated, are near Cluster A (MSWI). The sample from site16 on Island V (□), where there is a small incinerator, and samplesfrom sites 22 and 24 on Island VII (-), where there is uncontrolledwaste burning are also in Cluster A. The remaining data are spread outon the left of the figure, and more farther from combustion sourceclusters as the proportion of higher chlorinated homologues increases,

506 A. Colombo et al. / Science of the Total Environment 497–498 (2014) 499–507

in particularly as theOCDD contribution raises. Other potential emissionsources may exist in particular in the developed area of the archipelago.More effective and imperative activities should be done to collect moreinformation about the sources and the distributions of the PCDD/Fs inthis tropical area.

4. Conclusions

The aim of the study was to provide a first survey to assess thecurrent status of PCDD/F and DL-PCB concentrations in Maldiviansoils, where there is no legislation regulating the acceptable level ofdioxin-like compounds in soils, and the management of possibleemission sources. The study was carried out in the developed area onMalé Atoll and in the undeveloped area on Faafu Atoll, thus takinginto account different levels of urbanization.

The range for PCDD/F soil concentrations was 0.06–49.3 pgWHO2005-TEQ g−1 dw and 0.02–15.8 pg WHO2005-TEQ g−1 dw in thedeveloped and undeveloped area respectively, while DL-PCB concentra-tionswere in the range of 0.01–3.69 pgWHO2005-TEQ g−1 dwand 0.01–1.54 pg WHO2005-TEQ g−1 dw in the developed and undeveloped arearespectively. The good relationship between the WHO2005-TEQ valuesfor PCDD/Fs and DL-PCBs indicates that most of the investigatedlocation soil samples are exposed to similar emission sources.

WHO2005-TEQ values for PCDD/Fs tend to decreasewith the distancefrom the sites located on Islands I and V, where wastes are burnt.Consequently these sites can be considered a source of PCDD/Fs.

PCA identifiedwaste incineration as the emission source responsiblefor the PCDD/F soil concentrations collected from Island I, and site 16 onIsland V, where the highest concentrationswere found.Waste incinera-tion seems to be responsible of pollution of soils collected from sites 22and 24, despite the low PCDD/F concentrations.

The baseline data presented here identify waste combustion as thesource emissions responsible for PCDD/F and DL-PCB soil pollution inthe most contaminated locations. The findings from this study willhelp change waste management policies in the Archipelago to reducethe release of POPs in this fragile tropical environment.

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