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1504 Baseline / Marine Pollution Bulletin 56 (2008) 1486–1512

Presence and origin of polycyclic aromatic hydrocarbon in sediments of ninecoastal lagoons in central Vietnam

Silvia Giuliani a,*, Mario Sprovieri b, Mauro Frignani a, Nguyen Huu Cu c, Cristian Mugnai a,Luca Giorgio Bellucci a, Sonia Albertazzi a, Stefania Romano a, Maria Luisa Feo b, Ennio Marsella b,Dang Hoai Nhon c

a CNR-ISMAR, Consiglio Nazionale delle Ricerche, Istituto di Scienze Marine, Sede di Bologna, Via Gobetti 101, 40129 Bologna, Italyb CNR-IAMC, Calata di Porta di Massa, Naples, Italyc IMER, 246 Da Nang Street, Haiphong City, Viet Nam

Several natural and anthropogenic processes can lead to the for-mation of polycyclic aromatic hydrocarbons (PAHs), a well knownclass of compounds, many of which with mutagenic and carcino-genic properties (Nielsen et al., 1995), that are regarded as prioritypollutants by the US Environmental Protection Agency (US EPA,1993). Anthropogenic sources include combustion of fossil fuels,coal gasification and liquification processes, petroleum cracking,waste incineration and production of: coke, carbon black, coal tarpitch and asphalt, (McCready et al., 2000). Another commonanthropogenic source of PAHs is spillage of fossil fuels, both unre-fined and refined products. PAHs also stem from natural combus-tion sources such as forest fires, and certain compounds(perylene and retene) are thought to be diagenetically produced(Wakeham et al., 1980).

Because of their hydrophobic nature, PAHs in the aquatic envi-ronment are easily adsorbed onto settling particles and finallyaccumulate in sediments. This adsorption-settling process is con-tinuous over time, therefore sediments can act as recorders of con-

* Corresponding author. Tel.: +39 051 6398864; fax: +39 051 6398940.E-mail address: silvia.giuliani@bo.ismar.cnr.it (S. Giuliani).

taminant inputs as well as of general environmental change overtime (Kannan et al., 2005). It follows that the study of sediment re-cords can provide information on levels, history and trends of pol-lutants in aquatic environments. Moreover, under particularerosive and resuspending conditions, sediments can represent asource for toxic substances in aquatic environments and may affectwildlife and humans via the food chain.

In Vietnam, information on pollutant sources and distribution isvery poor, despite the strong impact on the environment that mayhave been caused by both the Indochinese Wars and related events(1945–1975) as well as the recent economic development. There-fore, the major objective of the current study was to assess historyof PAH contamination, relative importance of the sources, presenttrends, and potential toxicological significance in central Vietnamlagoons. These areas are valuable and diverse ecosystems, impor-tant tourist attractions and sites for fishing and aquaculture activ-ities, and therefore represent key environments for the sustainabledevelopment of the Vietnamese economy.

The nine lagoons (Fig. 1) are situated in central Vietnam be-tween 11�N and 16�N in the provinces of Thua Thien-Hue, Da Nang,Quang Nam, Quang Ngai, Binh Dinh, Phu Yen, Khanh Hoa and Ninh

Fig. 1. Locations of central Vietnam coastal lagoons with sampling dates, coordinates of sampling sites and core lengths. Porosity, sand content and excess 210Pb (210Pbex)depth profiles are also shown for the eight minor lagoons: LC, TG, NM, NN, TN, OL, CR and DN.

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Thuan. They are diverse in typology, scale, shape, size, stability ofinlets, water features and in geological and geographical distribu-tion (Cu, 1995). Their surface area ranges from 2.8 to 216 km2

and determines their rating into four categories: very small (DamNai, DN), small (Lang Co, LC; Nuoc Man, NM; Nuoc Ngot, NN andO Loan, OL), medium (Truong Giang, TG and Cam Ranh, CR) andlarge (Tam Giang-Cau Hai, TG-CH and Thi Nai, TN). It is worthnoticing that the TG-CH Lagoon is the largest in Southeast Asiaand one of the largest in the world (Cu, 1995). In this environment,water features are much dependent on seasonal and spatialchanges in salinity that increases significantly during the dry sea-son and follows a decreasing trend from the inlets towards the riv-er mouths and the innermost part of the lagoons thus causing thewater stratification (Cu, 1999).

The environmental quality of the lagoons has been deeply af-fected over time by anthropogenic pollution, as shown by highconcentration of oil, nitrate and coliforms in water (Dieu, 2006;Thom, 2006). This evident environmental stress may be mainly re-lated to the highly populated areas surrounding the lagoons. It fol-lows that the assessment of sediment quality with respect tochemical contaminants has to be considered one of the mostimportant indicator of the overall health of the system.

Two sediment cores (02 and 10) were collected from the TG-CHLagoon in December 2002. The LC Lagoon was sampled in June2004 and the other seven minor lagoons in June 2005 (Fig. 1). Inall campaigns, a manual piston corer was used to retrieve the sed-iment cores that were immediately extruded and subsampled atintervals 1–4 cm thick. Sediment sections were kept frozen untilthe arrival in the lab and then freeze-dried and homogenised be-fore the analysis.

Porosities were calculated according to Berner (1971), assuminga particle density of 2.5 g cm�3. Grain size analyses were carriedout by wet sieving, to separate sands, after a pre-treatment withH2O2. Silt and clay fractions were determined with a X-ray Micro-metric SediGraph.

210Pb activities were determined through the extraction and al-pha counting of the daughter 210Po, considered to be in secularequilibrium with the father. The radiotracer was extracted withhot HNO3 and H2O2 then taken to dryness, treated with conc. HClto eliminate nitrates, and dissolved with 1.5 N HCl. After ironreduction with ascorbic acid, polonium was spontaneously platedon silver discs overnight at room temperature. Alpha decays werecounted by a silicon surficial barrier detector connected to amultichannel analyser. 209Po was used as an internal standard toaccount for extraction and counting efficiencies. 137Cs determina-tions were obtained by gamma counting of dry samples in stan-dard vessels of suitable geometries. Efficiencies were calculatedfor each counting geometry, using a series of standards obtainedby spiking old sediment with a known amount of a multi-peakstandard solution (QCY58). Analytical accuracy was checked usinga Certified Reference Material (IAEA 300 Sediment).

For PAH analysis a 2 g sediment fraction was spiked withextraction standards (six deuterated PAHs) including: acenaph-thene d-10; fluoranthene d-10; phenantrene d-10; benzo(a)anthra-cene d-12; benzo(a)pyrene d-12; dibenzo(a,h)anthracene d-12.Samples were then subjected to accelerate solvent extraction (DIO-NEX ASE 200) using a mixture of hexane/acetone (80:20 v/v). Theextraction cells were heated to 113 �C until the pressure reached1500 psi. The extracts, concentrated and re-dissolved with 0.5 mlof cicloexane, were purified by column chromatography using solidphase extraction cartridges containing 2 g of silica and eluted firstwith 10 ml of n-hexane and then with 20 ml of a cicloexane:acetone(70:30) mixture. Then they were concentrated and re-dissolvedwith 400 ll of a two deuterated PAHs (acenaphthylene d-8 andchrysene d-12) solution, for the qualitative analyses, and finallyanalysed by GC–MS with DB-5 capillary column (95% dimetil-5%

diphenilpolisiloxane). The injection volume was 1 lL in splitlessmode and the operative temperatures were 280 �C at the ion sourceand 250 �C at the inlet, with He as carrier gas at 1.2 ml min�1. Themass spectrometer was operated at an EI of 70 eV and in selectiveion monitoring (SIM) mode.

Laboratory quality control procedures included analyses ofblanks, reference material and spiked samples. The reference mate-rial used for quality control was BCR 535. Instrument stability andresponse was checked using NIST standard solutions. Recoveriesranged between 94 and 107% for the different congeners. Accuracy,estimated on multiple analysis of the reference material, was bet-ter than ±10% for each congener. Precision was always better than10% with a detection limit of 1 ng g�1.

Eighteen PAH congeners were determined in all samples, 16 ofwhich were the priority pollutants recommended by US EPA(1993): naphthalene (Na), acenaphthylene (Ac), acenaphthene(Ace), fluorene (F), phenanthrene (Phe), anthracene (An), fluo-ranthene (Flu), pyrene (Py), benzo(a)anthracene (B[a]An), chrysene(Ch), benzo(b)fluoranthene (B[b]Flu), benzo(k+j)fluoranthene(B[k+j]Flu), benzo(e)pyrene (B[e]Py), indeno(1,2,3-cd)pyrene (I),dibenzo(a,h)anthracene (D[a,h]An), benzo-(g,h,i)perylene(B[g,h,i]Pe), plus perylene (Pe) and benzo(a)pyrene (B[a]Py). Pery-lene is thought to be produced also by in situ diagenesis of marineand terrestrial organic matter, whereas benzo(a)pyrene is a prod-uct of incomplete combustion at temperatures between 300 and600 �C (Silliman et al., 2001; Lima et al., 2003).

Porosity and sand content profiles are shown in Fig. 1. They areinversely correlated in most cases, defining the same depositionalprocesses. Sites 02 and 10 of the TG-CH Lagoon are described in de-tail by Frignani et al. (2007), therefore they are not represented. Insynthesis, these measurements account for a major environmentalchange in the TG-CH Lagoon at some point in the past that was as-cribed to the onset of higher hydrodynamic processes, with the re-moval of fine sediments. In more recent times the water dynamicsdecreased again as recorded by the porosity increase and the sandcontent decrease close to the sediment–water interface (Frignaniet al., 2007). A similar pattern is observed for the LC Lagoon(Fig. 1), the closest to TG-CH, thus suggesting the influence of sim-ilar processes operating at a local scale.

Sub-surface sand content maxima, followed by a more recentsignificant decrease were observed in most of the minor lagoons,i.e. NM, NN, OL and CR (Fig. 1). On the contrary, cores collectedfrom TG, DN and TN lagoons present the coarsest composition atthe surface. In particular, TN shows a dramatic increase of sandcontent from 20 cm depth upward, accompanied by the sudden de-crease of porosity, due to the strong reinforcement of hydrody-namic processes. On a whole, fine sediments characterise thelagoons of LC, NM, OL and CR, whereas coarse fractions are pre-dominant at DN. An intermediate situation can be observed forTG, while TN and NN are much variable (Fig. 1).

In this study 137Cs activities found in most lagoon sedimentswere similar or lower than detection limits and, as a consequence,provided inventories much lower than the mean value of643 Bq m�2 reported for the soils of the Vietnam territory (Hienet al., 2002). In addition, 137Cs activities in the TG-CH Lagoon sed-iments are much lower than those measured by Quang et al. (2004)in surficial soils close to the area (2.80–3.78 Bq kg�1). A plausibleexplanation for the ‘‘missing radionuclide” is that the input of137Cs from the mainland, already low, is very diluted by the hugeamount of sediment delivered to the lagoon by rivers, and a frac-tion is probably lost to the sea with the finest particles. Due tothe absence of a useful 137Cs signal, inferences on sediment chro-nologies can be obtained only from 210Pb activity-depth profiles.However, especially for the TG-CH Lagoon, the application of themost common conceptual models to the calculation of rates anddates (Robbins, 1978; Appleby and Oldfield, 1978; McCaffrey and

assumptions. These values are rather low and are probably the re-sults of strong hydrodynamic processes and an efficient exchangewith the sea. 210Pbex values measured in the LC Lagoon are defi-nitely higher than in the other sites, up to 25 times when comparedto the lowest surficial measurement in the DN Lagoon (Fig. 1). Eventhe TG-CH Lagoon is characterized by high 210Pb values at surface,180 and 280 Bq kg�1 for cores 02 and 10, respectively (Frignaniet al., 2007). The 210Pb enrichment observed in this area is probablyascribable to natural causes, limited to the zone where mineralisedzircon sands (Kušnír, 2000), that contain large amounts of ura-nium-238 and its decay products, were observed.

Total concentrations of the US-EPA Clear Water Act 16 priorityPAHs (Na, Ac, Ace, F, Phe, An, Flu, Py, B[a]An, Ch, B[b]Flu, B[k+j]Flu,B[a]Py, I, B[g,h,i]Pe and D[a,h]An) vary from 95 to 465 ng g�1 (Table2). These are the congeners for which ambient water quality crite-ria must be established and effluent limitations need to be fixed(US EPA, 1993). When all measured congeners are considered(18), the range slightly increases to 103–697 ng g�1. In particular,surficial samples span the interval 112–628 ng g�1, whereas thedowncore maximum values are comprised between 103 and697 ng g�1.

Fig. 2 shows PAH concentration–depth profiles of the US-EPApriority congeners, plus B[e]Py and Pe, in cores from all studiedVietnamese lagoons, with congener abundances at some selecteddepths. Contaminant distributions are also plotted against esti-mated years of deposition, calculated from 210Pb derived SARs (Ta-ble 1). In six cases (02, LC, TG, NM, TN and DN) concentrations arestill presently increasing, whereas in the others a very recent de-crease was recorded. Most cores present one (02, NN, OL andDN) or two (10 and CR) subsurficial peaks that reach values higheror comparable to surficial ones. According to the estimated chro-nologies, the deepest peaks at 10 and CR correspond to the early

Table 1Excess 210Pb inventories (R210Pbex), average sediment accretion rates (SARs) andaverage mass accumulation rates (MARs) for the studied lagoons in Central Vietnam

R210Pbex (Bq cm�2) SARs (cm y�1) MARs (g cm�2 y�1)

TG-CH 02 2.1 0.60 0.56TG-CH 10 1.8 0.31 0.31LC 2.9 0.17 0.12TG 0.71 0.28 0.36NM 1.0 0.19 0.23NN 0.67 0.14 0.16TN 0.61 0.14 0.15OL 0.34 0.09 0.06CR 0.21 0.18 0.14DN 0.15 0.10 0.13

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Thomson, 1980) is not straightforward, since 210Pb concentrationchanged over time, mainly due to variations of sediment accumu-lation. In practice, it can be hypothesised that most of the modelassumptions, which refer to the inputs of particles and/or radio-tracer onto the sediment, are not met in these environments. Thedating of cores 02 and 10 from TG-CH was discussed by Frignaniet al. (2007). As a first approximation, we can assume that thedepth of ca. 31 cm in core 10, where 210Pb reaches the backgroundvalue (that supported by in situ decay of 226Ra), corresponds to 100years. This provides a mean sediment accumulation rate of0.31 cm y�1 (Table 1). According to core correlation, based on themajor shifts in grain size composition (Frignani et al, 2007) themean sediment accumulation rate (SAR) at 02 is set to ca.0.60 cm y�1 (Table 1). Since neither physical mixing nor bioturba-tion were taken into account, these apparent average rates couldbe considered as upper limits, valid only for the year of collection.

The other cores provide apparent SARs ranging from 0.10 to0.28 cm y�1 (Table 1, Fig. 1), calculated using the above mentioned

Table 2List of maximum, minimum and surficial values for the following PAH parameters, measured in all analysed lagoons of Central Vietnam: total (R) and priority (EPA)concentrations (values are in ng g�1); RTEQs, in ng TEQ g�1 and calculated multiplying congener concentrations with total toxic equivalents (TEFs) relative to B[a]Py (Schleicheret al., 2004); Flu/Flu+Py, B[a]An/B[a]An+Ch and Phe/An ratios

R PAHsa EPA PAHsb R TEQs Flu/ Flu+Py B[a]An/ B[a]An+Ch Phe/An

TG-CH 02 Max 697 465 98 0.49 0.60 4.2Min 309 212 22 0.11 0.43 0.89Surf 628 465 27 0.46 0.50 0.89

TG-CH 10 Max 502 418 57 0.45 0.57 2.0Min 175 133 8 0.035 0.43 0.37Surf 373 331 34 0.41 0.57 0.71

LC Max 381 337 44 0.63 0.45 5.8Min 128 112 7 0.55 0.30 0.61Surf 381 337 44 0.55 0.44 0.61

TG Max 208 199 14 0.58 0.43 7.7Min 127 115 4 0.27 0.23 3.2Surf 262 246 14 0.58 0.32 5.3

NM Max 278 262 34 0.61 0.47 9.2Min 221 208 7 0.27 0.26 1.4Surf 264 238 34 0.51 0.47 1.4

NN Max 321 283 27 0.59 0.43 10Min 106 95 4 0.29 0.33 2.3Surf 118 109 11 0.59 0.38 3.1

TN Max 159 145 14 0.58 0.46 16Min 103 95 2 0.30 0.26 3.7Surf 159 145 14 0.58 0.31 8.1

OL Max 271 247 18 0.55 0.44 14Min 155 136 7 0.18 0.34 2.0Surf 212 190 18 0.55 0.41 2.0

CR Max 421 393 27 0.54 0.41 13Min 112 105 4 0.26 0.24 1.5Surf 112 105 4 0.49 0.38 1.5

DN Max 359 315 42 0.58 0.42 5.9Min 113 103 6 0.41 0.29 1.5Surf 162 151 10 0.46 0.29 3.2

a Sum of congeners (18) analysed in all cores.b Sum of the 16 priority PAHs (Na, Ac, Ace, F, Phe, An, Flu, Py, B[a]An, Ch, B[b]Flu, B[k+j]Flu, B[a]Py, I, B[g,h,i]Pe and D[a,h]An) as defined by US EPA (1993).

1900s. The same can be observed for the single peak at OL and,even if somewhat earlier in time (mid-19th century), at DN. Themost recent sub-surficial peaks (02, 10, NN and CR) are contempo-rary to the period 1970–1990.

Despite some similarities with porosity and, consequently,water content (LC, TG, NM, TN and CR, see Figs 1 and 2), the depthdistribution of PAHs in all the cores seem not to be influenced bysediment characteristics, due to the absence of any significant cor-relation with the grain size composition.

As for congener distributions, phenanthrene is the most impor-tant contributor for the majority of minor lagoons (P15%), where 2and 3 rings PAHs are definitely dominant, showing some differ-ences among levels (Fig. 2). 02, 10 and LC are an exception to theabove described situation (Fig. 2). Specifically, 02 presents an abso-lute predominance of perylene in most analysed layers (between19 and 25%) with an increasing importance of other heavy congen-ers (B[a]Py, B[e]Py) in the deepest levels. The situation for 10 ismore complicated: the surficial level shows high concentrationsof Py and Flu, the layer 8–10 shows a predominance of Pe andAn, then the layer 23–26 shows the predominance of the B[b]Fluand other high weight congeners (5–6 rings); Phe, together withNa and F, becomes predominant only in the deepest layer of thiscore. As for LC, two high molecular weight (HMW) congeners(B[b]Flu and B[g,h,i]Pe) are predominant in surficial samples,whereas three low molecular weight (LMW) PAHs (Na, F andPhe) increase in the deepest sections.

Spatially, average RPAHs show a North-South decreasing trendfrom 02 to TN, with the exception of NM, then concentrations in-crease at OL and CR and decrease again at DN (Fig. 3b). This is truefor both PAH sums, whether all 18 analysed congeners (Total,Fig. 3b) or just the 16 priority ones (US-EPA, Fig. 3b) are taken intoaccount. The relatively high concentrations in samples from theTG-CH Lagoon (265–469 ng g�1, cores 02 and 10) account for theproximity of larger urban settlements and productive activities(including boat traffic) to this system (Nga, 2006), whereas the

other sites are located in less industrialised areas, with agriculture,fishery and cattle breeding as the main economic activities.

The potential threats to biota of Vietnamese lagoons sedimentscan be evaluated through the comparison of measured concentra-tions with internationally accepted guidelines that define thresh-old values above which adverse effects can be observed.Throughout the years many different guidelines have been pub-lished and the threshold effect level (TEL), below which we can as-sume any effect to rarely occur (Burton, 2002), appears the mostrestrictive one. Its value (870 ng g�1) is always higher than thesum of congeners (Table 2) and the individual PAHs present veryfew values (generally relative to low weight congeners, Ace in par-ticular) higher than their respective TELs. In addition, availabletoxic equivalency factors (TEFs) can be used to quantify toxicequivalents relative to B[a]Py. Toxic equivalents (TEQs) were thencalculated for Ac, Ace, An, B[a]An, B[b]Flu, B[k]Flu, B[g,h,i]Pe,B[a]Py, Ch, D[a,h]An, Flu, F, I, Phe and Py (US EPA, 1993; Schleicheret al., 2004) and summed together. Total TEQs (RTEQs, Table 2)varied from 2 to 98 ngTEQ g�1. Maximum values were observedat the northernmost locations (02, 10 and LC) indicating the pre-dominance of local sources with respect to a widespread distrib-uted contamination. As expected, in cores LC, TG, NM, TN, OL andDN, RTEQ increasing trends characterise recent sediment layers.

To provide a comprehensive view of the contamination level byPAHs measured in the Vietnamese lagoon, a comparison was madebetween these sites and others located all over the world, based onaverage surficial values (first 2 or 5 cm) calculated with respect tosediment dry weights. The data reported in Fig. 3a were separatedinto three major groups, to account for different anthropogenicpressures and environmental settings: Harbours and pollutedAreas (Simpson et al., 1996; Baumard et al., 1998; McCreadyet al., 2000; Wang et al., 2001; Basheer et al., 2003; Bertolottoet al., 2003; Frignani et al., 2003), coastal areas (Witt, 1995; Baum-ard et al., 1998; Khim et al., 1999; Soclo et al., 2000; Yamashitaet al., 2000; Yang, 2000; Notar et al., 2001; Charlesworth et al.,

Fig. 2. Concentration profiles of PAHs versus depth and estimated year of deposition, as sum of the 16 priority congeners (US EPA, 1993), plus B[e]Py and Pe, in cores from allstudied Vietnamese lagoons. Some congener distributions (as%, in the order: Na, Ac, Ace, F, Phe, An, Flu, Py, B[a]An, Ch, B[b]Flu, B[k + j]Flu, B[a]Py, B[e]Py, Pe, I, D[a,h]An andB[g,h,i]Pe) are also presented for selected depths.

1508 Baseline / Marine Pollution Bulletin 56 (2008) 1486–1512

2002; Dahle et al., 2003; Savinov et al., 2003; Grabe and Barron,2004; Oros anf Ross; Boonyatumanond et al., 2006) and lagoons(Soclo et al., 2000; Frignani et al., 2003; Secco et al., 2005; Culotta

et al., 2006). PAH concentrations in surficial sediments of the Viet-namese lagoons are among the lowest, from 2 to 3 orders of mag-nitude lower than values measured in the highly polluted areas,

Fig. 3. (a) Comparison between PAH values in surficial sediments of the Vietnamese lagoons (far right, indicated by the arrow) and those in other sites of interest located allover the world (see text); (b) Average total PAHs for all studied Vietnamese lagoons; (c) Pattern of LMW/HMW and Flu/Py diagnostic indices estimated on analyzed sample.

Baseline / Marine Pollution Bulletin 56 (2008) 1486–1512 1509

but even lower than in many coastal areas and lagoon sites. There-fore, PAHs seem not to be of major concern for these environments.

Anthropogenic PAHs are introduced to coastal areas via urbanrunoff (Hoffman et al., 1984; Benlahcen et al., 1997; McCreadyet al., 2000), industrial processes (Simpson et al., 1996), vehicle ex-hausts and spillage of fossil fuels (Pettersen et al., 1997; Wanget al., 1999a). Other congeners are produced naturally by woodand fossil fuel incomplete combustion. Their presence in theenvironment is therefore ubiquitous and can be found even inpre-industrial sediments. Generally, in marine sediments, PAHcongeners belong to three categories, relative to different origins:petrogenic, pyrogenic and biogenic. The association of the ob-served PAH assemblages to one of these categories is based uponthe predominance of different PAHs congeners and/or diagnosticratios (Bence et al., 1996; Boehm et al., 1998; Page et al., 1999;Yamashita et al., 2000; Dahle et al., 2006). For example, highmolecular weight PAHs (i.e. Flu, Py, B[a]An, Ch, B[a]Py, and Pe)originate from combustion processes (e.g., Wang et al., 1999b)whereas petrogenic PAHs are characterized by a predominance oflow molecular weight (2–3 rings) and alkylated congeners. Thisis the case of the majority of minor lagoons, where 2 and 3 ringsPAHs are definitely dominant, as already discussed in the sectionregarding PAH concentrations, depth profiles and trends.

Diagnostic ratios for selected PAH groups, or pairs of the samemolecular mass, are also frequently used to provide informationabout PAH origin and sources. This approach is based on: (i) thedifferent thermodynamic stability of congeners, (ii) the character-istic composition of different PAH sources, and (iii) the changes inPAH relative abundances between source and sediment (e.g., Yun-ker et al., 1999; Kannan et al., 2005). A first insight on differentcontributions by combustion processes and petrogenic sourcescan be made by comparing LMW and HMW congener abundances,provided that low values of LMW/HMW ratios suggest a prevailinginfluence of combustion processes. Further information can be of-ten obtained from the proportion between less stable congeners

and more stable ones (Budzinski et al., 1997). For example, Fluand Py, both with a mass of 202, have the greatest range in stabilityand hence are good as indicators of thermodynamic vs. kinetic (e.g.petroleum vs. combustion) effects. Generally, Flu/Py ratios above 1indicate a pyrogenic origin, whereas values below 1 are typical ofpetroleum hydrocarbons (Khim et al., 1999). Else, a Flu/Flu+Py ra-tio of 0.50 is usually defined as the petroleum/combustion transi-tion point (Yunker and MacDonald, 2003). The Flu/Flu+Py ratio isbelow 0.50 for most unburned petroleum polluted samples (butalso for gasoline, diesel, fuel oil and crude oil combustion andemissions from cars and diesel trucks) and above 0.50 in kerosene,grass, most coal and wood combustion samples and creosote.

Moreover, when considering just PAHs of pyrogenic origin, theycan be the result of both low and high temperature processes. Thecouple Phe and An is also used to distinguish between the two dif-ferent combustion sources (Budzinski et al., 1997; Soclo et al.,2000), the Phe/An ratio being temperature dependant and withdecreasing values with the increase of PAH production tempera-ture. Therefore, high temperature processes (420–540 �C) can becharacterized by low (4–10) Phe/An ratios and vice versa (Dahleet al., 2006). Finally, a B[a]An/B[a]An+Ch over 0.50 indicates com-bustion while a ratio below 0.50 has been attributed to low tem-perature diagenesis (Soclo et al., 2000).

In the present case, all above defined ratios (LMW/HMW, Flu/Py, Flu/Flu+Py, Phe/An, B[a]An/B[a]An+Ch) were calculated to eval-uate the relative contribution of different PAH contaminationsources. In general, we observed a good agreement betweenLMW/HMW and Flu/Py results in all minor lagoons (Fig. 3c), defin-ing a predominance of petroleum hydrocarbons with respect tocombustion originated congeners. Available information on humanactivities, that can be related to petrogenic PAH pollution in theseareas, are scarce and account for the presence of several ports in TG(Ky Ha and Sa Ky ports) and TN (Quy Nhon oil port and Thi Naiport) whereas the other small lagoons are generally crossed bysmall and bigger boats just for fishing or housing in case of storms.

Complete LinkageEuclidean distances

Link

age

Dis

tanc

e

0

10

20

30

40

50

60

70

80

90H

UE2

(26-

28)

HU

E2(2

0-23

)H

UE2

(14-

16)

TN(1

8-20

)TG

(35-

38)

OL(

14-1

6)TG

(14-

16)

NM

(14-

16)

TN(6

-8)

NM

(6-8

)O

L(35

-38)

NM

(35-

38)

CR

(35-

38)

CR

(6-8

)O

L(6-

8)C

R(2

3-26

)C

R(2

-4)

HU

E2(6

6-70

)H

UE2

(41-

44)

HU

E2(4

7-50

)H

UE2

(8-1

0)H

UE1

0(38

-41)

HU

E2(0

-2)

HU

E10(

8-10

)H

UE2

(32-

35)

HU

E10(

23-2

6)H

UE1

0(12

-14)

HU

E10(

2-4)

HU

E10(

0-2)

HU

E10(

18-2

0)LC

(0-1

)O

L(0-

1)N

M(0

-1)

DN

(23-

26)

LC(3

-5)

NN

(2-4

)D

N(1

4-16

)LC

(36-

39)

LC(2

4-27

)LC

(15-

17)

LC(1

1-13

)LC

(7-9

)TG

(23-

26)

TG(0

-1)

DN

(6-8

)H

UE1

0(47

-50)

TN(2

6-29

)O

L(23

-26)

NM

(23-

26)

NN

(23-

26)

DN

(35-

38)

TN(0

-1)

DN

(2-4

)N

N(1

4-16

)N

N(6

-8)

DN

(0-1

)TG

(6-8

)N

N(0

-1)

TN(1

2-14

)N

N(3

5-38

)TN

(2-4

)C

R(1

4-16

)C

R(0

-1)

Fig. 4. PAH cluster analysis for all measured layers, based on the Euclidean distance calculated over percent amounts of each measured congener.

1510 Baseline / Marine Pollution Bulletin 56 (2008) 1486–1512

Aquaculture is increasingly developing in most lagoons (TG-CH,TG, TN, NM, OL and DN among the others) and might produce adetectable effect in the next future. Nevertheless, the influence ofcombustion sources is increasing in recent layers.

A peculiar situation is observed in the LC Lagoon where both ra-tios account for high temperature combustion processes as pre-dominant PAH sources to the environment. The prevalence ofpetroleum originated PAHs is confirmed by Flu/Flu+Py ratios lowerthan 0.50 in most samples, with the exception of LC and recent lay-ers of minor lagoon cores (Table 2).

A much more complex situation is observed in the TG-CH La-goon, where LMW/HMW and Flu/Py ratios lead to opposite conclu-sions (Fig. 3c): LMW/HMW suggests a combustion dominatedsetting, whereas a general petrogenic origin is accounted by Flu/Py. Truthfully, different sources implying both pyrogenic andpetrogenic inputs are impacting the TG-CH Lagoon environment.Nevertheless, the Flu/Flu+Py seems to indicate a petrogenic originin both cores (Table 2). Additional information is provided by theB[a]An/B[a]An+Ch ratio, which resulted to be less than 0.50 andseems to account for low temperature diagenesis in most samples,with the exception of TG-CH (Table 2). Finally, Phe/An ratios ac-count for high temperature combustion processes as major sourcefor pyrogenic PAHs for all cores, with very few exceptions. It shouldbe noted that, in petrogenic dominated environments (as most ofthe minor lagoons and TG-CH) this result involves only a smallfraction of PAHs, whereas it can be fully applied to the Lang Co La-goon, where combustion was clearly identified as the major source.

In order to highlight the similarities among the different PAHassemblages found in the lagoon sediments, a simple cluster anal-ysis was performed, based on the Euclidean distance calculatedover percent amounts of each measured congener. The resultsare shown in Fig. 4 and account for a great dissimilarity betweenthe three consecutive levels from 14 to 28 cm depth in core 02(TG-CH Lagoon) and all the others. Interestingly, these levels pro-vide a considerable subsurface concentration peak, their LMW/HMW ratios are the lowest for the entire data set (0.14, 0.25 and0.12 for levels 14–16, 20–23 and 26–28, respectively, Fig. 3c),and they seem contemporary to the Indochinese War period(1950–1975, Fig. 2). What follows, then, is that between 1950and 1975, a strong PAH input, mainly composed by combustiongenerated congeners, reached the northern sector of the TG-CHLagoon, probably vehicled by the O Lau River, the closest to the17th parallel and the DMZ (DeMilitarised Zone). The origin of suchPAH assemblage might be explained by forest fires that were arti-ficially set in the area to facilitate military operations. No suchgreat differences are observed among the other lagoons and inthe southern sector of the TG-CH Lagoon. On the contrary, LC pre-sents the most homogeneous PAH assemblage throughout the en-tire sedimentary record (Fig. 4), strongly linked to a pyrogenicsource.

Acknowledgements

Funds for this work were provided, in the framework of a bilat-eral project, by the Italian Ministry of Foreign Affairs (MAE), theVietnamese Ministry of Science and Technology (MOST) and theItalian scientific institutions involved in the research. We are in-debted to G. Capodaglio for his help in sample collection, subsam-pling and handling. This is contribution No. 1601 from the Istitutodi Scienze Marine, Bologna (Italy).

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