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

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Cairns, D.K., 1987. Seabirds as indicators of marine food supplies. Biological Oceanography 5, 261–271. Coe, J.M., Rogers, D.B., 1997. Marine Debris – Sources, Impacts and Solutions. Springer-Verlag, New York. Edwards, D.B., Mallory, M.L., Forbes, M.R., 2005. Variation in baseline haematology of northern fulmars (Fulmarus glacialis) in the Canadian high arctic. Comparative Clinical Pathology 14, 206–209. Frederiksen, M., Edwards, M., Richardson, A.J., Halliday, N.C., Wanless, S., 2006. From plankton to top predators: bottom-up control of a marine food web across four trophic levels. Journal of Animal Ecology 75, 1259–1268. Furness, R.W., 1985. Plastic particle pollution: accumulation by procellariiform seabirds in Scottish colonies. Marine Pollution Bulletin 16, 103–106. Furness, R.W., Camphuysen, C.J., 1997. Seabirds as monitors of the marine environment. ICES Journal of Marine Science 54, 726–737. Gaston, A.J., Mallory, M.L., Gilchrist, H.G., O’Donovan, K., 2006. Status, trends and attendance patterns of the Northern Fulmar Fulmarus glacialis in Nunavut, Canada. Arctic 59, 165–178. Hatch, S.A., 1989. Diurnal and seasonal patterns of colony attendance in the northern fulmar, Fulmarus glacialis, in Alaska. Canadian Field-Naturalist 103, 248–260. Hatch, S.A., Nettleship, D.N., 1998. Northern Fulmar (Fulmarus glacialis). In: Poole, A., Gill, F. (Eds.), The Birds of North America, No. 361. The Birds of North America Inc., Philadelphia, PA. Laist, D.W., 1997. Impacts of marine debris: entanglement of marine life in marine debris including a comprehensive list of species with entanglement and ingestion records. In: Coe, J.M., Rogers, D.B. (Eds.), Marine debris – Sources, Impacts and Solutions. Springer-Verlag, New York, pp. 99–143. Mallory, M.L., Forbes, M.R., 2005. Sex discrimination and measurement bias in northern fulmars (Fulmarus glacialis) from the Canadian arctic. Ardea 93, 25–36. Mallory, M.L., Forbes, M.R., 2007. Does sea-ice cover constrain the breeding schedules of high arctic northern fulmars? Condor 109, 894–906. Mallory, M.L., Robertson, G.J., Moenting, A., 2006a. Marine plastic debris from northern fulmars in Davis Strait, Nunavut, Canada. Marine Pollution Bulletin 52, 813–815.

Mallory, M.L., Braune, B.M., Forbes, M.R., 2006b. Breeding and contaminant concentrations in northern fulmars (Fulmarus glacialis L.) from the Canadian high arctic. Chemosphere 64, 1541–1544. Mallory, M.L., Forbes, M.R., Galloway, T.D., 2006c. Ectoparasites of northern fulmars Fulmarus glacialis (Procellariformes: Procellariidae) from the Canadian Arctic. Polar Biology 29, 353–357. Mallory, M.L., Akearok, J.A., Edwards, D.B., O’Donovan, K., Gilbert, C.D., 2008. Autumn migration and wintering of northern fulmars (Fulmarus glacialis) from the Canadian high Arctic. Polar Biology 31, 745–750. McLaren, P.L., 1982. Spring migration and habitat use by seabirds in eastern Lancaster Sound and western Baffin Bay. Arctic 35, 88–111. Moser, M.L., Lee, D.S., 1992. A fourteen-year survey of plastic ingestion by western North Atlantic seabirds. Colonial Waterbirds 15, 83–94. Robards, M.D., Piatt, J.F., Wohl, K.D., 1995. Increasing frequency of plastic particles ingested by seabirds in the subarctic North Pacific. Marine Pollution Bulletin 30, 151–157. Robards, M.D., Gould, P.J., Piatt, J.F., 1997. The highest global concentrations and increased abundance of oceanic plastic debris in the North Pacific: evidence from seabirds. In: Coe, J.M., Rogers, D.B. (Eds.), Marine debris – Sources, Impacts and Solutions. Springer-Verlag, New York, pp. 71–80. Ryan, P.G., 1987. The effects of ingested plastic on seabirds: correlations between plastic load and body condition. Environmental Pollution 46, 119–125. Ryan, P.G., Jackson, S., 1987. The lifespan of ingested plastic particles in seabirds and their effect on digestive efficiency. Marine Pollution Bulletin 18, 217–219. Salomonsen, F., 1965. The geographical variation of the fulmar (Fulmarus glacialis) and the zones of marine environment in the North Atlantic. Auk 82, 327– 355. Thompson, P.M., Ollason, J.C., 2001. Lagged effects of ocean climate change on fulmar population dynamics. Nature 413, 417–420. Van Franeker, J.A., 1985. Plastic ingestion in the North Atlantic fulmar. Marine Pollution Bulletin 16, 367–369. Van Franeker, J.A., Meijboom, A., 2007. Fulmar litter EcoQO monitoring in the Netherlands 1982–2005 in relation to EU Directive 2000/59/EC on port reception facilities. IMARES Texel report C019/07, Wageningen.

0025-326X/$ - see front matter Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2008.04.017

Presence and origin of polycyclic aromatic hydrocarbon in sediments of nine coastal 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, Italy CNR-IAMC, Calata di Porta di Massa, Naples, Italy c IMER, 246 Da Nang Street, Haiphong City, Viet Nam b

Several natural and anthropogenic processes can lead to the formation of polycyclic aromatic hydrocarbons (PAHs), a well known class of compounds, many of which with mutagenic and carcinogenic properties (Nielsen et al., 1995), that are regarded as priority pollutants 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 tar pitch and asphalt, (McCready et al., 2000). Another common anthropogenic source of PAHs is spillage of fossil fuels, both unrefined and refined products. PAHs also stem from natural combustion 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 environment are easily adsorbed onto settling particles and finally accumulate in sediments. This adsorption-settling process is continuous over time, therefore sediments can act as recorders of con* Corresponding author. Tel.: +39 051 6398864; fax: +39 051 6398940. E-mail address: [email protected] (S. Giuliani).

taminant inputs as well as of general environmental change over time (Kannan et al., 2005). It follows that the study of sediment records can provide information on levels, history and trends of pollutants in aquatic environments. Moreover, under particular erosive and resuspending conditions, sediments can represent a source for toxic substances in aquatic environments and may affect wildlife and humans via the food chain. In Vietnam, information on pollutant sources and distribution is very poor, despite the strong impact on the environment that may have been caused by both the Indochinese Wars and related events (1945–1975) as well as the recent economic development. Therefore, the major objective of the current study was to assess history of PAH contamination, relative importance of the sources, present trends, and potential toxicological significance in central Vietnam lagoons. These areas are valuable and diverse ecosystems, important tourist attractions and sites for fishing and aquaculture activities, and therefore represent key environments for the sustainable development of the Vietnamese economy. The nine lagoons (Fig. 1) are situated in central Vietnam between 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

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

210

Pb (210Pbex)

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Thuan. They are diverse in typology, scale, shape, size, stability of inlets, water features and in geological and geographical distribution (Cu, 1995). Their surface area ranges from 2.8 to 216 km2 and determines their rating into four categories: very small (Dam Nai, DN), small (Lang Co, LC; Nuoc Man, NM; Nuoc Ngot, NN and O Loan, OL), medium (Truong Giang, TG and Cam Ranh, CR) and large (Tam Giang-Cau Hai, TG-CH and Thi Nai, TN). It is worth noticing that the TG-CH Lagoon is the largest in Southeast Asia and one of the largest in the world (Cu, 1995). In this environment, water features are much dependent on seasonal and spatial changes in salinity that increases significantly during the dry season and follows a decreasing trend from the inlets towards the river mouths and the innermost part of the lagoons thus causing the water stratification (Cu, 1999). The environmental quality of the lagoons has been deeply affected over time by anthropogenic pollution, as shown by high concentration of oil, nitrate and coliforms in water (Dieu, 2006; Thom, 2006). This evident environmental stress may be mainly related to the highly populated areas surrounding the lagoons. It follows that the assessment of sediment quality with respect to chemical contaminants has to be considered one of the most important indicator of the overall health of the system. Two sediment cores (02 and 10) were collected from the TG-CH Lagoon in December 2002. The LC Lagoon was sampled in June 2004 and the other seven minor lagoons in June 2005 (Fig. 1). In all campaigns, a manual piston corer was used to retrieve the sediment cores that were immediately extruded and subsampled at intervals 1–4 cm thick. Sediment sections were kept frozen until the arrival in the lab and then freeze-dried and homogenised before the analysis. Porosities were calculated according to Berner (1971), assuming a particle density of 2.5 g cm3. Grain size analyses were carried out by wet sieving, to separate sands, after a pre-treatment with H2O2. Silt and clay fractions were determined with a X-ray Micrometric SediGraph. 210 Pb activities were determined through the extraction and alpha counting of the daughter 210Po, considered to be in secular equilibrium with the father. The radiotracer was extracted with hot HNO3 and H2O2 then taken to dryness, treated with conc. HCl to eliminate nitrates, and dissolved with 1.5 N HCl. After iron reduction with ascorbic acid, polonium was spontaneously plated on silver discs overnight at room temperature. Alpha decays were counted by a silicon surficial barrier detector connected to a multichannel analyser. 209Po was used as an internal standard to account for extraction and counting efficiencies. 137Cs determinations were obtained by gamma counting of dry samples in standard vessels of suitable geometries. Efficiencies were calculated for each counting geometry, using a series of standards obtained by spiking old sediment with a known amount of a multi-peak standard solution (QCY58). Analytical accuracy was checked using a Certified Reference Material (IAEA 300 Sediment). For PAH analysis a 2 g sediment fraction was spiked with extraction standards (six deuterated PAHs) including: acenaphthene d-10; fluoranthene d-10; phenantrene d-10; benzo(a)anthracene d-12; benzo(a)pyrene d-12; dibenzo(a,h)anthracene d-12. Samples were then subjected to accelerate solvent extraction (DIONEX ASE 200) using a mixture of hexane/acetone (80:20 v/v). The extraction cells were heated to 113 °C until the pressure reached 1500 psi. The extracts, concentrated and re-dissolved with 0.5 ml of cicloexane, were purified by column chromatography using solid phase extraction cartridges containing 2 g of silica and eluted first with 10 ml of n-hexane and then with 20 ml of a cicloexane:acetone (70:30) mixture. Then they were concentrated and re-dissolved with 400 ll of a two deuterated PAHs (acenaphthylene d-8 and chrysene d-12) solution, for the qualitative analyses, and finally analysed by GC–MS with DB-5 capillary column (95% dimetil-5%

diphenilpolisiloxane). The injection volume was 1 lL in splitless mode and the operative temperatures were 280 °C at the ion source and 250 °C at the inlet, with He as carrier gas at 1.2 ml min1. The mass spectrometer was operated at an EI of 70 eV and in selective ion monitoring (SIM) mode. Laboratory quality control procedures included analyses of blanks, reference material and spiked samples. The reference material used for quality control was BCR 535. Instrument stability and response was checked using NIST standard solutions. Recoveries ranged between 94 and 107% for the different congeners. Accuracy, estimated on multiple analysis of the reference material, was better than ±10% for each congener. Precision was always better than 10% with a detection limit of 1 ng g1. Eighteen PAH congeners were determined in all samples, 16 of which were the priority pollutants recommended by US EPA (1993): naphthalene (Na), acenaphthylene (Ac), acenaphthene (Ace), fluorene (F), phenanthrene (Phe), anthracene (An), fluoranthene (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). Perylene is thought to be produced also by in situ diagenesis of marine and terrestrial organic matter, whereas benzo(a)pyrene is a product of incomplete combustion at temperatures between 300 and 600 °C (Silliman et al., 2001; Lima et al., 2003). Porosity and sand content profiles are shown in Fig. 1. They are inversely correlated in most cases, defining the same depositional processes. Sites 02 and 10 of the TG-CH Lagoon are described in detail by Frignani et al. (2007), therefore they are not represented. In synthesis, these measurements account for a major environmental change in the TG-CH Lagoon at some point in the past that was ascribed to the onset of higher hydrodynamic processes, with the removal of fine sediments. In more recent times the water dynamics decreased again as recorded by the porosity increase and the sand content decrease close to the sediment–water interface (Frignani et al., 2007). A similar pattern is observed for the LC Lagoon (Fig. 1), the closest to TG-CH, thus suggesting the influence of similar processes operating at a local scale. Sub-surface sand content maxima, followed by a more recent significant decrease were observed in most of the minor lagoons, i.e. NM, NN, OL and CR (Fig. 1). On the contrary, cores collected from TG, DN and TN lagoons present the coarsest composition at the surface. In particular, TN shows a dramatic increase of sand content from 20 cm depth upward, accompanied by the sudden decrease of porosity, due to the strong reinforcement of hydrodynamic processes. On a whole, fine sediments characterise the lagoons of LC, NM, OL and CR, whereas coarse fractions are predominant at DN. An intermediate situation can be observed for TG, while TN and NN are much variable (Fig. 1). In this study 137Cs activities found in most lagoon sediments were similar or lower than detection limits and, as a consequence, provided inventories much lower than the mean value of 643 Bq m2 reported for the soils of the Vietnam territory (Hien et al., 2002). In addition, 137Cs activities in the TG-CH Lagoon sediments are much lower than those measured by Quang et al. (2004) in surficial soils close to the area (2.80–3.78 Bq kg1). A plausible explanation for the ‘‘missing radionuclide” is that the input of 137 Cs from the mainland, already low, is very diluted by the huge amount of sediment delivered to the lagoon by rivers, and a fraction is probably lost to the sea with the finest particles. Due to the absence of a useful 137Cs signal, inferences on sediment chronologies can be obtained only from 210Pb activity-depth profiles. However, especially for the TG-CH Lagoon, the application of the most common conceptual models to the calculation of rates and dates (Robbins, 1978; Appleby and Oldfield, 1978; McCaffrey and

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Baseline / Marine Pollution Bulletin 56 (2008) 1486–1512 Table 1 Excess 210Pb inventories (R210Pbex), average sediment accretion rates (SARs) and average mass accumulation rates (MARs) for the studied lagoons in Central Vietnam

TG-CH 02 TG-CH 10 LC TG NM NN TN OL CR DN

R210Pbex (Bq cm2)

SARs (cm y1)

MARs (g cm2 y1)

2.1 1.8 2.9 0.71 1.0 0.67 0.61 0.34 0.21 0.15

0.60 0.31 0.17 0.28 0.19 0.14 0.14 0.09 0.18 0.10

0.56 0.31 0.12 0.36 0.23 0.16 0.15 0.06 0.14 0.13

Thomson, 1980) is not straightforward, since 210Pb concentration changed over time, mainly due to variations of sediment accumulation. In practice, it can be hypothesised that most of the model assumptions, which refer to the inputs of particles and/or radiotracer onto the sediment, are not met in these environments. The dating of cores 02 and 10 from TG-CH was discussed by Frignani et al. (2007). As a first approximation, we can assume that the depth of ca. 31 cm in core 10, where 210Pb reaches the background value (that supported by in situ decay of 226Ra), corresponds to 100 years. This provides a mean sediment accumulation rate of 0.31 cm y1 (Table 1). According to core correlation, based on the major shifts in grain size composition (Frignani et al, 2007) the mean sediment accumulation rate (SAR) at 02 is set to ca. 0.60 cm y1 (Table 1). Since neither physical mixing nor bioturbation were taken into account, these apparent average rates could be considered as upper limits, valid only for the year of collection. The other cores provide apparent SARs ranging from 0.10 to 0.28 cm y1 (Table 1, Fig. 1), calculated using the above mentioned

assumptions. These values are rather low and are probably the results of strong hydrodynamic processes and an efficient exchange with the sea. 210Pbex values measured in the LC Lagoon are definitely higher than in the other sites, up to 25 times when compared to the lowest surficial measurement in the DN Lagoon (Fig. 1). Even the TG-CH Lagoon is characterized by high 210Pb values at surface, 180 and 280 Bq kg1 for cores 02 and 10, respectively (Frignani et al., 2007). The 210Pb enrichment observed in this area is probably ascribable to natural causes, limited to the zone where mineralised zircon sands (Kušnír, 2000), that contain large amounts of uranium-238 and its decay products, were observed. Total concentrations of the US-EPA Clear Water Act 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) vary from 95 to 465 ng g1 (Table 2). These are the congeners for which ambient water quality criteria 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 g1. In particular, surficial samples span the interval 112–628 ng g1, whereas the downcore maximum values are comprised between 103 and 697 ng g1. Fig. 2 shows PAH concentration–depth profiles of the US-EPA priority congeners, plus B[e]Py and Pe, in cores from all studied Vietnamese lagoons, with congener abundances at some selected depths. Contaminant distributions are also plotted against estimated years of deposition, calculated from 210Pb derived SARs (Table 1). In six cases (02, LC, TG, NM, TN and DN) concentrations are still presently increasing, whereas in the others a very recent decrease was recorded. Most cores present one (02, NN, OL and DN) or two (10 and CR) subsurficial peaks that reach values higher or comparable to surficial ones. According to the estimated chronologies, the deepest peaks at 10 and CR correspond to the early

Table 2 List 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 g1); RTEQs, in ng TEQ g1 and calculated multiplying congener concentrations with total toxic equivalents (TEFs) relative to B[a]Py (Schleicher et al., 2004); Flu/Flu+Py, B[a]An/B[a]An+Ch and Phe/An ratios

TG-CH 02

TG-CH 10

LC

TG

NM

NN

TN

OL

CR

DN

a b

Max Min Surf Max Min Surf Max Min Surf Max Min Surf Max Min Surf Max Min Surf Max Min Surf Max Min Surf Max Min Surf Max Min Surf

R PAHsa

EPA PAHsb

R TEQs

Flu/ Flu+Py

B[a]An/ B[a]An+Ch

Phe/An

697 309 628 502 175 373 381 128 381 208 127 262 278 221 264 321 106 118 159 103 159 271 155 212 421 112 112 359 113 162

465 212 465 418 133 331 337 112 337 199 115 246 262 208 238 283 95 109 145 95 145 247 136 190 393 105 105 315 103 151

98 22 27 57 8 34 44 7 44 14 4 14 34 7 34 27 4 11 14 2 14 18 7 18 27 4 4 42 6 10

0.49 0.11 0.46 0.45 0.035 0.41 0.63 0.55 0.55 0.58 0.27 0.58 0.61 0.27 0.51 0.59 0.29 0.59 0.58 0.30 0.58 0.55 0.18 0.55 0.54 0.26 0.49 0.58 0.41 0.46

0.60 0.43 0.50 0.57 0.43 0.57 0.45 0.30 0.44 0.43 0.23 0.32 0.47 0.26 0.47 0.43 0.33 0.38 0.46 0.26 0.31 0.44 0.34 0.41 0.41 0.24 0.38 0.42 0.29 0.29

4.2 0.89 0.89 2.0 0.37 0.71 5.8 0.61 0.61 7.7 3.2 5.3 9.2 1.4 1.4 10 2.3 3.1 16 3.7 8.1 14 2.0 2.0 13 1.5 1.5 5.9 1.5 3.2

Sum of congeners (18) analysed in all cores. 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).

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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 all studied 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 and B[g,h,i]Pe) are also presented for selected depths.

1900s. The same can be observed for the single peak at OL and, even if somewhat earlier in time (mid-19th century), at DN. The most recent sub-surficial peaks (02, 10, NN and CR) are contemporary 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 depth distribution of PAHs in all the cores seem not to be influenced by sediment characteristics, due to the absence of any significant correlation with the grain size composition. As for congener distributions, phenanthrene is the most important contributor for the majority of minor lagoons (P15%), where 2 and 3 rings PAHs are definitely dominant, showing some differences among levels (Fig. 2). 02, 10 and LC are an exception to the above described situation (Fig. 2). Specifically, 02 presents an absolute predominance of perylene in most analysed layers (between 19 and 25%) with an increasing importance of other heavy congeners (B[a]Py, B[e]Py) in the deepest levels. The situation for 10 is more complicated: the surficial level shows high concentrations of Py and Flu, the layer 8–10 shows a predominance of Pe and An, then the layer 23–26 shows the predominance of the B[b]Flu and other high weight congeners (5–6 rings); Phe, together with Na and F, becomes predominant only in the deepest layer of this core. 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 and Phe) increase in the deepest sections. Spatially, average RPAHs show a North-South decreasing trend from 02 to TN, with the exception of NM, then concentrations increase at OL and CR and decrease again at DN (Fig. 3b). This is true for both PAH sums, whether all 18 analysed congeners (Total, Fig. 3b) or just the 16 priority ones (US-EPA, Fig. 3b) are taken into account. The relatively high concentrations in samples from the TG-CH Lagoon (265–469 ng g1, cores 02 and 10) account for the proximity 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 sediments can be evaluated through the comparison of measured concentrations with internationally accepted guidelines that define threshold values above which adverse effects can be observed. Throughout the years many different guidelines have been published and the threshold effect level (TEL), below which we can assume any effect to rarely occur (Burton, 2002), appears the most restrictive one. Its value (870 ng g1) is always higher than the sum of congeners (Table 2) and the individual PAHs present very few values (generally relative to low weight congeners, Ace in particular) higher than their respective TELs. In addition, available toxic equivalency factors (TEFs) can be used to quantify toxic equivalents relative to B[a]Py. Toxic equivalents (TEQs) were then calculated 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; Schleicher et al., 2004) and summed together. Total TEQs (RTEQs, Table 2) varied from 2 to 98 ngTEQ g1. Maximum values were observed at the northernmost locations (02, 10 and LC) indicating the predominance of local sources with respect to a widespread distributed contamination. As expected, in cores LC, TG, NM, TN, OL and DN, RTEQ increasing trends characterise recent sediment layers. To provide a comprehensive view of the contamination level by PAHs measured in the Vietnamese lagoon, a comparison was made between these sites and others located all over the world, based on average surficial values (first 2 or 5 cm) calculated with respect to sediment dry weights. The data reported in Fig. 3a were separated into three major groups, to account for different anthropogenic pressures and environmental settings: Harbours and polluted Areas (Simpson et al., 1996; Baumard et al., 1998; McCready et al., 2000; Wang et al., 2001; Basheer et al., 2003; Bertolotto et al., 2003; Frignani et al., 2003), coastal areas (Witt, 1995; Baumard et al., 1998; Khim et al., 1999; Soclo et al., 2000; Yamashita et al., 2000; Yang, 2000; Notar et al., 2001; Charlesworth et al.,

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

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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 all over 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.

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 Vietnamese lagoons are among the lowest, from 2 to 3 orders of magnitude lower than values measured in the highly polluted areas,

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Complete Linkage Euclidean distances 90

80

70

Linkage Distance

60

50

40

30

20

10

HUE2(26-28) HUE2(20-23) HUE2(14-16) TN(18-20) TG(35-38) OL(14-16) TG(14-16) NM(14-16) TN(6-8) NM(6-8) OL(35-38) NM(35-38) CR(35-38) CR(6-8) OL(6-8) CR(23-26) CR(2-4) HUE2(66-70) HUE2(41-44) HUE2(47-50) HUE2(8-10) HUE10(38-41) HUE2(0-2) HUE10(8-10) HUE2(32-35) HUE10(23-26) HUE10(12-14) HUE10(2-4) HUE10(0-2) HUE10(18-20) LC(0-1) OL(0-1) NM(0-1) DN(23-26) LC(3-5) NN(2-4) DN(14-16) LC(36-39) LC(24-27) LC(15-17) LC(11-13) LC(7-9) TG(23-26) TG(0-1) DN(6-8) HUE10(47-50) TN(26-29) OL(23-26) NM(23-26) NN(23-26) DN(35-38) TN(0-1) DN(2-4) NN(14-16) NN(6-8) DN(0-1) TG(6-8) NN(0-1) TN(12-14) NN(35-38) TN(2-4) CR(14-16) CR(0-1)

0

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

but even lower than in many coastal areas and lagoon sites. Therefore, PAHs seem not to be of major concern for these environments. Anthropogenic PAHs are introduced to coastal areas via urban runoff (Hoffman et al., 1984; Benlahcen et al., 1997; McCready et al., 2000), industrial processes (Simpson et al., 1996), vehicle exhausts and spillage of fossil fuels (Pettersen et al., 1997; Wang et al., 1999a). Other congeners are produced naturally by wood and fossil fuel incomplete combustion. Their presence in the environment is therefore ubiquitous and can be found even in pre-industrial sediments. Generally, in marine sediments, PAH congeners belong to three categories, relative to different origins: petrogenic, pyrogenic and biogenic. The association of the observed PAH assemblages to one of these categories is based upon the predominance of different PAHs congeners and/or diagnostic ratios (Bence et al., 1996; Boehm et al., 1998; Page et al., 1999; Yamashita et al., 2000; Dahle et al., 2006). For example, high molecular 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 of low molecular weight (2–3 rings) and alkylated congeners. This is the case of the majority of minor lagoons, where 2 and 3 rings PAHs are definitely dominant, as already discussed in the section regarding PAH concentrations, depth profiles and trends. Diagnostic ratios for selected PAH groups, or pairs of the same molecular mass, are also frequently used to provide information about PAH origin and sources. This approach is based on: (i) the different thermodynamic stability of congeners, (ii) the characteristic composition of different PAH sources, and (iii) the changes in PAH relative abundances between source and sediment (e.g., Yunker et al., 1999; Kannan et al., 2005). A first insight on different contributions by combustion processes and petrogenic sources can be made by comparing LMW and HMW congener abundances, provided that low values of LMW/HMW ratios suggest a prevailing influence of combustion processes. Further information can be often obtained from the proportion between less stable congeners

and more stable ones (Budzinski et al., 1997). For example, Flu and Py, both with a mass of 202, have the greatest range in stability and hence are good as indicators of thermodynamic vs. kinetic (e.g. petroleum vs. combustion) effects. Generally, Flu/Py ratios above 1 indicate a pyrogenic origin, whereas values below 1 are typical of petroleum hydrocarbons (Khim et al., 1999). Else, a Flu/Flu+Py ratio of 0.50 is usually defined as the petroleum/combustion transition point (Yunker and MacDonald, 2003). The Flu/Flu+Py ratio is below 0.50 for most unburned petroleum polluted samples (but also for gasoline, diesel, fuel oil and crude oil combustion and emissions 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, they can be the result of both low and high temperature processes. The couple Phe and An is also used to distinguish between the two different combustion sources (Budzinski et al., 1997; Soclo et al., 2000), the Phe/An ratio being temperature dependant and with decreasing values with the increase of PAH production temperature. Therefore, high temperature processes (420–540 °C) can be characterized by low (4–10) Phe/An ratios and vice versa (Dahle et al., 2006). Finally, a B[a]An/B[a]An+Ch over 0.50 indicates combustion while a ratio below 0.50 has been attributed to low temperature 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 evaluate the relative contribution of different PAH contamination sources. In general, we observed a good agreement between LMW/HMW and Flu/Py results in all minor lagoons (Fig. 3c), defining a predominance of petroleum hydrocarbons with respect to combustion originated congeners. Available information on human activities, that can be related to petrogenic PAH pollution in these areas, 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 Nai port) whereas the other small lagoons are generally crossed by small and bigger boats just for fishing or housing in case of storms.

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Aquaculture is increasingly developing in most lagoons (TG-CH, TG, TN, NM, OL and DN among the others) and might produce a detectable effect in the next future. Nevertheless, the influence of combustion sources is increasing in recent layers. A peculiar situation is observed in the LC Lagoon where both ratios account for high temperature combustion processes as predominant PAH sources to the environment. The prevalence of petroleum originated PAHs is confirmed by Flu/Flu+Py ratios lower than 0.50 in most samples, with the exception of LC and recent layers of minor lagoon cores (Table 2). A much more complex situation is observed in the TG-CH Lagoon, where LMW/HMW and Flu/Py ratios lead to opposite conclusions (Fig. 3c): LMW/HMW suggests a combustion dominated setting, whereas a general petrogenic origin is accounted by Flu/ Py. Truthfully, different sources implying both pyrogenic and petrogenic inputs are impacting the TG-CH Lagoon environment. Nevertheless, the Flu/Flu+Py seems to indicate a petrogenic origin in both cores (Table 2). Additional information is provided by the B[a]An/B[a]An+Ch ratio, which resulted to be less than 0.50 and seems to account for low temperature diagenesis in most samples, with the exception of TG-CH (Table 2). Finally, Phe/An ratios account for high temperature combustion processes as major source for pyrogenic PAHs for all cores, with very few exceptions. It should be noted that, in petrogenic dominated environments (as most of the minor lagoons and TG-CH) this result involves only a small fraction of PAHs, whereas it can be fully applied to the Lang Co Lagoon, where combustion was clearly identified as the major source. In order to highlight the similarities among the different PAH assemblages found in the lagoon sediments, a simple cluster analysis was performed, based on the Euclidean distance calculated over percent amounts of each measured congener. The results are shown in Fig. 4 and account for a great dissimilarity between the three consecutive levels from 14 to 28 cm depth in core 02 (TG-CH Lagoon) and all the others. Interestingly, these levels provide a considerable subsurface concentration peak, their LMW/ HMW ratios are the lowest for the entire data set (0.14, 0.25 and 0.12 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 1950 and 1975, a strong PAH input, mainly composed by combustion generated congeners, reached the northern sector of the TG-CH Lagoon, probably vehicled by the O Lau River, the closest to the 17th parallel and the DMZ (DeMilitarised Zone). The origin of such PAH assemblage might be explained by forest fires that were artificially set in the area to facilitate military operations. No such great differences are observed among the other lagoons and in the southern sector of the TG-CH Lagoon. On the contrary, LC presents the most homogeneous PAH assemblage throughout the entire sedimentary record (Fig. 4), strongly linked to a pyrogenic source. Acknowledgements Funds for this work were provided, in the framework of a bilateral project, by the Italian Ministry of Foreign Affairs (MAE), the Vietnamese Ministry of Science and Technology (MOST) and the Italian scientific institutions involved in the research. We are indebted to G. Capodaglio for his help in sample collection, subsampling and handling. This is contribution No. 1601 from the Istituto di Scienze Marine, Bologna (Italy). References Appleby, P.G., Oldfield, F., 1978. The calculation of lead-210 dates assuming a constant rate of supply of unsupported210 Pb to the sediment. Catena 5, 1–8.

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