PCBs in Central Vietnam coastal lagoons: Levels and trends in dynamic environments (original) (raw)

Abstract

PCBs were analysed in surficial sediments and selected sediment cores collected between 2002 and 2008 in Central Vietnam coastal lagoons. The aim was to determine contamination levels and trends, and to evaluate the effects of anthropogenic pressures and natural events. Samples were mostly fine-grained with low total PCB concentrations (0.367-44.7 lg kg À1 ). Atmospheric transport and post depositional processes modify to some degree the fingerprint of PCB inputs to the environment favouring the predominance of 3, 4 and 5 chlorinated congeners. The similarity of congener distributions in contemporary surficial samples also suggests the presence of a unique source over the entire study area, probably connected to mobilisation and long range transports from land-based stocks. The removal of consistent sediment layers is hypothesised based on repeated samplings of the same area. Natural meteorological events (such as typhoons) are suspected to be responsible for these sediment losses.

Figures (8)

Fig. 1. Sample locations in Central Vietnam coastal lagoons.  210Pb activities were determined through acid extraction and alpha counting of the daughter 7!°Po spontaneously deposited onto silver disks. ?°°Po was used as an internal standard to account for methodological and counting efficiencies. 1*”Cs determinations were obtained by gamma counting of dry samples in standard  vessels of suitable geometries. Radiotracer analyses were described in detail by Bellucci et al. (2007).  Sampling locations in Central Vietnam coastal lagoons are shown in Fig. 1. Sediment cores were sampled multiple times from 2002 to

Fig. 1. Sample locations in Central Vietnam coastal lagoons. 210Pb activities were determined through acid extraction and alpha counting of the daughter 7!°Po spontaneously deposited onto silver disks. ?°°Po was used as an internal standard to account for methodological and counting efficiencies. 1*”Cs determinations were obtained by gamma counting of dry samples in standard vessels of suitable geometries. Radiotracer analyses were described in detail by Bellucci et al. (2007). Sampling locations in Central Vietnam coastal lagoons are shown in Fig. 1. Sediment cores were sampled multiple times from 2002 to

.d. = Not detected. * Grain sizes are calculated considering only the fraction <2 mm. > The sediment is entirely sandy; a silt plus clay value of 1% was assumed for normalisation.  © Samples from OL, CR and DN contain 21.5%, 6.3% and 6.3% of shell fragments and small gravels, respectively; normalising with respect to the real content of fines would give PCB concentrations of 5.52, 1

.d. = Not detected. * Grain sizes are calculated considering only the fraction <2 mm. > The sediment is entirely sandy; a silt plus clay value of 1% was assumed for normalisation. © Samples from OL, CR and DN contain 21.5%, 6.3% and 6.3% of shell fragments and small gravels, respectively; normalising with respect to the real content of fines would give PCB concentrations of 5.52, 1

Fig. 2. Depth distributions of porosity, contents of sand and fines, 7!°Pb and total PCBs in sediment cores collected from TG-CH, LC, TN and OL coastal lagoons during different sampling campaigns (2002-2008). PCB homologue patterns at selected depths are also shown.  Core sample porosity ranges from 0.51 (TG-CH 10 in 2004) to 0.78 (OL in 2005) and is generally higher at surface, follows a decreasing trend in the intermediate layers, then remains quite  constant down to the core bottom. TG-CH 02 in 2007 and TN in 2005 differ slightly from this pattern, in that they have deep sedi- ment values that are higher than surface ones. In addition, porosi- ties of TN in 2008 constantly increase with depth and the value measured at surface is among the lowest. Despite these limited

Fig. 2. Depth distributions of porosity, contents of sand and fines, 7!°Pb and total PCBs in sediment cores collected from TG-CH, LC, TN and OL coastal lagoons during different sampling campaigns (2002-2008). PCB homologue patterns at selected depths are also shown. Core sample porosity ranges from 0.51 (TG-CH 10 in 2004) to 0.78 (OL in 2005) and is generally higher at surface, follows a decreasing trend in the intermediate layers, then remains quite constant down to the core bottom. TG-CH 02 in 2007 and TN in 2005 differ slightly from this pattern, in that they have deep sedi- ment values that are higher than surface ones. In addition, porosi- ties of TN in 2008 constantly increase with depth and the value measured at surface is among the lowest. Despite these limited

Fig. 3. Worldwide distribution of average PCB levels in surficial sediments compared to Central Vietnam coastal lagoons. Values are grouped into three major sections: contaminated sites (Van Bavel et al., 1995; Camacho-Ibar and McEvoy, 1996; Sundberg et al., 2005), Coastal and industrial areas (Tolosa et al., 1997; Khim et al., 1999; Laane et al., 1999; Miiller et al., 1999; Nhan et al., 1999, 2001; Pettersen et al., 1999; Frignani et al., 2001; Lee et al., 2001; Ma et al., 2001; Santschi et al., 2001; Barakat et al., 2002; Fillman et al., 2002; Bertolotto et al., 2004; Frignani et al., 2004; Saponizhnikova et al., 2004; Colombo et al., 2005; Kuzyk et al., 2005; Denton et al., 2006; Hung et al., 2006) and Lagoons (Frignani et al., 2001, 2004; Konat and Kowalewska, 2001; Menone et al., 2001; Moret et al., 2001; Fillman et al., 2002; Secco et al., 2005). Maximum and minimum range bar for Central Vietnam lagoons is also shown. International sediment quality guidelines are indicated as horizontal continuous (ERM) or dotted (ERL) lines.

Fig. 3. Worldwide distribution of average PCB levels in surficial sediments compared to Central Vietnam coastal lagoons. Values are grouped into three major sections: contaminated sites (Van Bavel et al., 1995; Camacho-Ibar and McEvoy, 1996; Sundberg et al., 2005), Coastal and industrial areas (Tolosa et al., 1997; Khim et al., 1999; Laane et al., 1999; Miiller et al., 1999; Nhan et al., 1999, 2001; Pettersen et al., 1999; Frignani et al., 2001; Lee et al., 2001; Ma et al., 2001; Santschi et al., 2001; Barakat et al., 2002; Fillman et al., 2002; Bertolotto et al., 2004; Frignani et al., 2004; Saponizhnikova et al., 2004; Colombo et al., 2005; Kuzyk et al., 2005; Denton et al., 2006; Hung et al., 2006) and Lagoons (Frignani et al., 2001, 2004; Konat and Kowalewska, 2001; Menone et al., 2001; Moret et al., 2001; Fillman et al., 2002; Secco et al., 2005). Maximum and minimum range bar for Central Vietnam lagoons is also shown. International sediment quality guidelines are indicated as horizontal continuous (ERM) or dotted (ERL) lines.

Fig. 4. Cluster analysis (Ward’s method as aggregative clustering, using the Euclidean distance) comparing the composition of PCBs in surficial samples from Central Vietnam coastal lagoons with the most common Aroclor commercial mixtures. Main clusters (a-d) are indicated.  In order to evaluate the origin of the PCB patterns found in sur- ficial samples from all sampling campaigns, the homologue com- position was compared with that of the principal commercial mixtures. Aroclor 1016, 1242, 1254, 1260 and 1268 were consid- ered, and their compositions were normalized with respect to the list of congeners found in samples. Autoscaled data were processed by a cluster analysis (Ward’s method as aggregative

Fig. 4. Cluster analysis (Ward’s method as aggregative clustering, using the Euclidean distance) comparing the composition of PCBs in surficial samples from Central Vietnam coastal lagoons with the most common Aroclor commercial mixtures. Main clusters (a-d) are indicated. In order to evaluate the origin of the PCB patterns found in sur- ficial samples from all sampling campaigns, the homologue com- position was compared with that of the principal commercial mixtures. Aroclor 1016, 1242, 1254, 1260 and 1268 were consid- ered, and their compositions were normalized with respect to the list of congeners found in samples. Autoscaled data were processed by a cluster analysis (Ward’s method as aggregative

Fig. 5. 7!°Pb activity-depth profiles from repeated samplings in the TG-CH, LC, TN and OL lagoons. Two subsequent campaigns are compared (2002-2004 and 2004-2007 for TG-CH 02 and TG-CH-10, 2004-2008 for LC and 2005-2008 for TN and OL), the values of the older ones being corrected for *!°Pb natural decay. Depths relative to one sample  are shifted downward (as specified in the relative legend) to provide a satisfying superposition of the two profiles. Grey areas identify the hypothesized thicknesses of removed sediments.  carried out in the nearby Phuong Mai peninsula in the framework of the Nhon Hoi Economic Zone (NEZ) development plan. Indeed, the NEZ is a new urban centre (120 km? wide) east of Quy Nhon City in the Binh Dinh province where the TN Lagoon is located. It was completed in 2010 and includes residential areas, an industrial park (14 km?), a deep water port, and a resort (BDEZ, 2010). The NEZ is connected to Quy Nhon’s city centre by the Thi Nai Bridge that was under construction in 2005, just when the TN core was  inant composition. Additionally, this sample shows the highest PCB concentration of the entire dataset and is the only one in the sed- iment core composed entirely of sand (Table 1; Fig. 2). The pres- ence of a relatively high PCB concentration in a completely sandy sediment (not suited to interact with and store contaminants) is very unusual. These evidences, together with the contemporary observation of a different congener distribution, account for the ef- fect of external point sources, most likely linked to the activities

Fig. 5. 7!°Pb activity-depth profiles from repeated samplings in the TG-CH, LC, TN and OL lagoons. Two subsequent campaigns are compared (2002-2004 and 2004-2007 for TG-CH 02 and TG-CH-10, 2004-2008 for LC and 2005-2008 for TN and OL), the values of the older ones being corrected for *!°Pb natural decay. Depths relative to one sample are shifted downward (as specified in the relative legend) to provide a satisfying superposition of the two profiles. Grey areas identify the hypothesized thicknesses of removed sediments. carried out in the nearby Phuong Mai peninsula in the framework of the Nhon Hoi Economic Zone (NEZ) development plan. Indeed, the NEZ is a new urban centre (120 km? wide) east of Quy Nhon City in the Binh Dinh province where the TN Lagoon is located. It was completed in 2010 and includes residential areas, an industrial park (14 km?), a deep water port, and a resort (BDEZ, 2010). The NEZ is connected to Quy Nhon’s city centre by the Thi Nai Bridge that was under construction in 2005, just when the TN core was inant composition. Additionally, this sample shows the highest PCB concentration of the entire dataset and is the only one in the sed- iment core composed entirely of sand (Table 1; Fig. 2). The pres- ence of a relatively high PCB concentration in a completely sandy sediment (not suited to interact with and store contaminants) is very unusual. These evidences, together with the contemporary observation of a different congener distribution, account for the ef- fect of external point sources, most likely linked to the activities

Fig. 6. Linear regression of the upper portion of 2002 and 2004 ?!°Pb activity-depth profiles at TG-CH 02. Assuming the similarity of the angular coefficients, the lines almost superimpose themselves if they are shifted of 19.6-12.6 = 7 cm.

Fig. 6. Linear regression of the upper portion of 2002 and 2004 ?!°Pb activity-depth profiles at TG-CH 02. Assuming the similarity of the angular coefficients, the lines almost superimpose themselves if they are shifted of 19.6-12.6 = 7 cm.

Fig. 7. Profiles of porosity and sand content modified according to the depth shifts shown in Fig. 5. As for TG-CH Lagoon, only the first two sampling campaigns (2002 anc 2004) are considered here.

Fig. 7. Profiles of porosity and sand content modified according to the depth shifts shown in Fig. 5. As for TG-CH Lagoon, only the first two sampling campaigns (2002 anc 2004) are considered here.

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