Environ. Sci. Technol. 1997, 31, 1777-1784
Patterns and Sources of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in Sediments from the Venice Lagoon, Italy ELENA FATTORE,* EMILIO BENFENATI, GIULIO MARIANI, AND ROBERTO FANELLI Istituto di Ricerche Farmacologiche “Mario Negri”, Via Eritrea 62, 20157 Milano, Italy ERIK H. G. EVERS Ministry of Transport, Public Works and Water Management, Directorate General for Public Works and Water Management, National Institute for Marine and Coastal Management/RIKZ, P.O. Box 20907, 2500 EX The Hague, The Netherlands
This study was a part of a research program concerning the pollution of the Venice Lagoon, in the north of Italy. The purpose was to evaluate the contamination due to polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F), a class of pollutants arising mainly from combustion and chemical manufacture. Six selected stations of the lagoon were investigated by analysis of surface sediment samples using gas chromatography-mass spectrometry (GC-MS). Principal Component Analysis and Regularized Discriminant Analysis, two chemometric approaches, were applied to the data set of the lagoon and to source-related samples from the literature. The results showed a moderate contamination due to PCDD/F in the investigated areas, and the levels within the lagoon were substantially higher than in the open sea. The investigation of the homologue profiles and the comparison with published PCDD/F data indicated different dioxin sources within the lagoon and some similarities of these with two environmental sources. Samples collected near Marghera Harbour and some samples collected at Sacca Sessola were similar to samples contaminated from ethylene dichloride production effluents while the profiles of most of the other samples were similar to those of gasoline and diesel engine emissions.
Introduction The Venice Lagoon (Figure 1) is part of the Adriatic Sea in northeast Italy. It has a surface area of 550 km2, average depth of 0.6 m, and a salinity of about 25-36‰. It is halfmoon shaped extending from the Sile River outlet, in the north, to the Brenta Bacchiglione River in the south. The water exchange with the Adriatic Sea (1.6-5.2 × 108 m3 day-1) occurs through three entrance channels dividing the lagoon into the homonymous hydrological basins: Lido, Malamocco, and Chioggia. Freshwater (30.7 m3 s-1) enters the lagoon through about 24 tributaries (1-4). The deposition rate of the sediment in the lagoon is quite variable: it ranges between the lowest values of about 0.2 cm/yr near the entrance channels of the Adriatic Sea, characterized by high water * Corresponding author e-mail address: FATTORE@IRFMN. MNEGRI.IT; telephone: (02)39014499; fax: (02)39001916.
S0013-936X(96)00886-3 CCC: $14.00
1997 American Chemical Society
exchanges, and the highest one in the areas receiving large contributions of freshwaters. At the mouth of the Dese River, sedimentation ratios of 0.81 and 0.59 have been detected, while a ratio of about 0.3 cm/yr has been calculated in the area between Marghera Harbour and Venice (1). The Venice Lagoon is a particularly vulnerable system, both because of its shallow waters and the poor water exchange in many areas. For several decades now it has been undergoing far-reaching changes caused by human activities (5-11). In 1920, the first industrial district at Marghera Harbour was built at the inner edge of the lagoon (12). This area was developed, and now more than 200 chemical and oil-refining plants, shipyards, thermoelectric power stations, etc. are in operation there (9). Other activities, which could severely contaminate the lagoon, are the untreated domestic wastes from the historical center of Venice and the motorboats continuously crossing the lagoon. As a consequence, the lagoon ecosystem has seriously deteriorated, mainly because of severe eutrofication and diffusive chemical pollution (511). This study is part of a more extensive research program to characterise pollution in the Venice Lagoon. The present research concerns levels, toxicity equivalents (TEQ) (13, 14), and homologue profiles of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) in sediments from different locations in the lagoon (Figure 1). These compounds constitute a class of ubiquitous pollutants with a tricyclic aromatic structure, high chemical stability, and extremely poor water solubility. They pose a risk to human and environmental health since their carcinogenic potential, their toxic effects on reproductive and immune systems, and their high potential for accumulation through the food chain have been demonstrated (15, 16). The principal sources of these contaminants are combustion and chemical production processes where PCDD/F are formed as unwanted byproducts. They enter aquatic systems through atmospheric deposition or directly via municipal and industrial wastes. Different homologue profiles (different contributions of each class of PCDD/F presenting the same degree of chlorination) may be associated with different origins of these pollutants. Differences and similarities in the homologue or congener profiles have been used for source identification (17-25) by principal component analysis (PCA). It is a very powerful technique based on multivariate statistical analysis whose main purpose is to explore and detect patterns within a set of data (26-28). The method allows investigation of the original data matrix using the smallest number of variables while preserving the greatest possible amount of information. This technique was performed to compare the data obtained on the Venice Lagoon with some source-related homologue profiles of PCDD/F selected from published data. Moreover published data from the literature were employed too as a training set for a classification model based on the source of these pollutants. The regularized discriminant analysis (RDA), a probabilistic classification method that models each class on its centroid and its covariance matrix (28, 29), was used for this purpose.
Experimental Section Sample Sites. Surface sediment samples of about 2500 cm2 area were collected by a steel dredge from the bottom 10-cm layer. A first preliminary sampling campaign was carried out in July 1992. Six stations (Figure 1) were chosen as representative of different pollution sources and hydrologic situations: Station 1, Marghera Harbour: near the industrial district of Marghera, an area of the lagoon with slow water exchange.
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FIGURE 1. Map of the Venice Lagoon showing the sampling stations (upper map) and the corresponding sampling sites (enlarged maps). Station 2, Cona Marsh: near the mouth of the Dese River, a zone with slow water exchange, receiving considerable amounts of freshwater (about 8 m3 s-1) draining a largely agricultural basin. Station 3, Venice: an area with heavy pollution due to untreated sewage, moderate water exchange. Station 4, Sacca Sessola: an area influenced by a relatively small load of urban and industrial contaminants, quite good water exchange. Station 5, Chioggia Basin: quite far from any industrial source but close to the town of Chioggia, with an ample water exchange, since it is situated near the homonymous exchange channel with the sea. Station 6, Adriatic Sea: landmark outside the lagoon. In July 1994 a second sampling (Figure 1) was carried out to examine the levels of these pollutants more closely and to evaluate the variability of the concentrations inside the lagoon.
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Other sediment samples were collected at the five sampling stations within the lagoon (not in station 6). The distance between sampling points at the same station ranged between approximately 500 and 1500 m. The locations of all sample sites are shown in Table 1. Extraction and Cleanup. Sediment samples were preserved and stored at -20 °C until analysis. Then they were allowed to dry at room temperature to constant weight, and 100 g of dry sediment for each sample was extracted with a mixture of pesticide-grade acetone/n-hexane (Carlo Erba, Milano, Italy) 1/1, in a Soxhlet apparatus for 24 h. Before extraction, a mixture of 10 13C-labeled 2,3,7,8-substituted congeners (Cambridge Isotope Laboratories, Woburn, MA) was added as internal standards. Samples were concentrated by a rotatory evaporator and purified on an Extrelut column (70-230-mesh, Merck, Darmstad, Germany) coated with concentrated sulfuric acid and later eluted with n-hexane. A
TABLE 1. Sample Locations sample sampling code campaign
geographical position sampling station
latitude
longitude
1S 1B 1D 1F 1H
I II II II II
1 (Marghera Harbour) 45°25′16′′ 45°25′20′′ 45°25′32′′ 45°24′53′′ 45°24′53′′
12°15′50′′ 12°16′17′′ 12°16′44′′ 12°16′22′′ 12°16′51′′‘
2S 2A 2C 2F
I II II II
2 (Cona Marsh)
45°30′30′′ 45°31′04′′ 45°30′46′′ 45°30′30′′
12°24′07′′ 12°23′29′′ 12°23′50′′ 12°24′24′′
3S 3C 3E 3H
I II II II
3 (Venice)
45°26′08′′ 45°25′57′′ 45°25′33′′ 45°25′53′′
12°19′42′′ 12°20′28′′ 12°20′34′′ 12°19′24′′
4S 4B 4C 4D 4G
II II II II II
4 (Sacca Sessola)
45°24′36′′ 45°24′49′′ 45°24′29′′ 45°24′16′′ 45°24′36′′
12°19′38′′ 12°19′42′′ 12°19′42′′ 12°19′38′′ 12°19′18′′
5S 5C 5E 5F 5G
I II II II II
5 (Chioggia Basin)
45°16′01′′ 45°15′52′′ 45°16′00′′ 45°16′12′′ 45°16′36′′
12°14′36′′ 12°15′31′′ 12°14′29′′ 12°15′21′′ 12°15′06′′
6S
I
6 (Adriatic Sea)
45°18′50′′ 12°30′30′′
second purification was obtained using a neutral alumina column (Merck) previously activated at 400 °C for 4 h. The sample was added on the column with n-hexane, and PCDD/ F, were recovered eluting with carbon tetrachloride first then with dichloromethane (30). Further purification was with activated carbon AMOCO PX 21 (31). This column was eluted with a mixture of cyclohexane/methylene chloride 1/1 and of methylene chloride/methanol/benzene 75/20/5 in the forward direction; and toluene in the reverse one. The last fraction was collected and evaporated, and the residue dissolved in methylene chloride was ready for gas chromatography-mass spectrometry (GC-MS). Instrumental Analysis. A gas chromatography-mass spectrometer HP 5890 VG-TS 250 was used. The mass spectrometer was operated in the electron ionization mode with 33 eV ionizing potential, 200 °C source temperature, and 2000 resolution power. A Chrompack capillary column CP Sil 8 CB, 25 m × 0.25 mm, with 0.25 µm film thickness, and splitless injections were used for analysis of PCDD/F homologues. The temperature program was 160 °C maintained for 1 min, 20 °C until 300 °C, and then maintained for 20 min. Head column pressure was 140 kPa; injector temperature was 280 °C. For the analysis of PCDD/F isomers, a Chrompack CP Sil 88 column, 50 m × 0.25 mm, film thickness 0.25 µm was used. Temperature program was as follows: 100 °C maintained for 1 min, 30 °C/min until 190 °C, then 5 °C/min until 240 °C, and maintained for 40 min. Column head pressure was 180 kPa; injector temperature was 240 °C. The GC-MS was employed in the selected ion recording (SIR) mode. For each homologue, four ions were monitored, two relative to the native compound and two to the labeled 13C isomer. Identification was obtained from the retention time and intensity ratio between the two ions monitored. The ions recorded were M+ and M+2 for tetrachlorinated and pentachlorinated homologues and M+2 and M+4 for hexachlorinated, heptachlorinated, and octachlorinated homologues. Method blanks were routinely analyzed, and no contributions were detected. Data Analysis. PCA and a classification model by RDA were used to explore and classify our data. These, and the
data from the literature, were organized into a matrix having n objects (samples) and p variables (PCDD/F values), normalized to the total concentration of PCDD/F by expressing each homologue value as a percentage of the sum of the total PCDD/F. All values under the limit of detection were treated as half of this limit. The analyses were performed with a 486 PC-compatible and scan, Software for Chemometric Analysis (Minitab Inc., State College, PA).
Results and Discussion First Sampling Campaign. Table 2 shows the concentrations of each congener class and the TEQ in the sediment samples of the first sampling campaign. Tetrachlorinated dibenzop-dioxins (TCDD) and pentachlorinated dibenzo-p-dioxins (PnCDD) were under the limit of detection (LOD) in all samples except sample 5S where every class of PCDD/F was detectable. Values were highest in sample 3S (1090 ( 58 ng/kg dry weight for total PCDD/F). This sample was collected in the Canal Grande in the middle of the city of Venice, so it might be affected more than other samples by some local sources of contamination such as combustion from the intense motorboat traffic or the domestic wastewaters that are discharged directly into this canal without any treatment. Sample 1S, collected near the industrialized area of Marghera Harbour, also showed higher levels than other samples (809 ( 16.4 ng/kg dry weight for total PCDD/ F), mostly for PCDF (Table 2). The lowest concentrations, as expected, were in sample 6S, in the open sea, where only small amounts of octachlorinated dibenzo-p-dioxin (OCDD) and octachlorinated dibenzofuran (OCDF) were detected (4.1 ( 1.08 and 2.6 ( 0.03 ng/kg, respectively). Within the lagoon, the sample from station 2 (2S) had the lowest levels, but it was still much higher than outside the lagoon (sample 6S). Similar results were obtained from another research laboratory participating in the same research project (32). The levels of the TEQ showed a similar pattern to the total PCDD and PCDF levels and ranged from 0.007 in sample 6S to 37.2 ng/kg dry sediment in sample 3S (Table 2). 2,3,7,8TCDD was always under the LOD (2 ng/kg), as was 2,3,7,8substituted PnCDD. Total concentrations of PCDD/F in samples 2S, 4S, 5S, and 6S were similar to those detected in pristine or rural areas, where atmospheric background is their only source (33). However, there are some differences in homologue profiles (Figure 2). For example, the PCDF/PCDD ratio (Table 2) ranges between 0.6 (sample 2S) and 6.7 (sample 1S). Usually this ratio is e1, and OCDD levels are higher than other homologues when the contamination arises from combustion sources after varying distances of transport (19, 22, 33, 34). Indeed atmospheric transformation seems to enrich OCDD in comparison to the less chlorinated homologues because of its lower photodegradation potential (35). Thus sample 1S, because of high PCDF levels, could be affected by a source different from that of other locations in the lagoon. Sample 4S, in spite of low total PCDD/F, also had a higher PCDF/PCDD ratio (3.6) than the other samples, meaning that this sample might be influenced by the same source. Sample 5S is different from all the others because of the presence of low chlorinated homologues of dioxins (TCDD, PnCDD). It may suffer from some point source of contamination; nevertheless, the absolute levels are low, and this sample site seems to be far from potential contamination sources. Moreover samples collected during the subsequent campaign did not confirm this profile. Second Sampling Campaign. During the second sampling campaign, sediments from the same stations within the lagoon were collected for further investigation. Table 3 shows the concentrations of each homologue class of PCDD/ F, and the PCDD/F ratio. For all samples, the TCDD and PnCDD homologues were always below the LOD. The highest values were found in
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6.7 ( 2.1 0.6 ( 0.1 1.2 ( 0.1 3.6 ( 0.6 1.4 ( 0.4 0.8 ( 0.3 16.4 0.16 37.2 6.36 4.28 0.01 809 ( 16.4 51.6 ( 6.15 1090 ( 58 214 ( 9.51 164 ( 10 7 ( 0.03 76.3 ( 25.3 19.9 ( 3.22 347 ( 4.45 28.0 ( 7.19 27.6 ( 3.57 4.1 ( 1.08 34.7 ( 10.6 12.4 ( 2.3 153 ( 45.6 16.4 ( 0.54 13.8 ( 1.98
