RMZ - Materials and Geoenvironment, Vol. 52, No. 1, 55-20, 2005
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Sedimentary record of PAHs pollution in the Gulf of Trieste
(Northern Adriatic Sea)
Ester Heath1, Nives Ogrinc1, Jadran Faganeli2, Stefano Covelli3
'Department of Environmental Sciences, "Jozef Stefan" Institute, Jamova 39, 1000 Ljubljana, Slovenia PMarine Biological Station, National Institute of Biology, Fornace 41, 6330 Piran, Slovenia QDepartment of Geological, Environmental and Marine Sciences, University of Trieste, Via E. Weiss 2, 34127 Trieste, Italy
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic contaminates in coastal sediments derived from natural and anthropogenic sources. The waters of the Gulf of Trieste are extensively used for tourism and Maricultural purposes. Hence, extensive areas of the Gulf are affected by organic pollution. In addition, fresh water inflows of the tributary rivers, draining industrial and agricultural areas are another source of pollution.
In this work the authors present a historical reconstruction of PAH contamination in the Gulf of Trieste. For this, two long (~ 2 m) sediment cores taken from the central part of the Gulf, were collected and analysed.
Materials and methods
Cores GTI (200 cm long) and GT3 (120 cm long) were taken by gravity core sampler and sediments extruded and subsampled at 1 cm intervals. Samples were freeze-dried and ground to a fine powder for analysis. Organic carbon (Corg) and total nitrogen (Ntot) contents were determined by a Carlo Erba el-
emental analyzer (model EA 1108) after acidification with 1N HCl. The precision of the measurements was ±3 %. The isotopic composition of sedimentary C was deter-
r	J org
mined after treatment with 1M HCl to remove carbonate material, while isotopic composition of Ntot was determined directly on bulk powdered samples. The 513C and 515N of C and N „ fractions were analysed
org	tot
using a Europa 20-20 continuous-flow stable isotope analyser with ANCA-SL preparation module. Isotopic ratios are expressed in the usual 5-notation in parts per mil (%o). For carbon, the standard is the V-PDB carbonate, while for nitrogen the standard is atmospheric (air) nitrogen. The overall analytical precision was ±0.2 % for 513C values and ±0.3 %o for 515N values. The 1RC ages of bulk sedimentary C were determined at the Na-
orgF
tional Ocean Sciences Accelerator Mass Spectrometer Facility (Woods Hole Oceano-graphic Institution, MA, USA). The counting error in the reported 1RC measurements averaged ±2 % of the measured "age".
To determine the PAH concentration in the sediment samples the authors used gas chro-matography with mass spectrometric detec-
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Heath, E. et al.
tion (GC/MSD) combined accelerated solvent extraction (ASE) and supercritical fluid extraction (SFE). For extraction an ISCO (Lincoln, NE, USA) supercritical fluid extractor (SFX2-10) was adopted in our study. Detailed extraction is published in details elsewhere (Notar & Leskovsek, 2000). For extraction we used 10 mL disposable high temperature crystalline polymer extraction cartridges (ISCO, Lincoln, NE, USA) that were packed with 5g of sediment sample, 2 g of activated copper powder (to reduce the amount of sulphur present) and 2 g of wet support. Extracts were collected in glass-stopped 100 mL vials. Qualitative and quan-
titative analysis of PAHs in marine sediment extracts were performed by gas chromatograph equipped with split/splitless injection port and mass selective detector operating in the selected ion monitoring (SIM) mode using a Hewlett-Packard model 6890 GC/ MSD with automatic liquid sampler. The GC was equipped with a HP5-MS cross-linked 5 % phenyl-methyl-siloxane capillary column (30m x 0.25 mm i.d., 0.25 mm film thickness). An internal standard mixture containing four deuterated PAHs (acenaphthene-d10, chrysene-d12, phenantherne-d10, perylene-d12) was added directly to the sample prior to extraction. Response factors
Lithology GT3
0.0-
S13Crg[%o] CJwt.%] PAH [ng/g] -27-24-210 2 4 0 500 1000
0.2-
0.4-
0.6-
0.8--
1.0-
1.2-
Clayley silt
Silty clay
Silty sand Silty sand
J
Peaty
—i—■—I—"*T
X
m
j
4560 ±35
■
/

/
1.4-1
Figure I. Vertical profiles of lithology, organic carbon (Corg) content, SI3Corg values and poly-cyclic aromatic hydrocarbons (PAH) content in sediment core GT3. Conventional I4Corg ages are also shown.
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Sedimentary record of PAHs pollution in the Gulf of Trieste (Northern Adriatic Sea)
57
and retention times were determined relative to four deuterated internal standards and a standard PAH test mixture. The recovery data, precision, accuracy and method detection limits (MDL) were evaluated statistically and are presented elsewhere (Notar & Leskovsek, 2000).
Results and discussion
The vertical profiles of C show a decrease
r	org
in the upper part of the core until reaching a nearly constant value of about 0.6 %. The average 513Corg value and C/N ratio of -22.3 ± 0.6 %o and 9.2 ± 1.9, respectively indicate that -70 % of organic material is of marine origin. The 1RCorg dating shows the presence of old sedimentary organic matter in the upper predominantly marine sequence of the core (Fig. 1). The terrigenous sequence starts below a depth of 150 and 90 cm in GT1 and GT3 cores, respectively, which has the characteristic higher C contents, low 513C
org	org
values, and high C/N ratios. These parameters indicate that sedimentary organic matter originates from terrestrial plant material and according to 1RCorg dating is approximately 9000 years old (Ogrinc et al., 2005). The mean sedimentation rate from the upper 65 cm marine part of the core GT3 is 0.14 mm yr1 and is more than 10-fold lower than the value of 1.8 mm yr1 calculated from the Hg content (Covelli et al., in prep.). Mercury was previously correlated with 210Pb and can be used as a geochronological tracer in recent sediments of the Gulf of Trieste (Covelli et al., 2001). This difference is a likely result of a recent increase in the rate of sedimentation.
Concentrations of PAH decrease from the surface to deeper layers in the core (Figure 1). Concentrations vs. depth profiles of three representative pyrogenic PAHs; pyrene, benzofluoranthenes and phenantrene are similar to that of total PAHs. Using Hg as a recent geochronological tracer it emerges that the sediment layer in the core GT3 located at the depth of 10 cm dated to about 50 years BP, i.e. after the Second World War. Below this depth only low levels of PAHs were observed. The concentration of retene, considered as a product of the burning of coniferous timber, increases indicating an increased terrigenous input, about 50 years BP, and in the Middle Age. Geochronology suggests that the present-day PAHs accumulation flux amounts to about 0.1 mg cm-2 yr1 while in sediments deposited before the Second World War the flux average was <0.03 mg cm2 yr1. The PAH contents in the terrigenous peat layer dated to about 9000 years BP are about 3-fold lower than in the pre-industrial marine sediments. There was no significant correlation between the total PAH and C contents observed probably in-
org
dicating relatively polluted sediment. No correlation was found between PAHs and black C (BC) vertical distribution in the core GT1 either suggesting a lack of association between both substances. The ratios of methylphenentrenes to phenantrene, as an indicator of anthropogenic influences such as combustion of organic matter around the gulf, were low (<0.5). Therefore, the high combustion processes as the main sources of PAHs in the gulf are through fresh water inflows and atmospheric inputs. The same conclusion appears from the predominance of high molecular weight (4, 5, 6 rings) over low molecular weight (2, 3 rings) PAHs in
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upper layers of both cores. Also, phenantrene /anthracene ratios of about 10 and lower, and fluorantene/pyrene ratios of about 1 and lower suggest pyrolytic contamination of sediments. The lower phenantrene/an-thracene ratios in the surficial layer probably indicate that the PAHs received by the sediment in the 20th Century came from nearby sources.
References
Covelli, S., Faganeli, J., Horvat, M., Brambati, A. (2001): Mercury contamination of coastal sediments as the result of long-term cinnabar mining activity (Gulf of Trieste, Northern Adriatic sea). Appl. Geochem. 16, S41-SS8.
Ogrinc, N., Fontolan, G., Faganeli, J., Covelli, S. (200S): Carbon and nitrogen isotope compositions of organic matter in coastal marine sediments (the Gulf of Trieste, N Adriatic Sea): indicators of sources and preservation. Mar. Chem. 9S, 163-181.
Notar, M. & Leskovsek, H. (2000): Determination of polycyclic aromatic hydrocarbons in marine sediments using a new ACE-SFE extraction procedure. Presenius J. Anal. Chem. 366, 846-8S0.
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