Rapp. Comm. int. Mer Médit., 37,2004
206
PAH DISTRIBUTION IN WATER COLUMN AND SURFACE SEDIMENTS OF THERMAIKOS GULF, GREECE
I. Hatzianestis*, E. Sklivagou
Hellenic Centre for Marine Research, 19013 Anavyssos Attikis, Greece - *jhat@ncmr.gr
Abstract
The distribution of polycyclic aromatic compounds (PAH), was studied in the water column and surface sediments collected from
Thermaikos gulf, in order to investigate the effects of resuspension events on the cycling and impact of these organic pollutants. The PAH
compositional patterns and the application of various diagnostic criteria suggested that in February 2002 the increased values of their
concentrations measured in the water column were clearly related to resuspended material from sediments.
Keywords: Thermaikos Gulf, resuspension, PAH
Introduction
PAHs show a high affinity to aquatic particles, especially to the
organic carbon or lipid component. Because the sediments are the
main repositories for such particle reactive contaminants, it is
important to understand the processes that control chemical ?uxes.
Two major processes can move chemicals from the sediments to the
overlying water column [1]: a) diffusive ?ux of dissolved species and
2) resuspension of in-place sediments with potential for redistribution
of organic contaminants from the sediment to the water column. The
aim of this work was to study the effects of natural resuspension
occurred during stormy conditions and of anthropogenic resuspension
induced by the intense trawling activities in the area of Thermaikos
Gulf on the cycling and impact of PAHs.
Materials and methods
Surface sediment samples (0-2 cm) and seawater samples (20 L)
were collected from 10 stations in Thermaikos Gulf during September
2001 (before the trawling activity), October 2001 (during trawling
activity) and February 2002 (during natural/stormy induced
resuspension events) (Fig. 1). Polycyclic aromatic hydrocarbon
concentrations were determined by gas chromatography / mass
spectrometry after extraction, cleanup and fractionation [2]. PAHs
determined included the parent compounds with 2 – 6 aromatic rings,
dibenzothiophene, retene and the methylated derivatives of
dibenzothiophene and phenanthrene
Fig. 1. The sampling locations in Thermaikos Gulf.
Results and discussion
Concentrations of total polycyclic aromatic hydrocarbons in
surface sediments ranged from 27.2 to 280.5 ng/g (mean value 164.3
ng/g) in September, from 59.6 to 261.9 ng/g (mean value 160.7 ng/g)
in October and from 62.7 to 285.9 ng/g (mean value 165.8 ng/g) in
February. These values can be generally characterized as low and are
similar to those found in relatively unpolluted marine areas. Slightly
elevated concentrations were found in station 1, whereas considerably
low values were recorded in station 18. No differences in PAH
concentrations were observed among the three sampling periods. PAH
with 4 or 5 aromatic rings originating from pyrolytic sources
dominated the PAH composition in all cases, whereas petroleum
related compounds accounted for less than 15% of the total PAHs.
Concentrations of total polycyclic aromatic hydrocarbons in the
water column ranged between 0.8 and 13.4 ng/L (mean value 5.8
ng/L) in September, between 1.5 and 16.9 ng/L (mean value 7.0 ng/L)
in October and between 4.4 and 16.8 ng/L (mean value 8.9 ng/L) in
February. No important spatial variation was observed, whereas
increased values were measured in the whole water column during
October and February. These higher values are probably related with
increased inputs of riverine or atmospheric inputs of land derived
PAHs. In most cases and in all sampling periods PAH values in
bottom water were slightly higher than those in the overlaying water
masses. PAH compositional patterns can be used in order to examine
their sources and pathways. It is known that low MW PAHs are more
water soluble and usually predominate in the water column, whereas
the high MW pyrolytic PAHs with negligible water solubility but high
stability towards physicochemical or biological degradation are easily
accumulated in sediments. In the water samples of Thermaikos gulf
combustion PAHs accounted for the 0.1-7.6% of the total PAHs in
September (mean value 3.3%), whereas in October and especially in
February these percentages were clearly higher (1.9-17.6%, mean
value 6.1% and 4.6-14.2%, mean value 7.6% respectively). This
increase, which was more pronounced in the bottom water samples
(Fig. 2), is a strong indication that there was a contribution from
sedimentary PAHs in the water column in October and February,
probably related to the resuspension events occurred during these
periods.
Fig. 2. Combustion PAH percentages in the water column.
References
1-Latimer, J.S, Davis, W.R and Keith, D.J., 1999. Mobilization of PAHs
and PCBs from In-Place Contaminated Marine Sediments During
Simulated Resuspension Events, Estuarine, Coastal and Shelf Science, 49:
577-595.
2-UNEP/IOC/IAEA, 1992 Determination of petroleum hydrocarbons in
sediments. Reference Methods for Marine Pollution Studies, No 20,
UNEP.
