Polychlorinated biphenyls (PCBs) and Polybrominated Diphenyl Ethers (PBDEs) in surface sediments from Monastir Bay (Tunisia, Central Mediterranean): Occurrence, distribution and seasonal variations
Introduction
Polychlorinated biphenyls (PCBs) and Polybrominated Diphenyl Ethers (PBDEs) are organic halogenated compounds exclusively of anthropogenic origin, which have become ubiquitous in environmental media. They are characterized by their hydrophobic character, long half-time and their environmental persistence (Bergen et al., 1993, Alaee, 2003). Like other persistent organic pollutants (POPs), PCBs and PBDEs are noted for their potential to bioaccumulate in biological tissues of organisms and biomagnify throughout the food web (Fasola et al., 1998, Suutari et al., 2010). In the past decade, concerns have been raised in regard to these compounds because they have shown potentiality to cause a number of adverse health effects, including reproductive, immunologic and neurologic disruptions (Hallgren et al., 2001, Suutari et al., 2010). PBDEs are now believed to act as endocrine disruptors (De Boer et al., 1998, Hood, 2006, Hoppe and Carey, 2007).
PCBs constitute a group of 209 congeners, from three monochlorinated isomers to the fully chlorinated decachlorobiphenyl isomer. They have excellent heat transfer and electrical properties which led to their widespread use in a variety of industrial, commercial and domestic applications. Their production and use were banned in most industrial countries since the 1970s/1980s. In Tunisia, the use and trade of most groups of POPs, including PCBs, were prohibited by virtue of the convention of Stockholm (2001). In 2005, the PCB-contaminated equipment and wastes were estimated at 455 tones and 117 tones of PCB-contaminated oils (MEDD, 2007). Thus, today PCBs can still be released into the environment from different sources such as poorly maintained waste sites that contain PCBs, illegal dumping of PCB wastes or by the burning of some wastes in municipal and industrial incinerators.
PBDEs are more recent arrivals, used as flame retardant additives in polymers, especially in the manufacture of electrical appliances, building materials, paints and textiles. There are three major commercial mixtures of PBDEs depending on the degree of bromination: Penta-, Octa- and Deca- mixtures. These mixtures were voluntary banned in the European Union (UN), and Octa- and Penta-mixtures have been banned nationally in the US with certain states banning the Deca-formulation (Birnbaum and Staskal, 2004). In Tunisia, There is no regulation which prohibits or limits the use of PBDEs until now.
PBDEs have the same generic structure of PCBs with 209 possible congeners according to the number of substitutions and the positions of the bromines on the biphenyl. Physicochemical properties PBDEs and PCBs are similar and depend directly on the position and halogenations degree of the molecule (De Boer and Cofino, 2002). Properties of these compounds such as their volatility and degradability are significantly reduced when their halogenation degree decreases (Loganathan and Kannan, 1994). In aquatic environment, the behavior and fate of hydrophobic contaminants, including PCBs and PBDEs, depend on multiple and interdependent parameters. Some of these parameters are linked to the intrinsic physicochemical properties of these compounds that control their partition between dissolved and particulate phases. Others are related to hydrological and geochemical characteristics of the environment including water turbidity (Abarnou et al., 1987, Vuksanovic et al., 1996), sediment grain-size distribution (Karickhoff et al., 1979, Piérard et al., 1996, Zhao et al., 2010) and organic matter content (Persson, 2003, Hung et al., 2006, Nam et al., 2008).
The present work expands on our previous environmental monitoring in Monastir Bay, which has been focused on PAH (Polycyclic Aromatic Hydrocarbons) pollution (Nouira et al., 2012). This work is a field study based on chemical analysis of surface sediments with the aim to evaluate the current contamination situation with selected halogenated compounds (PCBs and PBDEs) and also to examine the effects of seasonal variation and the characteristics of the environment on the distribution of these compounds.
Section snippets
Characteristics of the study area
Monastir Bay is a semi enclosed lagoon lying on the Eastern shore of Tunisia (Fig. 1). This littoral fringe forms a receptacle of multiple wastewater effluents from urban zones. In the whole Bay, waters are generally characterized by a weak agitation. The shoal of Tebulba, of very low depth, isolates more or less the Bay from the open sea. The only winds likely to generate agitations that can reach the coastline and affect the hydrodynamics inside the Bay are the Northern and NE winds blowing
Results and discussion
Table 1 exhibits PCBs and PBDEs concentrations (dry weight basis) determined at each site for each individual congener and during the wet and dry seasons of the year. Total PCB concentrations (∑7 marker PCBs) ranged from 3.1 to 9.3 ng g in winter and from 1.1 to 8.1 ng g−1 in summer. In winter, PBDE concentrations (∑4 PBDEs) ranged from not detect to 0.1 ng g−1, and only the congener BDE-47 was detected in surface sediments. Whereas in summer, none of PBDE congeners was detected in all sampling sites.
Conclusion
A preliminary investigation of aromatic halogenated compounds (PCBs and PBDEs) in surface sediments of Monastir Bay was performed. Results indicated a PCB contamination from land-based sources. PBDEs, represented by the BDE-47 congener, were suspected to originate from atmospheric deposition. Spatial distribution and seasonal variations of these contaminants have been discussed taking into account different aspects such as the temporal variability of inputs, hydrodynamics and sediment
Acknowledgments
We would like to thank Dr. Yosra Belaïd-Nouira for proofreading the article, Mr. Faissal Ghachem and Chebil Mohsen for their assistance in sampling.
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