ORGANOCHLORINE CONTAMINATION IN SEDIMENTS COLLECTED FROM A RURAL-, URBAN- AND INDUSTRIAL-IMPACTED AQUATIC SYSTEM (DANUBE, SERBIA)

The spatial distribution of various organochlorinated compounds (PCBs and ОCPs (DDTs, HCB, and HCHs)) were investigated in sediments of Serbia's stretch of the Danube River. The obtained concentrations appeared to be relatively low in comparison with other river sediments worldwide. The results demonstrated a wide range of concentrations (μg/kg dry weight) with the following decreasing order: Σ6DDTs (0.70 16.65) > Σ 7PCBs (0.25 3.54) > Σ 5HCH (0.04 2.28) > HCB (0.06 0.62), with a dominance of o,p’ -DDT. Relatively higher ΣDDT concentrations and high DDT/DDE + DDD ratios in two sampling locations near the industrial cities indicates a current DDT usage, probably linked to public health concerns. Compositional analyses indicated that hexaand hepta-PCBs were dominant for PCBs. Our results indicated that the contamination with PCBs came from nonpoint deposition, such as atmospheric contribution and surface runoff, for lightly chlorinated congeners and point source deposition, such as the industrial sources along river flow, for highly chlorinated congeners, whereas OCPs originate mainly from old residues and new usage of pesticides in agriculture and aquaculture. These results contribute to the sparse regional database for organochlorinated compounds in the Danube basin.


INTRODUCTION
In recent years, the accelerated accrual in the human population and industrialization has led to an increase in the waste and emission of contaminants in all environmental compartments. Among all types of contaminants, the lipophilic chemical species raise major concern due to their ecological and socioeconomic implications (loss of biodiversity, contamination of food, degradation of habitat, deprivation of livelihood) as well as their impact on human health [1].
Polychlorinated biphenyls (PCBs) and chlorinated pesticides (e.g., DDTs, HCB, HCHs, etc.), are an important group of persistent organic compounds (POPs) included in the Stockholm Convention: they are globally distributed and their properties cause worldwide concern as toxic environmental contaminants [2,3] in a warming world. Organochlorinated compounds have been widely used, with both industrial and agricultural sources contributing significant amounts to the environment through leakage, disposal and evaporation. Although production and use of these pollutants are prohibited, human activities may still release PCBs and OCPs into the environment, such as the maintenance of electrical equipment, re-use of fluids, demolition of buildings, recycling operations, incineration of industrial and domestic products, inadequate waste disposal and illegal discharges. In the aquatic ecosystems, chlorinated compounds cause great concern due to their persistent nature, hydrophobic character, low water solubility, long-range transport, bioaccumulation, toxicity as well as carcinogenicity [4]. As a result, sediments are usually regarded as the ultimate sink for many classes of anthropogenic contaminants to the environment and are one of the best media for the long-term monitoring of many POPs [5]. As sediments may receive these pollutant discharges, trapping and accumulating contaminants over time, this compartment is widely recognized as important natural reservoir and large environmental sink and is used for evaluating the health of aquatic ecosystem [6].
In view of the above, the present study provides valuable information on concentration levels and spatial distribution of polychlorinated biphenyls (PCBs) and organochlorine pesticides (DDTs, HCB, and HCH) in surface sediments to ascertain the contamination status of the Serbia's stretch of Danube river.

Sediment analysis
About 7 -8 g of the freeze-dried sediment samples were extracted with dichloromethane in a Büchi System B-811 automatic extractor. One laboratory blank and one reference material were analysed with each set of ten samples. Surrogate recovery standards (PCB 30, PCB 185 in amount of 10 ng for PCBs analysis) were spiked in each sediment prior to extraction. After extraction, the sample volume was reduced to about 1 -1.5 ml and transferred to hexane using azeotrope principle on Kuderna-Danish evaporation unit resulting in the end with 1 ml of extract in hexane. For OCPs and PCBs clean up and analysis, the extract went through 8 g of activated silica gel modified with sulphuric acid column and eluted with 30 ml hexane: dichloromethane. The volume of the extracts was again reduced and transferred to hexane using Kuderna-Danish evaporation unit to about 1 ml in hexane. The extracts were further reduced under soft nitrogen flow to about 0.5 ml. The extract was quantitatively transferred to GC-MS vial and the final volume was brought to 1 ml. For quantification of OCPs and PCBs, 10 ng of PCB 121 was added as syringe internal standard. The extract was quantitatively transferred to GC-MS vial and the volume was reduced to about 0.

RESULTS AND DISCUSSION
The spatial trend of polychlorinated biphenyls in the collected samples of sediment within the research at 10 sampling sites is presented in Figure 2. The highest concentration levels of PCBs were detected in the areas of the most developed industrial centers in AP Vojvodina near Bačka Palanka city (Neštin: 3.54 µg/kg dry weight (d.w.)) and Pančevo (Ritopek: 3.27 µg/kg d.w.), which is the consequence of today's active industrial activities amplified by the historical pollution of industrial waste released into the environment of such past, but also possible accumulation of these toxic pollutants in the Danube sediment after NATO bombing in 1999. The PCB values obtained in this study were lower compared to the Joint Danube Survey 1 and 2 [7] expedition, which examined     Ritopek indicates that DDT in our country continues to be used although its use was prohibited at the end of the 1980s. At other sites, this ratio is < 1 and points to pollution caused in the past.
The total organic carbon (TOC) content in sediment samples ranged from 0.3 to 1.3 %, indicating a significant variation in spatial distribution, but without a clear trend. In this study, a correlation analysis was performed to obtain information about the interactions between PCBs, OCPs, and TOC. There was a positive, significant linear correlation between the sum of the concentration of PCBs and TOC sediment contents in the Danube River (r = 0.93; p < 0.01), but a significant correlation was also observed between the content of organic matter and the individual values of PCB congeners detected in the samples sediment and ranged from r = 0.71 (for PCB 28) to r = 9.52 (for PCB 118). The values obtained are much higher than the correlation coefficients obtained in other studies [10,11]. The values of TOC were significantly correlated with ΣDDE concentrations (r = 0.68; p < 0.05) and ΣDDD (r = 0.66; p < 0.05) and to a lesser extent with ΣDDT (r = 0.34; p < 0.05). Significant correlations between ΣDDT and ΣDDE concentrations (r = 0.77; p < 0.05) were found. These results suggest that organic matter in the sediment can play a more important role in the levels of PCBs and OCPs. PCBs are highly lipophilic and TOC content in sediment is a major factor in controlling the biological availability of PCBs. Sediment with lower TOC generally results in a higher percentage of PCBs and OCPs partitioned in interstitial water and thus have the ability to be absorbed more easily in benthic organisms.

CONCLUSION
The research under this study was based on the monitoring carried out in 2012 to determine the concentration levels and spatial distribution of polychlorinated biphenyls and organochlorine pesticides, specific lipophilic persistent organic pollutants in the complex aquatic sedimentation system of the river Danube on sites with significant anthropogenic influence in the Republic of Serbia. Based on the overall analysis of the obtained results, it can be established that the specificity of the spatial distribution of individual congeners at selected sites may be related to agricultural activities, uncontrolled wastewater discharge, uncontrolled burning, but also destruction of the facility during the NATO bombing in 1999, especially near the town of Pančevo, the confirmation of which requires further research Also, it can be concluded that the Danube riverbank flow at the territory of Serbia still has significant potential pollution sources of aquatic systems with organochlorine pesticides, which is necessary to detect more extensive monitoring and prevent further use by adequate controls of pesticides imported and produced today in our country, thus diminishing the extremely negative ecotoxicological effects currently present in the aquatic system. Within the framework of such a systematized research process it would be necessary to include more media (biotic and abiotic) in the analysis as well as more specific points. and distribution of persistent organochlorine pesticide residues in water and sediments of Gomti River