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Polychlorinated Biphenyls and Chlorinated Pesticides in Sediments along the Semi-Closed Areas of Alexandria, Egypt

The residues of 19 EPA-organochlorine pollutants were analyzed in sediments collected from 49 different locations along the semi-closed areas of Alexandria, Egypt. The pollutants studied were 7 individual polychlorinatedbiphenyl (PCB) congeners, α,β,γ-hexachlorocyclohexane (HCHs), cyclodienes (aldrin, endrin, dieldrin) and dichlorodiphenyltrichloroethanes (DDTs) (o,p-DDE, p,p-DDE, o,p-DDD, p,p-DDD, o,p-DDT, p,p-DDT). The concentration of total DDTs ranged between ND and 123.76 ng·g (dry wt) whereas the concentration of PCBs, HCHs and cyclodienes ranged from ND to 192.24 ng·g; ND to 20.78 ng·g and ND to 8.04 ng·g dry wt, respectively. The average total organic carbon (TOC) percent was varied from 0.04% to 7.65%.


Introduction
Organochlorines (OCs), including PCBs and OCPs, represent an important group of persistent organic pollutants (POPs) that have caused worldwide concern as toxic environmental contaminants. They are strongly particle associated in aquatic ecosystems due to their hydrophobic properties, and tend to accumulate in sediments [1]. Also, residues of these chemicals have long half-life, they continue to be detected in sediment through out the world after banning 20 years later [2]. Sediments have been extensively used to assess the pollution of water bodies and to reflect the sources and history of pollution, because of the general importance of sediment phase in fate and transport of contaminants. In addition, contaminated sediments may constitute a particular threat for associated biota and even for other organisms throughout marine food web [3]. Being one of the principle reservoirs of environmental OCs, the estuary represents a source from which residues can be released to the atmosphere, groundwater and living organisms. It is one of the best media for long-term monitoring of many contaminants [4]. To date, POPs in estuarine and rivers sediments have been studied in several parts of the world [5,6]. The results show that POPs were detected in most estuary areas, especially in estuaries close to urbanized and industrialized areas. They receive and retain large quantities of organic pollutants, and have negative impacts on both the surrounding ecological environment and human health. OCPs such as hexachlorocyclohexane (HCH) and DDT are ubiquitous anthropogenic environmental contaminants. They are persistent, broad-spectrum toxicants that accumulate in the food web with high risks to ecosystem and human health. Many of these compounds are considered to act as hazardous environmental hormones, which disrupt reproductive cycles of humans and wildlife [7][8][9]. PCBs are man-made chemicals and synthesized by substituting variable number of chlorine atoms (from 1 to 10 chlorine atoms) onto the biphenyl aromatic molecular structure to produce 209 congeners. These congeners were manufactured and processed primarily for use as insulating fluids and coolants in electrical equipment and machinery in USA from 1929-1977, with a peak production in the year 1970 about 100,000 tons [10].
The present work is the first systematic record to be undertaken along the semi-closed areas of Alexandria (Egyptian Mediterranean Sea coast) as a comparative study between four sectors of different identity.
during January 2010 at sites shown in Figure 1. Sediments were collected utilizing a stainless-steel grab. Six grabs were taken from each location from which the top 3 cm were scooped into pre-cleaned wide-mouth glass bottles, frozen and transported to the laboratory and stored at −20˚C until analysis. The procedure for extracting OCPs and PCBs from sediments was modified from the USEPA Method [11][12][13][14]. Before chemical treatment, individual samples were removed from the refrigerator and allowed to thaw at room temperature for about 5 hr. Each sample was then thoroughly mixed and 30 g of the sediment was mixed with 90 g of anhydrous sodium sulfate. Duplicates were taken from each sediment sample. The sediment sample was then extracted with 250 ml (1:1) of n-hexane-dichloromethane for 8 hr in a Soxhlet apparatus cycling 5 -6 times·h −1 [14]. The extracts were then combined and desulfurized through activated copper powder and then concentrated to a few milliliters in a rotary evaporator at temperature of 35˚C. Anhydrous sodium sulfate (90 g) was extracted in the same fashion as the sample and used as the blank. The extracted samples and blanks were then concentrated with a pure nitrogen gas stream down to a volume of 2 ml. The remaining extract was transferred to the top of a glass column (50 ml) packed with 20 g Florisil followed by elution with 70 ml of hexane for PCBs congeners fraction (F1). Then the column was eluted with 60 ml of mixture containing 70% of hexane and 30% of dichloromethane for the pesticide fraction (F2). Activation of the Florisil was achieved by heating at 130˚C for 12 h, followed by partial deactivation with 0.5% water by weight and stored in a tightly sealed glass jar with ground glass stopper and the mixture were allowed to equilibrate for one day before use. Each fraction was concentrated and injected into a Gas chromatograph (Thermo Scien-tific Company) equipped with 63 Ni electron capture detector. A fused-silica capillary column; Thermo TR-35 MS (30 m, 0.25 mm, 0.25 μm) with 35% phenyl polysilphenylene-siloxane was used for the quantification. The temperature was programmed from 90˚C -140˚C with rate of 5˚C·min −1 , then held at 140˚C for 1min, and from 140˚C -250˚C with rate of 3˚C·min −1 and was held at 250˚C for 1min, and from 250˚C -300˚C with rate of 20˚C·min −1 and was held at 300˚C for 1 min. The injector and detector temperatures were set at 280˚C and 310, respectively. Three μL volume of each sample was injected in the split less mode and the purge time was 1 min.
To control the analytical reliability and assure recovery efficiency and accuracy of the results, four analyses were conducted on organochlorine compounds reference material SRM-2974a freeze-dried mussel tissue (Mytilus edulis) provided by EIMP-IAEA. The laboratory results showed that recovery efficiency ranged from 92% to 108% with coefficients of variation of 8% -15% for all organochlorine compounds. The limit of detection in the present study was estimated to be 0.015 ng·g −1 for PCB and 0.016 ng·g −1 for pesticides based on the minimum quantity of sample required for a discernible peak appeared on the chromatogram. For comparison, the data given by GC-ECD was qualitatively confirmed by GC-MS with the same method and column.

Results and Discussion
Sediments showed the presence of a wide variety of organochlorine including α, β, and γ-HCH, dieldrin, aldrin, endrin, DDT and the metabolites of DDT as well as PCBs (Tables 1 and 2). The concentrations of organochlorines  [15][16][17]. The concentration of total DDTs showed a range of 45% -100% of total pesticides concentration ( Figure  2(a)). These high concentrations may reflect the intensive use of pesticides (especially DDT) in cotton fields of Egypt over many years. Average concentrations of HCHs in sediments were 3.08 ng·g -1 ; dry wt with a range of 3 -13-fold lower than those of DDTs ( Table 1). Although use of HCHs in agriculture has been greater than DDTs, the relatively low concentration of HCHs in sediments reflects their lower potential for bioaccumulation. Furthermore, higher vapor pressures of HCHs facilitate relatively rapid atmospheric dissipation in the tropics, leaving fewer residues in soil and water [18].
The concentrations of cyclodienes (aldrin, endrine and dieldin) in sediments were in concentrations the range of 0.06 ng·g -1 ; dry wt at St. 6, and 7 -8.04 ng·g -1 ; dry wt at St. 20 with average of 1.31 ng·g -1 ; dry wt. These were on average, 15-fold less than DDTs ( Table 2) and almost the same as the concentrations of HCHs (Figure 2(b)).
PCBs were at 2 nd concentrations relative to other organochlorines in this study ( Table 2). The PCBs concentrations were in the range of 1.70 -194.20 ng/g·ng·g -1 dry wt at St. 42 and St. 36 (Figure 2(c)), respectively, with an average concentration of 28.01 ng·g -1 dry wt. PCBs concentration were on average, 2-fold lower than DDTs.
Concentrations of PCBs recorded in present work were much lower than concentrations observed in Mediterranean Sea sediments and in other coastal sediments in different geographical positions except for the northwestern basin of the Mediterranean Sea, Barcelona Offshore, Spain, and the Western Baltic Sea ( Table 3). At the same time detected concentrations of DDTs in the bay sediments in the present study were lower than concentrations previously recorded in Mediterranean Sea coastal sediments, but higher than concentrations recorded in other coastal sediments worldwide ( Table 3). Concentration of HCHs recorded in present work was generally lower than concentration previously recorded in sediments, but concentrations of Aldrin, Dieldrin, DDTs, and PCBs were slightly higher than concentrations previously recorded in sediments ( Table 3). De-  tected concentrations of organochlorine pesticides (Aldrin, and Dieldrin) in sediments were generally slightly higher compared to concentrations observed in other parts of the world ( Table 3). No significant correlation between total pesticides and total organic carbon (TOC) for sediment samples (Figure  3(a)). But it was detected a significant positive correlation between PCBs and TOC for sediment samples where r = 0.31 at P > 0.01 (Figure 3(b)); this is due to low solubility of PCBs in water, so precipitate until reach to the bottom water and contaminate with sediment.
For comparison, the data given by GC-ECD was quali-tatively confirmed by GC-MS. 25% from all samples in different areas (Abu-Qir Bay, Eastern Harbour, Western Harbour, and El-Max Bay) were randomly selected. Good results were obtained by coinciding between both techniques. The identification of different detected compounds was more pronounced using GC-ECD more than that obtained by GC-MS. This is due to the selectivity of ECD detector for chlorinated hydrocarbons.

Hazard Levels
The maximum permissible levels of organochlorine pol-Copyright © 2012 SciRes. JEP lutants recommended by the National Academy of Sciences and National Academy of Engineering (NAS-NAE, 1972) [41] are 1000 -5000 ng·g -1 for PCBs and 100 ng·g -1 for cyclodienes (wet wt). The recommended levels by Swedish Food Regulation are 5000 ng·g -1 for DDTs, 2000 ng·g -1 for PCBs and 200 ng·g -1 for HCB (SFR, 1983) [42]. The US Food and Drug Administration (FDA) tolerance limit of 2000 ng·g -1 wet wt for total PCBs in fish and shellfish. Our results clearly indicate that PCBs concentrations (ND to 192.24 ng·g -1 ; wet wt), DDTs (ND and 123.76 ng·g -1 (dry wt), cyclodienes (ND to 8.04 ng·g -1 dry wt), HCHs (ND to 20.78 ng·g -1 dry wt) recorded in this study were much lower than that recorded as permissible levels.