Environ. Sci. Technol. 1996, 30, 2776-2783
Grain-Size Distribution of Polychlorobiphenyls in Coastal Sediments C . P I EÄ R A R D , H . B U D Z I N S K I , A N D P. GARRIGUES* URA 348 CNRS, Universite´ Bordeaux I, 351 Cours de la Libe´ration, 33405 Talence, France
Congener-specific analyses of PCBs in marine sediments were undertaken to gain a better understanding of the distribution of this class of contaminants in relation to the grain-size of sediments. Twenty PCB congeners, selected for their potential toxicity and/or for their occurrence in the environmental samples, were studied in five grainsize sediment fractions (from φ > 800 µm to φ < 15 µm) and in the vegetal fragment fraction collected by flotation. PCB content and distribution profiles were observed in different grain-size fractions, and these were compared to that of the bulk sediments. Despite different contamination levels shown by the three studied sediments (from 29 to 181 ng g-1 in dry sediment for the sum of the 20 PCB congeners), trends were observed: preferential accumulation of PCBs with finest fractions and vegetal fragment fraction and specific association of low chlorinated congeners with the sand-size fractions (φ > 63 µm) and of high chlorinated congeners with the silt-size fractions (φ < 63 µm). This study illustrates the requirement of a good knowledge of the sediment grain-size composition when evaluating the toxicity and the availability of PCBs to aquatic biota.
Introduction Polychlorinated biphenyls (PCBs) are ubiquitous contaminants. Their presence in freshwater and marine sediments is the result of their widespread diffusion and environmental persistence. They are carried from terrestrial sources to the sea through various pathways, such as atmospheric and fluvial transports (1-3). PCBs are apolar, lipophilic (hydrophobic) compounds characterized by large octanolwater partition coefficients (log Kow ≈ 4-8). Such compounds interact strongly with abiotic and biotic surfaces. Such interactions of organic contaminants are determined by the organic matter content, the surface area, and the nature of the surface (4-6). PCBs accumulate in soils and sediments, particularly on clays and fine particles that have demonstrated to be rich in organic matter and to exhibit the greatest surface to volume ratio (7-10). * Corresponding author telephone: 33 56 84 63 05; fax: 33 56 84 66 45; e-mail address:
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Concern has increased over the last 10 years with regard to ecotoxicological implications of sediments contaminated by PCBs, since fine particles are bioavailable for marine organisms, such as fishes (11), burrowing invertebrates (12), or filtering organisms (13). In order to understand the effects and behavior of PCBs in the environment, information is needed about the quantitation and distribution of individual congeners, which often exhibit varying biological activity depending on the chloro substitution pattern (14, 15). In this work, PCB concentrations and distributions were determined in several grain-size fractions of three coastal sediments, collected in the Mediterranean Sea, in order to evaluate the extent of the relationship between the size of sediments particles and the PCB content. The 20 PCB congeners determined were selected for their range of potential toxicity (16) and for their abundance in environmental samples (17, 18). They represent a wide range of chlorination degrees (from 2 to 10 chlorine atoms) and display differences in their substitution patterns and physical properties. They can be considered as being representative of their respective groups of congeners found in the various technical PCB mixtures (18-20).
Materials and Methods Study Area and Sampling. The studied sediment samples were collected from several locations (Figure 1). They are representative of the sediments collected in the Mediterranean Sea over more than 8 years in the framework of the GICBEM program (21, 22). Superficial sediments (0-5 cm) from three sites on the French Mediterranean Coast, named Laz (Lazaret Bay near Toulon Harbor), Roq (Roquebrune Bay near Monaco), and Por (Porquerolles Island, a marine natural park), were collected by scuba divers. Sediment samples were frozen on-board and freeze-dried at the laboratory. The samples are representative of sediments of various textures presenting moderate or high contamination levels (23). Sediment Fractionation. Prior to analysis, bulk sediments were wet sieved (2 mm). Sediments samples were gently shaked by hand in large beakers filled with water (MilliQ water, Millipore, Boston, MA). Wet sieving and manual stirring were employed to avoid possible carryover of finer particles, which could get into the coarser fractions if dry sieving was performed (24). The weight of each subfraction of sediment was carefully measured to estimate the relative contribution of each fraction to the mass of the sediment. During the sieving, attempts were made to minimize sediment weight loss, and the weight recovery was higher than 90% for all the samples. Five grain-size subfractions were defined as follows: very coarse sands (φ > 800 µm) fraction numbered 1, medium to coarse sands (800 µm < φ < 300 µm) fraction numbered 2, medium to fine sands (300 µm < φ < 63 µm) fraction numbered 3, medium silts (63 µm < φ < 15 µm) fraction numbered 4, and fine silts/clays (φ < 15 µm) fraction numbered 5. A sixth fraction composed of low-density material, mainly small remains of degraded plants, was collected by flotation. Extraction and Cleanup. Dry sediments samples (1040 g) were extracted by Soxhlet between 30 and 70 h
S0013-936X(96)00003-X CCC: $12.00
1996 American Chemical Society
FIGURE 1. Sampling locations: French Mediterranean Coast. The collection points are noted with arrows.
(depending on the contamination level) with dichloromethane (volume 250-500 mL) (HPLC grade, Scharlau, Spain). The organic extract was reduced using a rotary evaporator (Bu ¨chi R-114, RFA), evaporated to dryness under a stream of nitrogen, and rapidly redissolved in isooctane (volume 2 mL) (spectroscopy grade, SDS, France).The purity of all the solvents was tested before use by gas chromatography with electron capture detection (GC-ECD). Sulfur was removed with the sodium sulfite (Prolabo, France) treatment according to Jensen (25). Pure sulfuric acid (volume 2 mL) (Fluka Chemie, Buchs, Switzerland) was vigorously shaken with the isooctane in the separating funnel to eliminate interfering organic co-extractants and macromolecules, then run off, and discarded. The procedure was repeated until the acid layer remained colorless. The isooctane extract was then washed with water (volume 3 × 20 mL, MilliQ water, Millipore, MA) and dried with anhydrous sodium sulfate (Fluka Chemie, Buchs, Switzerland). The extract volume was reduced for analysis to about 100-200 µL. Recovery tests for each analysis were based on octachloronaphthalene (OCN) (95% purity) (Ultra Scientific, North Kingston, RI), routinely added as an internal standard prior to extraction. Recoveries ranged from 50% to 90%. It was assumed that the loss was the same for the internal standard as for the PCBs, and thus the PCB concentrations were corrected accordingly. POC Analyses. Each fraction of the Mediterranean sediments was analyzed with a LECO CS 125 carbon analyzer (LECO Corporation, MI) to evaluate the particulate organic carbon (POC) content. This is representative of the organic matter content (26, 27). High-Resolution Gas Chromatography. Gas chromatographic separation and identification of the PCBs were performed by capillary gas chromatography using the following columns: Column 1: CP-SIL8-CB (Chrompack, Netherlands); length, 50 m; i.d., 0.25 mm; film thickness, 0.25 µm; temperature program: 60 °C (2 min)s6 °C/ mins120 °C (5 min)-2 °C/min-280 °C (20 min); carrier gas, helium (200 kPa); injection technique, splitless (280
°C); detector temperature, 290 °C. Column 2: CP-SIL19CB (Chrompack, Netherlands); length, 50 m; i.d., 0.32 mm; film thickness, 0.20 µm; temperature program: 60 °C (2 min)s6 °C/mins120 °C (5 min)s2 °C/min-280 °C (20 min); carrier gas, helium (120 kPa); injection technique, splitless (280 °C); detector temperature, 290 °C. Analyses were performed on an HP 5890 Series II gas chromatograph (Hewlett-Packard, Avondale, MA) equipped with a 63Ni electron capture detector (ECD). For both columns, the ECD makeup gas was nitrogen at 65 mL/min flow. Storage, handling, and processing of data were performed by a HP Vectra QS/20 microcomputer with a Chemstation Software. Quantitation of the PCB Congeners. ECD quantitation was carried out using the relative response factors of the selected 20 PCB congeners with respect to the OCN (17, 28, 29). Calibration was performed with the Standard Reference Material SRM 2262 (NIST, Washington, DC), a solution containing 29 PCB congeners in isooctane. A solution of 15 organochlorine pesticides in hexane (SRM 2261, NIST, Washington DC) was injected to observe possible coelution of these compounds with the analyzed PCB congeners. It should be noted that the PCB concentrations reported in Table 1 are based on the assumption that most of the chromatographic peaks contain only one PCB congener. There are several congeners that have the same retention times as the 20 PCB congeners studied, and despite the use of two columns of different polarity, several coeluting congeners cannot be separated, i.e., PCB 66 with PCB 95; PCB 138 with PCB 160 and PCB 163; PCB 200 with PCB 157; and PCB 170 with PCB 190 (20, 30, 31). Thus, the concentrations of these 20 PCBs are likely to be overestimated somewhat. For example, the concentration of PCB 163 generally contributes approximately 20-30% to the concentration of PCB 138 (32).
Results and Discussions PCB Content in Bulk Sediments. The total concentration of the 20 PCBs in the three sediments are presented in Table 1. The contamination range of the bulk sediments, based on dry sediment weight, is quite broad from 29 ng g-1 (Porquerolles sediment) to 181 ng g-1 (Lazaret Bay sediment). According to the criteria proposed by Marchand (33), the Mediterranean sediments may be considered as moderately to strongly contaminated samples since the pollution levels observed are in the range 50-500 ng g-1 (dry sediment weight). The most contaminated sediments being those situated near potential urban contamination sources: Lazaret Bay near Toulon (∑[PCB] ) 181 ng g-1) and Roquebrune Bay near Monaco (∑[PCB] ) 127 ng g-1) (33). From the three profiles shown in Figure 2 for the three sediments, it can be stated that there is a difference in PCB distributions in sediment from Lazaret on one side and sediments from Roquebrune and Porquerolles on the other side. PCB distributions are similar for both Porquerolles and Roquebrune sediments with a predominance of both tetra- and pentachlorobiphenyls; PCBs 44, 52, 66, 101, and 118 being the dominant congeners. They contribute between 50% and 70% of the total PCB content determined in these sediments. This PCB distribution patterns may be due to two effects. First, the high proportion of four and five chlorine atom congeners could indicate that the main contamination sources contain low chlorinated industrial
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8* 18 28 44 52 66* 87 101 105 118 128 138* 153 170* 180 187 195 200* 206 209
ditritritetratetratetrapentapentapentapentahexahexahexaheptaheptaheptaoctaoctanonadeca∑PCBs (ng/g)
2.0 2.4 3.2 6.8 15 16 4.7 15 6.8 17 3.4 26 29 6.2 13 9.5 1.6 0.50 2.6 1.6 181
Laz.2 Laz.3 800-300 300-63 µm µm
Laz.4 63-15 µm
Laz.5
