Environ. Sci. Technol. 2000, 34, 3323-3329
Temporal Trend of Organochlorine Marine Pollution Indicated by Concentrations in Mussels, Semipermeable Membrane Devices, and Sediment Å K E G R A N M O , * ,† R O L F E K E L U N D , † MATZ BERGGREN,† EVA BRORSTRO ¨ M - L U N D EÄ N , ‡ A N D PER-ANDERS BERGQVIST§ Kristineberg Marine Research Station, SE-450 34 Fiskeba¨ckskil, Sweden, Swedish Environmental Research Institute, P.O. Box 47086, SE-402 58 Go¨teborg, Sweden, and Institute of Environmental Chemistry, Umea˚ University, S-901 87 Umea˚, Sweden
To assess the short-term trend of pollution by hexachlorobenzene (HCB), chlorophenols, and polychlorinated biphenyls (PCB) emitted to a marine environment, existing and former loads were estimated based on pollutant concentrations in water, blue mussels, and sediment, using partitioning calculations. The study included chemical analyses of organochlorines in sediment samples, caged mussels, and semipermeable membrane devices (SPMD) incubated in the water column and in the outflow from an adjacent plant in order to find out whether the high pollutant concentrations found in the superficial sediment corresponded to former or existing discharges. A comparison was made of hypothetical water concentrations calculated from values determined in SPMDs, mussels, and sediment, assuming equilibrium in the distribution of the pollutants between mussels and water or sediment and water. Sediment-derived water concentrations of HCB in the vicinity of the outlet were much higher than the water concentrations calculated from SPMDs or mussels, indicating that the discharges of HCB from a local source were strongly reduced during the past decade. It is concluded that partitioning calculations applied on analytical data from mussels and superficial sediment, when combined with SPMD data, make possible the detection of short-term changes of environmental loads of hydrophobic pollutants.
Introduction Results from chemical analyses of superficial sediments sampled in a Swedish bay close to an industrial area indicated elevated concentrations of hexachlorobenzene (HCB) in the vicinity of one of the plants. An investigation was therefore initiated in order to find out whether the high pollutant concentrations found in the sediment corresponded to former or existing discharges. Since the period of interest * Corresponding author fax: +46-523-18502; phone: +46-52318534; e-mail:
[email protected]. † Kristineberg Marine Research Station. ‡ Swedish Environmental Research Institute. § Umea ˚ University. 10.1021/es991107t CCC: $19.00 Published on Web 07/11/2000
2000 American Chemical Society
was short and sediment bioturbation was extensive, it was not possible to use sediment chronology to establish the temporal trend of the pollution. The chosen alternative was to estimate the existing water concentration and compare it with a previous level in water calculated from the contents in the sediment using partitioning theory. The study included chemical analyses of organochlorines in sediment samples, caged mussels, and semipermeable membrane devices (SPMD) (1) incubated in the water column and in the outlet from the adjacent plant. A comparison was made of hypothetical water concentrations calculated from levels determined in SPMDs, mussels, and sediments assuming equilibrium in the distribution of the pollutants between mussels and water or sediment and water. Chlorobenzenes, chlorophenols, and PCBs were chosen as target analytes because they are known to be emitted in connection with PVC manufacture. The new technique using SPMDs was chosen in the present study as it seems to be the best available method to get a time-integrated short-term measure of levels of hydrophobic organic pollutants dissolved in the water column. The same devices have been used by Herve et al. (2) in comparing the levels of chlorophenols, chloroanisols, and chloroveratroles in SPMDs and mussels outside a paper pulp mill. Hofelt and Shea (3) also compared SPMDs and mussels. They found that the accumulation of organochlorine pesticides and PCBs was most efficient in the mussels. Axelman et al. (4) determined concentrations of PAHs in SPMDs, mussels, and suspended solids. They obtained much higher BCF values than those reported in the literature and concluded that the distribution of the PAHs between particles and water was far from equilibrium.
Materials and Methods Description of the Investigated Area. The wastewater from the studied plant is mixed with cooling water giving a total flow of 1500 m3 h-1, a temperature of +15 ( 2 °C, and a pH value around 7. Via an open channel, the water enters the sea in a shallow bay with a depth of 3-9 m. The water exchange is considerable with a dominant northward current. In the strait outside the bay the water depth is 15-25 m. Samples. Sediment samples were taken at six sites close to the plant and at a more distant reference site outside the industrial area (Figure 1). The samples were taken by a Ponar grab, and the upper 2 cm were collected in glass vials and immediately frozen for later chemical analyses. Common mussels (Mytilus edulis L.), 40-60 mm length, were taken from an area known to be relatively unpolluted and were caged at five sites (Figure 1). Around 100 specimen were frozen before deployment for determination of background levels. At each site three cages, i.e., three true replicates, were used. Each cage contained 60 specimen and was placed 1-2 m above the sea floor. To estimate the amount of dissolved organochlorines in the water, three sets of standard size (90 × 2.5 cm) semipermeable membrane devices (SPMDs) containing triolein (EST, St Joseph, MO, U.S. patents 5,098,573 and 5,395,426) (1) were exposed at each site and in the outlet channel from the plant. After 30 days, the mussels and SPMDs were retrieved. Ten mussels were taken from each cage, the shells were removed, and the soft tissues were frozen. Feral mussels were also sampled. Cleanup Procedures and Chemical Analyses. Target analytes were chlorobenzenes, chlorophenols, and polychlorinated biphenyls (PCBs). About 25 g of wet sediment was used for the chemical analyses. The content of organic VOL. 34, NO. 16, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Area investigated and sampling sites. Estimated levels of hexachlorobenzene (HCB) in water, derived from sediment, mussels, and semipermeable membranes (SPMD). carbon was determined by using a C/N analyzer (Fisons Instruments, NA 1500 NC). For determination of the organic contaminants, the samples were extracted by Soxhlet for 24 h with acetone followed by 24 h with hexane. To get a more efficient extraction of the chlorophenols, the acetone was acidified with sulfuric acid after 12 h. After the Soxhlet extraction, water was added to the acetone fraction, which was further acidified, and the organic compounds were transferred by extraction into 9:1 pentane/ether. The chlorophenols were separated from the neutral components by extracting the organic phase with a solution of potassium hydroxide. The hexane extract was partitioned with water and then combined with the pentane/ether extract. Before the analysis of chlorobenzenes, the samples were treated with concentrated sulfuric acid and then fractionated on an aluminum oxide column deactivated with 2% of water. Chlorobenzenes and PCBs were analyzed using gas chromatography-mass spectrometry (GC-MS) (Finnigan INCOS 50 connected to a Varian 3400 GC equipped with a 25-m capillary column with phase CP-Sil-8, CB, Chrompack, The Netherlands). For PCB analysis, a Varian 3400 GC with a 50-m capillary column with phase CP-Sil-8 and electron capture detection (ECD) was used. Identification and quantification were performed by means of internal and external standards. Chlorophenols in the potassium hydroxide fraction were acidified with concentrated phosphoric acid and were extracted with hexane/tert-butyl methyl ether (TBME). To estimate recovery during cleanup, 2,4,6-tribromophenol was added to the samples. They were then acetylated by the addition of sodium acetate and acetic acid anhydride and incubation at 75 °C for 20 min. Afterward the extracts were further purified on a silica gel column. The chlorophenol analyses were performed by gas chromatography (HP 5890 A) with a 30-m capillary column with phase DB-5 (J&W. Scientific, Folsom, CA) and helium as a carrier gas at 300 °C and ECD. External standards of the analyzed compounds were used for quantification. The mussels were thawed and homogenized. About 20 g wet weight was used for analysis. Subsamples were taken for 3324
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determination of fat and dry weight. Samples for chemical analysis were treated in the same way as for sediment. After being exposed, the SPMD samples were wiped with Kleenex and immediately frozen in glass jars. After being cleaned with a soft brush, Kleenex tissue, and water, the samples and laboratory blank SPMDs were extracted by dialysis for 3 days in renewed cyclopentane (30 + 60 + 90 mL). Six 13C-labeled internal standards and 50 mL of 99% ethanol were added to the dialysate. The samples were concentrated and dried on a sodium sulfate column. After being evaporated, the extracts were dissolved in a mixture of hexane and methylene chloride (1:1). The cleanup procedure followed a method described earlier (5). The next enrichment steps and analyses were similar to those of mussels and sediment. Estimation Procedures. The concentrations of HCB and PCBs dissolved in the water column and in the outlet were calculated from the amount in the SPMDs by use of the known laboratory-determined sampling rate (Rs) of the SPMD expressed as water volume sampled per day (6). Corrections were made for recovery during dialysis (85%) and cleanup. As no Rs were available for pentachlorophenol (PCP), 2,3,4,6tetrachlorophenol, and 2,4,6-trichlorophenol (clp), the rates were estimated from a reported relationship between Kow and Rs of PAHs (7). Two fourth-grade equations describing this relationship at 10 and 18 °C, respectively, were constructed and used to estimate Rs of the chlorophenols from Kow. When estimating Rs of the chlorophenols in seawater or in the outlet, the degree of protolysis was taken into account because SPMDs do not sample ionized organic compounds (1). The proportion of unprotolysed compound, which is the sampled neutral species, was calculated according to
pH ) pKa + log
b (1 - b)
where b is the proportion of protolysed substance and (1 b) is the proportion of unprotolysed substance.
TABLE 1. Constants Used for Calculation of Concentrations of Organochlorines in Seawater and Industrial Effluenta uncorrected SPMD sampling rate, Rs (L/day)
Kow
compd hexachlorobenzene
3.2 × (12)
pentachlorophenol
1 × 105 (10)
2,3,4,6-clp
2.4 × 104 (14)
2,4,6-clp
5.3 × 103 (14)
PCB 28
4.7 × 105 (6) 2.4 × 106 (6) 8.3 × 106 (6)
PCB 101 PCB 153
106
2.0 [10 °C] 2.6 [18 °C] d (13) 3.68 [10 °C] 4.20 [18 °C] e 3.04 [10 °C] 2.73 [18 °C] e 2.10 [10 °C] 1.02 [18 °C] e 8.7 [12 °C] d ( 6) 6.4 [12 °C] d ( 6) 3.6 [12 °C] d ( 6)
fraction of unprotolysed compd
Rs corrected for degree of protolysis (L/day)
BCF
Koc
1
2.0 [10 °C] 2.6 [18 °C]
3.2 × c, f
0.0006, pH 7 effl pKa 4.75 0.02, pKa 5.3 pH 7 effl 0.025, pH 8.2 0.29, pH 7, effl pKa 6.61 1
0.025, pH 7 effl
130 ww d (10) ∼90 ww e
900 d (10) 3900 d (16) 85 e
1
6.4
1
3.6
4.7 × 105 c, f 2.4 × 106 c, f 8.3 × 106 c, f
2.9 × 105 c 1.5 × 106 c 5.1 × 106 c
0.055, pH 7, effl
106
0.053, pH 8.2 0.30, pH 7, effl 8.7
2.0 × 106 c
a The numbers in parentheses denote literature references. c, calculated value; d, determined value; e, estimated value; effl, effluent; f, fat-based value; ww, wet weight-based value.
The concentration of each compound in water according to the SPMD (Cwsp) was calculated by using
Cwsp )
AMD FRRs(1 - b)d
where AMD is the total mass of the analyte in the dialysate, FR is fraction recovered from the SPMD by dialysis, Rs is the sampling rate, and d is the immersion time in days. As biofouling on the SPMDs was moderate, no adjustment was made for influence of fouling. Furthermore, concentrations of HCB, chlorophenols, and PCBs in water were estimated based on analytical data from mussels and sediment samples using the equilibrium partitioning model. When using the values from mussels, it was assumed that HCB and PCBs would partition between the mussel lipids and the surrounding water in the same way as between n-octanol and water and that steady-state prevailed. Thus, the concentration in water was obtained by dividing the lipid-normalized concentration of the substance in the mussel by the Kow value of the compound. To calculate PCP and 2,3,4,6- clp concentration in water based on concentration in mussels, experimentally determined bioconcentration factors were used instead of Kow as it is hard to predict how the degree of protolysis affects bioaccumulation (8). As the mussels were not defecated, an estimation was made of how much the amount of analyte in the gut contents contributed to the determined value of each compound in the mussels. This was possible by using published data on the amount of organic carbon in the gut contents (9). Assuming that the distribution of the analyte between water and organic carbon in food had reached equilibrium before ingestion, we can calculate the mass of analyte in the gut (Mag) per weight of mussel using
Mag ) CwKocMocg where Cw is the analyte concentration in water, either estimated from SPMDs or mussels; Koc is the constant for distribution of the compound between water and organic carbon in the food; and Mocg is the mass of organic carbon in the gut contents per weight of mussel. The obtained value is compared with the determined concentration of analyte in the mussels to judge the contribution from the gut contents.
Also, sediment values were used to calculate water concentrations, based on the hypothetical case that the distribution of each organochlorine between the water column and the sediment was at equilibrium. The sediment values were expressed per organic carbon and were divided by the partition coefficient, Koc. For HCB, 2,4,6-clp, and PCBs, the Koc value was calculated according to Kenaga and Goring (10) from
log Koc ) log Kow - 0.21 The calculated Koc value of 2,4,6-clp was adjusted for influence of pH on adsorption according to Schwarzenbach (11). When estimating water concentrations of PCP and 2,3,4,6clp, experimentally determined Koc values were used since it is impossible to predict Koc from Kow of these chlorophenols even if the degree of protolysis is taken into account (11). Constants used for the calculations are given in Table 1. Statistics. Statistical treatment of data was performed using the add-on program XLSTAT 4.2 for MS-Excel with the routine “comparison of two samples by a two-tailed Student’s test with unequal variances”. The H0 hypothesis was tested with a critical t-value for small samples (17).
Results Blank values were in most cases below the detection limit (DL), but the laboratory SPMD blanks showed a significant amount of HCB (0.9 ng) and PCBs (0.2-2.6 ng). The recovery of the analytes from the SPMDs by dialysis was estimated to be 85% from tests made with model compounds. The given values have been corrected for recovery. The levels of organochlorines in the sediment expressed per organic carbon are shown in Table 2. For HCB, all other sites indicated higher levels than the reference. The highest values of PCP in the sediment were found at stations 1, 5 and 6, i.e., in the vicinity of the outlet. PCB-28 also indicated an elevation closer to the discharge point. Water temperature was 10.5-15.0 °C (mean +13 °C). No mortality occurred among the mussels during the exposure period. The analytical results on mussels from the different sites are shown in Table 3. The background value of HCB, i.e., the concentration in mussels before caging, was approximately half of that found in mussels from the reference site and indicated an elevation of HCB in the whole studied VOL. 34, NO. 16, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Concentrations (mg/kg Organic Carbon) of Hexachlorobenzene (HCB), Pentachlorophenol (PCP), Other Chlorophenols (clp), and Polychlorinated Biphenyls (PCBs) in Sediments Sampled at the Studied Sites outside a PVC-Producing Planta site
HCB DL 0.02-0.03
PCP DL 0.03
2,3,4,6-clp DL 0.03
2,4,6-clp DL 0.03
PCB-28 DL 0.007
PCB-101 DL 0.007
PCB-153 DL 0.007
1 2 3 4 5 6 ref hist
0.68 2.20 1.44 0.37 1.36 0.63 0.02 nd
12.4 3.6 5.6 0.7 10.3 7.2
3.89 2.20 2.05 0.33 3.96 2.96
1.01 0.99 0.41 0.03 2.32 0.24
0.037 0.031 0.038 0.015 0.096 0.074 0.012 0.010
0.045 0.051 0.072 0.023 0.090 0.10 0.035 nd
0.031 0.051 0.056 0.023 0.062 0.091 0.073 nd
a Only one sample from each site was analyzed. Detection limits (DL) are given for each compound in a sediment with 3% organic carbon. Hist, a historical value of a sample taken from a 40-42-cm sediment depth. nd, not detected.
TABLE 3. Concentrations of HCB, PCP, and 2,3,4,6-Tetrachlorophenol (2,3,4,6-clp) in µg/kg dry weight (dw) and in µg/kg lipid weight (lw) (95% CI Found in Caged (C) and Feral (F) Blue Mussels from the Studied Sitesa site
HCB dw DL 0.2
HCB lw DL 1
PCP dw DL 0.05
2,3,4,6-clp dw DL 0.1
lipid content %/dw
1 (C) 1 (F) 2 (C) 2 (F) 3 (C) 4 (C) ref (C) ref (F) backgrd
*0.67 ( 0.24 1.20 0.65 ( 0.40 0.74 *0.70 ( 0.03 0.41 ( 0.21 0.37 ( 0.06 0.44 nd
*3.4 ( 1.0 5.0 5.9 ( 6.5 3.8 3.4 ( 2.0 2.0 ( 1.1 2.0 ( 0.3 2.3 nd
1.5 ( 4.2 5.5 2.7 ( 2.8 12 1.5 ( 3.4 1.1 ( 2.3 0.33 ( 0.68 0.6 nd
1.9 ( 2.6 0.8 2.1 ( 2.8 6.7 2.1 ( 2.5 0.33 ( 0.68 0.30 ( 0.58 nd nd
19.2 24.0 12.4 19.3 21.9 20.4 19.3 19.0 26.5
a An asterisk (*) denotes a value significantly different (P < 0.05) from that of the reference site. Detection limits (DL) are given for each compound.backgrd, background; nd, not detected.
The agreement between water concentrations indicated by mussels and SPMDs, respectively, was usually good for PCBs, differing at most with a factor of 5 (Table 10). However, SPMDs consistently indicated 10-60 times higher HCB levels than the mussels (Table 6). Closer to the outlet, water concentrations of HCB and chlorophenols according to sediment were generally much higher than those according to mussels or SPMDs, but for all PCBs there was only a slight difference. The results on proportion of HCB in the gut contents of the mussels show that, if the calculations are based on the higher water concentration according to SPMDs, the amount of analyte in the gut contributed 30% to the determined value. For all the analyzed PCBs, the contribution was less than 4%, and for PCP and 2,3,4,6-clp, it was less than 3%. If the HCB calculations are based on concentration in water according to the mussels, a much lower proportion of HCB in the gut contents is indicated.
Discussion TABLE 4. Contents (ng) ( 95% CI of HCB, PCP, and Other clp in SPMDs Incubated for 30 d at the Studied Sitesa site
HCB ( CI DL 0.1
PCP DL 5
2,3,4,6-clp DL 5
2,4,6-clp DL 10
2,4-clp DL -
outlet 1 2 3 4 ref
67 *4.0 ( 1.7 1.8 ( 1.1 *1.4 ( 0.5 *1.2 ( 0.3 0.37 ( 0.26
690
1200
772 26 19 nd 29 27
480 470 11 10 38
a An asterisk (*) denotes a value significantly different from that of the reference site (P < 0.05). For the chlorophenols, only one chemical analysis per site was made. Detection limits (DL) are given for each compound. nd, not detected.
area. SPMDs from station 1 had the highest HCB content (Table 4) corresponding to a water concentration of 66 pg/L (Table 6 and Figure 1). The level found in the outlet was higher, i.e., 1300 pg/L. As in the mussels, no lower chlorinated benzenes were detected in the SPMDs. PCP and 2,3,4,6-clp were found in the mussels (Table 3) with the highest concentrations at sites 1-3. In the SPMDs, neither PCP nor 2.3.4.6-clp were found, but contrary to the mussels, 2,4-clp and 2,4,6-clp were detected (Table 4). The existing distribution of the latter seemed to be uniform in the area. Among the analyzed PCBs only PCB-28 and -101 showed a weak pollution gradient according to the mussels (Table 5) with stations 1 and 3 being significantly different from the reference. The concentrations of HCB in water, derived from mussel, SPMD, and sediment data are given in Table 6. The corresponding values for chlorophenols are given in Tables 7-9 and for PCBs in Table 10. 3326
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Elevated levels of HCB, PCP, and 2,3,4,6-clp in all three sampling matrixes in the outlet area show that the PVC plant is an important local source, but 2,4,6-clp and PCBs only indicated a weak or no concentration gradient. The latter observation and the low concentrations in the outlet show that the local source contributed very little to the exisiting 2,4,6-clp and PCB pollution in the area. The similarity between feral and caged mussels regarding the HCB level indicates that the level in the latter had reached steady state after the 30-day incubation period at 13 °C. According to Pruell et al. (18), the distribution of organochlorines between mussels and water had reached steady state after 20-25 days at +15 °C. In view of this, it is hard to explain why SPMDs indicated higher water concentrations of HCB than the mussels did. Rather it is expected that SPMDs and mussels should indicate similar concentrations if the proper constants are used, if equilibrium partition was the determining mechanism and transformation, active excretion, and biomagnification were of minor importance. Also the PCB levels were similar between feral and caged mussels, but in this case mussels and SPMDs, as expected, indicated equivalent concentrations in water. The estimated proportion of organochlorine in the gut contents of the mussels indicates that defecation before analysis is less important except for HCB where the gut contents contributed to the determined value with 30%. This is a conservative estimate based on the higher HCB concentration in water as indicated by SPMDs. Temporal trends of pollution may sometimes be traced by means of sediment chronology if laminated sediments are available in the investigated area. However, as bioturbation was extensive and the study period was relatively short (roughly 5-10 years based on a sedimentation rate of 2-4
TABLE 5. Concentrations of PCB-28, -101, and -153 in µg/kg Dry Weight (dw) and in µg/kg Lipid Weight (lw) ( 95% CI Found in Caged Blue Mussels from the Studied Sitesa mussels
SPMD
site
PCB-28 DL 0.2
PCB-101 DL 0.2
PCB-153 DL 0.2
PCB-28 DL 1.0
PCB-101 DL 0.5
PCB-153 DL 0.5
1 3.5 ( 1.3 lw 2 3.9 ( 6.0 lw 3 2.9 ( 2.1 lw 4 1.6 ( 0.4 lw ref 1.6 ( 0.7 lw
*0.7 ( 0.3 dw 19 ( 2.9 lw 0.4 ( 0.4 dw 25 ( 29 lw *0.6 ( 0.1 dw 18 ( 12 lw. 0.3 ( 0.1 dw 13 ( 5.1 lw 0.3 ( 0.04 dw 14 ( 4.8 lw
*3.7 ( 0.4 dw 21 ( 1.9 lw 2.6 ( 1.5 dw 33 ( 36 lw *3.6 ( 0.6 dw 22 ( 14 lw 2.7 ( 1.0 dw 18 ( 8.4 lw 2.5 ( 0.3 dw 20 ( 10 lw
4.2 ( 0.1 dw
3.5 ( 2.2
1.3 ( 0.3
0.6 ( 0.3
3.6 ( 2.0 dw
5.1 ( 0.2
1.4 ( 0.8
0.7 ( 0.3
4.4 ( 0.4 dw
3.3 ( 2.4
1.1 ( 0-6
nd
3.7 ( 1.5 dw
2.8 ( 2.6
nd
nd
3.7 ( 0.7 dw
3.5 ( 1.5
nd
nd
a An asterisk (*) denotes a value significantly different (P < 0.05) from that of the reference site. Detection limits (DL) are given for each compound. nd, not detected.
TABLE 6. Estimated Concentrations (pg/L) of HCB in Water ( 95% CI, Calculated from the Respective Levels in Mussels (Cwm), SPMDs (Cwsp), and Sediment (Cws) from the Studied Sitesa site
Cwm ( CI
Cwsp ( CI
outlet 1 1 2 2 3 4 1-4 (mean) ref ref background Offshore Kattegat Go¨ teborg inner archipelago
*1.1 ( 0.3 (C) 1.6 (F) 1.8 ( 2.0 (C) 1.2 (F) 1.0 ( 0.6 (C) 0.63 ( 0.34 (C) 1.1 ( 0.4 (C) 0.61 ( 0.08 (C) 0.71 (F) 0.22 1.8 (C) 22 (F)
1300 *66 ( 28 31 ( 18 *24 ( 8 *20 ( 6 35 ( 11 6.1 ( 6.0
ratio Cws/Cwm
Cws 340 340 1100 1100 720 180 590 ( 480 7.7 7.7
320 220 610 940 690 290 13 11
5.7 70
3 3
a Ratio between sediment-derived and mussel-derived water concentration is also given for each site. C and F stand for caged and feral mussels, respectively. An asterisk (*) denotes a value significantly different from that of the reference site.
TABLE 7. Estimated Concentrations (pg/L) of PCP in Water ( 95% CI, Calculated from Levels in Mussels (Cwm), SPMDs (Cwsp), and Sediment Samples (Cws)a site
Cwm ( 95% CI
Cws
outlet 1 1 2 2 3 4 1-4 (mean) ref 870 (F) background
1100000 (Cwsp) 2600 ( 7400 (C) 6300(F) 4600 ( 4700 (C) 14000(F) 2700 ( 6300(C) 2000( 4200(C) 3100 ( 1500 (C) 560 ( 1200(C)
14 × 14 × 106 4.0 × 106 4.0 × 106 6.3 × 106 0.79 × 106 (6.2 ( 6.5) × 106
ratio Cws/Cwm
TABLE 8. Estimated Concentrations (pg/L) of 2,3,4,6-Tetrachlorophenol in Water ( 95% CI, Derived from the Respective Levels in Mussels (Cwm), SPMDs (Cwsp), and Sediment Samples (Cws)a site
106
5300 2200 880 290 2300 400
< 65
outlet 1 1 2 2 3 4 1-4 (mean) ref nd (F)
Cwm ( CI
Cws
1000000 (Cwsp) 4700 ( 6600 (C) 10 × 105 1400 (F) 10 × 105 5200 ( 7000(C) 5.6 × 105 11000(F) 5.6 × 105 5300 ( 6000 (C) 5.3 × 105 850 ( 1900 (C) 0.9 × 105 3800 ( 1900 (C) (5.6 ( 4.4) × 105 700 ( 1500 (C)
ratio Cws/Cwm 210 740 110 50 100 100
a
Ratio between sediment-derived and mussel-derived water concentration is also given. C and F stand for caged and feral mussels, respectively.
mm/year and 2 cm of sampled sediment), sediment chronology could not be used. Therefore, we chose to compare the results of our estimates of organochlorine concentration in the water column with that of an earlier period of time, as calculated from superficial sediment data using the equilibrium partitioning approach. To avoid the introduction of different errors when using coefficients for calculations of water concentrations from HCB and PCB levels in sediment and mussels, Kow was used both to estimate a theoretical Koc value and as a lipid-based bioconcentration factor. The use
a Ratio between sediment-derived and mussel-derived water concentrations is also given. C and F stand for caged and feral mussels, respectively. nd, not detected.
of Kow for the latter purpose is considered justified as the bioconcentration of a persistent hydrophobic pollutant may be regarded as a partitioning process between the surrounding water and the lipids of the animal and since these have similar dissolving properties as n-octanol (1, 3, 4, 8, 19, 20). When using such a theoretical bioconcentration factor, transformation and active excretion are disregarded. We consider this reasonable as HCB and PCBs are only slowly metabolized by mussels (20). Biomagnification is not taken VOL. 34, NO. 16, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 9. Estimated Concentrations (pg/L) of 2,4,6-Trichlorophenol in Water, Calculated from the Levels in SPMDs (Cwsp) and Sediment Samples (Cws)a Cwsp
site
Cws
ratio Cws/Cwsp
outlet 100 × 1 19 × 103 1200 × 104 2 14 × 103 1200 × 104 3 6.0 × 103 480 × 104 4 22 × 103 29 × 104 1-4 (mean) (15 ( 8) × 103 (720 ( 660) × 104 ref 20 × 103 103
610 820 810 13
a Ratio between sediment-derived and SPMD-derived water concentration is also given. Only one sample from each site was analyzed.
TABLE 10. Estimated Concentrations (pg/L) ( 95% CI of PCBs in Water, Calculated from the Respective Levels in Mussels (Cwm), SPMDs (Cwsp), and Sediment (Cws) Exposed at the Studied Sitesa site outlet
PCB-28 PCB-101 PCB-153 1 PCB-28 PCB-101 PCB-153 1 PCB-28 PCB-101 PCB-153 2 PCB-28 PCB-101 PCB-153 2 PCB-28 PCB-101 PCB-153 3 PCB-28 PCB-101 PCB-153 4 PCB-28 PCB-101 PCB-153 1-4 PCB-28 (mean) PCB-101 PCB-153 ref PCB-28 PCB-101 PCB-153 ref PCB-28 PCB-101 PCB-153 background PCB-28 PCB-101 PCB-153 hist PCB-28 PCB-101 PCB-153
Cwm ( CI
Cwsp ( CI
Cws
26.8 9.9 94.8 7.4 ( 2.7 (C) 13.6 ( 8.4 130 7.9 ( 1.2 (C) 7.0 ( 1.6 30 2.6 ( 0.2 (C) 5.4 ( 3.1 6.0 4.3 (F) 130 6.3 (F) 30 1.8 (F) 6.0 8.3 ( 12.9 (C) 19.5 ( 0.8 110 10.4 ( 12.0 (C) 7.4 ( 4.1 35 4.0 ( 4.3 (C) 6.5 ( 3.1 10 8.1 (F) 110 10.4(F) 35 3.5 (F) 10 6.1 ( 4.5 (C) 12.1 ( 8.4 130 7.4 ( 5.1 (C) 5.7 ( 3.2 49 2.6 ( 1.7 (C) nd 11 3.5 ( 0.8 (C) 11 ( 10 52 5.6 ( 2.1 (C) nd 15 2.2 ( 1.0 (C) nd 4.4 6.3 ( 3.3 (C) 14 ( 6.1 105 ( 58 7.8 ( 3.2 (C) 6.7 ( 2.1 32 ( 22 2.8 ( 1.3 (C) nd 7.9 ( 5.0 3.5 ( 1.5 (C) 14 ( 5.7 39 5.7 ( 2.0 (C) nd 23 2.4 ( 1.2 (C) nd 22 4.1 (F) 39 6.7 (F) 23 3.4 (F) 22 2.1 4.6 2.0 34 nd 0.1
ratio Cws/Cwm
17 4 2 30 5 3 13 3 3 14 4 3 22 7 4 15 3 2
11 4 9 10 3 7
a Ratio between sediment-derived and mussel-derived water concentration is also given for each site. C and F stand for caged and feral mussels, respectively. Hist, a historical value of a sample taken from a 40-42-cm sediment depth. nd, not detected.
into account either, but this will only introduce a minor error since biomagnification of hydrophobic pollutants is considered to be slight in gill-breathing aquatic organisms of small size (21). From a comparison of water concentrations of HCB, obtained from SPMDs or mussels with sediment-derived water concentrations (Table 6), it is seen that the distribution of HCB between the water column and the sediment organic carbon is far from equilibrium. In the outlet area, the water concentrations calculated from sediment are 200-900 times higher than those obtained from mussels and 5-36 times 3328
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higher than those obtained from SPMDs. As only one sediment analytical value is available for each site and chemical, a statistical comparison of sediment-derived (former loads) and mussel- or SPMD-derived water concentration (existing loads) can only be made on the contaminated area as a whole, i.e., a comparison of values, each representing a mean from sites 1-4. Thus, for HCB a mean sediment-derived water concentration (Cws) of 590 ( 480 pg/L may be compared with a mussel-derived water concentration (Cwm) of 1.1 ( 0.4 pg/L. According to the statistical test, these two values are significantly different (P < 0.07). A corresponding comparison of Cws versus Cwm or Cwsp of chlorophenols and PCB-153 shows no significant differences, whereas Cws versus Cwm or Cwsp of PCB-28 and -101, respectively, are significantly different (P < 0.05). That the sediment-derived water concentration is significantly higher than the mussel- or SPMD-derived one for HCB, PCB-28 and -101 indicates that, during the period of time when the sampled sediment layer was formed, the suspended particles were surrounded by water with higher concentrations of these organochlorines than recent levels estimated from SPMDs and mussels indicate. In other words, the discharges of HCB, PCB-28 and -101 seem to have been reduced during the past decade. The ratios between sediment-derived and mussel-derived water concentrations of HCB are also given (Table 6). The highest ratios (200-900) were obtained for stations in the discharge area indicating a strong decrease of HCB emission from the local source. At the reference site the ratio was 12. This shows that the less the contribution from the local point source was, the weaker the trend of decreasing pollution. For two sites, one offshore and one close to Go¨teborg, both representing the much weaker general trend of decreasing HCB pollution (22), the corresponding calculations have been made. The same obtained ratio for both sites, 3, shows that the calculation method gives reasonable results. For PCP, the corresponding ratios between sedimentderived and mussel-derived water concentrations were even higher than for HCB (Table 7), i.e., 300-5000. This is not necessarily due to a stronger reduction of discharges but may be caused by PCP formation from HCB in the environment (23). However, the rate of the subsequent PCP degradation in the sediment is not known. For 2,3,4,6-clp a similar pattern as HCB and PCP is seen (Table 8). The Cws/ Cwsp ratios of 2,4,6-clp (Table 9) likewise point to decreasing emission from the local source. The lower persistence of 2,4,6-clp (24) will however lead to declining concentration in the sediment and will cause an underestimation of Cws, i.e., its former concentration in the water column and a corresponding underestimation of the decrease. The existing HCB, PCB, and chlorophenol concentrations in the water column are probably the combined result of discharges from the local source, background contamination, and, to some extent, release from the contaminated sediment. The latter source is probably more important for the less hydrophobic chlorophenols. The trend of higher PCP level in the bottom-dwelling feral mussels as compared to the caged ones (Table 7) may be due to release from the sediment. From the results of the present study, it is concluded that SPMDs make possible the detection of compounds additional to those found in mussels. In future investigations SPMDs will be a very valuable tool to increase the knowledge of bioavailability and distribution in the environment of hydrophobic organic pollutants, provided that SPMD sampling rates will be available for more compounds.
Acknowledgments We thank Dr. J. N. Huckins, Midwest Science Center, Colombia, SC, for valuable comments on the manuscript and Drs. M. Remberger and J. Mowrer, The Swedish
Environmental Research Institute, Stockholm, for chemical analyses of chlorophenols. Mr. L. Alleska¨r and his staff at Hydro Plast AB are acknowledged for their assistance with field exposure and sampling. This work was financed by the Swedish Environmental Protection Agency and Hydro Plast AB, Stenungsund.
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Received for review September 28, 1999. Revised manuscript received April 19, 2000. Accepted May 5, 2000. ES991107T
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