Organochlorine pesticides and polychlorinated biphenyls in livers of cod from the southern Baltic, 1981

471 samples of livers of cod netted in July 1981 in seven fishing grounds in the southern part of the Baltic were analysed for polychlorinated biphenyls (PCBs), DDT and its metabolites (DDE and DDD), hexachlorobenzene (HCB), and isomers of benzenehexachloride (alpha-, beta-, gamma- and delta-BHC). Polychlorinated biphenyls resembling Chlopten A 60 were the predominating pollutants and their level ranged from trace amounts to 79 mg/kg. In the individual wet cod livers sigma DDT level ranged from 0.22 to 15 mg/kg. alpha-BHC, gamma-BHC and HCB levels ranged from not detectable levels to 0.29, 1.1 and 0.42 mg/kg, respectively. beta-BHC was detectable in most of the samples in trace amounts and delta-BHC was undetected. The levels of HCB, DDT and analogues and PCBs in the cod livers correlated with the length of the fish. The residue levels of sigma DDT in cod livers declined. The larger cod contained in their livers substantial levels of PCBs, and also of sigma DDT. However some local differences in pollution pattern were observed. The livers of cod from the Southern Baltic are relatively highly contaminated with these substances and the use of these products for human consumption is still questionable.     

Organochlorine pesticides and polychlorinated biphenyls in cod from the southern Baltic, 1983

Hexachlorobenzene (HCB), alpha-, beta-, gamma- and delta-benzenehexachloride (BHC; HCH), p,p'-DDE, o,p'-DDD, o,p'-DDT, p,p'-DDD and p,p'-DDT (sigma DDT) and polychlorinated biphenyls (PCB) levels have been determined in muscle tissue of 207 cod (Gadus morhua) netted during 1983 in different regions in the southern part of the Baltic Sea. The mean levels found for cod muscle tissue (microgram/kg) related to wet weight were: 0.65 HCB, 1.2 alpha-BHC, 9.0 beta-BHC, 2.8 gamma-BHC, delta-BHC remained undetected, 13 sigma BHC, 4.4 p,p'-DDE, o,p'-DDD and o,p'-DDT remained undetected, 4.0 p,p'-DDD, 1.8 p,p'-DDT, 10 sigma DDT and 55 PCBs. The results are compared with levels found in cod caught in different regions of the Baltic Sea during 1967-1983, and reported previously by other authors.     

Dioxin and dioxin-like PCB levels in cod-liver and -muscle from different fishing grounds of the North- and Baltic Sea and the North Atlantic

The contaminant levels of dioxins, dioxin-like PCBs and non dioxin-like PCBs were determined in pooled samples of cod liver and corresponding cod muscle from different fishing grounds of the North- and Baltic Sea and from East Greenland. The dependence of the contaminant concentrations was studied on cod of three different sizes caught at the same fishing ground. Samples were taken during different research trips at 11 fishing grounds of the Baltic Sea, and 3 fishing grounds of the North Sea and of East Greenland in 2006 and 2007, respectively. Cod liver from the Baltic- and the North Sea were highly contaminated. Mean concentrations were 93 and 83 ng WHO-TEQ/kg wet weight (w.w.), respectively. Cod livers from East Greenland had only low contaminant levels of 3.4 ng WHO-TEQ/kg w.w. Highest concentrations were found in livers from the Bay of Kiel. Within the same fishing area the concentrations increased with the size of the cod. The WHO-TEQ amounts of the cod fillets were below 1 ng WHO-TEQ/kg w.w. and thus within the commonly observed low range for lean fish.     

Organochlorine pesticides and polychlorinated biphenyls in cod from the southern Baltic, 1981

98 samples of muscle tissue of cod ranging form 51 to 60 cm in total length and netted in 1981 in the southern part of the Baltic Sea were analysed for polychlorinated biphenyls (PCBs), DDT and its metabolites (DDE and DDD), hexachlorobenzene (HCB), and isomers of benzenehexachloride (alpha-, beta-, gamma- and delta-BHC). Mean values obtained related to wet weight for cod muscle tissue were: 0.77 micrograms kg/HCB, 0.71 micrograms kg/alpha-BHC, 3.8 micrograms kg/gamma-BHC, 5.2 micrograms kg/p,p'-DDe, 2.6 micrograms kg/p,p'-DDD, 2.6 micrograms kg/p,p'-DDT, 10 micrograms kg/sigma DDT and 180 micrograms kg/PCB; beta-BHC was detectable in trace amounts and delta-BHC was undetected. Generally residue levels of organochlorine pesticides and PCBs found in the muscles were low, and substantial decrease of sigma DDT and less of PCB levels in recent years when compared with data noted in 1969-1970 and 1972-1974 is noticeable.     

Aluminium content in edible parts of seafood

Samples of the edible parts of different fish species and of crustacean and molluscan shellfish were collected in the North Sea, the Barents Sea, the Baltic Sea, the Northeast Atlantic, and in Greenland waters. Most of the aluminium concentrations in fillets of lean and fatty fish were lower than 0.2?mg Al/kg wet weight. Exceptions were the aluminium concentrations in fillets of fish caught near an aluminium smelting plant (up to 1?mg Al/kg wet weight). Presumably a connection between the aluminium content in sea water and the fish fillets is responsible for this. The investigations of fillets of saithe, haddock, and cod with different lengths (age) showed that the aluminium levels decreased with increasing length, however, the decrease was not significant. An aluminium accumulation in muscle tissue with increasing age could not be detected. A comparison between fillets and different organs of cod showed higher aluminium concentrations in organs, especially in gills. The aluminium intake via gills, which are in continuous contact with the ambient water, is responsible for this. In the edible part of crustacean and molluscan shellfish higher aluminium concentrations (up to 5?mg Al/kg wet weight) were detected. The different feed spectrum and metabolism of these species seem to be responsible for the higher aluminium accumulation in marine crustacean and molluscan shellfish.     

Organochlorine pesticides and polychlorinated biphenyls in livers of cod from the southern Baltic, 1983

Hexachlorobenzene (HCB), alpha-, beta-, gamma- and delta-benzenehexachloride (BHC; HCH), p,p'-DDE, o,p'-DDD, o,p'-DDT, p,p'-DDD and p,p'-DDT (sigma DDT) and polychlorinated biphenyls (PCB) levels have been determined in livers of 210 cod (Gadus morhua) netted during 1983 in a different regions in the southern part of the Baltic Sea. The mean levels found for cod livers related to wet weight (mg/kg) were: 0.096 HCB, 0.15 alpha-BHC, beta-BHC was found in trace amounts, 0.098 gamma-BHC, delta-BHC remained undetected, 0.26 sigma BHC, 1.1 p,p'-DDE, o,p'-DDD and o,p'-DDT remained undetected, 1.1 p,p'-DDD, 0.39 p,p'-DDT, 2.6 sigma DDT and 7.2 PCB. The levels of sigma DDT, sigma BHC and HCB found are comparable with those noted in livers taken from cod of the same length class and netted in 1981, whilst-for PCB somewhat lower levels were found. Because of heavy contamination with PCBs, sigma DDT, sigma BHC and HCB the livers of cod caught in Baltic Sea still remain insuitable for human consumption.     

Trace metals in muscle tissue of fish taken from the southern Baltic

The determination of Fe, Mn, Ni, Pb, Cu, Co, Zn and Cd was investigated on 123 samples of muscle tissue of cod, herring, sprat and some other species of fish caught in 1981 in the southern Baltic Sea. The ranges and mean levels of metals recorded in this paper are compared with values reported previously by other authors for cod, herring and sprat from different regions of the Baltic Sea. The correlation coefficients between the metal concentrations in cod and herring muscles were calculated. The species-dependent changes of some metals in species analysed were observed.     

Organochlorine pesticides and polychlorinated biphenyls in flatfish from the southern Baltic, 1983

Hexachlorobenzene (HCB), alpha-, beta-, gamma- and delta-benzenehexachloride (BHC; HCH), p,p'-DDE, o,p'-DDD, o,p'-DDT, p,p'-DDD and p,p'-DDT (espilon DDT) and polychlorinated biphenlys (PCBs) levels have been determined in muscle tissue of 37 turbots Psetta maxima, 27 plaices Pleuronectes platessa and 106 flounders Platichthys flesus netted during 1983 in a different regions in the southern part of the Baltic Sea. The mean levels found for flatfish muscle tissue related to wet weight were: 0.7, 0.88 and 1.1 microgram/kg HCB; 1.3, 2.6 and 3.0 micrograms/kg alpha-BHC; 11, 10 and 11 micrograms/kg beta-BHC; 4.4, 4.9 and 5.5 micrograms/kg gamma-BHC; delta-BHC remained undetected; 17, 18 and 20 micrograms/kg epsilon BHC; 5.1, 5.2 and 8.7 micrograms/kg p,p'-DDE; o,p'-DDD remained undetected; o,p'-DDT was detected in 10 of 106 samples of the muscle tissue of flounder at the mean level of 17 micrograms/kg; 4.6, 5.0 and 7.6 micrograms/kg p,p'-DDD; 3.1, 4.0 and 11 micrograms/kg p,p'-DDT; 13, 14 and 29 micrograms/kg epsilon DDT and 71, 66 and 94 micrograms/kg PCBs for turbot, plaice and flounder, respectively. Generally, the levels of organochlorine pesticides and PCBs in wet muscle tissue of fish followed the increased lipids content of muscles. Some local differences in pollution pattern of organochlorines have occurred. The results are compared with levels found in flatfish collected in a different regions of the Baltic Sea during 1966-1981, and reported previously by other authors.     

Predicting effects of exploitation rate on weight-at-age, population dynamics, and bioaccumulation of PCDD/Fs and PCBs in herring (Clupea harengus L.) in the Northern Baltic Sea

The Baltic Sea ecosystem and fish stocks contain high concentrations of environmental chemicals such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs). This study forecasts how changes in fishing or natural mortality would probably influence concentrations of PCDD/F and PCB in the Bothnian Sea (Northern Baltic) herring (Clupea harengus L.). An age-structured simulation model was developed to forecast herring stock dynamics, catches, and weight-at-age under different assumptions about exploitation and natural mortality. The simulated herring weight-at-age estimates were employed in a bioenergetics model capable of simultaneous estimation of bioaccumulation of 17 PCDD/F and 37 PCB congeners. Although the natural variability in recruitment greatly influences the stock dynamics, considerable changes in weight-at-age would ensue changes in exploitation rate or in natural mortality rate. If exploitation rates increase, growth rates would be higher and herring in the weight categories of commercial fisheries would be younger and contain less PCDD/F and PCB. Hence, the average toxicant concentrations in catches would also decline. However, it is likely that only fairly small changes would occur in toxicant concentrations-at-age. On the other hand, a drastic decrease in herring fishing would substantially increase PCDD/F and PCB concentrations in herring. The study indicated that, in spite of the clear influences of fishing on the toxicant concentrations, fishing alone cannot resolve the problems associated with a high concentration of toxicants in herring; further decreases in loading are still required.     

Trace metals in cod from the southern Baltic, 1983

The cadmium, lead, copper, zinc, iron, manganese, and nickel concentrations have been determined in muscle tissue of 201 cod (Gadus morhua) netted in 1983 in different regions in the southern part of the Baltic Sea. The method of measurement was atomic absorption spectrophotometry. The mean values obtained related to wet weight (mg/kg) for cod muscle tissue were: 0.005 Cd, 0.086 Pb, 0.15 Cu, 3.9 Zn, 3.7 Fe, 0.21 Mn, and 0.081 Ni. The results are compared with values reported previously for cod from the Baltic Sea by other authors.     

Evaluation of mercury levels in pangasius and cod fillets traded in Sicily (Italy)

Predator fishes at the top of the aquatic food chain can accumulate large concentrations of metals and their consumption, consequently, makes a significant contribution, in particular, to mercury intake. The aim of this study was to determine mercury levels in fillets of two predatory species: pangasius (Pangasius hypophthalmus) from the Vietnam region of Megong and Chao Pharayai and cod (Gadus morhua) from the Baltic and North Sea, both being commercially important in the Italian market. A comparative analysis of these two imported fish species was carried out as a risk assessment for consumer safety. The results showed the presence of higher mercury levels in pangasius (0.41 ± 0.08 mg kg(-1)) than in cod (0.11 ± 0.004 mg kg(-1)) fillets. These data underline the importance of monitoring on imported fish before marketing, to evaluate better the risk of mercury exposure through fish and seafood consumption, and of selecting safer fishes for consumption by those groups more sensitive to the toxic effects of this metal.     

Organochlorine pesticides and polychlorinated biphenyls in herring from the southern Baltic, 1983

Hexachlorobenzene (HCB), alpha-, beta-, gamma- and delta-benzenehexachloride (BHC, HCH), p,p'-DDE, o,p'-DDD, o,p'-DDT, p,p'-DDD and p,p'-DDT (sigma DDT) and polychlorinated biphenyls (PCB) levels have been determined in muscle tissue of 187 herring (Clupea harengus) netted during 1983 in a different regions in the southern part of the Baltic Sea. The mean levels found for herring muscle tissue related to wet weight (microgram/kg) were: 14 HCB, 18 alpha-BHC, 23 beta-BHC, 14 gamma-BHC, delta-BHC remained undetected, 56 sigma BHC, 115 p,p'-DDE, o,p'-DDD and o,p'-DDT remained undetected, 84 p,p'-DDD, 51 p,p'-DDT, 250 sigma DDT and 530 PCB. The levels of organochlorine pesticides determined in wet muscles or extractable lipids of herring are nearly 2-3 times as high as those noted in fish sampled in the same area in two years before, whilst for PCBs the wet weight levels were comparable, and when based on a lipid weight are somewhat higher. The results are compared with levels found in herring collected in different regions of the Baltic Sea during 1965-1983, and reported previously by other authors.     

Spatial distibution and temporal accumulation of polychlorinated dibenzo-p-dioxins,dibenzofurans, and biphenyls in the Gulf of Finland

Dated sediment cores and surface sediments were analyzed from the Gulf of Finland, a part of the Baltic Sea, to study the sources, levels, distribution, and total amounts of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs). The gulf was found to be severely polluted, with PCDD/F sum concentrations as high as 101000 ng/kg and 479 ng/kg WHO-TEQ in dry weight. The source of pollution was the former manufacturing and use of a chlorophenol based wood preservative along the Kymijoki River. It was estimated thatthe impacted sedimentary area stretched a distance of 75 km away out from the coast and that the PCDD/F sum load attributed to the wood preservative source was 1770 kg of PCDD/Fs or 12.4 (+/-2.8) kg WHO-TEQ. The surface sediments contained 24-66% of the maximum concentrations present in the 1960-1970s, showing that the river still acts as a significant PCDD/F source and may contribute to the high levels in fish. Moreover, the reduced PCDD/F and PCB concentrations were partly due to the dilution by increased dry matter deposition. PCBs were uniformly distributed over the gulf, and the PCB load in the polluted area was 2020 kg or 0.14 kg WHO-TEG.     

Trace metals in cod from the southern Baltic, 1983

Zusammenfassung Die Konzentration von Cadmium, Blei, Kupfer, Zink, Eisen, Mangan und Nickel wurde in den Muskelgeweben von 201 Kabeljaus (Gadus morhua), gefangen in verschiedenen Regionen der südlichen Ostsee 1983, bestimmt. Die Mcßmethode war Atomabsorptions-Spektrometrie. Die mittleren erhaltenen Werte für das Frischgewicht des Muskelgewebes betrugen: 0,005 mg/kg Cd, 0,086 mg/kg Pb, 0,15 mg/kg Cu, 3,9 mg/kg Zn, 3,7 mg/kg Fe, 0,21 mg/kg Mn und 0,081 mg/kg Ni. Die Ergebnisse wurden mit den früher veröffentlichten Werten für Kabeljau und mit den anderer Autoren aus der Ostsee verglichen.Summary The cadmium, lead, copper, zinc, iron, manganese, and nickel concentrations have been determined in muscle tissue of 201 cod (Gadus morhua) netted in 1983 in different regions in the southern part of the Baltic Sea. The method of measurement was atomic absorption spectrophotometry. The mean values obtained related to wet weight (mg/kg) for cod muscle tissue were: 0.005 Cd, 0.086 Pb, 0.15 Cu, 3.9 Zn, 3.7 Fe, 0.21 Mn, and 0.081 Ni. The results are compared with values reported previously for cod from the Baltic Sea by other authors.[/p]

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Spurenelemente im Kabeljau aus der südlichen Ostsee, 1983

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Partially with financial support under grant PR-4 (Sea Fisheries Institute)     

Organochlorine pesticides and polychlorinated biphenyls in sprats from the southern Baltic, 1981

102 samples of the muscle tissue of sprat netted in 1981 in the southern part of the Baltic Sea were analysed for polychlorinated biphenyls (PCBs), DDT and its analogues (DDE and DDD), hexachlorobenzene (HCB), and isomers of benzenehexachloride (alpha-, beta-, gamma-, and delta-BHC). The mean values obtained related to wet weight for sprat muscle meat were: 6.4 micrograms HCB/kg, 11 micrograms alpha-BHC/kg, 20 micrograms gamma-BHC/kg, 33 micrograms p,p'-DDE/kg, 42 micrograms p,p'-DDD/kg, 31 micrograms p,p'-DDT/kg, 110 micrograms sigma DDT/kg and 670 micrograms PCB/kg; beta-BHC was detectable in trace amounts and delta-BHC was undetected. The results are compared with values reported previously by other authors.     

Polychlorinated biphenyls (PCBs) and their congener-specific accumulation in edible fish from the Gulf of Gdańsk, Baltic Sea.

Concentrations and composition profiles of polychlorinated biphenyls (PCBs) were investigated in composite samples of 10 species of edible fish from the Gulf of Gdańsk, in the southern part of the Baltic Sea, Poland, to understand the status of contamination and possible human exposure risk. Apart from the total PCBs, planar non-ortho (IUPAC nos 77, 126, 169) and mono-ortho (nos 105, 114, 118, 123, 156, 157, 167, 189) chlorobiphenyls were also quantified and their dioxin-like toxicity assessed. The absolute total PCB concentrations in fish ranged from 43 to 490 ng g(-1) wet wt (910-11000 ng g(-1) lipids), while of TCDD TEQs of planar members were from 0.15 to 3.1 pg g(-1) wet wt (8.1-81 pg g(-1) lipids). The penta- and hexa-CBs usually comprised 70-80% of the total PCBs and were followed by hepta-, tetra- and tri-CBs, and for a specific site tri- and tetra-CBs comprised as much as 22%. Among the individual CB congeners, nos 118, 153 (+132) and 138 (+160 +163 +164) were the most abundant, while no. 110 comprised between 6.8 and 9.3% of the total PCBs in some species. Principal component analysis (PCA) was applied to examine the interdependences among CB congeners in the factor space. The PCA model and cluster analyses were further used to examine site- and species-specific differences and similarities of PCB composition, and the results are discussed. An assessed daily intake rate of TCDD TEQ of planar PCBs with the fishmeal of the Gulf of Gdańsk in the 1990s was between 78 and 96 pg per capita or between 1.3 and 1.6 pg kg(-1) body weight.     

Marine and farmed fish in the Polish market: Comparison of the nutritional value

The proximate composition and fatty acids profiles of the muscle tissues of nine fish species that are popular on the Polish market were examined. The nine studied fish species were: Baltic fish (cod, herring, salmon), fish farmed in Poland (carp, trout), oceanic fish imported from China (walleye pollock, sole), and farmed fish imported from Vietnam and China (sutchi catfish, tilapia). The lowest lipid content (below 0.1%) was noted in the muscle tissues of Baltic cod and walleye pollock caught in the Pacific. The muscle tissue of walleye pollock also had the lowest protein content (12.2 ± 2.0%). The highest lipid content was noted in the muscle tissues of Baltic salmon (13.1 ± 2.4%). The highest percentage content of eicosapentaenoic (C20:5 n − 3 – EPA) and docosahexaenoic (C22:6 n − 3 – DHA) acids (over 40%) was noted in the fat extracted from the oceanic fish and Baltic cod. However, due to the low fat content, the concentrations of EPA + DHA in these fish species and in imported farmed fish expressed in mg/100 g of muscle tissues are the lowest and range on average from 24.8 ± 5.7 mg/100 g (sutchi catfish) to 207.4 ± 125.4 mg/100 g (sole). This is why the consumption of these fish species has no significant meaning for coronary heart disease prevention. Consumers with symptoms of cardiovascular diseases should include the following fish species, which have high concentrations of EPA + DHA: Baltic salmon (3807.2 ± 666.3 mg/100 g); Polish farmed trout (1804.0 ± 279.2 mg/100 g); and Baltic herring (940.9 ± 306.6 mg/100 g) in their diets. However, the consumption of Baltic salmon must be limited on account of the levels of persistent organic pollutants found in it.     

Reevaluation of air-water exchange fluxes of PCBs in Green Bay and southern Lake Michigan

Air-water exchange of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) is an import process for the delivery of contaminants to water bodies, as well as for their removal, and is thus a pivotal parameter in the construction of mass balances in aquatic systems. Simultaneous measurements of PCB concentrations in the gas and dissolved phases conducted in Green Bay in 1989 and in southern Lake Michigan in 1994-1995 were used to estimate air-water exchange fluxes. In this work, improved Henry's law constants for PCBs and new mass-transfer rates across the air-water interface were used to update the previous calculations. The new model calculations suggest that the net volatilization flux of PCBs out of Green Bay ranges from +170 to +5300 ng m(-2) day(-1), which is 2-20 times larger than previous estimates. The flux of PCBs in southern Lake Michigan exhibits net volatilization of +0.5 to +230 ng m(-2) day(-1) throughout the study period (May and July 1994, January 1995), whereas previous estimates reported that the net flux was seasonally absorptive. Thus, water-to-air fluxes are more important for the removal of PCBs from both Green Bay and Lake Michigan than previously recognized.     

Thawed Chilled Barents Sea Cod Fillets in Modified Atmosphere Packaging-Application of Multivariate Data Analysis to Select Key Parameters in Good Manufacturing Practice

The purpose of the present study was to select key parameters in good manufacturing practice for production of thawed chilled modified atmosphere packed (MAP) cod (Gadus morhua) fillets. The effect of frozen storage temperature (−20 and −30 °C), frozen storage period (3, 6, 9 and 12 mo) and chill storage periods up to 21 d at 2 °C were evaluated for thawed MAP Barents Sea cod fillets. Sensory, chemical, microbiological and physical quality attributes were evaluated and multivariate data analysis (principal component analysis and partial least-squares regression) applied for identification of key parameters in good manufacturing practice for this product. Frozen storage of up to 12 mo had no significant effect on quality attributes and shelf-life at 2 °C was above 14 d irrespective of the time of frozen storage. As compared to a previous study with Baltic Sea, cod drip losses during chill storage was low for thawed MAP Barents Sea cod and this fish raw material seemed the more appropriate for production of thawed chilled MAP products. Frozen storage inactivation of the spoilage bacteria of Photobacterium phosphoreum was modest in Barents Sea cod, possibly due to high trimethylamine oxide (TMAO) and NaCl contents.     

Abundances, depositional fluxes, and homologue patterns of polychlorinated biphenyls in dated sediment cores from the Pearl River Delta, China

Despite the recent efforts to investigate the distribution and fate of persistent organic pollutants in the tropical and subtropical regions of Asia, very little was known about the temporal change of polychlorinated biphenyls (PCBs) in the environmental ecosystem of China. In this study, three dated sediment cores collected from the Pearl River Delta of southern China were analyzed for a large suite of PCB congeners, from which the temporal profiles of PCB abundances, fluxes, and homologue patterns were constructed. The sedimentary inventories of total PCBs at the sampling sites ranged from 480 to 1310 ng/cm2, at the low end of the worldwide figures. Although production and use of PCBs have been banned or highly restricted in China since the early 1980s, the fluxes of total PCBs continued to increase in the Pearl River Delta sediments. There was a concurrent increase of PCB fluxes and gross domestic product per capita in the region from 1980 to 1997, and a decline of agricultural land use was evident at the same time. Apparently, large-scale land transform since the early 1980s as well as emissions from the PCB-containing electrical equipments were responsible for the sharp rise of PCB fluxes in the recent sediments. The difference in the PCB homologue patterns from 1940 to the mid-1970s was probably indicative of the different timelines of PCB usage in Macao/Hong Kong and mainland China and the differenttypes of technical PCBs commercially used. PCBs were detectable in sediments deposited well before the time frame when production of PCBs began (before 1930) and were relatively enriched in the less chlorinated homologue groups (3Cl and 4Cl PCBs), suggesting the downward mobility of lightly chlorinated PCB congeners in the sediment column.