Age and sex-related changes in organochlorine compound levels in fin whales (Balaenoptera physalus) from the eastern North Atlantic

Marine Environmental Research 25 (1988) 195-211

Age- and Sex-related Changes in Organochlorine Compound Levels in Fin Whales (Balaenoptera physalus)

from the Eastern North Atlantic

Alex Aguilar & Asunci6n Borrell

Department of Animal Biology (Vertebrates), Faculty of Biology, University of Barcelona,

08071 Barcelona, Spain

(Received 21 November 1987; revised version received 23 March 1988; accepted 4 April 1988)

A B S T R A C T

Patterns of variation in organochlorine burdens with age and sex in cetaceans are poorly understood and differ between species. This paper presents the results of a survey on fin whales in this respect. Blubber from 166 individuals of known age and sex was analyzed for DDTs and PCBs. In young whales, pollutant burdens in specimens from the two sexes were indistinguishable but, from the onset of sexual maturity, concentrations of all organochlorines increased with age and body size in males and decreased in females. The relationships were not linear and in both cases tended to reach a plateau. The decrease observed in female blubber concentrations is attributed to reproductive transfer, mainly through lactation, and occurs throughout all the female's li['e span, suggesting absence of reproductive senescence in this species. Relative abundance of degraded forms of pollutants increased with age in males and decreased in females. The tDDT/PCB ratio was negatively correlated with age in males and positively correlated in females. Different PCB congeners showed dissimilar trends. All these dissimilarities between sexes in the pattern of accumulation of the d(fferent forms of organochlorines are associated with differential activation of microsomal enzymes and with dissimilar tran.~fer rates during reproduction in jk~males. Because o[ ~ these d(ff'erences, pollutant burdens in males are characterized by higher levels o1" pollutants and by higher DDE/tDD T and tDDT/PCB ratios than those for [~males.

195 Marine Era'iron. Res. 0141-1136/88/$0350 C 1988 Elsevier Science Publishers Ltd, England. Printed in Great Britain

196 Alex Aguilar, Asunci6n Borrell

INTRODUCTION

Age and sex are important sources of variation for the concentration of organochlorine pollutants in mammals. In man and other long-lived mammals, there is often a progressive build-up of pollutants with age which usually appears more clearly in males than in females (Wassermann et al., 1972; 1974; Mori et al., 1983; Wagemann & Muir, 1984; Mes, 1986; Aguilar, 1987). The only exceptions to this general pattern seem to be mammals at early stages of growth, in which rapid deposition of lipids may temporarily produce dilutions of organochlorines in the fat tissues (Hayes, 1975; Hansen & Welborn, 1977), and those exposed to abnormally highly polluted environments (i.e. people working in formulating plants), in which residue levels may eventually reach a storage plateau level and remain constant afterwards (Hayes, 1975).

Although this age-related increase occurs in both sexes, females are on the average less contaminated than males. The reason for this difference seems to be the transfer oflipophilic pollutants from the body of the mother to her offspring, which occurs both during gestation and lactation.

In marine mammals, most surveys in this respect have been focused on pinnipeds and the results for the males of most species are essentially concurrent with the pattern found in man. In females, however, age-related trends in organochlorine residue levels are usually not clear or, in some cases, even decreasing slopes as opposed to the typical male trend (Addison et al., 1973; Addison & Smith, 1974; Helle et al., 1976; 1983; Reijnders, 1980; Donkin et al., 1981; Zande & Ruiter, 1983). This is probably due to the fact that reproductive cycles are more numerous, occur often, and are more prolonged in wild pinniped populations than in humans, thus greatly increasing the magnitude and frequency of lipophilic xenobiotic discharge.

In cetaceans, only a few species have hitherto been studied in this respect and the results show considerable interspecific variation in the age- and sex- related trends of organochlorine pollutant levels, making it difficult to establish general patterns of variation. The aim of this study is to present the results of the organochlorine (DDT and polychlorinated biphenyls or PCB) residue analysis made in the blubber of North Atlantic fin whales (Balaenoptera physalus) and to examine the relationship between the levels found and the age, sex and reproductive condition of the specimens sampled.

MATERIAL

Ninety-seven female and 69 male fin whales were sampled in the summers of 1982, 1983, and 1984 at the whaling factories of the Industria Ballenera SA

Organochlorines in fin whales 197

located in northwestern Spain. The population exploited by this fishing operation inhabits the temperate waters of the eastern North Atlantic, and it is believed that its distribution ranges from the north of the British Isles to southern Moroccan coasts (International Whaling Commision, 1977).

From each whale examined, a sample of blubber weighing about 30-50 g was taken from the region posterior to the dorsal fin including all the fat layers, as recommended by Aguilar (1985a). Samples were then wrapped in aluminum foil, labeled, and kept in deep freeze. Post-mortem times ranged from 12 to 20 h. Ear plugs for age determination were also collected from all specimens.

METHODS

Age determination

Age was determined by counting growth layers in a longitudinal section of the ear plug core, following the procedures described by Lockyer (1984a). Each plug was read by more than one reader, and about 70% of the plugs were read twice by the same reader. Whales with incomplete or damaged plugs, or with plugs in which growth layers did not appear clear across the whole core were not used in this study. In cases of disagreement between different readers or between readings by the same reader, the average of all age estimates was used, unless the difference between the readings was greater than 10% of the lowest reading, in which case the specimen was not used in the calculations. To allow comparison between whales of similar growth stage of the two sexes, the sample was divided into three growth stages: sexually immature whales (age-classes 2 to 7 years old), sexually mature but young whales (age-classes 8 to 15), and sexually mature, fully- grown whales (age-classes 16 years old or older).

Analytical

A piece of about 2-5 g of blubber containing equal representation of all the strata was ground with anhydrous sodium sulphate in a mortar. The mixture was extracted with n-hexane for 4 h in a Soxhlet apparatus.

The extract was then concentrated to 40 ml, from which a 10 ml subsample was taken to determine tissue fat content. An aliquot of the remaining extract containing 1 g of lipid was mixed with sulphuric acid for the clean- up, following the procedures described by Murphy (1972).

After centrifugation and phase separation, the lipid-free extract was concentrated to 1 ml and was injected into a Perkin Elmer Sigma 3B gas

198 Alex Aguilar, Asuncibn Borrell

chromatograph (injector temperature: 250°C), equipped with an electron capture detector of 63Ni (temperature: 350°C), and a Perkin Elmer Sigma 15 computing integrator. For all the analyses a fused-silica capillary column of 0-25 mm internal diameter, 60 m length, and a stationary phase SPB-1 with a film thickness of 0.25/~m was used. Pure nitrogen at a flow rate of 1 ml/min was used as carrier gas.

Temperature was programmed according to the following sequence: injection at 40°C. Oven steady for the first 2 min and then an increase from 40 ° to 160°C at a rate of 25°C/min. Oven maintained at steady temperature for 1 min and then an increase from 160 ° to 250°C at a rate of 2°C/min. From this point onwards until the end of the analytical run, the column remained isothermal at a temperature of 250°C.

Heptachlor was used as internal standard to calibrate fluctuations in the operational conditions. Purified extracts were concentrated or diluted in order to fit pollutants concentrations into previously determined linearity ranges of ECD response. The identity of the DDT group compounds was confirmed by an alkali conversion to their respective olefins and re-analysis by GLC. PCBs were identified and quantified by their peak characteristics and retention times in relation to a 1"1 standard mixture of Aroclors 1254 and 1260, and confirmed by their resistance to the chemical derivations detailed above. Eight replicates of samples fortified with standards gave the following percentages of recovery for the whole analytical process (mean _+ coefficient ofvariation):p,p'-DDE:72.56% _ 15.8;p,p'-TDE:87.41% _+ 8.4; o,p-DDT:81.91%_+8-3; p ,p ' -DDT'98.13%_+7-6; P C B : 9 0 . 9 7 % ± 8 - 0 . Analytical results were not corrected for losses during extraction. Ten replicate chromatographic runs of a mixture of the DDT and PCB standards gave the following coefficients of variation in the quantification: p, p,'-DDE: +_7.9%; p,p'-TDE: +6"5%; o,p-DDT: _+5"5%; p,p'-DDT: _+8.2%; PCBs (mean of the eight peaks commonly used in the quantification): _+ 8"7%.

PCB congeners were identified according to Ballschmiter & Zell (1980). The relative abundance of the 12 PCB congeners most conspicuously found in the present samples (2,3,Y,4,5-penta- (IUPAC No. 106), 2,Y,4,4',5-penta- (IUPAC No. 118), 2,2',3,4',5',6-hexa- (IUPAC No. 149), and 2,2',3,4,5',6- hexachlorobiphenyls (IUPAC No. 144), the four resolved in one peak, 2,2',3,3',4,4'-hexa- (IUPAC No. 128) and 2,3,Y,4',5,6-hexachlorobiphenyls (IUPAC No. 163) resolved in another peak, and 2,2',4,4',5,5',-hexa- (IUPAC No. 153), 2,2',3,4,4',5'-hexa- (IUPAC No. 138), 2,2',3,Y,4,5,6-hepta- (IUPAC No. 173), 2,2',3,Y,4,5,6'-hepta- (IUPAC No. 174), 2,2',3,4,4',5,5'-hepta- (IUPAC No. 180), and 2,2',3,3',4,4',5-heptachlorobiphenyl (IUPAC No. 170) all of which were resolved in single peaks) was estimated as the ratio between their peak concentration and that of the sum of all peaks.

Organochlorines in fin whales 199

RESULTS

Males

Residue levels of all organochlorine pollutants increased with age and size in males. Correlation coefficients, however, were higher for age (always P < 0.001) than for length (P < 0-07 for p,p'-DDT, and P < 0-05 for the remainder). Analysis of residuals in the regression of pollutant con- centrations against age indicated that the relationship was far from linear, older males tending to reach a plateau. Transformation to a semilogarithmic scale improved the lineal fit, so log-age values were finally used. The ratios DDE/tDDT (tDDT = DDE + TDE + o,p'-DDT + p,p'-DDT) and tDDT/ PCB also significantly increased with age (P < 0.001) (Figure 1), but the p,p'- DDT/tDDT decreased with it (P<0.001). The relative abundance of 2,2',3,3',4,4'-hexa- (IUPAC No. 128), 2,3,3',4',5,6-hexa- (IUPAC No. 163), 2,2',3,3',4,5,6-hepta- (IUPAC No. 173), 2,2',3,3',4,5,6'-hepta- (IUPAC No. 174), and 2,2',3,4,4',5,5'-heptachlorobiphenyls (IUPAC No. 180) correlated

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200 Alex Aguilar, Asunci6n Borrell

positively with total PCB concentration in males (P < 0.05 for the first two compounds, and P < 0"001 for the remaining cases). No significant trend was observed in the remaining seven PCB congeners investigated.

F e m a l e s

Organochlorine compounds in females decreased with age and size. However, pollutants were more closely correlated to size (P -- 0.003 for PCB; P < 0.001 for the remainder) than to age (P < 0.002 for all DDT forms, and P non- significant for PCB). Regression residual analysis also showed a non-linear relationship, so a logarithmic transformation of size was used. Similarly, ratios between compounds also behaved in opposition to those for males. That is, the p,p'-DDE/tDDT and the tDDT/PCB ratios were negatively correlated with size (P < 0.03 and P < 0.001, respectively) (Figure 2), and the p,p'-DDT/tDDT ratio was positively correlated with it.

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Organochlorines in fin whales 201

Differences between sexes

A t-test between male and female pollutant concentrations showed highly significant differences between the sexes for all the organochlorine compounds and their ratios (P always <0-01). Because fin whales attain sexual maturity at 6-7 years of age, and growth in size greatly diminishes after age 15-17 (Aguilar, 1985b; Aguilar & Lockyer, 1987), data were divided into three growth-stages, as described above: sexually immature whales, sexually mature but young whales, and sexually mature, fully-grown whales. For each sex and growth stage, Table 1 details sample size and mean values for age, total length, and percentage of extractable lipids, and Table 2 depicts mean residue levels for each compound expressed on an extracted lipid basis and the levels of significance for t-tests performed between sexes. Pollutant concentrations on a fresh weight basis can be readily calculated from the tissue lipid contents detailed on Table 1.

Pollutant burdens and ratios of sexually immature males were indistinguishable from those of sexually immature females. In the young sexually mature whales, pollutant levels were significantly different (P always < 0.001), but ratios were not. In fully grown whales, pollutant levels in males and females showed even greater differences than in the young mature ones and ratios were also significantly different (P always <0.001 both in residue levels and ratios).

T A B L E ! Means and Standard Deviations (Between Brackets) of the Variables of the Sample used in Each Growth Stage for Males and Females (I: Sexually Immature Individuals (2-7 years old); YM: Young Mature Individuals (8--15

years old); OM: Old Mature Individuals (older than 16 yearslJ

Age-stage No. Lipid Age Body size (%) O'earst Ira)

1

Males YM

OM

I

Females YM

OM

20 71.60 5'35 (_+ 14.9) (-!-_ 1.4)

27 76.76 10.59 (+6.6) (+_2.1)

22 67.27 39.95 ( + 11.7) ( +_ 27.4)

41 75.85 5.39 ( +_ 8'21 ( _+ 1'21

28 72.45 11.21 (_+11'9) (+2'11

24 62-86 26.62 (_+17.1) (+12.2)

17'56 _+ 1,0) 18.74 +0,7) 19.13 _+0,5)

18.17 +0.8) 19.47 +0.9~ 20.55 _+ 1.0)

202 Alex Aguilar, Asunci6n Borrell

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Organochlorines in fin whales 203

DISCUSSION

Pollutant residue levels

Organochlorine pollutant levels in this population are very similar to those previously detected in other North Atlantic fin whale populations (Saschenbrecker, 1973; Holden, 1975; Sergeant, 1980). Because baleen whales have a pelagic distribution and because they feed at lower trophic levels than other marine mammals, their blubber organochlorine con- centrations are usually much lower (Wagemann & Muir, 1984).

Males In males, our results show that DDTs and PCBs increase with age throughout the whale's whole life-span. This is similar to the results of related surveys carried out in the blubber of striped dolphins (Stenella coeruleoalba) from Japan (Fukushima & Kawai, 1981), harbour porpoises (Phocoena phocoena) and belugas (Delphinapterus leucas) from eastern Canadian waters (Gaskin et al., 1982, 1983; Martineau et al., 1987), minke whales (Balaenoptera acutorostrata) from the Antarctic (Tanabe et al., 1985), and a number of pinniped species (Addison et al., 1973; Addison & Smith, 1974; Helle et al., 1983; Zande & Ruiter, 1983). Pollutant levels in the liver of adult Antarctic minke whales (Balaenoptera acutorostrata) also showed an age-increasing trend, but the pattern of the younger whales was confused by heterogeneities in feeding and distribution of individuals (Tanabe et al., 1984b).

However, Tanabe et al. (1981), after studying Japanese striped dolphins, concluded that, after an initial increase in younger age-classes, there was a decline in organochlorine body burdens at older ages as a result of a gradual decrease in the rate of food intake of the older dolphins. Nevertheless, their plots suggest a leveling-off in the organochlorine levels of older animals rather than an actual decrease. This agrees with our findings for fin whales, in which the rate of increase of pollutant concentrations is high in younger animals but becomes progressively lower in older ones (this pattern appears linearized by the log-transformation of age in Fig. 1).

The positive relationship between organochlorine levels and age found in this and other surveys on cetaceans as well as pinnipeds (Aguilar, 1987) can probably be explained by a sustained pollutant intake which exceeds the animal's body capacity for pollutant excretion. However, increasing organochlorine tissue concentrations in growing animals seems to increase the activity of hepatic microsomal enzymes, which will, in turn, increase the whale's ability to get rid of pollutants, thus producing the observed leveling- off in the age-trend of organochlorine residues in older animals.

204 Alex Aguilar, Asuncibn Borrell

This assertion seems supported by experimental findings in different species of cetaceans. Goksoyr et al. (1986) suggested that the activity of hepatic microsomal Cytochrome P-450-systems increases in minke whales with age. Borrell & Aguilar (1987) found that fin and sei whales with high DDT levels accumulate proportionally higher levels of DDE (the main DDT metabolite) than whales of the same population with lower DDT levels. This latter finding was taken by the authors as evidence of increased activity of monoaminooxidases when tissue organochlorine concentrations rise. Similar results were found by Martineau et al. (1987) in the blubber of beluga whales from eastern Canada.

F e m a l e s

In female fin whales, levels of organochlorine compounds were found to decrease with age and body size. These results coincide with those of Gaskin et al. (1982, 1983) in harbour porpoises, with those of Tanabe et al. (1985) in minke whales, and with those of Holden (1978) and Born et al. (1981) in pinnipeds, but disagree with the apparent absence of clear patterns observed in striped dolphins by Fukushima & Kawai (1981), and with the age-related increasing trend found by Martineau et al. (1987) in beluga whales. These latter authors, however, worked only on stranded animals which may not be representative of the actual pattern in the population. Tanabe et al. (1987) found an age-related increasing trend in female pilot whales up to about 10 years of age, a decline from then up to 25 years of age, and a further increase in animals older than 25 years.

This decrease in organochlorine compound burdens is attributable to the transfer of pollutants from the mother to her offspring which occurs during pregnancy and lactation, which is thought to exceed the pollutant intake rate. No estimates of transfer rates are available for fin whales or for any other mysticete species, but it has been estimated that, during gestation, striped dolphin females reduce their organochlorine body loads by 4% 9°/,, (Fukushima & Kawai, 1981; Tanabe et al., 1982), and harbour porpoises do so by 15% (Duinker & Hillebrand, 1979). During lactation, total load reduction in striped dolphin females has been estimated to be between 72% and 98% (Fukushima & Kawai, 1981). Gestation transfer rates in fin whales are probably similar to the above values, but those of lactation should be lower because in this species lactation lasts about 6 7 months (Lockyer, 1984b), while in striped dolphins it extends over 15-18 months on the average (Perrin & Reilly, 1984).

Logically, organochlorine transfer to offspring begins to take place when females become reproductively active. Thus, Tanabe et al. (1987) found that DDE and PCB levels in blubber from short-finned pilot whales from Japan increased up to about age at sexual maturation and declined thereafter in

Organochlorines in fin whales 205

reproductively active individuals. Because sexual maturity in fin whales is more dependent on body size than on age (Aguilar, 1985b), pollutant loads are more closely correlated to the length of the whale than to its age.

However, Tanabe et al. (1987) found a slight increase in pollutant burdens in the oldest female pilot whales, and attributed it to a reduction in reproductive potential (senescence) in the very old individuals of this species. In the present survey, despite having sampled quite old individuals (up to 64 years of age), the declining trend in organochlorine concentrations seems to happen throughout all the whale's lifespan posterior to sexual maturity. This agrees with the general belief that no age-specific variations in pregnancy rates occur in fin whales, or in baleen whales in general (Mizroch, 1981; Marsh & Kasuya, 1986).

Differences between males and females Aguilar & Jover (1982) studied the pollutant burdens in the muscle of individuals from the same population of fin whales as that studied here and observed that males were carrying slightly higher organochlorine levels than females, although the differences were not significant. In the present survey, males had, overall, significantly higher pollutant levels than females, but differences showed up with growth. Thus, sexually immature whales of both sexes had almost identical pollutant levels, but sexually mature males had higher levels than females of the same age, the difference between the sexes tending to increase with age.

This sex-related difference in pollutant burden seems to be the rule for marine mammals except for the North Atlantic sperm whale (Physeter macrocephalus) in which concentrations in the blubber of females were found to be significantly higher than in males. This finding was associated with the lower diving capacity of female sperm whales which restricts them to feeding in surface - - and more polluted - - waters and with the different migratory movements of males and females, which produce a seasonal geographic segregation of the two sexes and keep females in lower - - and again, more polluted - - latitudes (Aguilar, 1983).

According to Helle (1985), if a female seal becomes sterile, its pattern of accumulation in relation to age resembles that of males. This, together with the fact that differences in the age trends between sexes become apparent from the age at which sexual maturity is attained, indicates that reproductive transfer is the only factor producing these observed sexual differences in the pattern of accumulation of organochlorine compounds.

Variation with growth Fin whale pollutant levels tended to increase in males and to decrease in females in an apparently steady fashion. Gaskin et al. (1983) found a peak of

206 Alex Aguilar, Asunci6n Borreil

PCB concentrations in harbour porpoises of both sexes around the ages at which the onset of sexual maturity occurs, and associated it with the pubertal growth spurt which takes place at this time. In our study, no peak around the age of puberty or any other specific age or length was observed for any of the compounds analyzed.

Ratios between pollutants

The pattern of variation of the p ,p ' -DDE/ tDDT and p , p ' - D D T / t D D T ratios shows an increase in the relative abundance of metabolized forms of DDT with age in males and a decrease in females. The similarity of this trend with that of pollutant concentrations indicates that the variation in these ratios is attributable to modifications of liver enzymatic activity (and thus, body detoxification capability) produced by increased or decreased organo- chlorine levels. This is consistent with previous findings of DDE/ tDDT variation in the blubber of fin and sei whales (Borrell & Aguilar, 1987) and of beluga whales (Martineau et al., 1987), which indicate that higher tissue pollutant levels induce enzymatic activity and result in proportionally higher abundance of metabolized forms.

This reasoning is also invoked to explain the differences in the DDE/ tDDT ratio observed between adult males and females. As can be seen in Table 2, this ratio is indistinguishable in sexually immature and young mature whales of both sexes, but becomes radically different in old mature ones. This is associated with the increasing divergence in pollutant concentrations which occurs with age and size in males and females. Thus, the overall higher body burden of organochlorines in males seems to be the reason for the high DDE/ tDDT ratios observed in this sex. This concurs with previous findings by Martineau et al. (1987) in beluga whales.

Goksoyr et al. (1986) proposed that cytochrome P-450-dependent monoxygenase activities in the liver ofminke whales increased with age and attributed this increase to the variation in enzymatic activity which commonly occurs in mammals with the onset of puberty. However, these authors studied a small number of samples (seven) covering a narrow age range and, in view of the present results, we conclude that the changes in enzymatic activity are more a consequence of variation in body pollutant load associated with age than of intrinsic age-related enzymatic variation.

The tDDT/PCB ratio also shows an increasing trend with age (and with pollutant burdens) in males and a decreasing one in females, resulting in higher overall ratios in adult males than in adult females. Again, this ratio is similar in immature whales of both sexes but becomes different in adult individuals. The reason for this variation does not appear clear as in the case

Organochlorines in fin whales 207

of the D D E / t D D T ratio, though it is suggested that it may be the result of differential degradative rates for the two groups of compounds.

Moreover, in sexually mature females, the above trends might also be affected by dissimilar transfer rates of the different compounds to offspring during gestation or lactation. Ease of reproductive transfer seems to be inversely related to lipophilia, so the discharge of DDT compounds appears to be more intense than that of the more lipophilic PCBs (Aguilar, 1987). For example, in grey seals (Halichoerus grypus), transfer of tDDT from maternal blubber to milk during lactation ranged from 49%-79%, while that of PCBs only ranged from 13%-48% (Addison & Brodie, 1987). This coincides with similar studies on other marine mammal species (Addison & Brodie, 1977; Holden, 1978; Fukushima & Kawai, 1981; Tanabe et al., 1982).

This differential transfer would tend to favour a progressive decrease in the tDDT/PCB ratio as the female reproduces and grows older. However, in apparent contradiction with this, Subramanian et al. (1986) found that PCBs were cleared faster in female Dali's porpoises than in males of the same species. Thus, it can be calculated from their raw data that the PCB/DDE ratio for the northern North Pacific, the only location in which the two sexes were sampled for this study, was higher in males (mean: 1-0; sd: + 0.08) than in females (mean: 0.8; sd: +0.08).

Future research is needed in order to ascertain reproductive transfer rates in females lbr each compound and their effect on the tDDT/PCB ratio trends. It is not clear either whether the various DDT compounds are differentially transferred to the offspring or not, so the effect of reproductive discharge on the p,p ' -DDE/tDDT or the p,p ' -DDT/tDDT ratios is unpredictable.

In the sample of fin whales studied here, not all PCB congeners seemed to follow the same pattern and, while some of them showed no apparent trend, others did so clearly, their relative abundance varying with the absolute pollutant load of the whale. In particular, the congeners 2,2',3,3',4,4'-hexa- (IUPAC No. 128), 2,3,3',4',5,6-hexa- (IUPAC No. 163), 2,2',3,3',4,5,6-hepta- (IUPAC No. 173), 2,2',3,3',4,5,6'-hepta- (IUPAC No. 174), and 2,2',3,4,4',5,5'- heptachlorobiphenyls (IUPAC No. 180) correlated positively with total PCB concentration in males. Except for the 2,2',3,3',4,5,6'-heptachlorobiph- enyl (IUPAC No. 174), the rest of these congeners were also detected in a related study on tissues of beluga whales (Mass6 et al., 1986). All this seems to indicate a higher persistence and a more difficult degradability of such compounds in relation to other PCB forms when tissue pollutant concentrations are high and enzymatic activity is enhanced. This apparently contradicts Zell & Ballschmiter's (1980) hypothesis according to which 2,2',3,3',4,5,6- (IUPAC No. 173) and 2,2',3,3',4,5,6'-heptachlorobiphenyls

208 Alex Aguilar, Asuncidn Borrell

(IUPAC No. 174) were non-recalcitrant PCB components, more easily degradable and thus of less persistence in aquatic food chains.

In general terms, however, the concentration of higher chlorinated PCBs in the blubber of male fin whales appears to progressively increase with total PCB concentrations and thus, with age, indicating more difficult degradability and higher persistence of these congeners in relation to the lower chlorinated ones. This is further substantiated by previous findings by Hidaka et al. (1983), Zande & Ruiter (1983), Tanabe et al. (1984a), and Addison & Brodie (1987) which evidence higher degradation or transfer rates for the lower chlorinated PCBs in marine mammals.

ACKNOWLEDGEMENTS

The Fisheries Subsecretariat of Spain's Ministry of Agriculture, Fisheries and Food partially funded this research. A. Aguilar received financial support while doing this work from Spain's Ministry of Education and Science. C. H. Lockyer (Sea Mammal Research Unit, NERC, UK) kindly cooperated in the age determination of whales,

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