Presented by Brandi Obman and Amy Willman

Abstract

Massive industrialization and agricultural activities have led to the accumulation of environmental contaminants including PCB, DDT, mirex, mercury, and numerous other organochlorine compounds in coastal waters. These chemicals are very persistent and are not easily degraded, because of this that they have been banned in many developed countries. Despite the decrease in their production these chemicals continue to cause problems for ocean dwelling organisms.

Marine mammals are exceptional indicators of the bioaccumulation of many contaminants found in the oceans. These contaminants accumulate in the tissues of the mammals including their blubber and the females milk. PCB’s are of particular concern due to the increasing amount of evidence that they are responsible for reproductive complications, disruption in the endocrine system, and skeletal deformities. Since accumulation of contaminants is positively correlated with increasing trophic level, this makes many cetaceans prone to their toxic effects The Killer whales of British Colombia are thought to be some of the most contaminated marine mammals in the world.

Introduction

The killer whales of British Columbia can be divided into to three distinct populations. There are two resident populations (divided into Northern and Southern residents) and one transient population. The resident populations spend most of their time in the coastal waters of British Columbia, Alaska, and Washington. In these waters they feed on almost exclusively on salmon fish. The transients also make frequent visits to these waters, but their diet is drastically different consisting of mostly pinnepeds and cetaceans. These transients do not consume fish as the residents do.

Killer whales occupy the highest trophic level in the aquatic food web. The organochlorines they take in are extremely lipophilic but are slow to degrade(Borrell 1993). The more contaminated organisms they ingest the more concentrated their contaminate level becomes. Either residing in or passing through British Columbia’s waters these three populations of whales are continuously feeding on contaminated organisms. Approximate concentrations of these pollutants can be determined by examining the tissues (skin and blubber) or bodily fluids (blood and milk) of the whales.

The age and sex of the whale are also determining factors on the mammals individual level of contamination. The sex of the animal is best established through DNA analysis. As males age they become increasingly contaminated, but females may transfer some of their contaminants to their young during pregnancy and lactation. Marine mammals produce milk that is exceptionally rich in lipids which accounts for most of the lipophilic contaminants that are transferred to the young. Some contaminants are transferred during fetal development, but this is a small amount compared to the portion transferred in the milk (Addison and others 1987).

Due to an extensive photo identification study, the killer whales that frequent the coastal waters of the Pacific have been well cataloged. Approximate ages and sex is known for all of the resident population as well a large portion of the transient population. A study examining the DNA of these populations has determined that there has been virtually no inter breeding between the groups. Therefore by looking at their group membership their dietary habits and feeding ground can be determined.

The large catalog of information on these whales presented an opportunity to analyze their contaminant levels using factors such as age, sex, and diet. The tissue samples are easily obtained by biopsy darting techniques, which are minimally evasive to the whales. These samples may lead to potential sources of the contaminants and serve as a guide for comparison of other contaminated cetacean populations.

Materials and Methods

Forty-seven blubber biopsies were collected to be analyzed for contaminant levels. The samples were taken from whales of various ages and sexes, and representatives of all three communities were sampled. Samples were collected between 1993-96 in the coastal waters of the central potion of British Columbia. The sample sizes consisted of 26 northern residents, 15 transients, and 6 southern residents. The low number of southern resident s sampled was due to heavy vessel traffic in their feeding grounds.

The biopsy darts were designed to obtain a small portion of skin from each whale(about .1~.2g). The skin obtained from t he darts was used mainly for DNA examination, and the attached blubber for contaminant analysis. The darts were fired from a variable power dart projectors aboard small boats distanced around 5~25m from the whales. The identity of each whale was confirmed by using a photographic catalog of the three populations. The lightweight darts were untethered and designed to float after dropping from an area near the dorsal fin of the whales. The darts were retrieved immediately after impact, and the skin samples were removed. The skin samples were separated for DNA studies, and the blubber was stored in glass viles covered with foil. The blubber was stored at -20 degrees Celsius until contaminant analysis.

All blubber samples were analyzed for lipid content, as well as PCB’s, PCDDs, and PCDFs. To initiate this, the samples were thawed and ground in a porcelain mortar containing 200g of anhydrous sodium sulfate and a mixture of ¹³C₁₂- labeled PCB’s, PCDDs, and PCDFs, along with some pesticides. This mixture was placed in an extraction column and extracted with 250ml of dichloromethane hexane. The extracted material was evaporated until dry and its weight was measured and compared to the samples original weight. This was done to determine each samples lipid content. The same residue was resuspended again using dichloromethane hexane and divided into two portions. The larger portion, consisting of around 75% of the mixture, was used to determine PCB, PCDD, and PCDF concentrations by means of high-resolution gas chromatography/mass spectrometry. The rest of the mixture was stored for use in future studies.

The total PCB concentration of the blubber was defined as the some of the concentration of all detectable congeners. All concentrations were reported as a function of lipid weight, using a mean lipid value for the samples which were not analyzed for lipid content. The Total Toxic Equivalents (TEQ) were determined for all PCB’s, PCDDs, and PCDFs by using the international Toxic Equivalency Factors (TEF).

A one way ANOVA was used to determine differences in contaminant levels within the community. This statistical test proved that there was significant differences between the populations. Leading into a t-test which was used to asses the amount of differentiation in contaminant levels between the males and females. The results were graphed according to population and contaminant type.

Results and Discussion

The PCB concentrations in British Columbia’s killer whales were extremely high compared to marine mammals from other industrialized areas of the world. The contaminant concentrations of the northern residents was significantly higher than that of other marine mammals they were compared to, but were lower compared to the southern residents or the transient population. Similar differences in contaminant concentrations due to geographic variation have also been found in Short-Finned pilot whales off the coast of Japan (Tanabe and others 1987). Further evidence for the extremely high levels of PCB in the southern and transient populations is seen when comparing their results to those of the beluga whales of the St. Lawrence (Gauther and others 1998). This beluga population is considered endangered due to their high level of environmental contaminants, and yet the southern and transient killer whales of British Columbia are show even higher concentrations.

The major reason for such elevated levels of PCB appears to be the diet of these whales. Up to 96% of both the resident populations diets consists of adult salmon. These salmon also occupy a high trophic level compared to other salmon fish, and are accumulating PCB’s themselves. They are then ingested by the whales passing on their PCB to the predators. It is thought that the predators then accumulate these contaminants over time due to the fact that they lack the ability to metabolize them as other mammals would (Jarman and others 1996). In this study, the southern residents receive a higher dose of contaminant than their northern counterparts because they feed in a highly industrialized area were the prey themselves are already highly contaminated.

The transient killer whales do not feed on the salmon fishes as the residents do, but primarily on other marine mammals. Harbor porpoises, harbor seals, Stellar sea lions, and Dall’s porpoises are the main constituents of their diet. The transients are not frequent visitors to the highly industrialized coastal areas, but their prey have a fundamentally coastal distribution. These transients appear to receive a high dose of contaminants from their prey, which are often found geographically closer to the sources of pollution (Aguilar 1984).

Although the three populations had elevated PCB concentrations, the total amounts of PCDD and PCDF did not follow the same trend. This result was surprising due to the local pulp mills which routinely input large amounts of these compounds into coastal waters. These mills have been the cause of frequent local contamination leading to many fishery closures. The lack of PCDD and PCDF accumulation can be attributed mainly to their selective diet (Jarman and others 1996).

Relating the variables of sex and age to these results, contaminant levels of adult females showed drastic differences from those of adult males. In immature whales of either sex, the contaminant levels showed steady increase with increasing age. It has been suggested that this because the contaminants are being taken in faster than they can be metabolized or excreted (Borrell 1993). At the time of their first calving the contaminant levels in females began to decrease, and did so continually until around the age of 50. At this point the females again began to accumulate PCB.

The decline of contaminants during calving occurs because the females transfer a portion of their organochlorines to their calf. The contaminants are transferred mainly through lactation, while only a small amount is transferred during fetal development. This transfer also accounts for the increasing contaminant levels in the calves who are constantly feeding on milk (Addison and Brodie 1987). When the females approach the age of 50, they cease to reproduce and no longer have the means to offload their contaminants.

PCDD and PCDF concentrations did not follow the same age and sex related trend as the PCB’s did. All three populations showed only low levels of these contaminants. This may have been the result of low concentrations in the prey of the whales, but s more likely due to the whales ability to metabolize and excrete compounds that are dioxin like. This ability has been identified in other cetaceans as well as some pinnepeds, and may be explained by the differing ingredients in commercial PCB mixtures (Jarman and others 1996). Therefore, even if the whales showed high levels of PCB the amount of PCDD and PCDF in their system could be virtually undetectable. This is demonstrated by the TEQ profiles for the immature males and females where only the globular PCB concentrations showed dramatic differences.

After examining the TEQ profiles, the northern resident adult males showed the highest level of contamination. PCBs accounted for 97% of the TEQ values in these males. Immature whales and adult females showed a lower TEQ value than the males, but had a higher proportion of PCDDs and PCDFs in their system. Overall the TEQ values proved to be around 23% lower than their original estimated values.

Focusing more on the resident populations previously generated life tables for these communities proved to be a useful tool in estimating the total PCB mass of the communities. A model, which was generated by using the mean ratios of observed PCB in southern and northern residents, estimated the PCB levels of the southern males to be four times higher than the northern males. The southern females were estimated to have up to six times more PCB than their northern counterparts.

The elevated TEQ values and PCB concentrations in all of the populations put these whales at risk for experiencing toxic effects. PCBs have been documented as being responsible for disruption of reproductive hormones and the reproductive cycles associated with them, as well as tumors and occlusions of the uterus (Borrell 1993). Organochlorines are also known to depress the immune system making the mammals susceptible to disease and in some cases causing large die-offs (Borrell 1993). These adverse effects have been well documented in seals, and the toxicity level for the whales sampled in this study greatly surpasses the threshold set for the seals. This puts these killer whale populations at particular risk for reproductive failure and makes them extremely susceptible to disease.

Conclusions

By using the biopsy darting technique it was possible to obtain skin and blubber samples from the resident and transient populations of British Columbia’s killer whale populations. Their previously recorded life history made it possible to correlate their contamination levels to such variables as age, sex, and dietary preference. These variables proved to have a strong bearing on the amount of PCB, PCDD, and PCDF found in each whales system. The relative concentration of these chemicals displayed a pattern suggesting that the whales system was able to selectively retain or metabolically remove some of these compounds.

The transient population of British Columbia’s killer whales was found to be particularly contaminated due to their intense feeding on other marine mammals. This trend can be observed throughout a number of carnivorous species, and consistently shows contamination increasing with increasing trophic level. As the contaminant levels in their prey increase they will continually be ingesting higher doses of these chemicals putting them at the greatest risk for factors like reproductive failure.

This transient population combined with the southern resident population a representative of the most contaminated whales in the world. Their current levels of contaminants have already surpassed the thresholds for endocrine disruption and immunotoxicity set for other marine mammals. Even though no new inputs of PCB are currently being introduced into their habitat, the whales current toxicity levels may continue to increase as a result of bioaccumulation. The existing residues currently in their environment are continually being redistributed in particulate matter, sediments, and smaller organisms in the water. These existing residues will eventually work their way through the food web, and once again find their way into the systems of the killer whales of British Columbia.

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