Abstract

This paper discusses the results of the analyses of tissue samples from several species of cetaceans and pinnipeds for heavy metals (lead, copper, chromium, nickel, cadmium, and iron). The levels found in the heart are considered baseline data. Also, this is the first report of nickel concentrations. These data, in general, support the theory that feeding relationships of animals may shed light on causes of strandings.

Introduction

Data on the levels of heavy metal accumulations in the tissues of members of the Cetacea and Pinnepedia are found widely scattered in the literature The data recorded indicates that there is a lack of information; both as to the variety of metals and number of species or tissues examined. This, of course, is due to the availability of material to analyze and the condition of the tissues sampled. Viale (1) suggests that in the case. of stranded beached whales, there may be a direct correlation between the levels of heavy metals he found in the animals and the cause of the strandings. This is further supported by Stoneburner (2) with his findings on short-finned pilot whales, where metal levels were 3-4 times higher in stranded animals then in assumed healthy animals. Gaskin (3,4) suggests that mercury levels, particularily in liver tissue, may be a reflection of metal levels in the food chain and an indication of feeding locations. The results published by Arima, et al. (5) show a direct correlation between age and concentration of mercury and selenium in such animals as the Gill's bottle-nosed dolphin, blue-white dolphin, and pilot whale.

The toxicity of heavy metals is difficult to determine because of factors such as age, health, metabolic state, stress, reproduction, and synergistic effects with other metals or toxins in the environment. Of further note is the fact that any metal, if present in high enough concentration, is potentially toxic. Hoste (6) demonstrates the variability of results in his study on Northern fur seals.

This paper presents the results of analyses of tissues from both cetaceans and pinnepeds. Its purpose is to illustrate the wide variation of heavy metal levels in four tissues obtained from six species of cetaceans and pinnepeds. The discussion revolves around both the striking differences between the species and similarities in metal concentrations.

Materials and Methods

Tissue samples (heart, muscle, kidney, and liver) were obtained from six species of cetaceans and pinnepeds (courtesy of the New England Aquarium and the Marine Animal Resource Center, Seattle, WA). The species list consists of samples from Phocoena phocoena, Lagenorhynchus alba, Styenella caeruleoabla, Delphinus delphis, Phoca vitulina, and Cystophora cristata.

Analyses were conducted for lead, copper, nickel, cadmium, chrome, and iron.

Tissue samples were cut frozen, weighed, acid digested, and @shed using a modification of the technique suggested by Pinta (7). This modification was developed by the authors (6). The heavy metal levels were then determined by flame Atomic Absorbtion Spectroscopy using both nitrous oxide and acetylene gas techniques.

Results

The results of this study are presented in Tables 1-4 which are separated by tissue analyzed. The numbers in parentheses following the species name indicate the number of animals sampled. The numbers in parentheses within the tables indicate a single value recorded from replicate samples. The two entries for Phoca vitulina represent the seven animals from the Atlantic coast (A) and the single animal from the Pacific coast (P). None of the samples showed recordable levels of lead. These data are presented as mean values for both animal number and replicate analyses, in ppm.

Heart Tissue

The heavy metal levels indicate baseline data for this tissue.

Table 1: Heavy Metal Concentrations in Heart Muscle Tissue (ppm)

Muscle Tissue

This tissue, as espected, produced the most stable results, however, muscle tissue is probably the least valuable for interpretation, since accumulation of metals often depends upon the fat content of the specific tissue.

Table 2: Heavy Metal Concentrations in Muscle Tissue (ppm)

Kidney Tissue

Both Phocoena phocoena and Phoca vitulina had values outside the expected, in particular, copper and cadmium.

Table 3: Heavy Metal Concentrations in Kidney Tissue (ppm)

Liver Tissue

This was the most interesting of the tissues analyzed. Once again, the Phocoena phocoena and Phoca vitulinaspecimens gave the more unusual results particularly the 0.0 ppm for lead and the very low 0.070 and 0.191 ppm for copper, respectively.

Table 4: Heavy Metal Concentrations in Liver Tissue (ppm)

Comparison of samples of the four tissues from the animals analyzed indicated that Delphinus delphis had the greatest range of metal levels for cadmium (0.0 - 0.55 ppm in the muscle) and for chromium (0.0 - 0.13 ppm in the kidney). Lagenorhynchus acutus had an apparent significant level of nickel in the heart tissue (0.0-0.11). The specimens of Phoca vitulina, from the Atlantic, demonstrated the greatest variation of both iron and copper in the liver tissue (3 - 250 ppm and 0.0 - 1.08 ppm).

Discussion

The data resulting from this ongoing research tends support to the theory that heavy metal levels in the tissues of marine mammals may play a role in the cause of strandings, as stated by Stoneburner (2). It may also serve as an indication of the food chain and feeding behavior of the animals. Both Phocoena phocoena and Phoca vitulina are considered to be inshore, sub-surface, and benthic feeders; preying upon molluscs, crustaceans, and bottom-feeding fish such as cod, sole, and herring. At any particular time, this might result in sub-clinical dosages of heavy metals which may produce detrimental or synergistic effects, particularly if the animals are in a stressful situation.

Examination of the data from this study illustrates the wide range of variation of metal levels between tissues and between species. The three species -- L. acutus, C. cristata, and D. delphis -- are behaviorly offshore deeper-water animals and, in general, show low Metal concentrations with less variation or range. The results of this study, when compared to the information presented by Pinta (7), indicate that animals from different habitats show wide variation, and investigators can well expect the same variation between individual stranded animals.

In summary, the reader is cautioned that the data presented is not a definitive work and that much more data must be accumulated before definitive statements are made. In particular, data from a single animal is not representative of all animals in the population nor comparable with other animals in different populations.

References

1. Viale, D. Evidence of metal pollution in Cetacea of the Western Mediterranean. Ann. Inst. Oceanogr. 54(1): 5-16 (1978).
2. Stoneburner, D.L. Heavy metals in tissues of stranded short-finned pilot whales. Sci. Total Environ. 9(3): 293-297 (1976).
3. Gaskin, D.E., et al. Mercury, DOT, and PCB in harbour seats from the Bay of Fundy and Gulf of Maine. J. Fish. Res. Board Can. and Gulf of Maine. J. Fish. Res. Board Can. 30(3): 471-475. 30(3): 471-475 (1973).
4. Gaskin, D.E., et al. Changes in mercury levels in harbour porpoises from the Bay of Fundy, Canada, and adjoining waters during 1969 - 1977. Arch. Environ. Contam. Toxical. 8(6): 733-762 (1974).
5. Arima, S.,and Nagakura, K. Mercury and selenium content of Odontoceti. Bull. Jap. Soo. Sci. Fish. 45(5): 623-626 (1979).
6. Hoste, R.,et al. Heavy metal analysis in the Northern fur seal Callorhinus ursinus. Master's Thesis, John Carroll University, Cleveland, OH, 44118 (1984).
7. Pinta, M. Detection and Determination of Trace Elements. Dunod. Pub., Paris, 1962.