Abstract

Anatomically specific - site tissues obtained from two rookeries of Northern fur seals were analyzed for differences in heavy metal concentrations. This paper presents the results of this project.

Introduction

Information is sparse on heavy metal accumulations in marine mammals. High concentrations of mercury (172.00 ppm) (1) in Northern fur seals (Callorhinus ursinus) and lead (34.20 ppm) (2) in California sea lions (Zalophus californianus) have been reported even though these animals appeared healthy. Cadmium was found to be concentrated in the kidney of many pinnipeds. Northern fur seals from Kitovi, in the Pribilof chain, showed kidney cadmium levels of 184.81 ppm/gm dwt. Although no definite links have been made between marine mammal deaths and heavy metal poisoning, it has been suspected in one case. (4)

Materials and Methods

Northern fur seals from two different rookeries, Little Zapadni (A) and Kitovi (B) on St. Paul Island In the Pribilofs, were obtained for analysis. Tissue from each group was collected in the exact same manner during the 1984 harvest. All specimens were four year old males. Ages were determined at the time of collection.

Tissue samples were cut frozen, microwave dried, weighed and acid digested using a technique modified by the authors.

The heavy metal concentrations were then determined by flame Atomic Absorption Spectrophotometry using both acetylene and nitrous gas techniques. The following specific - site tissues were analyzed: head of the spleen, right lobe of the liver, left anterior lobe, of the kidney, left ventricle of the heart, left inguinal fat and the right pectoral muscle. Specific tissue sites were chosen to alleviate variation within organs which could influence interpretation. The metals analyzed for were cadmium, nickel, copper, lead, chromium, zinc and selenium.

Results

The following two tables show a wide range of mean values for each metal and tissue examined. Cadmium levels were found to be the highest in kidney. The highest copper mean values were found in the liver. Some unexpectedly high chromium and zinc levels were found in the kidney from Kitovi, Table 2.

Table 1. Mean Values (ppm/gm dwt) of Metals in the Fur Seal: A

Table 2. Mean Values (ppm/gm dwt) of Metals in the Fur Seal: B

Cadmium Results - Figure 1

In all tissues except heart, the samples from Kitovi (B) were higher for cadmium, with the highest mean value at 184.81 ppm. Muscle showed the greatest variation between the two rookery sites with mean values of 2.01 ppm at Little Zapadni (A) and 115.83 ppm at Kitovi (B). Heart from A was highest with a mean value of 3.46 ppm., Blubber and muscle showed the lowest levels of cadmium.

Figure 1

Nickel Results - Figure 2

For every organ sampled, B showed higher concentrations of nickel. Blubber showed the lowest level for both groups analyzed with concentrations of 6.86 ppm (A) and 9.04 ppm (B).

Figure 2

Copper Results - Figure 3

Copper ranges did not vary much between the two rookeries except in the case of muscle where B had a mean value of 47.03 ppm and A had a mean value of only 7.55 ppm.

Figure 3

Lead Results - Figure 4

Once again, all mean values from B were higher in all organs. The highest mean value was found in the kidney with 30.03 ppm. The lowest mean value was found in the liver with 10.88 ppm, from A. Chromium.

Figure 4

Results - Figure 5

Chromium showed some interesting variations both between rookeries and between tissues. The highest-mean value was found in the kidney with 111.56 ppm from B. The lowest mean value was found in the liver with 10.94 ppm from A. Zinc.

Figure 5

Results - Figure 6

Zinc levels were basically the same, with the exception of kidney with a mean value of 114.56 ppm from B and muscle with a mean value of 61.34 ppm from A. Selenium.

Figure 6

Results - Figure 7

Heart mean values (48.29 ppm) were unexpectedly higher from A, whereas the spleen from B showed a mean value for selenium of 51.29 ppm, as compared to a (24.96 ppm).

Figure 7

Discussion

In general, samples collected from Kitovi had higher mean values than those collected from Little Zapadni. The extreme differences between the two rookeries is not thought to be due to the location of each rookery on St. Paul, but rather due to the differing migration routes and feeding areas of each population.

Closer examination of the data reveals unusually high concentrations of cadmium, zinc and selenium. It is known that these metals can be toxic in high concentrations. However, it has been found that these three metals are mutually antisynergistic. The presence of high zinc levels lowers the toxicity of cadmium and selenium. (3) High levels of cadmium and selenium are mutually detoxifying and we suspect that this is also the case for chromium.

Most of the variation in the analysis appeared in blubber samples. Problems arose during the drying and digestion processes. Removal of the phospholipids is crucial to preserve the sample.

From a clinical point of view, it was determined that these animals can withstand high levels of heavy metals without adverse effects. This is presumed on the basis that these animals sampled were in the breeding condition and healthy. Breeding seals do not actively feed and thus use up fat reserves for energy.

The authors firmly believe that the best tissues to look at are kidney, liver and spleen due to their metabolic and excretory properties. These are the best organs for metal loading. Next desirable tissue is heart, followed by muscle and blubber. There is still much research to be done on the effects of heavy metals on marine mammals. Further studies in this area can only provide additional information on the effects of heavy metal toxins on the environment.

References

1.  Anas, R.E. Heavy Metals in the Northern Fur Seal, Callorhinus ursinus, and the Harbor Seal, Phoca vitulina richardi. Fish. Bull. 71 (1): 133-137 (1974).

2.  Braham, H.W. Lead in the California Sea Lion , Zalophus californianus. Environ. Poll. 5 : 253-258 (1973).

3.  Casarett, L.J., Doull, J. Toxicology: The Basic Science of Poisons. Macmillan Publishing Co., New York, (1980) pp. 454-456.

4.  Stoneburner. D.L. Heavy Metals in Tissues of Stranded Short-finned Pilot Whales. Sci. Total Environ. 9 (3): 293-297 (1978).