Volume 2 Pages 1 - 58 (March 1987)

Citation: Wren, C.D. (1987) Contaminant Research in Canada.  IUCN Otter Spec. Group Bull. 2: 9 - 11

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Contaminant Research in Canada

Christopher Wren

Department of Chemistry, University of Trondheim, 7055 Dragvoll, Norway

During the 1983/84 and 1984/85 trapping seasons, carcasses of river otter (Lutra canadensis) were collected for contaminant analysis from trappers in Ontario. The annual harvest of otters in Ontario has remained relatively stable at about 10,000 animals per year since accurate records were kept beginning in 1945. This harvest provides a lot of potential material for studies but surprisingly little has been done with it. Also, the trappers themselves are often extremely knowledgeable about the habits and numbers of otters within an area. Their knowledge is based on many years of personal observations and practical experience.

To date, the otter tissues have been analyzed only for metals, although the Canadian Wildlife Service who funded the research, has archived the tissues in Ottawa for future potential analysis for organochlorines, pesticides or other chemicals. The studies identified clear differences in tissue levels of Hg, Pb and Cd between different collection areas. In some cases the differences could be attributed to natural geological occurrences of these elements, or to direct anthropogenic activity. For example, Hg levels were high in otters caught along a river in northwestern Ontario which had been contaminated with Hg from a chlor-alkali plant during the 1960's and early 1970's. The fact that otter Hg levels remain elevated more than a decade after Hg discharge into the river stopped, attests to the persistent threat of Hg to wildlife. Some high (> 10 ppm ww) Hg levels in otter brain tissue suggests the animals were likely suffering from chronic Hg poisoning.

There is evidence to support Hg poisoning as the cause of death in at least one otter along this river system, with anecdotal evidence from trappers of more widespread furbearer mortality (Wren, 1985). The otter in question was found dead by a trapper who followed the tracks which showed the animal behaving erratically, travelling in circles and falling over.  Subsequent tissue analysis revealed extremely high Hg levels of 97 ppm in liver and over 30 ppm (w/w) in brain.

Bone Pb levels in Ontario otter were highest in the areas nearest industrial activity and with the greatest reported levels or atmospheric deposition of Pb. Liver Cu levels were also elevated in otters collected near Sudbury, Ontario, which is the location of large Cu-Ni smelters. Sulphur and nitrogen emissions emissions from the smelters have caused widespread acidification of Lakes around Sudbury. Surprisingly, however, Hg levels in fish and otters near Sudbury are very low. There is no obvious explanation for this apparent anomaly, but may be related to reduced Hg uptake due to interference by Se, which is also emitted from the smelters. However, further work is required to elucidate the factors affecting Hg uptake in wildlife.

Generally, liver and kidneys are the best organs for sampling of metals, although bone is preferred for Pb. Hair has often been suggested as a good medium for element analysis, but this is not feasible when the animal is being hunted for its fur. Trapper co-operation would quickly decline if we started snipping at the valuable pelt.

Recent experiments showed that a combination of PCB plus methyl mercury was more toxic to mink (Mustela vison) kits than either chemical singly. Furthermore, the toxicity of methyl mercury was greater to adult mink under cold stress than in controlled laboratory conditions (Wren et al., 1987). I think it is reasonable to extrapolate these findings on mink to the otter. The studies emphasize the potential interactions of toxic chemicals with each other and with natural stresses (e.g. cold, starvation, disease). More research is required along these lines since simultaneous exposure to more than one chemical and other stresses is more typical of conditions in the wild.

There are currently no studies of contaminants in otters being conducted in Ontario, or anywhere else in Canada to my knowledge. However, otters are a very good biological indicator for many contaminants, and their use in environmental monitoring should be encouraged.

References

Wren, C. D. 1985. Probable case of mercury poisoning in a wild otter (Lutra canadensis) in northwestern Ontario. Can. Field-Naturalist 99 (1): 112-114

Wren, C.D. Hunter, D.B., Leatherland, J.L. and Stokes, P.M. 1987. The effects of polychlorinated biphenyls and methyl mercury, singly and in combination, on mink. Arch. Environ. Contam. Toxicol. (in press,).

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