Abstract

In 1988, ten carcasses of stranded beluga whales from the polluted St. Lawrence River were necropsied. Some lesions were commonly seen, like gastric Ulcerations and erosions, digestive parasitism, pneumonias and mammary gland problems. We also found some tumors. The common findings in the carcasses examined are the high levels of contaminants, mostly organochlorines, whose effects have been well studied. Many of the lesions observed in the beluga whale population of the St. Lawrence River could be related to the toxicity of the chronic exposure to organochloric contaminants.

A distinct population of about 500 beluga whales lives in the estuary of the St. Lawrence River, They don't migrate or mix with any other population. When those whales die and strand ashore, they are reported to us by the residents. We go get the carcasses and carry them to the necropsy room of the Veterinary Medicine School of Montreal University, in St. Hyacinthe where the necropsy is performed. We routinely make gross necropsy, with histopathology, bacteriology, virology, parasitology and toxicology.

The necropsy results showed lesions on the skin, in the digestive tract in the mouth stomach and intestine, in the lungs, liver, spleen, urinary bladder, adrenals, mammary glands, testis. Those lesions are associated with bacteria, which are mostly opportunistic ones, parasites of all kinds, or neoplastic. III tact, we found many extensive infections, and three malignant and three benign tumors on ten animals. Such lesions strongly suggest immunosuppression.

Toxicological analysis revealed high concentrations of industrial and agricultural contaminants, mostly organochlorines with heavy metals. Those mostly considered are PCB, which are found at high levels, are increasing with age, and are higher in males than in females who nurse their calf; PCB which are liposoluble pass through the milk which contains about 45% fat. The calves themselves receive very large amounts of contaminants in their first months of life, so they can be very heavily contaminated.

We know the effects of PCB on laboratory animals, because it was the easiest way to study them. We know they can affect the liver, functionally and structurally, and we had liver lesions. We know they can cause atrophy of the thymus and spleen; we found only one thymus on ten animals, although we had a few young ones, and we also found two atrophied and fibrosed spleens. Immunologic impairment caused by PCB is the most important effect suspected on beluga whales of the St. Lawrence, given all the lesions, the bacteria and the tumors we found. Hormonal imbalance is known to happen with thyroid hormones and estrogens whose metabolism is impaired. Estrogen problems can lead to reproductive inefficiency.

The small population of the St. Lawrence does not enlarge even though hunting stopped many years ago, and we suspect such a reproductive inefficiency. We also suspect a cortisol imbalance with the adrenal lesions we found and the gastric ulcers that could also result from vitamin A deficiency, another effect of PCB, that weaken the epithelium.

PCB is also known to cause skin lesions, and weight loss. About their carcinogenic effect, we now know that PCB are not mutagens, but they are promoters of tumors, meaning that if a mutation occurs, they will "encourage" it to develop as a tumor.

In conclusion, the adverse effects of contaminants taken one by one have been proven on laboratory animals. The effects of a mixture of them at high levels on a population of beluga whales will be very hard to prove scientifically, but we have strong reasons to think this could be so given the wide variety of lesions that suggest some level of immunosuppression.