Biological effects of dietary bleached kraft pulp mill effluent on mink (Mustela vison)
Date
1996
Authors
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ORCID
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Degree Level
Doctoral
Abstract
Semi-aquatic predators such as mink are exposed to anthropogenic contaminants
directly through the water and through bioaccumulation in the food chain. The
biological impact of dietary bleached kraft pulp mill effluent (BKME) on mink (Mustela
vison) was investigated. In a pilot study and two subchronic studies of 8 and 7 month
duration, mink were fed diets containing 75% (year 1) and 45% (year 2) fish caught
downstream of a BKME discharge point, and drinking water contained 25% BKME. In
year two, the 45% fish diet had 15% soft-wood run BKME incorporated into the feed.
The investigation was tiered. In the pilot study, behavioural, clinical,
biochemical, hematological, and pathological effects were investigated. Repeating these
variables, reproductive factors were added in Year one, while in Year two, hepatic
enzyme ( ethoxyresorufin-O-deethylase (EROD) induction, cell mediated and humoral
immune function, and hepatic vitamin A levels were evaluated. In vivo and in vitro
immunotoxicity assays were developed for mink. Peripheral blood mononuclear cell
(PBMC) proliferation was measured in response to mitogens in vitro. An enzyme-linked
immunosorbent assay for antibody detection was developed for mink. Delayed type
hypersensitivity (DTH) tests and antibody production responses were used to measure
cell-mediated and humoral immunity in vivo in the experimental mink.
No adverse effects were found on behavioural, gross pathological,
histopathological, hematological or biochemical variables, on gestation, kit birth weight,
kit survival, libido, estrus, sperm quality or hormone levels. In the Year two subchronic
study, the relative liver size was increased in BKME-exposed males. Hepatic EROD activity was 1. 8 times greater in exposed females (p=0.0001) and 2. 0 times greater in
exposed males (p=0.0004) relative to control mink. No difference in PBMC
proliferation was seen between the control and exposed mink with any of the mitogens
used. The DTH response was impaired (p=0.014), while the antibody response was
enhanced (p=0.029) in the BKME-exposed mink. Hepatic vitamin A levels were not
different in the females (mid-lactation), but were significantly decreased in the BKME-exposed
males (post-breeding) (p=0.0002).
These changes represent a primary effect of bleached pulp mill effluent on the
immune system, hepatic vitamin A stores, and hepatic detoxification enzyme system in
exposed mink. Hepatic EROD activity provides a useful indicator for evidence of
exposure to environmental toxicants in mink. The change in the immune response is
occurring at the level of T lymphocyte differentiation, and therefore, affects the relative
proportions of T lymphocyte subpopulations which are dedicated to cell mediated, or T
lymphocyte dependent, antibody mediated immunity. Immune deviation seen in the
female mink is not associated with changes in hepatic vitamin A stores, while the
decreased vitamin A in the males has an unknown effect on their immune response.
The biological impact of bleached kraft pulp mill effluent does not cause dramatic
or subclinical signs of toxicity in exposed mink. However, the interference with hepatic
vitamin A storage, and changes to the immune response, present concerns regarding long
term effects on health, reproduction and longevity in exposed mink.
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Degree
Doctor of Philosophy (Ph.D.)
Department
Veterinary Pathology
Program
Veterinary Pathology