Biological effects of dietary bleached kraft pulp mill effluent on mink (Mustela vison)

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.