Multigenerational study of the effects of consumption of PCB-contaminated carp from Saginaw Bay, Lake Huron, on mink. 1. Effects on mink reproduction, kit growth and survival, and selected biological parameters.

This study was conducted to determine the multigenerational effects of consumption of PCB-contaminated carp (Cyprinus carpio) from Saginaw Bay (Lake Huron) on mink (Mustela vison) reproduction and health and to examine selected biomarkers as potential indicators of polyhalogenated hydrocarbon toxicity in mink. The mink were fed diets formulated to provide 0 (control), 0.25, 0.5, or 1.0 ppm polychlorinated biphenyls (PCBs) through substitution of Saginaw Bay carp for ocean fish in the diets. To determine whether the effects of PCB exposure were permanent, half of the parental (P1) animals were switched from their respective treatment diets to the control diet after whelping the first of two F1 generations. Effects of in utero and lactational exposure to PCBs on subsequent reproductive performance of the F1 animals were examined by switching half of the first-year F1 offspring (kits) to the control diet at weaning, while the other half was continued on their parental diet (continuous exposure). Continuous exposure to 0.25 ppm, or more, of PCBs delayed the onset of estrus (as determined by vulvar swelling and time of mating) and lessened the whelping rate. Litters whelped by females continually exposed to 0.5 ppm, or more, of PCBs had greater mortality and lesser body weights than controls. Continuous exposure to 1.0 ppm PCBs had a variable effect on serum T4 and T3 concentrations. Compared to the controls, there were significant differences in kidney, liver, brain, spleen, heart, and thyroid gland weights of the mink continually exposed to 1.0 ppm PCBs. There was an increase in the incidence of periportal and diffuse vacuolar hepatocellular lipidosis in the P1 mink with continuous exposure to increasing concentrations of PCBs. Plasma and liver PCB concentrations of the adult and kit mink were, in general, directly related to the dietary concentration of PCBs and the duration and time of exposure. Short-term parental exposure to PCBs had detrimental effects on survival of subsequent generations of mink conceived months after the parents were placed on "clean" feed. The lowest observed adverse effect level (LOAEL) for dietary PCBs in this study was 0.25 ppm.

Multigenerational study of the effects of consumption of PCB-contaminated carp from Saginaw Bay, Lake Huron, on mink. 2. Liver PCB concentration and induction of hepatic cytochrome P-450 activity as a potential biomarker for PCB exposure.

This study examined the effect of polychlorinated biphenyls (PCBs) from Saginaw Bay (Lake Huron) carp on the hepatic cytochrome P-450 activity in mink (Mustela vison). Hepatic cytochrome P-450 activities are of interest for their possible use as biomarkers to indicate consumption and biological effects of PCBs in the environment. Adult mink were fed diets containing ocean fish (control diet, 0.0 ppm) or Saginaw Bay carp toprovide 0.25, 0.5, or 1.0 ppm PCBs. Mink were bred after 3 mo of exposure, and half of the parental mink (P1) and kits (F1-1) previously consuming diets containing Saginaw Bay carp were switched to control diet at weaning of the F1-1 kits. P1 and F1-1 mink were then bred within their age and dietary groups after 15 mo of exposure, to produce the second-year F1 (F1-2) and F2 kits. Mink were killed when the new kits were weaned. Transfer of half the animals to the control diet examined whether the effects of the PCB-containing diet on hepatic cytochrome P-450 activity were permanent. Continual exposure to diets containing PCBs from Saginaw Bay carp induced cytochrome P-450 activity in a generally dose-dependent manner. Cytochrome P-450 activity was not different from untreated controls in animals switched to the control diet from the PCB-containing diet. The response of cytochrome P-4501A1 (EROD) activity in a dose-dependent manner and the lack of induction after transfer to noncontaminated diets suggest that this hepatic enzyme activity is a potential biomarker for current exposure to PCBs and other similar cytochrome P-450 inducers.

Multigenerational study of the effects of consumption of PCB-contaminated carp from Saginaw Bay, Lake Huron, on mink. 3. Estrogen receptor and progesterone receptor concentrations, and potential correlation with dietary PCB consumption.

Mink (Mustela vison) were fed diets containing ocean fish (control diet, 0.0 ppm polychlorinated biphenyls, PCBs) or Saginaw Bay carp to provide 0.25, 0.5, or 1.0 ppm PCBs to examine the effect of PCBs on homeostasis of binding sites for ovarian steroid hormones. Ranch-raised mink fed Great Lakes fish contaminated with PCBs, or treated with PCBs directly, have demonstrated reproductive impairment including anovulation, fetal resorption, delayed ovulation, increased gestation, and decreased litter size. Previous studies have demonstrated that estrogen and progesterone levels are unaltered in mink treated with PCBs, suggesting that the effect of PCBs on reproduction is not mediated through alterations in hormone homeostasis. In vitro studies have demonstrated that the most likely means by which PCBs exert antiestrogenic ability is through a down-regulation of the estrogen receptor in normally estrogen-responsive tissues such as liver and uterus. Hepatic and uterine estrogen binding site concentrations were measured in female mink consuming diets containing PCBs for up to 18 mo at up to 1 ppm. Hepatic estrogen binding site concentrations generally decreased with increasing dietary PCB concentrations. Uterine estrogen binding site concentration did not decrease in these animals. Uterine progesterone receptor concentration also did not change with increasing PCB consumption. In total, the response of hepatic and uterine estrogen and uterine progesterone binding sites in mink fed diets containing Saginaw Bay carp suggests that concentrations of PCBs available to uterine tissue may not have been sufficient to decrease uterine estrogen receptor, despite their effect on hepatic estrogen receptor.

Chronic toxicity of fumonisins from Fusarium moniliforme culture material (M-1325) to mink.

Adult female mink (Mustela vison) were fed a diet that contained Fusarium moniliforme culture material that provided dietary concentrations of 89 ppm fumonisin B1, 21 ppm fumonisin B2, and 8 ppm fumonisin B3 for 87 days. During the trial, there was mild lethargy in the mink fed fumonisins, but no other clinical signs or differences in feed consumption (measured during the first two weeks), body weights, or survivability were observed between the fumonisin-treated and control mink. Several hematologic parameters (mean corpuscular hemoglobin concentration, plasma total solids, and lymphocyte concentration) and serum chemical concentrations (globulin, phosphorus, potassium, blood urea nitrogen, creatinine, bilirubin, and cholesterol) and activities (alkaline phosphatase, alanine aminotransferase, amylase, and aspartate aminotransferase) were greater in the mink fed fumonisins than in the controls. Serum albumin/globulin and sodium/potassium ratios and chloride concentrations were lower in the fumonisin-fed mink than in the controls. The concentrations of free sphinganine and the ratio of free sphinganine to free sphingosine in the liver and kidneys of the fumonisin-treated mink were greater than in the control mink. No histopathologic alterations were associated with fumonisin treatment. These results indicate that long-term dietary exposure to F. moniliforme culture material containing 118 ppm total fumonisins is not lethal to adult mink, but can produce adverse physiological effects in the animals.

Effects of supplemental dietary sodium chloride and restricted drinking water on mink.

Thirty-six male mink were fed diets that contained 0, 1, 2 or 4% supplemental salt (sodium chloride) and were given drinking water ad libitum for 7 d. Three mink on each diet were then placed on ad libitum, 50% ad libitum or 25% ad libitum drinking water for the next 14 d. Ad libitum water consumption was directly proportional to the salt content of the diets. Feed consumption was inversely related to the level of dietary salt, although water restriction had a greater effect in reducing feed consumption than did the supplemental salt. The clinical signs of salt toxicity-water restriction observed were increased thirst, mild dehydration, decreased feed consumption, decreased body weight, rough coat, crusty nose and eyes, irritability in the early stage, and lethargy in the later stages. In general, serum and urinary sodium and chloride ion concentrations increased with increasing dietary salt concentrations. Expressed as a percent of brain weight, liver, spleen, kidney and heart weights of mink fed supplemental salt were less than the control weights. Adrenal gland weights increased in response to water restriction. Brain sodium concentrations were not affected by salt supplementation when drinking water was provided ad libitum. However, restricting drinking water generally resulted in increased brain sodium concentrations. Mild to moderate micro- or macrovesicular vacuolar changes were observed in the livers of some mink fed each level of dietary salt, but were especially prominent in the mink restricted in drinking water.