S. J. Bursian

Dietary exposure of mink to carp from Saginaw Bay, Michigan. 1. Effects on reproduction and survival, and the potential risks to wild mink populations

Carp (Cyprinus carpio) collected from Saginaw Bay, Michigan, containing 8.4 mg total polychlorinated biphenyls (PCBs)/kg and 194 ng of 2,3,7,8-tetrachloro-dibenzo-p-dioxin equivalents (TEQs)/kg, were substituted for marine fish at levels of 0, 10, 20, or 40% in the diets of adult ranch mink (Mustela vison). The diets, containing 0.015, 0.72, 1.53, and 2.56 mg PCBs/kg diet, or 1.03, 19.41, 40.02, and 80.76 ng TEQs/kg diet, respectively, were fed to mink prior to and throughout the reproductive period to evaluate the effects of a naturally-contaminated prey species on their survival and reproductive performance. The total quantities of PCBs ingested by the mink fed 0, 10, 20, or 40% carp over the 85-day treatment period were 0.34, 13.2, 25.3, and 32.3 mg PCBs/mink, respectively. The corresponding quantities of TEQs ingested by the mink over the same treatment period were 23, 356, 661, and 1,019 ng TEQs/mink, respectively. Consumption of feed by mink was inversely proportional to the PCB and TEQ content of the diet. The diets containing Saginaw Bay carp caused impaired reproduction and/or reduced survival of the kits. Compared to controls, body weights of kits at birth were significantly reduced in the 20 and 40% carp groups, and kit body weights and survival in the 10 and 20% carp groups were significantly reduced at three and six weeks of age. The females fed 40% carp whelped the fewest number of kits, all of which were stillborn or died within 24 hours. Lowest observable adverse effect levels (LOAEL) of 0.134 mg PCBs/kg body weight/day or 3.6 ng TEQs/kg body weight/day for adult female mink were determined. The potential effects of exposure of wild mink to contaminated Great Lakes fish were assessed by calculating “maximum allowable daily intakes” and “hazard indices” based on total concentrations of PCB residues in several species of Great Lakes fish and mink toxicity data derived from the study.

Contaminants in fishes from Great Lakes-influenced sections and above dams of three Michigan rivers. II: Implications for health of mink

Populations of mink (Mustela vison) have declined in many areas of the world. Such declines have been linked to exposures to synthetic, halogenated hydrocarbons. In the Great Lakes region, mink are fewer in areas along the shore of the Great Lakes and their tributaries where mink have access to fish from the Great Lakes. Recently, there has been discussion of the relative merits of passage of fishes around hydroelectric dams on rivers in Michigan. A hazard assessment was conducted to determine the potential for adverse effects on mink, which could consume such fishes from above or below dams on the rivers. Concentrations of organochlorine insecticides, polychlorinated biphenyls (PCBs), 2,3,7,8-tetrachloridibenzo-p-dioxin equivalents (TCDD-EQ), and total mercury were measured in composite samples of fishes from above or below hydroelectric dams on the Manistee and Muskegon Rivers, which flow into Lake Michigan, and the Au Sable River, which flows into Lake Huron. Concentrations of organochlorine insecticides, PCBs, and TCDD-EQ were all greater in fishes from below the dams than those from above. Concentrations of neither organochlorine insecticides nor mercury in fishes are currently a risk to mink above or below the dams. All of the species of fishes collected from downstream of the dams contained concentrations of PCBs and TCDD-EQ, which represent a hazard to mink. The hazard index for PCBs was less than one for the average of all species from the upstream reaches of the Manistee and Au Sable Rivers, but not the Muskegon. The hazard index (concentration in fish/NOAEC) was greater than 1 for all of the species collected from below the dams, in all three rivers. The greatest hazard index was observed for carp (Cyprinus carpio) downstream on the Muskegon River. Because the concentrations of PCBs used in the hazard assessment were corrected for relative toxic potencies, the hazard ratios based on PCBs should be similar to those based on TCDD-EQ. This was found to be true. Thus, either total PCBs or TCDD-EQ could be used as the critical toxicant in the hazard assessment. However, if uncorrected concentrations of PCBs, expressed as Aroclors®, were used in the hazard assessment, the toxicity of the weathered mixture would have been underestimated by approximately five-fold, and, in that instance, TCDD-EQ would be the critical contaminant for the hazard assessment. The average maximum allowable percentage of fish from above the dams, which would result in no observable adverse effects of TCDD-EQ, was 70%. Based on the average TCDD-EQ concentrations in the fishes, an average of 8.6% of the diet could be made up of fishes from below dams on the rivers. The most restrictive daily allowable intakes were for carp on the Muskegon and steelhead trout (Onchorhyncus mykiss) on the Manistee Rivers. Only 2.7% of the diet could be made up of these two species from influenced portion of the Au Sable River, they would be exposed to 390 μg PCBs and 8.55 ng of TCDD-EQ per day, respectively (Giesy et al. 1994b). Thus, it would take 15.1 or 77 days for mink to receive their total annual dose of PCBs or TCDD-EQ, respectively. At least for chinook salmon, the critical contaminant for the purposes of hazard assessment would be total concentrations of PCBs. Consuming chinook salmon for as little as 2 weeks would deliver the annual allowable dose of PCBs to mink.

Effects of 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) injected into the yolks of chicken (Gallus domesticus) eggs prior to incubation

The yolks of White Leghorn chicken (Gallus domesticus) eggs were injected prior to incubation with either 3,3′,4,4′,5- pentachlorobiphenyl (PCB 126) at doses ranging from 0.1 to 12.8 μg/kg egg or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at doses ranging from 0.04 to 0.64 μg/kg egg. Chicks were subjected to necropsy within 24 h of hatching. The brain, bursa, heart, liver, and spleen were removed and weighed. Assessment of the rate of hatching indicated an LD50±S.E. of 2.3±0.19 μg/kg egg (7.1±0.58 nmol/kg egg) for PCB 126 and 0.15±0.012 μg/kg egg (0.47±0.037 nmol/kg egg) for TCDD. No significant differences in the incidence of developmental abnormalities (structural defects and edema) were observed in TCDD-exposed embryos, while PCB 126 caused significantly more developmental abnormalities at 3.2, 6.4, and 12.8 μg/kg egg than the vehicle control. PCB 126 caused lower hatchling weights and greater relative brain, heart, and liver weights when compared to the vehicle control group at a dose of 3.2 μg/kg egg which is greater than the LD50. TCDD at 0.08 μg/kg egg caused relative bursa weights to be less than those of the vehicle control. A toxic equivalency factor (TEF) of 0.07 was determined for PCB 126 in relation to TCDD based on overt lethality.

Acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin to mink

The effects of 2,3,7,8-tetrachlorodi-benzo-p-dioxin (TCDD) on adult male mink were assessed. TCDD was administered as a single oral dose (0, 2.5, 5.0, and 7.5 μg/kg body weight) and the mink observed for 28 days. There was a dose dependent decrease in feed consumption with corresponding body weight loss. Gross necropsy revealed mottling and discoloration of the liver, spleen, and kidneys. In mink exposed to higher doses of TCDD, brain, kidneys, heart, and thyroid and adrenal glands were enlarged when expressed as a percent of body weight. Hematologic and thyroid hormone measurements in surviving animals revealed no alterations resulting from TCDD exposure. A 28-day LD50 value of 4.2 μg/kg body weight was calculated. These results indicate that mink are among the most sensitive species to TCDD and that they can serve as a valuable model to study the impact of environmental dioxins on carnivorous mammalian species.

Mechanisms of TCDD-induced abnormalities and embryo lethality in white leghorn chickens

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds in birds has been well-established in laboratory and field studies. Observed effects of TCDD and related chemicals in birds include developmental deformities, reproductive failure, liver damage, wasting syndrome and death. The mechanism of action of TCDD at the cellular level is primarily mediated through the aryl hydrocarbon receptor (AhR). However, the mechanism of toxic action at the organism level is poorly understood. In this study, the role of radical oxygen species and mixed function oxidize (MFO; cytochrome P4501A) in the mechanism of TCDD-induced abnormalities and lethality were examined by co-injecting radical scavengers and an MFO inhibitor (piperonyl butoxide). Egg injection studies were conducted to determine if in ovo TCDD exposure can cause oxidative stress in white leghorn chicken eggs. Test agents were injected into the yolk prior to incubation. Treatments included TCDD (150 ng/kg), triolein (vehicle control), and various co-treatments including MnTBAP (a mimetic of superoxide dismutase), piperonyl butoxide, piroxicam, vitamin A acetate, and vitamin E succinate. Phenytoin, which is known to cause teratogenesis through oxidative stress was used as a positive control. Eggs were incubated until hatch and then the following parameters were assessed: mortality, hatching success, abnormalities, weights for whole body, liver, heart and brain, and biochemical endpoints for oxidative stress. As a measure of exposure, concentrations of TCDD and ethoxyresorufin-O-deethylase (EROD) activities were measured in tissues of hatchlings. While greater mortality and abnormalities were observed in the TCDD treatment groups, the number of the replicates were not great enough to detect statistically significant differences in abnormality rates for the co-treatments. Some of the observed developmental abnormalities included edema, liver necrosis and bill, eye and limb deformities with TCDD treatments, bill and brain deformities with phenytoin treatments, eye abnormalities with Vitamin E treatments, and abnormal feather pigmentation with piperonyl butoxide treatments.

Toxicity of 3,4,5,3',4',5'-hexachlorobiphenyl to mink.

Diets supplemented with 0.01 or 0.05 ppm (mg/kg) of 3,4,5,3′,4′,5′-hexachlorobiphenyl (345-HCB) were fed to mink to investigate the toxicological manifestations of this toxic polychlorinated biphenyl congener in a sensitive species. Dietary exposure of mink to 0.05 ppm 3,4,5,3′,4′,5′-hexachlorobiphenyl for 135 days resulted in 50% mortality while no deaths occurred on 0.01 ppm 345-HCB. Clinical signs of toxicity included anorexia, bloody stools, disrupted molting patterns, and thickened, elongated and deformed nails. Ascites and gastric ulcers were present in animals that died. Statistically significant increases in liver, kidney, and adrenal gland weights were found in the 345-HCB-treated mink. Decreases in total and free triiodothyronine concentrations were observed in mink fed the 345-HCB-treated diets and total thyroxine was decreased in the mink fed 0.05 ppm 345-HCB. No consistent histopathologic lesions were found in the thyroid or adrenal glands of the 345-HCB-treated mink, nor were there any statistically significant differences between the 345-HCB-treated and the control mink in serum epidermal growth factor levels, plasma 17β-estradiol and progesterone concentrations, hepatic aminopyrine N-demethylase, and benzo(α)pyrene hydroxylase activities, hypothalamic norepinephrine, dopamine, and serotonin concentrations or in the incorporation of (3H) thymidine by concanavalin-A-stimulated lymphocytes.

Contaminants in fishes from great lakes-influenced sections and above dams of three Michigan Rivers. I: Concentrations of organo chlorine insecticides, polychlorinated biphenyls, dioxin equivalents, and mercury

Fishes of the Great Lakes contain hazardous chemicals such as synthetic halogenated hydrocarbons and metals. These fish can move from the lakes into the Great Lakes tributaries of Michigan. In doing so, they transport concentrationsof contaminants which may represent a risk to wildlife. Concentrations of mercury (Hg), total polychlorinated biphenyls (PCBs), 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TCDD-EQ), total DDT complex, aldrin, endrin, dieldrin, heptachlor, heptachlor epoxide, lindane, hexachlorobenzene, cis-chlordane, oxychlordane, endosulfan-I, methoxychlor, trans-chlordane, and trans-nonachlor were determined in composite samples of fishes from above and below Michigan hydroelectric dams, which separate the fishes which have access to the Great Lakes from fishes that do not. Mean concentrations of total PCBs, TCDD-EQ, DDT, and most of the other pesticides were greater in composite samples of six species of fishes from below than above the dams on the Au Sable, Manistee, and Muskegon Rivers. Concentrations of mercury, were the same or greater above the dams than below. However, this difference was statistically significant only on the Au Sable. Mercury concentrations ranged from less than 0.05 mg/kg to 0.73 mg Hg/kg, ww. Total concentrations of PCBs ranged from 0.02 to 1.7 mg/kg, ww. Concentrations of 2,3,7,8-tetrachlordibenzo-p-dioxin equivalents varied among fishes and locations. The concentrations of TCDD-EQ ranged from 2.4 to 71 μg/kg, ww, with concentrations in carp being the greatest. Concentrations of TCDD-EQ were greater than the concentrations which would be expected to occur, due solely to the presence of polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF), and technical mixtures of PCBs.

Efficacy of hydrated sodium calcium aluminosilicate and activated charcoal in reducing the toxicity of dietary aflatoxin to mink

Mink were fed diets that contained 0, 34, or 102 ppb (μg/kg) aflatoxins with or without 0.5% hydrated sodium calcium aluminosilicate (HSCAS) and/or 1.0% activated charcoal (AC) for 77 days. Consumption of the diet that contained 34 ppb aflatoxins was lethal to 20% of the mink, while 102 ppb dietary aflatoxins resulted in 100% mortality within 53 days. The addition of AC to the diet containing 102 ppb aflatoxins reduced mortality and increased survival time of the mink while the addition of HSCAS, alone or in combination with AC, prevented mortality. Histologic examination of livers and kidneys from the mink demonstrated liver lesions ranging from extremely severe in mink fed 102 ppb aflatoxin to mild to moderate in those that received 34 ppb aflatoxins. The addition of HSCAS and/or AC to the diets that contained 102 ppb aflatoxins reduced or essentially eliminated histopathologic lesions in the livers. No histopathologic alterations associated with the dietary treatments were observed in the kidneys.

Dietary Exposure of Mink to Carp from Saginaw Bay, Michigan: 2. Hematology and Liver Pathology

The effects of consumption of environmental contaminants contained in carp (Cyprinus carpio) from Saginaw Bay, Michigan on various hematological parameters and liver integrity of adult female mink (Mustela vison) were determined. Mink were fed diets that contained 0 (control), 10, 20, or 40% carp prior to and throughout the reproductive period (182 days). The diets contained 0.015, 0.72, 1.53, and 2.56 mg polychlorinated biphenyls (PCBs)/kg diet and 1.0, 19, 40, and 81 pg 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs)/g diet, respectively. Mink fed the diets containing carp showed a general dose-dependent occurrence of clinical signs commonly associated with chlorinated hydrocarbon toxicity, including listlessness, nervousness when approached, anorexia, and melena. Erythrocyte counts were less in mink exposed to Saginaw Bay carp than in controls, while the number of white blood cells was greater than in controls. Significant differences (p<0.05) in the concentrations of neutrophils, lymphocytes, monocytes, and eosinophils were also found between the control and carp-fed groups, but are considered to be of limited clinical or biological importance. Hematocrit values for the mink fed the 20 and 40% carp diets were significantly less than those of mink in the control and 10% carp groups. There were no significant differences in hemoglobin concentrations among the groups. Necropsies revealed enlarged yellowish livers in many of the carp-fed mink, especially those fed the 40% carp diet. Liver, spleen, and lung weights of carp-fed mink were significantly greater than those of control mink. Histopathologic examination of the livers revealed various degrees of congestion, hepatocellular fatty changes, and scattered portal lymphocytic infiltration which were most prevalent in mink fed the carp diets. These clinical signs, hematological effects, and histologic alterations are similar to those previously described for chlorinated hydrocarbon toxicoses in mink.

The reproductive effects of dietary heptachlor in mink (Mustela vison)

Adult female mink were fed diets containing 0 (control), 6.25, 12.5, and 25 ppm (μg/g) technical grade heptachlor prior to and throughout the reproductive period (181 days) to evaluate the effects of heptachlor consumption on reproduction and offspring viability and to assess the extent of placental and mammary transfer of heptachlor epoxide to mink offspring. Feeding 12.5 and 25 ppm resulted in significant reductions in feed consumption and body weights of female mink. Mortality was 0, 8, 67, and 100% for the control, 6.25, 12.5, and 25 ppm groups, respectively. All females in the 25 ppm group died within 88 days. Mink fed the two higher heptachlor diets displayed clinical signs indicative of central nervous system involvement just prior to death. Females were mated with males on the same dietary treatments. Whelping success rates were 67, 83, 27, and 0% for the control, 6.25, 12.5, and 25 ppm groups, respectively. High mortality in the 12.5 and 25 ppm groups accounted for the lack of reproductive success. Gestation length, litter size and birth weight of kits were not significantly affected by adult female consumption of 6.25 ppm heptachlor while kits whelped by females on the 12.5 ppm diet weighed significantly less than control kits at birth. Survival of kits in the 12.5 ppm group from birth to three weeks of age was also adversely affected. At three and six weeks of age, kit body weights in both the 6.25 and 12.5 ppm groups were significantly less than body weights in control kits. Examination of heptachlor epoxide concentrations in newborn and developing kits indicated both placental and mammary transfer of the chemical from the dams to the kits. The LC50 for the 181-day exposure period for female mink was 10.5 ppm heptachlor and the LOAEL, based on reduced kit growth, was 6.25 ppm.