Robert K. Ringer

Current status of PCB toxicity to mink, and effect on their reproduction

Experiments were conducted from 1968 to 1974 to investigate reproductive complications and mortality in mink fed Great Lakes coho salmon and to ascertain the effects of polychlorinated biphenyls (PCBs) on this fur bearer. The results of mink feeding trials indicated that coho salmon, as such, were not responsible for the loss of reproduction in the adult, or the kit mortality. Mink diets that contained other species of Great Lakes fish caused similar reproductive complications, but to a lesser degree.Rancidity, mercury poisoning and chlorinated hydrocarbon pesticide contamination of the fish were all discounted as being responsible for the problem. The clinical signs and lesions noted in mink that died while receiving diets that contained Lake Michigan coho salmon were very similar to those observed in mink fed on rations that contained supplemental PCBs. These included anorexia, bloody stools, fatty liver, kidney degeneration, and hemorrhagic gastric ulcers. Analyses of tissues from mink that died when fed 30% Lake Michigan coho salmon or 30 ppm supplemental PCB diets showed similar PCB residues.PCB toxicity experiments revealed that mink are very sensitive to these compounds and that the lethal dose varied inversely with the chlorine content of the PCBs although only Aroclor 1254 exerted a detrimental effect on reproduction when fed at a low level (2 ppm) for 8 months. The reproductive failure encountered in feeding mink Lake Michigan coho salmon and Aroclor 1254 was shown to be of a non-permanent nature.

Polychlorinated biphenyls (Aroclors 1016 and 1242): Effects on survival and reproduction in mink and ferrets

Diets that contained various levels of supplemental Aroclor® 1242 or Aroclor® 1016 were fed to mink and ferrets to investigate the chronic toxicity of these PCBs in two closely related species.In mink, Aroclor 1242 was found to be more toxic than comparable or higher levels of Aroclor 1016. The Aroclor 1242 diets caused complete reproductive failure at levels as low as five ppm of the diet. Aroclor 1016 impaired reproduction less than Aroclor 1242. Although fewer females whelped and the four-week kit weights were less than the control animals, no outward signs of abnormalities beyond their smaller size were found in the kits whelped and nursed by dams fed Aroclor 1016.Ferrets were more resistant to the effects of either PCB mixture than were the mink, as noted by the lower mortality rate on the Aroclor 1242 diet and the almost normal level of reproduction on the Aroclor 1016 diet. Feeding Aroclor 1242 at 20 ppm resulted in complete reproductive failure, but was not fatal to adult ferrets. This finding is in sharp contrast to the 100% mortality of adult mink fed the same level. Although the chlorine content is similar in both compounds, Aroclor 1242 has a higher percentage of molecules with five or more chlorines per biphenyl. This difference in higher substituted biphenyl isomer content and/or the reduced levels of contaminants in the Aroclor 1016 mixture may be of major importance in evaluating the toxicity of these compounds.

Effects of dietary mercury on mink

A study was conducted to ascertain the effects of dietary mercury on mink. Five parts per million of dietary methylmercury was lethal to adult mink in about one month. Ten parts per million of mercuric chloride in the diet for five months did not produce adverse effects. Clinical signs of methyl mercurialism were anorexia, loss of weight, incoordination, tremors, and paroxysmal convulsions. The latency period was about 24 days; survival time averaged 33 days. Pathological changes were evident in the tissues of the mink that died of mercury poisoning. Tissue mercury residue analyses showed the highest concentration of mercury in tissues from mink fed methylmercury.

Toxic effects of dietary polybrominated biphenyls on mink.

Serial levels of fireMaster® FF-1, a commercial mixture of polybrominated biphenyls (PBB), and tissues from chickens and a cow that had previously consumed PBB were fed to mink to ascertain the chronic effects of the commercial and “metabolized” form of this compound on mink. Diets that contained 6.25 ppm (or more) PBB were lethal to adult mink within 10 months. One to 2.5 ppm dietary PBB fed for 9 months had an adverse effect on litter size, kit weight at birth, and kit survival. The data suggest that the PBB derived from contaminated beef and poultry was more toxic than the original PBB. The clinical signs of PBB poisoning in mink were food rejection, weight loss, an unthrifty appearance, and fatty infiltration of the liver. Based on these findings, mink must be considered highly susceptible to PBB toxicity. PBB residue levels 60 times the amount in the diet were found in the adipose tissue of the PBB-treated animals.

Effects of chronic dietary hexachlorobenzene exposure on the reproductive performance and survivability of mink and European ferrets

Feeding adult mink and European ferrets diets that contained 1, 5, or 25 mg/kg added hexachlorobenzene (HCB) resulted in reduced reproductive performance as indicated by decreased litter size, increased percentage of stillbirths, increased kit mortality, and decreased early kit growth. Diets treated with 125 or 625 mg/kg HCB were lethal to the adults of both species. In general, the mink were more sensitive to the toxic effects of HCB than were ferrets.In a second experiment, the cross-fostering of mink kits whelped by untreated dams to females fed 2.5 mg/kg HCB, andvice versa, resulted in increased kit mortality when compared to untreated controls. Thein utero exposure to HCB, however, resulted in higher kit mortality than exposure via the dams milk.

Thyroxine and triiodothyronine turnover in the chicken and the bobwhite and Japanese quail

Abstract Except for the data of Heninger and Newcomer (1964) on the t 1 2 of T 4 and T 3 in cardiac tissue of chickens and brief reports on the t 1 2 of T 4 in blood plasma of chickens (Tata and Shellabarger, 1959 ; Hendrich and Turner, 1967) and Japanese quail (McFarland et al. , 1966) , no information has been found in the literature on the degradation of thyroid hormones in birds. In the present investigations, thyroxine- and triiodothyronine-distribution spaces (TDS) and biological half lives ( t 1 2 ) of the two hormones are reported. The extrathyroidal thyroxine- (ETT) and thyroid-secretion rate (TSR) from thyroxine degradation have been calculated from T 4 turnover data in the chicken, bobwhite and Japanese quail. Protein-bound iodine values (PBI) in the three species of birds are also presented. In addition, the results of TSR by thyroxine degradation are compared in chickens receiving diets adequate or deficient in iodine. Thyroxine and triiodothyronine turnover was studied in the chicken, bobwhite quail and Japanese quail. The thyroid secretion rate (TSR) as determined by this method in 7-week normal chickens, 7-week goitrogen-treated chickens, 56-week normal chickens, bobwhite, and Japanese quail, averaged 2.03, 1.59, 1.02, 2.49, and 2.78 μg/100 gm body weight/day, respectively. The TSR of iodine-deficient chickens was found to be significantly decreased. The representative biological half lives of T 4 in the blood of chickens, bobwhite, and Japanese quail were 3.25, 4.60, and 5.50 hours, respectively. The half life of T 3 in each species of birds tested is not significantly different. The representative thyroxine-distribution space (TDS) in ml/100 gm body weight of chickens, bobwhite, and Japanese quail, respectively, measured 29.39, 28.08, and 55.29. TDS/unit body weight of 56-week old chickens is significantly lower than in 7-week chickens. T 3 -distribution spaces in all birds are higher than that of T 4 . The representative protein-bound iodine of chickens, bobwhite, and Japanese quail were measured as 1.12, 1.76, and 1.26 μg, respectively. Increased plasma radioactivity was found in cardiac blood samples as compared to those taken by venous puncture. It is believed that this represents discharge of unchanged hormone from extrathyroidal tissues, probably the liver, in response to the withdrawal of a relatively large volume of blood. The possible role of this mechanism in regulating thyroid hormone levels is discussed.

Assessment of primary vs. secondary toxicity of aroclor® 1254 to mink

Dietary tests were conducted, using mink as a surrogate mammalian wildlife carnivore, to develop and evaluate procedures for the assessment of primary vs secondary toxicity of potentially hazardous chemicals to mammalian carnivores. Test methods included comparison of mortality, body weight change, feed consumption and calculated LC50 values in mink fed diets that contained polychlorinated biphenyls (PCBs),i.e., Aroclor® 1254 (primary toxicity) with mink fed diets that contained the same concentrations of the metabolized xenobiotic (secondary toxicity). Mean feed consumption and body weight gains were lower for the mink fed the metabolized Aroclor 1254 (secondary toxicity) than for mink that received the same concentrations of Aroclor 1254. The tests yielded 28- and 35-day LC50 values of 79.0 and 48.5 ppm (mg/kg) for the primary toxicity test and 47.0 and 31.5 ppm (mg/kg) for the secondary toxicity test, respectively. The results indicated that mink were a suitable carnivorous species for secondary toxicity testing and showed the necessity of using a withdrawal period of appropriate duration.

BIOLOGICAL EFFECTS OF PCBs AND PBBs ON MINK AND FERRETS - A REVIEW

ABSTRACT A search for the cause of reproductive complications and excessive newborn mortality in mink fed Great Lakes fish in the late 1960s led to the demonstrated toxicity of polychlorinated biphenyls (PCBs) in this carnivore. Studies were undertaken to quantitate the toxicity of several PCBs on mink and ferrets, to contrast placental transfer to the fetus and milk biotransfer to the newborn, and to compare PCB to polybrominated biphenyl (PBB) toxicity. Dietary levels as low as 2 ppm of Aroclor® 1254 impaired mink reproduction. Complete fetotoxicity for Aroclors 1242 or 1254 was determined to be less than 5 ppm. The dietary concentration lethal to 50 percent of the adult mink was calculated as 8.6 and 6.65 ppm for Aroclors 1242 and 1254, respectively. The ferret was found to be somewhat less sensitive to several of these chlorinated hydrocarbon compounds. PCB transfer to the newborn via milk was greater than placental transfer. PBB was not as fetotoxic as PCBs but was lethal to the adult at a lower dietary concentration.

Stain Technology: A Phenylhydrazine-Leucofuchsin Sequence for Staining Nerves and Nerve Endings in the Integument of Poultry

This sequence for staining cutaneous nerves and nerve endings uses 1% formic acid as a fixative for 1 hr, followed by two treatments of 5 min each in 6% H2SO4. The tissue is then submerged in fresh 5% phenylhydrazine hydrochloride for 30 min, washed in running tap water for 10 min, and given a 5 min soak in distilled water. The specimen is placed in Lillies “cold Schiff” reagent for 4 hr; transferred to 6% H2SO4, 4 changes of 5 min each; washed in distilled water, 3 changes of 5 min each; dehydrated in acetone, 4 changes of 10 min each; and cleared in 2 changes of methyl benzoate, the 1st for 1 hr and the 2nd until the tissue clears. Nerve fibers stain pinkish-purple; muscles also take up the stain, yet the nerves are discernible from the muscles. All other tissue remain unstained.

Primary and secondary toxicity of warfarin, sodium monofluoroacetate, and methyl parathion in mink

The primary and secondary toxicity of warfarin, sodium monofluoroacetate (Compound 1080), and methyl parathion were assessed in the mink, a representative surrogate mammalian wildlife carnivore. In a 28-day test, a LC50 value for mink fed warfarinper se (primary toxicity) was calculated to be 11.7 ppm (mg/kg) with a 95% confidence interval of 9.2 to 15.0 ppm (mg/kg) and a slope of 2.03. Feeding mink warfarin-contaminated rabbit (minus digestive tract contents) incorporated into diets to provide warfarin residue levels equivalent to the warfarin concentrations fed in the LC50 primary toxicity test did not produce secondary toxicity, suggesting that warfarin may be readily bound and/or metabolized into non-, or less-toxic metabolites by a primary consumer. Toxic residues of sodium monofluoroacetate for mink (as in secondary toxicity) were not produced in rabbits fed a lethal dose of this compound when the gastrointestinal tract contents were removed from the rabbit carcasses. These results suggested that reports of secondary toxicity from sodium monofluoroacetate may be primarily due to consumption of the unmetabolized compound from the gut of prey species. Attempts to produce primary and secondary toxicity in mink by feeding methyl parathionper se (primary toxicity) or via contaminated rabbit (containing the gastrointestinal tract contents), as in secondary toxicity, were unsuccessful, as the mink rejected the methyl parathion-treated diets.