Effects of feeding coho salmon and other Great Lakes fish on mink reproduction

Effects of halogenated contaminants on reproductive development in wild mink (Neovison vison) from locations in Canada

The concept of the Anthropocene, that humans are now re-engineering global ecosystems, is in part evidenced by the pervasive pollution by persistent organic pollutants (POPs). Certain POPs are hormone mimics and can disrupt endocrine and hence reproductive processes, shown mainly by laboratory studies with model species. There are, in contrast, fewer confirmations of such disruption from eco-epidemiological studies of wild mammals. Here we used the American mink (Neovison vison) as a sentinel species for such a study. Over the period 1998-2006, 161 mink carcasses were obtained from commercial trappers in the Canadian provinces of British Columbia and Ontario. Mink were aged, sexed, measured, and body condition assessed. Livers were analyzed either individually or pooled for organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), and subsets for polybrominated diphenyl ethers (PBDEs). We primarily addressed whether contaminants affected male reproductive development by measuring baculum size and assessing the influences of age and body condition. We also considered the influence of spatial variation on relative exposure and size of baculum. Statistical models separated by age class revealed that significant relationships between baculum length or mass and juvenile mink were mostly positive, whereas for adults and first year mink they were mostly negative. A significant negative relationship for adult mink was determined between DDE and both baculum length and mass. For juvenile mink we found significant positive relationships between ∑PCBs, DDE and ∑PBDEs with baculum length. Our results provide some indication of negative effects of halogenated contaminants on male reproductive development in wild mink, and the most likely candidate chemical is the confirmed anti-androgenic compound, DDE, rather than PCBs or other compounds.

Organochlorine contaminants in wild mink from the lower Great Lakes basin, Canada, 1998-2006

Organochlorine contaminants were measured in livers of wild mink (Neovison vison) trapped in the lower Great Lakes basin from 1998 to 2006. To assess exposure and potential risk in mink feeding on Great Lakes biota, concentrations of contaminants were compared in mink trapped within 7.8 km of the shoreline as well as at inland sites (i.e., 8-40 km). Overall, significant spatial variation in mean hepatic concentrations of sum PCBs and seven other organochlorines was found in mink from 13 Great Lakes sites, many of which are within the Great Lakes Areas of Concern. Mean sum PCB concentrations, on a lipid weight basis, ranged from 2 μg/g in mink from inland Lake Ontario sites to 44 μg/g in mink from western Lake Erie. Concentrations of other organochlorines in mink were generally low. Mink from western Lake Erie had the highest mean cumulative organochlorine burdens dominated largely by PCBs. A significant age effect was found with 1-year-old mink having significantly higher PCB burdens than mink less than 1 year in age. With respect to published PCB threshold effect concentrations, some mink exceeded those associated with effects on reproduction and survival as well as the presence of jaw lesions. This was most consistently found in western Lake Erie where the health of populations of wild mink may be adversely affected and where no mink 2 years of age or older were collected.

Genetic variation and population structure of American mink Neovison vison from PCB-contaminated and non-contaminated locales in eastern North America

American mink Neovison vison may be particularly vulnerable to toxicities of persistent contaminants such as PCBs because of their aquatic-based diet, position near the top of the food web, and small deme sizes. Furthermore, ranched mink are sensitive to reproductive toxicities of fish diets from PCB-polluted sites. The upper Hudson River is highly contaminated with PCBs and previous studies have shown elevated hepatic burdens of total and coplanar PCBs in mink collected near the river compared with those from more distant locales in New York and elsewhere. We hypothesized that bioaccumulation of PCBs in Hudson River mink has reduced their levels of genetic diversity or altered their genetic population structure. To address this, we conducted microsatellite DNA analysis on collections made in proximity to and from more distant locales in the Hudson River watershed, elsewhere in New York State, and at other sites in eastern North America including New Brunswick, four locales in Ontario, multiple drainages in Maine, and two ecoregions in Rhode Island. We did not find reduced genetic diversity at the individual or population levels in mink collected near (<6 km) to PCB hotspots in the Hudson River nor evidence of altered population structure. Consistent with their distribution in small localized and isolated demes, we did find significant genetic population structure among many mink collections in New York State and elsewhere. Depending on the analytical approach used, genetically distinct populations numbered between 16 when using STRUCTURE to 19-20 when using Exact G tests, F ST, or AMOVA analyses. Genetically distinct population units were found among major ecoregions and minor ecoregions in New York State, among different hydrologic subunits within the Hudson River watershed, among spatially separate locales in Ontario, and among most watersheds in Maine. However, despite this localization and potential heightened impact of stressors, genetic diversity and genetic population structure in mink does not seem to be affected by their bioaccumulation of high levels of PCBs of Hudson River origin.

Wild mink (Neovison vison) as sentinels in environmental monitoring

Summary

For monitoring of endocrine disruptors and other contaminants in terms of exposure levels and possible effects on the reproductive system, suitable sentinel species have to be used. The wild mink is putatively a good sentinel, as it is a semi-aquatic top predator present in all parts of Sweden and it is hunted extensively. When studying the wild mink from an environmental health perspective, one has to consider advantages and disadvantages with different ways of sampling. Field studies often generate large data sets and the variables measured may show large variation due to intrinsic and extrinsic biological factors; this must be adjusted for when analyzing data in order to increase the chances of identifying associations between exposure and health effects. With focus on our own data from studies in wild mink in Sweden, this article describes how the mink can be used in large scale screening of exposure and effects of contaminants.

Toxicity reference values for mink exposed to 2,3,7,8-tetrachlodibenzo-p-dioxin (TCDD) equivalents (TEQs)

Dietary and tissue residue-based toxicity reference values (TRVs) were derived for mink from the published results of studies in which mink were exposed to polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), or related compounds. Because the primary mechanism of toxic action at the least concentration for these compounds is related to activation of the aryl hydrocarbon receptor (AhR), TRVs were described on the basis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TEQ). Each published study was critically reviewed for its usefulness in deriving a TRV based on the following criteria: (1) close relatedness of the test species to the wildlife receptor of concern (only mink studies were reviewed in this paper); (2) chronic duration of exposure which included sensitive life stages to evaluate potential developmental and reproductive effects; (3) measurement of ecologically relevant endpoints; (4) availability of congener-specific data to calculate TEQ concentrations; and (5) minimal impact of co-contaminants. Dietary TRVs for mink exposed to TEQ ranged from 12.1 to 56.6 ng TEQ/kg feed (wet weight) for the no observable adverse effect level (NOAEL) and from 50.4 to 242 ng TEQ/kg feed (wet weight) for the lowest observable adverse effect level (LOAEL). TRVs based on tissue residue concentrations ranged from 50.2 to 77.8 ng TEQ/kg liver (wet weight) for the no observable adverse effect concentration (NOAEC) and the value was 189 ng TEQ/kg liver (wet weight) for the lowest observable adverse effect concentration (LOAEC). Selection of a TRV should be based on studies of compounds that are most similar to those at a site of interest. In particular, it was determined that the effects of PCDFs could not be accurately predicted from the use of TEQ-based TRVs developed from studies of PCDDs or PCBs. Risk assessors should be aware that exceedance of these TRVs would not necessarily be expected to lead to ecologically relevant adverse effects because of the inherently conservative assumptions made in the TRV derivation process.

Mink as a sentinel species in environmental health

The concept of "sentinel species" is important in the environmental health sciences because sentinel species can provide integrated and relevant information on the types, amounts, availability, and effects of environmental contaminants. Here we discuss the use of mink (Mustela vison) as a sentinel organism by reviewing the pertinent literature from exposure- and effects-based studies. The review focuses on mercury (Hg) and polychlorinated biphenyls (PCBs), as they are persistent, ubiquitous, and bioaccumulative contaminants of concern to both humans and wildlife. Mink are widely distributed, abundant, and regularly trapped in temperate, aquatic ecosystems, and this makes them an excellent model to address issues in environmental pollution on both temporal and spatial scales. As a high-trophic-level, piscivorous mammal, mink can bioaccumulate appreciable concentrations of certain pollutants and have been shown to be sensitive to their toxic effects. The husbandry and life history of mink are well understood, and this has permitted controlled dosing experiments to be conducted using animals reared in captivity. These manipulative studies have yielded important quantitative information on exposure-response relationships and benchmarks of adverse health effects, and have also allowed the cellular mechanisms underlying toxic effects to be explored. Furthermore, the data accrued from the laboratory continue to validate observations made in the field. Research derived from mink can bridge and integrate multiple disciplines, and the information collected from this species has allowed environmental health scientists to better understand and characterize pollution effects on ecosystems.

Temporal and spatial trends in chlorinated hydrocarbon concentrations of mink in Canadian Lakes Erie and St. Clair

Mink (Mustela vison) carcasses were collected from local commercial trappers from fall 1998 to spring 2003 from tributaries and marshes within 4.8 km from the shores of Lakes Erie and St. Clair, including the Wheatley Harbour and St. Clair River Areas of Concern (AOCs), as well as from inland sites (8 to 40 km from shore). Liver concentrations, on a lipid weight basis, of chlorinated hydrocarbons were measured and compared among sites and to tissue concentrations of mink from two previous collections from similar sites over the past 25 years. Mink from the western Lake Erie sites, which included the Wheatley Harbour AOC, had significantly higher concentrations of sum PCBs and PCB Aroclors than those from the St. Clair corridor or inland sites, with concentrations from the rest of Lake Erie being intermediate. Dieldrin concentrations were also significantly higher in western Lake Erie than many other sites, and those of oxychlordane and mirex also tended to be higher (0.05 < p < 0.1). There were no differences in contaminant concentrations between the St. Clair River AOC and the downstream non-AOC Lake St. Clair site, with the exception of slightly higher levels of octachlorostyrene (OCS). Concentrations of PCBs and other chlorinated hydrocarbons in mink showed a general decrease over the past two decades. In contrast, PCBs and some organochlorine pesticides tended to increase, significantly so with oxychlordane, in western Lake Erie mink over the same time period. DDE declined at all sites. Currently, mink liver PCB concentrations are within the range associated with reproductive impairment, as determined from captive mink studies, in 11.7% of all animals collected from the Lakes Erie and St. Clair basin overall, but in almost 40% of individuals from western Lake Erie.

Comparison of risk assessment methodologies for exposure of mink to PCBs on the Kalamazoo River, Michigan

Risk assessments are generally based on exposures predicted by use of simple models of accumulation from abiotic compartments or the diet. The use of tissue-specific measurements of residue concentrations in wildlife tissues is more accurate and subject to less uncertainty, but these data are often not available. This report compares the results of two different site-specific approaches for assessing the risk of PCBs to mink residing along the Kalamazoo River, MI. The first approach was based on hepatic concentrations of PCBs and 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) of mink. The second approach was based on measured concentrations of both PCBs and TEQs in the diets of mink. For each of these methodologies, assessments were based on no observed adverse effect levels (NOAELs) or concentrations (NOAECs) and lowest observed adverse effect levels (LOAELs) or concentrations (LOAECs). Samples of mink (Mustela vison) and its diet were collected from within the Kalamazoo River Area of Concern (KRAOC) and an upstream reference area in the Fort Custer Recreation Area (FC). Hazard quotient (HQ) values were calculated based on congener-specific concentrations of PCBs or TEQs, several toxicity reference values (TRVs), and several assumed dietary compositions. Mean total hepatic concentrations of PCBs were 2.7 and 2.3 mg PCBs/kg, ww, in mink from the KRAOC and FC, respectively. HQs based on the LOAEC and mean hepatic PCB concentrations ranged from 0.37 to 0.87 at KRAOC and 0.31-0.73 at FC. HQs based on PCBs in the diet ranged from 0.20 to 1.8 at KRAOC and from 0.04 to 0.35 at FC. Dietary HQs were less than 10-fold different than tissue-based HQs.

Ranking terrestrial vertebrate species for utility in biomonitoring and vulnerability to environmental contaminants

The measurement of contaminant tissue concentrations or exposure-related effects in biota has been used extensively to monitor pollution and environmental health. Terrestrial vertebrates have historically been an important group of species in such evaluations, not only because many are excellent sentinels of environmental contamination, but also because they are valued natural resources in their own right that may be adversely affected by toxicant exposure. Selection of appropriate vertebrates for biomonitoring studies frequently relies on expert opinion, although a few rigorous schemes are in use for predicting vulnerability of birds to the adverse effects of petroleum crude oil. A Utility Index that ranks terrestrial vertebrate species as potential sentinels of contaminants in a region, and a Vulnerability Index that assesses the threat of specific groups of contaminants to these species, have been developed to assist decision makers in risk assessments of persistent organic pollutants, cholinesterase-inhibiting pesticides, petroleum crude oil, mercury, and lead shot. Twenty-five terrestrial vertebrate species commonly found in Atlantic Coast estuarine habitat (Rattner et al. 2001a) were ranked for their utility as biomonitors of contamination and their vulnerability to pollutants in this region. No single species, taxa, or class of vertebrates was found to be an ideal sentinel for all groups of contaminants. Although birds have overwhelmingly been used to monitor contaminants compared to other terrestrial vertebrate classes, the nonmigratory nature and dietary habits of the snapping turtle and mink consistently resulted in ranking these species as excellent sentinels as well. Vulnerability of Atlantic Coast populations of these species varied considerably among groups of contaminants. Usually a particular species was found to be at high risk to only one or two groups of contaminants, although a noteworthy exception is the bald eagle, which is highly vulnerable to all five of the contaminant groups examined. This index could be further enhanced by generation of additional comparative toxicity data to facilitate interspecific extrapolations. The Utility and Vulnerability Indices have application to many types of habitats in addition to estuaries and are of value to natural resource and risk managers that routinely conduct local, regional, or national environmental quality assessments.

A multigeneration study to ascertain the toxicological effects of Great Lakes salmon fed to rats: study overview and design

Fish from the Great Lakes can be contaminated with a plethora of industrial, agricultural, and environmental chemicals. These chemicals have been associated with reproductive and other toxicological effects in fish and fish-eating birds found in the Great Lakes basin. To obtain more insight into this association, several laboratory studies have been undertaken wherein fish have been incorporated into the experimental diets to determine the effect of their ingestion upon the test animals. In addition, several human epidemiological studies have found correlations between Great Lakes fish consumption and effects in neonates which have been attributed to polychlorinated biphenyls without any appreciable consideration as to what synergistic or antagonistic effects other chemicals or heavy metals may or may not have contributed to the observed findings. Herein is presented the design of a two-generation feeding-reproduction study that incorporated lyophilized chinook salmon (Oncorhynchus tsawytscha) fillets into the diets of Sprague-Dawley rats. The findings of this study will be presented in the sections which follow.

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 vision) 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Cause-effect linkages between chemicals and populations of mink (Mustela vison) and otter (Lutra canadensis) in the Great Lakes basin

Following outbreaks of reproductive failure in commercial ranching operations, laboratory experiments showed that mink are extremely sensitive to organochlorine chemicals, particularly PCBs and dioxins. The purpose of this paper is to test the hypothesis that, since wild mink are exposed to these compounds through consumption of Great Lakes fish, they might exhibit reproductive dysfunction and population declines. The otter, another piscivorous animal, should show the same effects. The available information is reviewed according to five epidemiological criteria. Harvest data are presented as a surrogate for the population status of mink and otters in certain locations around the Great Lakes. Data from Ohio show that the mink harvest between 1982 and 1987 from contaminated counties bordering Lake Erie was consistently lower (380 animals per year) than those from counties removed from Lake Erie (850 animals per year), suggesting an effect of chemicals on the status of mink populations. Preliminary studies from Ontario also suggest that mink harvest is lower in potentially "high PCB exposure areas" compared with lower exposure areas. Evidence is also presented on the harvest data for otters taken from four New York State counties adjacent to Lake Ontario and the St. Lawrence River. The harvest data from these four counties show that between 1960 and early 1970 otter harvest remained stable but has since increased. Increased harvest is consistent with improved water quality in Lake Ontario during the past 15 yr. Data relating to strength of association between chemicals and populations of mink and otter are weak and need to be further analyzed. The specificity of the effects of the chemicals on mink reproduction and mortality is well established from toxicological experiments, but there is poor resolution of the information on effects using field data. The strongest case for a causal relationship comes from consideration of the coherence criterion. In conclusion, before a causal link can be drawn between the status of mink and otter populations and exposure to organochlorine chemicals from the Great Lakes, a large amount of research and data analysis needs to be undertaken.

Effects of organochlorine chemicals on the reproductive outcome of humans who consumed contaminated Great Lakes fish: an epidemiologic consideration

Three sets of studies of the impacts of human exposure to PCB contaminated fish from the Great Lakes basin--the Michigan Sports Fisherman Cohort, the Michigan Maternal/Infant Cohort, and the Wisconsin Maternal/Infant Cohort-were evaluated using the epidemiologic criteria of Susser (1986). The studies were compared against each other, and against comparable data from other geographic locales. A total of seven major categories of exposure sequelae were evaluated. These ranged from the effects of primary exposure to contaminants upon maternal health status, to effects from secondary intrauterine fetal exposure, including alterations in birth size and gestational age, changes in neonatal health status, and effects persisting into early infancy. Results of the evaluations suggest that the causal hypothesis may be strongly affirmed for the relationship between PCB exposure and alterations in both neonatal health status and in health status in early infancy may be affirmed with reasonable certainty. While the evidence from the Michigan Maternal/Infant Cohort related to maternal exposure to PCB and infant size at birth and gestational age affirms the causal hypothesis, studies from other geographic locales tend only to be supportive. Analytic differences are likely responsible for this variation, but epidemiologically, the composite rating must be regarded as indeterminate. The relationship with observed alterations in maternal health status, composite activity ranking, and McCarthy Memory Scale deficits were also classified as indeterminate. No evidences of obvious negation were seen, although one portion of a study was disqualified because of incoherence.

Contaminant levels in colonial waterbirds from Green Bay and Lake Michigan, 1975-80

Residues of organochlorine pesticides, polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), polychlorinated styrenes (PCSs), and mercury were measured in the eggs of 10 species of colonial waterbirds nesting in areas around Green Bay or Lake Michigan from 1975 to 1980. Residues also were measured in the carcasses and brains of black-crowned night-herons (Nycticorax nycticorax). The highest residues were of PCBs, DDE, mercury, and dieldrin; for some species, levels of these chemicals possibly were high enough to have caused reproductive effects. Other organochlorine pesticides were found at low levels. Only trace amounts of PCSs and PBBs were found. Eggs of herring gulls (Larus argentatus) collected in 1977 from an island in Lake Michigan contained an average of 100 ppm PCBs and 33 ppm DDE; this was the most-contaminated species. Cattle egrets (Bubulcus ibis), the only bird that is not a fish eater, contained only small quantities of DDE and mercury.

Feeding Great Lakes fish to mink: effects on mink and accumulation and elimination of PCBS by mink

The effects of feeding Great Lakes fish or fish products (carp, sucker, perch scraps, whitefish racks, and alewife fishmeal) to mink were studied. Growth and furring of mink were normal for all species of fish tested. However, mink fed carp failed to reproduce, and the reproductive performance and/or kit survival in groups fed the perch, whitefish, and sucker were inferior to the control. Only the alewife fishmeal diet supported reproduction and kit survival comparable to the control. PCB residues (as Aroclor 1254) accumulated in mink subcutaneous body fat to as much as 38 times the dietary level, while some individual congeners accumulated up to 200 times. The half-life of PCB in mink adipose tissue was determined to be 98 d. The toxicity of PCBs derived from Great Lakes fish was greater than that observed in previous studies with mink fed comparable levels of technical-grade PCBs.

World PCBs map: storage and effects in man and his biologic environment in the 1970s

PCB residues are found in biota all over the world. A biologic magnification of PCBs has been demonstrated in the food chain: plankton-fish-fish eating birds. A world map of the PCBs residues in biota and some of their biologic effects are given in this study. The biologic effects of PCBs are varied and may generally be explained by the induction or inhibition of the activity of a large number of enzymes, which upsets quantitatively, normal biochemical processes. Harm to reproduction, growth, development, defense systems, tissues, and organs appeared in susceptible organisms as a result of such changes or as a chain reaction to heterostases. The adverse health effects, observed in persons occupationally exposed and in those accidentally poisoned, point to the risk for the general population of an ever-increasing environmental pollution by PCBs. There is need for an integrated approach, consisting of epidemiologic studies on high risk groups in the general population and in persons occupationally exposed, as well as periodic assessment of PCB residues in man, his food, and feed supplies.

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 (PCB's) 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 PCB's. These included anorexia, blood 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 PCB's 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.

Premature births in California sea lions: association with high organochlorine pollutant residue levels

Premature pupping in California sea lions has been noted on the breeding islands since 1968. Organochlorine pesticides and polychlorinated biphenyl residues were two to eight times higher in tissues of premature parturient females and pups than in similar tissues of full-term parturient females and pups collected on San Miguel Island in 1970.