Toxic effects in C57B1/6 and DBA/2 mice following consumption of halogenated aromatic hydrocarbon-contaminated Great Lakes coho salmon (Oncorhynchus kisutch Walbaum)

Influence of a contaminated fish diet on germline expanded-simple-tandem-repeat mutation frequency in mice

Herring gulls (Larus argentatus) in polluted areas on the North American Great Lakes were previously shown to have elevated germline mutation frequencies at minisatellite DNA loci. Airborne or dietary contaminants likely caused induced mutations, but the importance of each exposure type was unknown. Follow-up experiments with lab mice determined that air pollution significantly induced germline mutations; however, an evaluation of mutations induced by the diet of herring gulls has not yet been conducted. To address this issue, we fed mice a high-fish diet (58% wet mass) of the most common prey species for herring gulls nesting in Hamilton Harbour, a polluted industrial area on Lake Ontario. We bred the mice and screened pedigrees for germline mutations at expanded-simple-tandem-repeat (ESTR) DNA loci. Mutation frequencies were compared to those in a reference group that was fed fish from Atlantic Canada, and a control group that was fed commercial chow. Germline mutation frequencies were highest in mice fed contaminated fish, but were only marginally or not significantly affected by diet treatment. Statistical power to detect differences among treatment groups was low, and the effect of diet may have more clearly emerged if larger sample sizes were available. Levels of organic pollutants in the fish from Hamilton Harbour were higher than those from Atlantic Canada, but their ability to induce ESTR mutations is unknown. Our findings suggest that a contaminated fish diet may contribute to the elevated germline mutation frequencies observed previously in gulls at this site, but air pollution is likely a more important route of exposure.

An approach to feeding high-percentage fish diets to mice for human and wildlife toxicology studies

Experimental feeding of sport fish to rodents has been an important tool for the study of biological effects induced by a contaminated fish diet. Most rodent feeding studies have used low-to-moderate levels of tissue from large fish species incorporated into diets fed to rats and have given little consideration to issues of diet palatability or nutrition. There are currently no rodent diet models suitable for assessing the risk to human populations of diets very high in daily fish content or to wildlife species consuming high percentages of whole, small-bodied fish. In this study, we describe an approach to feeding mice high percentages (up to 50%) of homogenized, whole fish using Atlantic herring (Clupea harengus) as a test species. We created a novel gel diet medium for mice that contains a variety of nutritional supplements and is flexible in terms of the fish percentage that can be incorporated. In choice trials, mice preferred 30 and 35% fish gels to their regular commercial dry chow, indicating that the gel diet medium was palatable. In a longer feeding trial, mice ate 35% fish gel for 12 days and 50% fish gel for 12 days (total of 24 consecutive days) and did not differ in body mass compared to age- and sex-matched controls. We conclude that our fish-based gel diet is suitable for rodent feeding trials in toxicology studies that examine dose responses to fish consumption and risk in human and wildlife populations among which daily fish intake is very high. Our general approach may also be applicable for feeding mice materials other than fish.

Biomarkers and bioassays for detecting dioxin-like compounds in the marine environment

The presence of toxic chemical contaminants in some marine organisms, including those consumed by humans, is well known. Monitoring the levels of such contaminants and their geographic and temporal variability is important for assessing and maintaining the safety of seafood and the health of the marine environment. Chemical analyses are sensitive and specific, but can be expensive and provide little information on the actual or potential biological activity of the contaminants. Biologically-based assays can be used to indicate the presence and potential effects of contaminants in marine animals, and therefore, have potential for routine monitoring of the marine environment. Halogenated aromatic hydrocarbons (HAHs) such as chlorinated dioxins, dibenzofurans, and biphenyls comprise a major group of marine contaminants. The most toxic HAHs (dioxin-like compounds) act through an intracellular receptor protein, the aryl hydrocarbon receptor, which is present in humans and many, but not all, marine animals. A toxic equivalency approach based on an understanding of this mechanism provides an integrated measure of the biological potency or activity of HAH mixtures. Biomarkers measured in marine animals indicate their exposure to these chemicals in vivo. Similarly, in vitro biomarker responses measured in cell culture bioassays can be used to assess the concentration of 'dioxin equivalents' in extracts of environmental matrices. Here, I have reviewed the types and relative sensitivities of mechanistically-based, in vitro bioassays for dioxin-like compounds, including assays of receptor-binding, DNA-binding and transcriptional activation of native (CYP1A) or reporter (luciferase) genes. Examples of their use in environmental monitoring are provided. Cell culture bioassays are rapid and inexpensive, and thus have great potential for routine monitoring of marine resources, including seafood. Several such assays exist, or are being developed, for a variety of marine contaminants in addition to the dioxin-like chemicals. A battery of cell culture bioassays might be used to rapidly and sensitively screen seafood for the presence of contaminants of concern, including dioxin-like compounds as well as other contaminants such as natural toxins, hormonally active agents, and heavy metals. Such a battery of mechanism-based, in vitro bioassays could be incorporated into monitoring efforts under recently adopted hazard analysis and critical control point (HACCP) programs.

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.

Effects of Great Lakes fish consumption on the immune system of Sprague-Dawley rats investigated during a two-generation reproductive study

The effects of Great Lakes fish contaminants on several quantitative and functional aspects of the immune system were investigated in the first (F1) and second (F2) generations of Sprague-Dawley rats. The F0 rats were fed either a control diet or diets containing 5 or 20% lyophilized chinook salmon from the Credit River of Lake Ontario (LO) and Owen Sound point of Lake Huron (LH). The F1 and F2 pups were exposed to fish in utero, through the dam's milk to 21 days old, and through the dam's respective diets to 13 weeks of age. The study included an F1-reversibility (F1-R) phase in which rats at 13 weeks of exposure to fish or control diets were switched to the control diet for 3 months. The most outstanding finding was a statistically significant increase in absolute spleen leukocytes and absolute and percentage lymphocytes in the F2 male rats fed the LH fish diets compared to the control and to those fed the LO fish diets with the 20% fish diets having higher cell numbers compared to the LO-5% fish diets. A parallel increase in the T-helper/inducer T-lymphocyte subset numbers was observed. Increased but statistically insignificant plaque-forming cell (PFC) numbers were obtained in the F2 male rats fed the LH fish diets compared to those fed the LO fish diets and in the F1-R female group of rats fed the LH fish diet compared to those fed the LO fish diets. Phagocytosis by resident peritoneal macrophages was significantly increased in the F1 male and F2 female rats fed the fish diets compared to the control. The phagocytic activity was significantly higher in the F2-generation male and female rats fed the LO diets compared to those fed the LH diets. Other parameters including lymphocyte transformation in response to mitogens, the number of Listeria monocytogenes bacteria surviving in the rat spleens, and the natural killer cell activity were not affected significantly by any of the treatments. Overall, the effects of diets containing chinook salmon from the LO and LH sources on the immune system of rats were minimal and were on quantitative rather than on functional aspects of the system. Further focused research would be required in order to establish conclusively that the immune system of cohorts who ingest Great Lakes fish frequently is at a greater risk for adverse effects.

The toxicological effects following the ingestion of chinook salmon from the Great Lakes by Sprague-Dawley rats during a two-generation feeding-reproduction study

A two-generation reproduction-feeding study was undertaken with Sprague-Dawley rats to ascertain the effects of ingesting chinook salmon fillets caught in the Credit River, which empties into Lake Ontario (LO), or in the Owen Sound region of Lake Huron (LH). Rats (30/sex/group) were randomly assigned to groups whose dietary protein consisted of casein and/or lyophilized salmon [Group 1: 20% casein (controls); Group 2: 15% casein + 5% LO salmon (LO-5%); Group 3: 20% LO salmon (LO-20%); Group 4: 15% casein + 5% LH salmon (LH-5%); Group 5: 20% LH salmon (LH-20%)]. After 70 days on test, the males and females were mated on a 1:1 basis within diet groups. Approximately 70 days postweaning, one F1 male and one F1 female from 24 litters were mated within diet groups, avoiding sibling matings. At weaning, the F0 and F1 adults and the F1 and F2 neonates not randomly selected for further testing were necropsied. Evaluated parameters included growth, feed consumption, organ weights, reproduction indices, serum chemistry, hematology, and coagulation times. The only statistically significant effects which were present in both generations were increased relative liver and kidney weights of both sexes in the LO-20% and LH-20% groups; the LH-20% females had lower alanine transaminase activity than the controls; the controls had lower creatinine levels than the fish groups and the LO-20% females; the LH-20% and LO-20% males had a lower blood urea nitrogen than the controls; and the LH-20% females had a heavier terminal body weight than the controls and a lower number of red blood cells, hematocrit, hemoglobin values, and mean platelet volume. There was a tendency for the fish-fed groups to grow faster, eat more feed, and have larger litters with heavier pups. Overall, there was little to suggest that the myriad of contaminants in chinook salmon from the Great Lakes presented an appreciable toxicological risk to Sprague-Dawley growth and reproduction.

Effects of Great Lakes fish consumption on the immune system of Sprague-Dawley rats investigated during a two-generation reproductive study

The effects of Great Lakes fish on food consumption, body and organ weights, and hematological parameters were investigated in the first- (F1) and second- (F2) generation Sprague-Dawley rats assigned to immunological studies. The parent- (F0) generation rats were fed either a control diet or diets containing 5 or 20% lyophilized chinook salmon from Credit River (Lake Ontario, LO) or Owen Sound (Lake Huron, LH). The F1 and F2 pups were exposed to the fish diet in utero, through the dam's milk to 21 days of age and through the respective diets to 13 weeks of age. The study included an F1-reversibility (F1-R) phase in which rats at 13 weeks of exposure to fish or control diets were switched to the control diet for 3 months. Statistically significant effects included increased growth rates in the F1 male rats fed the LH fish diets compared to those fed the LO fish diets; increased liver weights in the F2-generation male rats fed the LH-20% and LO-20% diets compared to those fed the 5% fish diets; reduced thymus weights in the F1-R female rats fed the LO-20% fish diet compared to those fed the LO-5% or LH-20% fish diets and in the F2 male rats fed the LO diets compared to those fed the LH diets; increased kidney weights in the F2 male rats fed the LH-20% diet compared to those fed the LH-5% or LO-20% diets; reduced but reversible effects on red blood cell (RBC), white blood cell (WBC), neutrophil, lymphocyte, and monocyte numbers in the F1-generation female rats fed the fish diets; reduced red blood cell (RBC), white blood cell (WBC), and lymphocyte numbers in the F2 male rats fed the LO diets compared to those fed the LH diets; and reduced WBC and lymphocyte numbers in the F2 female rats fed the LO-20% diet compared to those fed the LH-20% fish diet. These results suggested that long-term exposure to Great Lakes fish contaminants may have adverse effects on some immune-related parameters. The impact of such changes on the functional aspects of the immune system of rats and consequently on human health needs to be further investigated.

Dietary and tissue residue analysis and contaminant intake estimations in rats consuming diets composed of Great Lakes salmon: a multigeneration study

To further characterize the toxicological risk associated with chemical contaminants in Great Lakes fish, a multigeneration rat reproduction study was designed. Mature chinook salmon (Oncorhynchus tsawytscha), collected during the Fall 1991 spawning runs from Sydenham River, Lake Huron, and Credit River, Lake Ontario, were filleted, lyophilized, and incorporated into standard rat diets at 25% (w/w) or 100% (w/w) of the normal protein compliment [casein, 20% (w/w)]. This resulted in diets composed of 5 or 20% (w/w) lyophilized fish and estimated daily fish intakes by the rats at levels approximately 15- and 60-fold greater, respectively, than the current estimate for the Canadian public for all fish and seafood. Both fresh and lyophilized fish were analyzed for the following groups of contaminants: halogenated aromatic hydrocarbons [polychlorinated biphenyls, dibenzodioxins, and dibenzofurans (PCBs, PCDDs, PCDFs)], polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, metals, volatile organics, and other extractable organics (chlorinated phenols and benzenes). In general, only minor site differences existed for the specific types of contaminants detected; however, fish from the Credit River contained slightly greater amounts of PCBs (2- to 3-fold), dioxin toxic equivalencies (TCDD TEQs; 1.5- to 2.0-fold), DDT and metabolites (1. 5-fold), and appreciably higher amounts of mirex (15-fold). This general pattern of contaminant differences continued when the various diets were prepared using the lyophilized fish. Tissue samples (adipose, liver) were taken from the animals at various stages of the study and also analyzed for the same groups of contaminants. In general, adipose tissue was the major reservoir for organochlorine (OC) pesticides and PCBs, while "dioxin-like" PCDD/DF congeners and mercury were found preferentially in the liver. Contaminant intake calculations and tissue residue levels are provided.

Changes in thyroid hormone economy following consumption of environmentally contaminated Great Lakes fish

Epizootics of thyroid lesions in fish and piscivorous birds that are resident in the Great Lakes region of North America suggest that there are environmental factors present in the Great Lakes ecosystem that act as potent endocrine disruptors, and that they are transferred along the food chain. This paper examines the results of wildlife studies, as well as related studies on fish-eating human populations in the region. It also re-examines the results of experimental studies of the effects of Great Lakes fish diets on the thyroid physiology of rodents and shows that the thyroid responses of fish-fed rats and mice were essentially similar to those found in rats that had been administered specific polyhalogenated aromatic hydrocarbon (PHAH) congeners or commercial polychlorinated biphenyl mixtures. However, the responses to the Great Lakes fish diets were found at PHAH exposure levels that were commonly several orders of magnitude lower than those applied in the classical toxicology studies. These findings, together with the results of the Great Lakes piscivorous bird studies and one in which captive common seals were fed "environmentally contaminated" fish, suggest that the "environmental" PHAH mixtures accumulated in fish represent a significant threat to the thyroid hormone economy, and the effects are greater than could be predicted by virtue of the known levels of active congeners in this naturally bioaccumulated PHAH mix.

Overripening as the cause of low survival to hatch in Lake Erie coho salmon (Oncorhynchus kisutch) embryos

We investigated the cause of the low survival to hatch of embryos of coho salmon (Oncorhynchus kisutch) from the Fairview, Pennsylvania, stock in Lake Erie. In 1988, survival to hatch of this stock was only 42%, whereas another Great Lakes coho salmon stock of similar genetic origin had an 84% survival to hatch. Laboratory cross-fertilization studies between the Fairview stock and a reference Lake Erie stock from Simcoe, Ontario, showed that eggs from the Fairview stock were the probable source of the low fertility. The presence of overripe eggs in Fairview females was associated with poor fertilization and low survival to hatch. Plasma gonadotropin II levels were similar in preovulatory females taken from the Fairview and Simcoe stocks, but testosterone and 17α, 20β-dihydroxy-4-pregnen-3-one levels were significantly lower in the Fairview females. Increasing the triiodo-L-thyronine (T3) content of the eggs by the administration of T3 to the preovulatory females did not enhance egg fertility. We propose that the low survival to hatch of the Fairview embryos is due to delayed oocyte maturation and ovulation and vent maturation, which may have been caused by exposure of the Fairview salmon to warmer water during the period of late ovarian maturation and migration.

Immunotoxicity of PCBs (Aroclors) in relation to Great Lakes

Polychlorinated biphenyls (PCBs) are among the most widespread environmental pollutants and a prominent contaminant of the Great Lakes basin. Due to their resistance to biodegradation and lipophilic properties, PCBs bioaccumulate in fish tissues and in fish-eating humans. PCBs are also known to cross the placenta and to be excreted into the mother's milk, thus predisposing the infant to potentially adverse health effects. For example, a higher incidence of bacterial infections was reported for breast-fed infants born to mothers who consumed large amounts of Great Lakes fish compared to the incidence in control infants whose mothers ingested low amounts of fish. While data regarding the PCB-induced immunotoxic effects in humans are scarce, data derived from the use of experimental animals, including nonhuman primates, indicate that the immune system is a potential target for the immunotoxic effects of PCBs. Such studies have used the commercially available PCB mixtures alone. However, PCBs have the potential of partially antagonizing the effects of other structurally related compounds including the highly toxic dioxins, which are also present in small amounts in the Great Lakes. Thus, to fully evaluate the magnitude of the immunotoxic risk PCBs pose to humans, consideration should be given to investigations in which the interactive effects of PCBs are combined with other contaminants present in the Great Lakes.

Carcinogenesis studies in rodents for evaluating risks associated with chemical carcinogens in aquatic food animals

Fish and shellfish caught in polluted waters contain potentially dangerous amounts of toxic and carcinogenic chemicals. Public concern was heightened when a large percentage of winter flounder taken from Boston Harbor was found to have visible cancer of the liver; winter flounder outside the estuary area had no liver lesions. Long-term chemical carcinogenesis studies could be easily and feasibly designed using laboratory rodents offered diets containing fish caught in polluted waters. Induced cancers in rodents would corroborate field observations in fish; positive results from these studies would provide further evidence about potential human health hazards from eating substantial amounts of chemically contaminated fish. Nonetheless, fish and aquatic organisms should be viewed as environmental biological monitors of pollution or of potential human health hazards, and authorities responsible for assuring clean and safe rivers, bodies of water, and biota should give more attention to these valid biological indicators or sentinels of environmental pollution. Consequently, fish and other sea creatures alone should serve as alarms regarding whether water areas constitute public health hazards.