Polychlorinated biphenyls (PCBs) as environmental contaminants often cannot be adequately described by reference to Aroclors or to total PCBs. Although there are 209 possible PCB configurations (congeners), perhaps half that number account for nearly all of the environmental contamination attributable to PCBs. Still fewer congeners are both prevalent and either demonstrably or potentially toxic. If potential toxicity, environmental prevalence, and relative abundance in animal tissues are used as criteria, the number of environmentally threatening PCB congeners reduces to about thirty-six. Twenty-five of these account for 50 to 75% of total PCBs in tissue samples of fish, invertebrates, birds, and mammals.A few PCB congeners that are sterically similar to 2,3,7,3,7, are directly toxic. Other PCB congeners, as well as those that are directly toxic, may also be involved in toxicity indirectly by stimulating the production of (inducing) bioactivating enzyme systems. The most consequential of these have the ability to induce aryl hydrocarbon metabolizing mixed-function oxidases (MFOs). A result can be an increased capacity for bioactivation of otherwise nontoxic foreign compounds such as certain polynuclear aromatic hydrocarbons (PAH) to cytotoxic or genotoxic metabolites. The effectiveness of specific PCB congeners as inducers of different types of cytochrome P-450-dependent MFO systems is determined by their stereochemistry. Although MFO induction is not a proximate cause, it is a strong correlate of certain kinds of toxicities. Structural patterns can thus be used to discriminate among PCB congeners on the basis of toxic potential, if not entirely on toxicity per se. Congeners that demonstrate 3-methylcholanthrene-type (3-MCtype) and mixed-type MFO induction have the greatest toxic potential. These congeners most closely resemble 2,3,7,8-TCDD in their structures and in their toxic effects. The larger group of phenobarbital-type (PBtype) inducers have considerably less potential for contributing to toxic effects. Weak inducers and noninducing congeners have the least potential for toxicity.Using the rationale described in this paper, we assigned the most environmentally threatening PCB congeners to four groups. Congeners assigned to Group 1 are considered most likely to contribute to adverse biological effects attributable to PCBs in an environmental sample. Group 1A contains the three most potent (pure 3-MC-type inducer) congeners, IUPAC numbers 77, 126, and 169. Six congeners, numbers 105, 118, 128, 138, 156, and 170, are assigned to Group 1B. These congeners are mixed-type inducers that have been reported frequently in environmental samples. Group 2 congeners are PB-type inducers that are also prevalent in the environment; these include numbers 87, 99, 101, 153, 180, 183, and 194. Group 3 congeners, numbers 18,44,49,52,70,74, 151, 177, 187, and 201, are weak or noninducers, but they occur frequently in the environment or in high concentrations in animal tissues relative to other PCB congeners, and so may be of ...

No abstract

The objective of this investigation was to determine whether differences in a suite of biomarker assays in brown bullhead liver tissues could be detected and related to the pollution histories of two Ohio locations, one a reach of the Black River that had historically been severely impacted by the effluents of a coking plant, the other at Old Woman Creek, a freshwater estuarine research preserve. There were no gross differences in pathologies detectable in fish from either site, and the major difference found in bullheads at the two sites was in the relative liver weight (RLW). Differential responses of glutathione reductase, glutathione-S-transferase, Se-dependent glutathione peroxidase, Se-independent glutathione peroxidase, and oxidized glutathione have been reported between fish from contaminated and uncontaminated sites in other studies, but no such differences were observed in the present study. Of the oxidative stress biomarkers included in this investigation, only the responses of superoxide dismutase, catalase, and total glutathione appeared to correlate with environmental exposure of brown bullhead to polycyclic aromatic hydrocarbons. Results with single-strand DNA and ethoxyresorufin-O-deethylase were the reverse of what has been reported in most other studies, and may reflect adaptation of the fish at the previously highly contaminated site. The fish at the Black River site appear to have responded to the xenobiotics present in their environment by increasing their overall liver size, thereby increasing the overall amount of enzymes rather than altering the specific activity of a select set of protective enzymes.http://link.springer-ny. com/link/service/journals/00244/bibs/37n2p236.html