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In-vitro metabolism of toxaphene in microsomes of harbour seal, eider duck, harbour porpoise, and rat: comparison to toxaphene patterns in marine wildlife
Boon, J.P.; Roex, E.; de Boer, J.; Wester, P. (1995). In-vitro metabolism of toxaphene in microsomes of harbour seal, eider duck, harbour porpoise, and rat: comparison to toxaphene patterns in marine wildlife, in: Dauvin, J.-C. et al. (Ed.) (1994). Actes de la 4ème Conférence internationale des Polychètes, Angers, France. Mémoires du Muséum national d'Histoire naturelle. Série A, Zoologie, 162: pp. 1-30
In: Dauvin, J.-C.; Laubier, L.; Reish, D.J. (Ed.) (1994). Actes de la 4ème Conférence internationale des Polychètes, Angers, France. Mémoires du Muséum national d'histoire naturelle. Série A, Zoologie, 162. Éditions du Muséum: Paris, France. ISBN 2-85653-214-4. 642 pp., more
In: Mémoires du Muséum national d'Histoire naturelle. Série A, Zoologie. Editions du Muséum: Paris. ISSN 0078-9747, more
Peer reviewed article  

Available in  Authors 
Document type: Project report

Keyword
    Marine

Authors  Top 
  • Boon, J.P., more
  • Roex, E., more
  • de Boer, J., more
  • Wester, P.

Abstract
    This paper is the result of a study carried out jointly by the Netherlands Institute for Sea Research (NIOZ) and the Netherlands Institute for Fisheries Research (RIVO-DLO). Subject is the biotransformation of the pesticide toxaphene in a microsomal assay that was validated for PCBs in the first part of this project (Annexes I and II) Biotransformation rates were derived from the disappearance of the parent compounds from the gas chromatograms; thus structures of polar metabolites could not be revealed at the present stage. The microsomes used originated from several species. Differences in metabolic capacities between animal species 'caused by different patterns of (iso- )enzymes that are able to metabolise anthropogenic compounds, can cause inter-species differences in the bioaccumulation of individual compounds. In the present study, the condition of the microsomes used was checked by the measurement of standard biochemical assays for the activity of different iso-enzyme subfamilies of cytochrome P450; the ethoxyresorufin-O-deethylase assay was used as a model reaction for the activity of the cytochrome P450 IA subfamily (CYPIA), whilst the aldrin epoxidase activity was used as a model reaction for the activity of the cytochrome P450 2B (CYP2B) subfamily. Microsomes from rat and a harbour seal showed the highest metabolic activities towards toxaphene in this study. Large differences were observed between the rates of biotransformation for the different peaks present in the technical toxaphene mixture. Rat microsomes from non-induced rats and rats induced with phenobarbital (PB) were used. Phenobarbital is a model inducer of CYP2B in rat. Since the PB-induced rats showed even higher rates of biotransformation, the CYP2B subfamily appears to be involved in the biotransformation of chlorinated norbornanes and norbornenes. Microsomes of the harbour seal were also used to test the biotransformation rates of 5 individually synthesised toxaphene congeners with a known environmental relevance. Of these toxicant B and Parlar no.69 were almost completely metabolised, whereas the compounds T2 and TI2 were completely persistent. Parlar no.62 was partially metabolised. Compared to the persistent compounds T2 and TI2, toxicant B and Parlar no.62 lack a chlorine substituent at one of the lateral positions of the ring formed by the carbon atoms C I-C6. The metabolic capacity of a harbour porpoise and a juvenile eider duck showed much lower metabolic activities towards the technical toxaphene mixture, indicating low levels of CYP2B activity. For the eider duck this seems to be a valid result, since EROD and Aldrin epoxidase activities were detected. In the case of the harbour porpoise these activities were very low, and thus it remains uncertain whether the persistence of toxaphene in this animal is characteristic for the species or due to a bad condition of the microsomes. However, lower activities of CYP2B in these species are in accordance with the published literature, reviewed by Boon el al. (1992). Since no peak in the chromatograms obtained with either electron capture detection (ECD) or negative chemical ionisation mass spectrometry (NCI-MS) detection were higher after metabolism, it can be concluded that the metabolites formed were not detected with the analytical methods used. thus formation of products that are only dechlorinated seems unlikely. Oxygen containing metabolites that might have been formed are likely to have been incompletely recovered in one or more stages of the analytical procedure.

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