The use of a microsomal in vitro assay to study phase I biotransformation of chlorobornanes (toxaphene (R)) in marine mammals and birds - Possible consequences of biotransformation for bioaccumulation and genotoxicity

The factors determining the bioaccumulation of lipophilic compounds in wild life are often poorly understood, partly because it is difficult to do in v ivo experiments with animals such as marine mammals and birds. To evaluate the role of phase I biotransformation in the bioaccumulation process of chl orobornanes (toxaphene(R)), this was studied in in vitro assays with hepati c microsomes of animals that could be sampled shortly after death. The capa city of microsomes to metabolise a technical toxaphene mixture decreased in the order Phoca vitulina (harbour seal) much greater than lagenorhynchus a lbirostris (whitebeaked dolphin) congruent to Diomedea immutabilis (Laysan albatross) > Physeter macrocephalus (:sperm whale). Harbour seal microsomes metabolised the chlorobornane (CHB) congeners CHB-32 and CHB-62; whitebeak ed dolphin and Laysan albatross microsomes only metabolised CHB-32. Metabol ism of CHB-26 and CHB-50 was never observed. The negative chemical ionisati on (NCI -) mass spectra of some of the hydroxylated metabolites were obtain ed. The number of peaks in the toxaphene residues of wildlife extracts decr eased in the order of increasing in-vitro biotransformation capacity. Thus, the results of the in vitro assays and residue analysis were in accordance , although assays with microsomes of more individuals of the same species a re required for a more general conclusion at the species level. Finally, th e effect of in vitro biotransformation was evaluated in terms of the genoto xic potential using the Mutatox(R) assay. Only technical toxaphene and CHB- 32 were genotoxic in the direct assay, whereas the addition of rat S9 fract ion or microsomes of harbour seal and albatross decreased the genotoxic res ponse. Thus, organisms with a low ability to metabolise chlorobornanes, suc h as whales, may be most affected by the carcinogenic properties of toxaphe ne. A hypothetical reaction which fits the experimental results is discusse d. Based on these results it is concluded that in vitro assays with microso mes of wildlife animals which died a natural cause can act as a valuable to ol to assess the occurrence and effects of phase I metabolism. Some precaut ions are discussed, that should be taken to reduce the chance of false nega tive results. (C) 1998 Published by Elsevier Science Inc. All rights reserv ed.