Turbot (Scophthalmus maximus) and mussel (Mytilus edulis) microsomes were incubated with DNA to examine if microsomal in vitro metabolism of BaP could result in DNA adducts detected by P-32-postlabelling. Turbot DNA was incubated with benzo[a]pyrene (BaP), NADPH and microsomal activating systems prepared from either livers of unexposed turbot, turbot exposed to BaP or beta-naphthoflavone (beta-NF) or digestive glands from mussels. The beta-NF activating system generated the highest levels of DNA adducts detected in this study (451.7 adducts per 10(8) nucleotides) and were distributed in three discrete adduct TLC spots, one of which (97% of the total adducts) co-migrated with the P-32-postlabelled BaP 7,8-diol, 9,10-epoxide-N-2-guanine adduct. Fewer adducts (P < 0.05) were generated by BaP-induced microsomes (9.4-30.6 adducts per 10(8) nucleotides) but levels were higher (P < 0.05) than those generated from untreated fish (3.5 adducts per 10(8) nucleotides). Co-incubation with 500 muM alpha-naphthoflavone (alpha-NF) resulted in 97-99% inhibition in adduct formation implicating cytochrome P450-dependent (CYP) bioactivation however there was some evidence for carry over of BaP in the liver microsomal preparations from BaP injected fish. In contrast to the fish activating systems, no DNA adducts were observed when mussel microsomes were incubated with BaP, DNA and NADPH. (C) 2002 Elsevier Science Ltd. All rights reserved.