2,3,7,8-TETRACHLORO-DIBENZO-P-DIOXIN IS A POTENT TOXIN AND INDUCES CYTOCHROME-P450 IN THE CRAYFISH, PACIFASTACUS-LENIUSCULUS

2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) is the most potent congene r of a family of environmental contaminants. We demonstrate that TCDD is a highly potent toxin in an invertebrate, the freshwater crayfish, Pacifastacus leniusculus, with an LD(50) of 30-100 mu g kg(-1) of body weight. Toxicity was characterised by delayed mortality, typically 15 -40 days after dosing, and anergia. No gross histological changes were seen in hepatopancreas. Treatment of crayfish with 3 mu g of TCDD kg( -1) body weight significantly induced cytochrome P450, as measured spe ctrally, but we were unable to measure associated enzyme activities, p resumably due to proteolysis of NADPH-P450 reductase. TCDD is thus a p otent toxin and enzyme inducer in crayfish. We hypothesise that the na ture of this pleiotropic response, together with its exceptional poten cy, suggests the presence of a receptor-mediated mechanism of TCDD tox icity in crayfish.