Temperature-dependent disposition of [14C]benzo(a)pyrene in the spiny lobster, Panulirus argus

[¹⁴C]Benzo(a) pyrene (BP) (1 mg/kg) was administered by intracardiac injection to groups of spiny lobsters which were killed at various times up to 7 weeks after dosing. Tissues and fluids were evaluated for BP-derived radioactivity. Two studies were conducted in successive summer and winter seasons, when seawater temperatures throughout were 26.5 to 29.0 and 13.5 to 16.5°C, respectively. Highest concentrations of BP-derived radioactivity were found in the hepatopancreas, stomach, intestine, intestinal contents, and the green gland. After an initial distribution phase, the dose was lost from the lobsters in a log linear manner. The elimination half-lives for overall elimination of BP-derived radioactivity were 1.11 weeks in the warmer (summer) and 2.25 weeks in the colder (winter) water. Similarly, for individual organs, elimination was more rapid in the warmer water. For the hepatopancreas, green gland, intestine, and tail muscle, respective $\text{t}\text{1}\text{2}$ values (week) were 1.02, 1.26, 1.71, and 1.42 in the summer and 2.50, 1.50, 5.04, and 2.11 in the winter. There was no suggestion of tissue accumulation of BP-derived radioactivity. HPLC analysis of hepatopancreas samples showed that, in summer, unmetabolized BP concentrations fell rapidly, accounting for only 5% of the total label in the hepatopancreas by 3 days. The fall in unmetabolized BP was accompanied by approximately equal increases in the percentages of both polar metabolites and conjugates. Although the time curve for metabolism of BP in the hepatopancreas was not studied in winter, the metabolic capacity was such that, by 3 days after the dose, only 5% of the ¹⁴C present in hepatopancreas was unmetabolized BP. Thus, it appears that, for this dose of BP, the more rapid elimination of ¹⁴C in summer was due to a more rapid excretion of metabolites, and not to increased metabolism of BP.