The disposition of p-nitroanisole by the sea urchin, Strongylocentrotus purpuratusI. Kinetics

Abstract

Investigation of the disposition kinetics of p-nitroanisole (PNA) by the sea urchin, Strongylocentrotus purpuratus, demonstrated the usefulness of our proposed protocol for assessing the disposition of xenobiotics in aquatic species. The protocol consists of four steps: toxicity rangefinding, acute static, dynamic (flowing water) and steady-state investigations of xenobiotic metabolism, and kinetics. Elimination kinetics from acute static investigations fit the form dQ w dt = K 1Q a − K 2Q w , where Q w is the quantity of compound in the water, Q a the quantity in the animal, K 1 the elimination rate constant, and K 2 the uptake rate constant. Estimates of the elimination and uptake rate constants were 0.57 ± 0.23 and 0.09 ± 0.05 hr −1 ( n = 32), respectively, for studies covering 1.5 years. A simpler method for estimating these rate constants is described. The elimination halflife was dependent on time held after collection and season, corresponding to the reproductive cycle. Steady-state studies indicated that the elimination of PNA is an active process. The turnover rate constant (1.3 ± 0.6 hr −1) was not different from the acute elimination rate constant. Overall the rapid elimination of PNA and the rapid approach to steady state (approximately 8 hr) will be the prime factors in the fate of PNA in sea urchins. For short-term exposure, upon termination the sea urchin will rapidly and actively eliminate the compound. For chronic, long-term exposures, the sea urchin will rapidly achieve steady state and the fate will be dependent upon biotransformation.