Induction of Phenol-Sulfate Conjugating Activity by Exposure to Phenols and Duration of Its Induced Activity in Short-necked Clam

A study was made of the induction of phenol-sulfate conjugating activity by exposure to some phenolic compounds and also the duration of its activity induced by pentachlorophenol (PCP) in the mid-gut gland of short-necked clam Ruditapes philippinarum. In a preliminary experiment comparing the inductivity of phenol-sulfate conjugating activity in short-necked clam among PCP, resorcinol, p-cresol, p-chlorophenol, p-nitrophenol and phenol; PCP was the most effective inducer, resulting in a 2.4-fold activity in the control clam during the 3-day exposure period to 0.1 ppm PCP. Therefore, a subsequent experiment was performed to elucidate the effect of long-term exposure to sublethal PCP (0.1 ppm) for 5 weeks on the phenolsulfate conjugating activity in clams, feeding on a unicellular green alga Dunaliella sp. by dipping the clams in its growing sea water-medium (ca. 4 x 10₄ cells/m/) for 2–3 h every other day, when the test PCP-water was replaced by a newly prepared one. The conjugating activity in the clam increased with the time of exposure to PCP and reached 42 nmol/min/g-tissue at 5-week period, corresponding to ca. 7-fold with that in the control. When the clams which were exposed to 0.1 ppm PCP for 2 weeks and then transferred to PCP-free sea water, its induced activity of 24 nmol/ min/g-tissue decreased gradually, but it was still at a level of 1.5-fold with that in the control even after 3 weeks, although the biological half-life of PCP accumulated in the clam was only ca. 1 h.