Effects of 4-nonylphenol, a xenoestrogen, and chlorpyrifos, an organophosphorus pesticide, on acetylcholinesterase activity in the clam Tapes philippinarum.

To confirm the hypothesis that 4-nonylphenol (NP), an estrogenic compound, has neurotoxic effects on the clam Tapes philippinarum, in the present study clams were exposed to NP (for 7 days to 0, 0+acetone, 0.0125, 0.025, 0.05, 0.1, and 0.2 mg NP/L, and for 14 days to 0, 0+acetone, 0.0125, 0.025, 0.05, and 0.1 mg NP/L), and the activity of acetylcholinesterase (AChE) was evaluated in gills. The effects on AChE activity were also studied after exposing clams for 96 h to chlorpyrifos (CP) (12 and 24 μg/L), an organophosphorus pesticide known to inhibit AChE in aquatic organisms. Exposure to NP for 7 days significantly increased AChE activity in 0.025, 0.1 and 0.2 mg NP/Ltreated clams, whereas no significant alteration in enzyme activity was recorded after 14 days' exposure. This allowed us to exclude AChE inhibition by NP. Interestingly, CP not only did not affect AChE activity, but also significant increases in enzyme activity were recorded in 12-μg CP/Lexposed animals with respect to controls. On the basis of these results, further research will be performed on T. philippinarum by increasing exposure levels, in terms of both time and concentration, to better define the possible application of AChE activity in clams as a biomarker of exposure to organophosphorus pesticides in biomonitoring.