Mixture Toxicity Assessment of Nickel and Chlorpyrifos in the Sea Bass Dicentrarchus labrax

The present research work was designed to study Dicentrarchus labrax biotransformation and detoxification responses to acute exposure to nickel (Ni) and chlorpyrifos (CHP). Sexually immature sea bass were treated by intraperitoneal injection of nickel chloride (500 mu g kg(-1)), chlorpyrifos (10 mg kg(-1)), and their binary mixture for 1, 3, and 7 days. Ni and CHP accumulation was quantified in liver after the exposure periods. The following biological responses were measured: (1) NADPH cytochrome P450 reductase (NCR) activity, as phase I biotransformation parameter; (2) gluthathione S-transferase (GST) activity as a phase II conjugation enzyme, acetylcholinesterase activity, and metallothionein (MT) content. Ni bioaccumulation in the liver resulted in an increasing uptake up to 15.48 mu g g(-1) wet weight (Ni-treated animals) and 16.73 mu g g(-1) wet weight (mixture-treated animals) after 7 days of exposure. CHP accumulation showed a distinct pattern in animals exposed to the mixture of chemicals in comparison with CHP-treated animals. NCR activity exhibited a marked activation in CHP and mixture-treated animals. GST activity was significantly increased starting from 1 day exposure in CHP-treated animals and after 3 days in Ni-treated animals. MT accumulation increased in all conditions, with a marked synergetic effect after 7 days of exposure. These data should be carefully considered in view of the biological effects of mixture pollutants, particularly in fish farming conditions.