The interaction of methyl-parathion with serum and albumin of the neo-tropical fish Piaractus mesopotamicus

The interaction of methyl-parathion with serum and albumin of pacu, Piaractus mesopotamicus, was studied, using the fluorescence quenching technique. Pacu is a neo-tropical fish specie inhabitant of rivers from western regions of Brazil. Methyl-parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate) is an organophosphorous pesticide still used in agriculture and fish farming in many countries. The quenching of fluorescence can be mathematically expressed by the Stern–Volmer equation to calculate quenching constants. Stern–Volmer curves analysis is able to give important information about the pesticide–albumin interaction. Our results showed that the serum quenching reached 10% when the molar ratio of pesticide/albumin was about 7:1 for the three temperatures of the experiment. For the pure albumin quenching of 10%, methyl-parathion concentrations were 6, 7 and 9 times higher than albumin at 20, 25 and 30 °C, respectively. The calculated Stern–Volmer constants at 25 °C were 9.73×103(±4.9×102) M−1 for serum and 9.20×103(±2.0×102) M−1 for albumin. It was observed that albumin quenching is the phenomenon contributing to the quenching of the pacu serum fluorescence for methyl-parathion concentration lower than 10 μM, suggesting that the protein is the most important carrier for the pesticide in serum.