An Approach to the Effects of Chlorpyrifos on Jenynsia lineata Exposed to Environmentally Relevant Concentrations: Biomarkers of Oxidative Stress, Neurotoxicity and Genotoxicity

Abstract

Chlorpyrifos (CPF) is a common organophosphate insecticide used for pest control in agriculture and nonagricultural settings, acting as an acetylcholinesterase (AChE) inhibitor. It is highly toxic to aquatic life and can persist in the environment (half- life: 81 days in surface water). The aim of the present study was to evaluate effects of oxidative stress and damage, neurotoxicity and genotoxicity in Jenynsia lineata exposed to environmentally relevant concentrations of CPF during 96 h. Five tanks (30 L) were set up, using females of J. lineata (n=6 per treatment; standard length: 4.31 ± 0.50 cm; total weight: 1.67 ± 0.51 gr), one as a control and four with CPF concentrations of 0.05, 0.5, 5, and 50 μg/L. Liver, gills, and brain were dissected and immediately frozen with liquid nitrogen and stored at -80°C until biomarkers analysis. The blood was extracted and smear were done and fixed with methanol for further analysis. During the course of the experiment, three individuals exposed at 50 ug/L and one exposed at 5 ug/L died at the first 24 hs indicating that this concentration is closed to the LC50. While the remaining three individuals exposed at 5o ug/L wereeuthanized because they looked moribund, and were used for measuring biomarkers. An increase in the activity of the enzymes catalase and glutathione-S-transferase in brain, and of superoxide dismutase in gills was observed at 0.05 μg/L (p<0.05). There were no significant differences in the activity of AChE between the control and the lowest concentration (0.05 μg/L) (p>0.05), while inhibition of AChE was observed at 0.5 μg/L (29.51%) and 5 μg/L (49.53%) (p<0.05). No significant differences were observed for micronuclei or other nuclear aberrations (p>0.05). At 50 μg/L, increased activity of CAT in liver and a 77.6% inhibition of AChE was observed (p<0.05). The results of this study demonstrate that environmentally concentrations of CPF can induce oxidative stress at concentrations lower than those at which AChE inhibition occurs. Although AChE is the target biomarker for organophosphates, it may not be as efficient early warning system as antioxidant enzymes, highlighting the approach of not always use the mode of action biomarkers. Taking into account that CPF values of the lethal concentration 50 (LC50) for other fish species are very high compared to the concentrations used in this experiment, next steps will include the evaluationof the LC50 in J. lineata.