Toxic Effect Of Trichlorfon On Growth And Reproduction Of The Freshwater Cladoceran Moina Macrocopa

Trichlorfon, a kind of organophosphorus pesticide (OPs), due to its efficiency and low toxicity, has been used as an insecticide on a large scale in aquaculture pest control. Meanwhile, the problem of its environmental pollution also become a hot topic in the world. Therefore, in the present study, the waterfleas (Moina macrocopa) was used as experimental materials to study the effects of trichlorfon on acute toxicity, growth and reproductive ability, nervous system, lipid peroxidation and antioxidant levels, as well as reserve status. According to the 48 h LC50, the waterfleas were exposed trichlorfon (0,1,2,4,8,16μg/L) for 6,12, 24 and 48 h, and the heart rate, body length, reproductive parameters and the intrinsic rate were determined. Then, to explore the mechanisms of toxicity, we studied effects of nervous system and antioxidant system, the test indicators include acetylcholinesterase (AChE), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities and malondialdehyde (MDA) content. In addition, energy-based biomarkers were also studied, including contents of glycogen, protein, lipid. Finally, we analyzed the changes of caloric content in waterfleas. The results showed that:(1)The half lethal concentration (LC50) of 24 and 48 hours were 72.09 and 31.70μg/L, respectively. With the increase of concentration of trichlorfon and time, the heart rate and body length were promoted in low concentration and suppressed in high concentration. Compared with the control group, trichlorfon prolonged the generation time significantly; the total fecundity and the breeding times showed a gradual downward trend, and the values reached the lowest at 16μg/L (P<0.01); however, lifespan and intrinsic rate were increased initially and decreased subsequently, and the values reached the highest at 2μg/L and 1μg/L (P<0.01), respectively, but both were significantly decreased at 16μg/L (P<0.01).(2)Treatment with trichlorfon caused a significant concentration-dependent and time-related inhibition of AChE activity at all treatment concentrations and time, since trichlorfon is a AChE inhibitor, and when exposed at 16μg/L of trichlorfon for 48 h, the AChE activity was decreased to the lowest compared with the control (P<0.01). While the activities of SOD and CAT increased initially and decreased subsequently, so did GPx activity in 6,12 and 24 h, but GPx activity showed no significant changes compared with the control after exposure for 48 h. However, the content of MDA, was improved significantly in a continuous way (P<0.05), except for the concentration of 1μg/L for 6 h.(3)With the increase of concentration of trichlorfon and time, the glycogen content was gradually reduced, and when exposed at 16μg/L for 48 h, the glycogen content was decreased to the lowest compared with the control (P<0.01). So did lipid content in 12,24 and 48 h, but lipid content showed no significant changes compared with the control after exposure for 6 h. In the concentration of 2μg/L at 6 h, protein content was significantly decreased (P<0.05); however, at 12 h and 24 h, some trichlorfon treatment groups were significantly increased (P<0.05); but the protein content showed no significant changes at 48 h. Caloric content is calculated from the energy equivalents of these three kinds of biomolecules as an index that offers an integrated parameter of the energy reserves. With the increase of concentration of trichlorfon, caloric content was gradually reduced. At 6 h, only in the concentration of 2μg/L, caloric content was significantly decreased (P<0.05); at 12 h and 24 h, in the concentrations of 8μg/L and 16μg/L, caloric content was significantly decreased (P<0.05); even more, all trichlorfon treatment groups were significantly decreased at 48 h (P<0.05).Conclusions:(1)Trichlorfon had significantly affected the growth, reproduction and intrinsic rate. Growth and population’s quantity were promoted in low concentration and suppressed in high concentration; however, trichlorfon inhibited the reproductive ability always.(2)AChE, SOD, CAT and MDA was significantly changed in the stress of trichlorfon, which showed that trichlorfon has apparently neurological toxicity and oxidative damage to Moina macrocopa.(3)Trichlorfon stress leads to the energy consumption increased, and induces compensatory changes in the organism’s energy metabolism. Because the organism’s energy is used for growth, reproduction, and basal metabolism, increased energy expenditure in basal metabolism to cope with the toxic stress will lead to a reduction in growth and reproduction.