不同藻密度下诺氟沙星对萼花臂尾轮虫生命表统计学参数的影响

诺氟沙星是一种被广泛使用的抗生素,但其对轮虫的毒性作用尚不清楚。为调查诺氟沙星对轮虫的毒性及其与藻密度之间的关系,以及各试验终点对诺氟沙星污染的相对敏感性,本文以萼花臂尾轮虫为受试生物,研究了不同斜生栅藻密度(1.0×10~6、2.0×10~6和4.0×10~6cells·m L~(-1))下不同浓度(0、5、20、35、50、65和80 mg·L~(-1))的诺氟沙星对其生命表统计学参数的影响。结果显示,与3个藻密度下的对照组相比,暴露于5～80 mg·L~(-1)诺氟沙星溶液中的轮虫生命期望和世代时间显著延长,净生殖率和种群内禀增长率显著提高。5 mg·L~(-1)的诺氟沙星使生命期望和世代时间的延长幅度随着藻密度的升高而增大,但6个处理组的平均提高幅度却随着藻密度的升高而减小; 5 mg·L~(-1)的诺氟沙星对净生殖率和种群内禀增长率的提高幅度随着藻密度的升高而增大,但6个处理组的平均提高幅度却在2.0×10~6cells·m L~(-1)的藻密度下最小,4.0×10~6cells·m L~(-1)的藻密度下最大。1.0×10~6cells·m L~(-1)的藻密度下,诺氟沙星浓度对轮虫后代混交率无显著性影响(P0.05); 2.0×10~6cells·m L~(-1)的藻密度下,暴露于5～35和80 mg·L~(-1)诺氟沙星溶液中的轮虫后代混交率显著降低; 4.0×10~6cells·m L~(-1)的藻密度下,暴露于5、35和80 mg·L~(-1)诺氟沙星溶液中的轮虫后代混交率显著降低。当藻密度为1.0×10~6和2.0×10~6cells·m L~(-1)时,诺氟沙星浓度与轮虫的生命期望、世代时间、净生殖率和种群内禀增长率之间具有显著的剂量-效应关系;当藻密度为4.0×10~6cells·m L~(-1)时,诺氟沙星浓度与轮虫的净生殖率和种群内禀增长率之间具有显著的剂量-效应关系。本研究表明,亚致死浓度的诺氟沙星促进轮虫的存活、发育、孤雌生殖和种群增长,促进作用的幅度受藻密度的显著影响。

Effects of Norfloxacin on Life-Table Demography of Brachionus calyciflorus under Different Scenedesmus obliquus Densities

Norfloxacin is a widely used antibiotic, but its toxicity to rotifers remains unknown. In order to investigate the chronic toxicity of sublethal concentrations of norfloxacin to rotifers, and its relation with algal food level, and to compare the relative sensitivity of various endpoints to norfloxacin exposure, the effects of different concentrations (5, 20, 35, 50, 65 and 80 mg L^-1) of norfloxacin on the life-table demographic parameters of Brachionus calyciflorus cultured at three densities (1.0×10⁶, 2.0×10⁶ and 4.0×10⁶ cells mL^-1) of Scenedesmus obliquus were studied by life-table method. The results showed that at 1.0×10⁶, 2.0×10⁶ and 4.0×10⁶ cells mL^-1 of S. obliquus, and compared with the controls, the rotifers exposed to norfloxacin at 5-80 mg L^-1 had significantly longer life expectancy at hatching and generation time, and higher net reproductive rate and intrinsic rate of population increase. With the rise of algal density, the prolonged magnitudes of life expectancy at hatching and generation time of the rotifers exposed to norfloxacin at 5 mg L^-1 increased successively from 39.4% to 59.6% and 62.2%, and from 36.4% to 59.4% and 62.5%, but the mean values of the six treatments decreased successively from 85.9% to 83.1% and 63%, and from 84.8% to 83.1% and 64.6%, respectively. Accordingly, the increased magnitudes of net reproductive rate and intrinsic rate of population increase of the rotifers exposed to norfloxacin at 5 mg L^-1 increased successively from 164.6% to 296.3% and 353.2%, and from 59.1% to 69.2% and 94.2%, but the mean values of the six treatments changed from 404.5% to 384.6% and 500.4%, and from 84.7% to 75.7% and 115.2%, respectively. At 1.0×10⁶ cells mL^-1 of S. obliquus, norfloxacin concentration did not significantly affect the proportion of sexual offspring of the rotifers (P>0.05). However, at 2.0×10⁶ cells mL^-1 of S. obliquus, the rotifers exposed to norfloxacin at 5-35 and 80 mg L^-1 had significantly lower proportion of sexual offspring. When Scenedesmus density was 4.0×10⁶ cells mL^-1, the rotifers exposed to norfloxacin at 5, 35 and 80 mg L^-1 had significantly lower proportion of sexual offspring. When Scenedesmus density was 1.0×10⁶ and 2.0×10⁶ cells mL^-1, there were significant dose-effect relationships between norfloxacin concentration and life expectancy at hatching, generation time, net reproductive rate as well as intrinsic rate of population increase. When Scenedesmus density was 4.0×10⁶ cells mL^-1, there were significant dose-effect relationships between norfloxacin concentration and net reproductive rate as well as intrinsic rate of population increase. The results indicated that sublethal concentrations of norfloxacin are beneficial to survival, development, asexual reproduction and population growth, and the affecting magnitudes are significantly affected by algal density.