Zn2+和Cd2+对萼花臂尾轮虫种群增长的单一和联合毒性效应

为探究Zn2+和Cd2+对轮虫种群增长的单一和联合毒性效应,在不同温度(15、20和25 ℃)和斜生栅藻(Scenedesmus obliquus)不同密度(0.5×106、1.0×106和2.0×106 mL-1)下,以萼花臂尾轮虫(Brachionus calyciflorus)为受试生物,采用3 d种群累积培养方法,研究了不同 Zn2+污染处理组〔ρ(Zn2+)分别为0.315、0.630和1.260 mg/L〕、Cd2+污染处理组〔ρ(Cd2+)分别为0.073、0.145和0.289 mg/L〕、Zn2+-Cd2+复合污染处理组〔ρ(Zn2+)、ρ(Cd2+)分别为0.315、0.073 mg/L,0.630、0.145 mg/L和1.260、0.289 mg/L〕 对轮虫种群增长率和混交雌体百分率的影响. 结果表明:当藻密度为0.5×106和2.0×106 mL-1时,与对照组相比,随着温度上升,对轮虫种群增长率产生抑制作用的处理组数明显增加,高温(25 ℃)下,所有处理组均显著降低轮虫种群增长率. 15和20 ℃下,与较低、中等藻密度(0.5×106、1.0×106 mL-1)相比,较高藻密度(2.0×106 mL-1)下轮虫种群受到毒性影响的处理组数明显减少；25 ℃下,各处理组轮虫种群增长率均随藻密度的升高而增加. 在温度为15和20 ℃、藻密度为0.5×106 mL-1条件下,Zn2+-Cd2+复合污染处理〔当ρ(Zn2+)、ρ(Cd2+)分别为1.260、0.289 mg/L时〕的轮虫种群增长率明显低于ρ(Zn2+)为1.260 mg/L和ρ(Cd2+)为0.289 mg/L时的轮虫种群增长率；温度为25 ℃、藻密度为2.0×106 mL-1条件下,Zn2+-Cd2+复合污染处理〔当ρ(Zn2+)、ρ(Cd2+)分别为0.630、0.145 mg/L时〕的轮虫种群增长率明显低于ρ(Zn2+)为0.630 mg/L和ρ(Cd2+)为0.145 mg/L时的轮虫种群增长率. 研究显示,温度、藻密度和重金属质量浓度之间的交互作用对轮虫种群增长率的影响大于其对混交雌体百分率的影响,随着温度的升高和藻密度的降低,Zn2+、Cd2+对轮虫的单一和联合毒性效应增加. 

Single and Combined Toxicities of Zn2+ and Cd2+ to the Population Growth of Brachionus calyciflorus

The single and combined toxicities of Zn2+ and Cd2+ have raised concerns in aquatic organisms for many years. However, chronic toxicities of the two metal ions to the population growth of rotifers were seldom known. In the present study, the toxic effects of Zn2+ (0.315,0.630 and 1.260 mg/L), Cd2+ (0.073,0.145 and 0.289 mg/L), and the combination of Zn2+ and Cd2+ (0.315 and 0.073,0.63 and 0.145, and 1.260 and 0.289 mg/L) on the population growth rate and the mictic rate of the freshwater rotifer Brachionus calyciflorus were evaluated at three temperatures (15,0 and 25 ℃) and three algae (Scenedesmus obliquus) densities (0.5×106,1.0×106 and 2.0×106 mL-1) using the 3-d population cumulative culture method. The results showed that compared to the controls, the number of the treatments which inhibited the population growth rate of the rotifers increased with the rise of the temperature. At 15 ℃ and 0.5×106 mL-1 of S. obliquus, Zn2+ at 1.260 mg/L, Cd2+at 0.289 mg/L, and the combination of Zn2+ and Cd2+at 1.260 and 0.289 mg/L, the population growth rate of the rotifers decreased. At 20 ℃ and the same algal density, five treatments including Zn2+ at 0.315 and 1.260 mg/L, Cd2+at 0.289 mg/L, and the combination of Zn2+ and Cd2+at 0.630 and 0.145 and 1.260 and 0.289 mg/L, the population growth rate of the rotifers decreased. However, at 25 ℃ and the same algal density, all treatments reduced the population growth rate of the rotifers. At 15 ℃ and 2.0×106 mL-1 of S. obliquus, all treatments had no effect on the population growth rate of the rotifers. At 20 ℃ and the same algal density, five treatments including Zn2+ at 0.630,1.260 mg/L, Cd2+ at 0.289 mg/L, and the combination of Zn2+ and Cd2+at 0.630 and 0.145 and 1.260 and 0.289 mg/L reduced the population growth rate of the rotifers. However, at 25 ℃ and the same algal density, all treatments decreased the population growth rate of the rotifers. At 15 and 20 ℃, and compared to the algal densities of 0.5×106 and 1.0×106 mL-1, the number of the treatments which inhibited the population growth rate of the rotifers decreased at the high (2.0×106 mL-1) algal density. At 25 ℃, the population growth rate of the rotifers increased with the rise of the algal density. At 15 and 20 ℃, and 0.5×106 mL-1 of S. obliquus, and compared to the treatments of Zn2+ at 1.260 mg/L and Cd2+ at 0.289 mg/L, the combination of Zn2+ and Cd2+at 1.260 and 0.289 mg/L reduced the population growth rate of the rotifers. At 25 ℃ and 2.0×106 mL-1 of S. obliquus, and compared to the treatments of Zn2+ at 0.630 mg/L and Cd2+ at 0.145 mg/L, the combination of Zn2+ and Cd2+ at 0.630 and 0.145 mg/L reduced the population growth rate of the rotifers. These results indicated that the population growth rate of the rotifers was more sensitive to the interaction among temperature, algal density and the concentration of treatments than the mictic rate, and with the rise of temperature and the decline of the algal density, the toxicities of Zn2+, Cd2+, and the combination of Zn2+ and Cd2+to the population growth of B.calyciflorus increased.