Juárez-Franco Marissa Fernanda, Sarma S S S, Nandini S
Postgraduate Program in Biological Sciences, UNAM, Mexico City, Mexico.
J Environ Sci Health A Tox Hazard Subst Environ Eng. 2007 Aug;42(10):1489-93. doi: 10.1080/10934520701480938.
We evaluated the effect of 3 sublethal concentrations of Cd (as CdCl(2), 209.50, 104.75 and 52.38 microg/L) and Zn (as ZnCl(2), 283.88, 141.94 and 70.97 microg/L) separately and together on the population growth of the common Mexican brachionid rotifer Brachionus havanaensis using 1 x 10(6) cells/mL of Chlorella vulgaris as the algal diet. The LC(50) (24-h bioassay conducted in the absence of food) for B. havanaensis was 419.0 +/- 8.1 microg/L for Cd and 2271.0 +/- 404.4 microg/L for Zn. The effect of different concentrations of Cd or Zn on the population growth of B. havanaensis showed decreased population abundance with increasing levels of the metal concentration in the medium. However, for Cd even at the highest tested concentration (i.e., 50% LC(50), 209.5 microg/L), there was some increase in the abundance of B. havanaensis, although much lower than in controls. On the other hand, for Zn at highest tested concentration (i.e., 12.5% LC(50), 283.88 microg/L), the population of B. havanaensis showed little growth and remained close to the initial density. Under the conditions of mixed metal exposure, B. havanaensis did not grow at the highest tested concentrations of Cd+Zn combination. The rate of population increase (r) varied from 0.11 to 0.43 per day, depending on the heavy metal concentration. Statistically r was adversely influenced by the heavy metal concentration in the medium. Tests of multiple comparisons indicated that r at the lowest level of Cd or Zn (alone or mixed) was not significantly different from controls. Our data from the acute toxicity tests showed that Cd was 5 times more toxic than Zn to B. havanaensis but this difference was much reduced based on the chronic toxicity studies.
我们分别及共同评估了3种亚致死浓度的镉（以CdCl₂形式存在，浓度分别为209.50、104.75和52.38微克/升）和锌（以ZnCl₂形式存在，浓度分别为283.88、141.94和70.97微克/升）对普通墨西哥臂尾轮虫哈瓦那臂尾轮虫种群增长的影响，其中使用1×10⁶个细胞/毫升的普通小球藻作为藻类食物。哈瓦那臂尾轮虫的LC₅₀（在无食物情况下进行的24小时生物测定），镉为419.0±8.1微克/升，锌为2271.0±404.4微克/升。不同浓度的镉或锌对哈瓦那臂尾轮虫种群增长的影响表现为，随着培养基中金属浓度水平的增加，种群丰度下降。然而，对于镉，即使在最高测试浓度（即50% LC₅₀，209.5微克/升）下，哈瓦那臂尾轮虫的丰度仍有一些增加，尽管远低于对照组。另一方面，对于锌，在最高测试浓度（即12.5% LC₅₀，28 + 3.88微克/升）下，哈瓦那臂尾轮虫种群几乎没有增长，且仍接近初始密度。在混合金属暴露条件下，哈瓦那臂尾轮虫在最高测试浓度的镉 + 锌组合下没有生长。种群增长率（r）每天在0.11至0.43之间变化，这取决于重金属浓度。从统计学角度来看，r受到培养基中重金属浓度的不利影响。多重比较测试表明，最低水平的镉或锌（单独或混合）下的r与对照组没有显著差异。我们急性毒性测试的数据表明，镉对哈瓦那臂尾轮虫的毒性比锌高五倍，但基于慢性毒性研究，这种差异大幅减小。
