Hoang Tham C, Gallagher Jeffrey S, Tomasso Joseph R, Klaine Stephen J
Department of Biological Sciences, Clemson Institute of Environmental Toxicology, 509 Westinghouse Road, Pendleton, South Carolina 29670, USA.
Arch Environ Contam Toxicol. 2007 Nov;53(4):579-89. doi: 10.1007/s00244-006-0266-1.
Aquatic organisms living in surface waters experience fluctuating contaminant exposures that vary in concentration, duration, and frequency. This study characterized the role of pulsed concentration, pulsed duration, and the interval between pulses on the toxicity of four metals (Cu, Zn, Se, and As) to Daphnia magna. During 21-d toxicity tests, neonatal D. magna were exposed to single or double pulses. Pulsed concentrations and durations ranged from 32 to 6000 microg/L and 8 to 96 h, respectively. Intervals between two pulses ranged from 24 to 288 h. Mortality, growth, and reproduction were characterized for exposures. For single-pulse exposures of Cu and As, metal concentration had a stronger effect on survival of D. magna than did pulsed duration: pulses with 2X concentration and 1Y duration resulted in more mortality than did pulses with 1X concentration and 2Y duration. In contrast, effects of pulsed duration were stronger than metal concentration for Zn. However, the effects of duration and concentration were similar for Se. The relative effects of pulsed concentration and duration found in the present study revealed that the common method using area under the curve (AUC = concentration x duration) may not always accurately estimate environmental risk from metals (e.g., for Cu, Zn, As). In addition, the occurrence of delayed mortality in the present study revealed that using continuous exposure bioassays might underestimate metal toxicity to aquatic biota. For double-pulse exposures, the toxicity of the second pulse was influenced by the first pulse for all four metals. This influence was dependent on the pulsed concentration and duration and the interval between pulses. Further, toxicity caused by the second pulse decreased as the time between the exposures increased. For all four metals, there existed an interval great enough that the toxicity of the two pulses was independent. This would result in less toxicity for multiple exposures than continuous exposures with the same total exposure duration. The interval time at which the effects of the two pulses were independent increased with increasing concentration. Growth and cumulative reproduction of D. magna over 21 d were not significantly affected by pulsed exposures examined in the present study, indicating recovery of the organisms.
生活在地表水层的水生生物所接触到的污染物浓度、持续时间和频率都处于波动状态。本研究探究了脉冲浓度、脉冲持续时间以及脉冲间隔对四种金属（铜、锌、硒和砷）对大型溞毒性的影响。在为期21天的毒性测试中，新生大型溞被暴露于单脉冲或双脉冲环境中。脉冲浓度和持续时间分别为32至6000微克/升和8至96小时。两个脉冲之间的间隔为24至288小时。对暴露后的死亡率、生长和繁殖情况进行了表征。对于铜和砷的单脉冲暴露，金属浓度对大型溞存活的影响比脉冲持续时间更强：浓度为2倍、持续时间为1倍的脉冲导致的死亡率高于浓度为1倍、持续时间为2倍的脉冲。相比之下，对于锌，脉冲持续时间的影响比金属浓度更强。然而，对于硒，持续时间和浓度的影响相似。本研究中发现的脉冲浓度和持续时间的相对影响表明，常用的曲线下面积法（AUC = 浓度×持续时间）可能并不总是能准确估计金属对环境的风险（例如对于铜、锌、砷）。此外，本研究中出现的延迟死亡现象表明，使用连续暴露生物测定法可能会低估金属对水生生物群的毒性。对于双脉冲暴露，所有四种金属的第二个脉冲的毒性都受到第一个脉冲的影响。这种影响取决于脉冲浓度、持续时间以及脉冲间隔。此外，随着两次暴露之间时间的增加，第二个脉冲所导致的毒性会降低。对于所有四种金属，都存在一个足够大的间隔，使得两个脉冲的毒性相互独立。这将导致多次暴露的毒性低于相同总暴露持续时间的连续暴露。两个脉冲影响相互独立的间隔时间随着浓度的增加而增加。本研究中所检测的脉冲暴露对大型溞21天内的生长和累积繁殖没有显著影响，表明生物体能恢复。
