Angel Brad M, Simpson Stuart L, Chariton Anthony A, Stauber Jenny L, Jolley Dianne F
Centre for Environmental Contaminants Research, CSIRO Land and Water Locked Bag 2007, Kirrawee, NSW 2232, Australia.
Centre for Environmental Contaminants Research, CSIRO Land and Water Locked Bag 2007, Kirrawee, NSW 2232, Australia.
Aquat Toxicol. 2015 Jul;164:1-9. doi: 10.1016/j.aquatox.2015.04.008. Epub 2015 Apr 9.
Intermittent, fluctuating and pulsed contaminant discharges result in organisms receiving highly variable contaminant exposures. Current water quality guidelines are predominantly derived using data from continuous exposure toxicity tests, and most frequently applied by regulators with the assumption that concentrations from a single sampling event will provide a meaningful approach to assessing potential effects. This study investigated the effect of single and multiple (daily) dissolved copper pulses on the marine diatom, Phaeodactylum tricornutum, including measurements of copper uptake and elimination to investigate the toxic mechanism. Copper pulses of between 0.5 and 24h and continuous exposures with equivalent 72-h time-averaged concentrations (TACs) resulted in similar biomass inhibition of P. tricornutum, with continuous exposures often being marginally more toxic. Rates of cell division generally recovered to control levels within 24h of the copper pulse removal. Upon resuspension in clean seawater, the extracellular copper per cell decreased rapidly, whereas the intracellular copper per cell decreased slowly. Negligible loss of copper from the total algal biomass indicated that P. tricornutum did not have an effective mechanism for eliminating copper from cells, rather the intracellular copper decreased as a result of dilution by cellular division as the algal growth rate recovered. The measurement of copper uptake after 72-h exposure and kinetics of elimination thereafter suggest that continuous exposures are marginally more toxic to P. tricornutum than pulsed copper exposures with equivalent TACs because slow internalization and saturation of algal membrane transport sites results in less copper uptake into pulse-exposed cells than continuously-exposed cells coupled with dilution of internalized copper via cellular division in the post-exposure period. In the case of P. tricornutum, the results indicate that water quality guidelines for copper based on continuous exposure will be conservative when applied to short-term discharges.
间歇性、波动式和脉冲式污染物排放导致生物体受到高度可变的污染物暴露。当前的水质准则主要是根据连续暴露毒性试验的数据得出的，监管机构在应用这些准则时，最常见的假设是单次采样事件的浓度将为评估潜在影响提供有意义的方法。本研究调查了单次和多次（每日）溶解态铜脉冲对海洋硅藻三角褐指藻的影响，包括测量铜的吸收和消除情况，以研究其毒性机制。持续0.5至24小时的铜脉冲以及具有等效72小时时间平均浓度（TACs）的连续暴露对三角褐指藻的生物量抑制作用相似，连续暴露的毒性通常略高。细胞分裂速率在铜脉冲去除后的24小时内通常恢复到对照水平。重新悬浮于清洁海水中后，每个细胞的细胞外铜迅速减少，而每个细胞的细胞内铜减少缓慢。藻类总生物量中铜的损失可忽略不计，这表明三角褐指藻没有有效的细胞内铜消除机制，相反，随着藻类生长速率恢复，细胞内铜因细胞分裂稀释而减少。72小时暴露后铜吸收的测量以及此后的消除动力学表明，与具有等效TACs的脉冲铜暴露相比，连续暴露对三角褐指藻的毒性略高，因为藻类膜转运位点的内化缓慢和饱和导致脉冲暴露细胞比连续暴露细胞摄取的铜更少，再加上暴露后时期通过细胞分裂对内化铜的稀释。就三角褐指藻而言，结果表明基于连续暴露的铜水质准则应用于短期排放时将较为保守。
