Department of Bioenvironmental Systems Engineering, National Taiwan University, Taipei, Taiwan, ROC.
Ecotoxicology. 2012 Mar;21(2):485-95. doi: 10.1007/s10646-011-0810-2. Epub 2011 Nov 2.
It has been proposed that irreversible responses of organisms exposed to contaminants are due to a systems-level feedback. Here we tested this hypothesis by reanalyzing the published data on toxicokinetics and survival probability based on a systems-level threshold damage model (TDM) incorporating with a positive damage feedback to explore the steady-state response and dynamic behavior of damage for tilapia and freshwater clam exposed to waterborne arsenic (As). We found that ultrasensitivity appeared in As-tilapia and freshwater clam systems with Hill coefficient n ≥ 4, indicating that the positive damage feedback mechanism has been triggered. We confirmed that damage can trigger a positive feedback loop that together with As stressor increases irreversibility. This study also showed that TDM with positive feedback gave a much better predictability than that of TDM at As concentrations ranging from 100 to 500 mg l(-1) for freshwater clam, whereas for tilapia, two models had nearly same performance on predictability. We suggested that mortality-time profile derived Hill coefficient could be used as a new risk indicator to assess the survival probability for species exposed to waterborne metals. We anticipated that the proposed toxicokinetics/toxicodynamics with a positive damage feedback may facilitate our understanding and manipulation of complex mechanisms of metal susceptibility among species and improve current risk assessment strategies.
有人提出，暴露于污染物的生物体的不可逆反应是由于系统水平的反馈。在这里，我们通过重新分析基于系统水平的损伤阈值模型（TDM）的已发表的毒代动力学和生存概率数据来检验这一假设，该模型纳入了正向损伤反馈，以探索鱼类和淡水贻贝类对水砷暴露的稳态损伤反应和动态行为。我们发现，阿氏鲷和淡水贻贝类系统的超敏性表现出 Hill 系数 n≥4，表明正向损伤反馈机制已被触发。我们证实，损伤可以触发正反馈回路，该回路与砷应激一起增加了不可逆性。这项研究还表明，对于淡水贻贝类，在 100 至 500mg/L 范围内的砷浓度下，带有正反馈的 TDM 比 TDM 的预测性要好得多，而对于阿氏鲷，两个模型的预测性能几乎相同。我们建议，死亡率时间曲线得出的 Hill 系数可作为一种新的风险指标，用于评估物种暴露于水金属的生存概率。我们预计，提出的具有正向损伤反馈的毒代动力学/毒效动力学可能有助于我们理解和操纵物种之间金属易感性的复杂机制，并改进当前的风险评估策略。
