Sediment toxicity testing with very hydrophobic organic chemicals (VHOCs) is challenging because of the chemicals’ low aqueous solubilities and slow kinetics. The present study presents the results of experiments investigating whether the standard exposure duration of 28 days with benthic invertebrates is sufficient for VHOCs; above which concentrations in sediment VHOCs are present as “free phase,” that is, crystals or non-aqueous-phase liquids (NAPLs); and whether it is possible to discriminate between actual VHOC toxicity and physical effects caused by NAPLs through fouling of the test organisms. The results suggest that the standard sediment toxicity test duration is sufficient for obtaining steady-state VHOC concentrations in Hyalella azteca and Lumbriculus variegatus, provided that spiking and equilibration are performed properly (i.e., no free phase present). Under these conditions, transient (days 3–20) peak-shaped toxicokinetics were observed, with steady-state concentrations reached at approximately 28 days. The concentration above which NAPLs are present, the so-called critical separate phase concentration (CSPC), was determined for several VHOCs by modeling and two experimental methods. Modeling resulted in unrealistic and variable data and therefore should be applied with caution. Experimentally determining CSPCs was successful and yielded values of approximately 1000 (400–2000) mg/kg dry weight, depending on the chemical. Finally, it was demonstrated that distinguishing actual toxicity from physical effects is possible by applying a well-considered test setup, combining toxicity tests with multiple invertebrates (including Lumbriculus, which serves as a negative control for fouling); a broad test concentration range, preferably up to at least 30 000 mg/kg; and passive sampling to localize the CSPC. Applying this setup, false-positive effects due to fouling, as well as false-negative results due to testing at too low concentrations (trying to stay below the CSPC), can be avoided. Environ Toxicol Chem 2024;00:1–12. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

中文翻译：

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改进高疏水性化学品的沉积物毒性测试：第 2 部分 - 暴露持续时间、测试浓度上限以及区分实际毒性和物理效应

由于疏水性有机化学品 (VHOC) 的水溶性低且动力学缓慢，因此对沉积物毒性测试具有挑战性。本研究提供了实验结果，调查底栖无脊椎动物 28 天的标准暴露时间对于 VHOC 是否足够；高于此浓度时，沉积物中的 VHOC 以“自由相”的形式存在，即晶体或非水相液体 (NAPL)；以及是否可以通过测试生物体的污染来区分实际的 VHOC 毒性和 NAPL 引起的物理效应。结果表明，只要正确进行加标和平衡（即不存在游离相），标准沉积物毒性测试持续时间足以获得Hyalella azteca和Lumbriculus variegatus中的稳态VHOC 浓度。在这些条件下，观察到瞬时（第 3-20 天）峰形毒代动力学，并在大约 28 天时达到稳态浓度。通过建模和两种实验方法确定了几种 VHOC 的 NAPL 存在浓度（即所谓的临界分离相浓度 (CSPC)）。建模会产生不切实际且可变的数据，因此应谨慎应用。实验测定 CSPC 是成功的，产生的值约为 1000 (400–2000) mg/kg 干重，具体取决于化学品。最后，事实证明，通过应用经过深思熟虑的测试设置，将毒性测试与多种无脊椎动物（包括作为污垢阴性对照的蚓属）相结合，可以区分实际毒性和物理效应；广泛的测试浓度范围，优选高达至少30000mg/kg；和被动采样来定位 CSPC。应用此设置，可以避免由于污染而导致的假阳性效应，以及由于在过低浓度（试图保持低于 CSPC）下测试而导致的假阴性结果。环境毒理学2024；00：1–12。 © 2023 作者。《环境毒理学和化学》由 Wiley periodicals LLC 代表 SETAC 出版。