Ecossa, Giselastr, 6, 82319, Starnberg, Germany.
Unilever, Safety & Environmental Assurance Centre, Colworth Science Park, Sharnbrook, Bedford, MK44 1LQ, UK.
Environ Sci Pollut Res Int. 2023 Sep;30(42):96290-96300. doi: 10.1007/s11356-023-29193-2. Epub 2023 Aug 12.
Caenorhabditis elegans is used for assessing the toxicity of chemicals in aqueous medium. However, chemicals can absorb to the bacterial food, which reduces the freely dissolved concentrations of the tested compounds. Thus, based on total or nominal concentrations, toxicity is underestimated, resulting in misleading assumptions on toxicity mechanisms or comparisons to other test organisms. As the verification of freely dissolved exposure concentrations (C) is challenging in small test systems, simple partitioning models might by a good option for estimating C. Therefore, C. elegans was exposed to seven differently acting organic chemicals with varying hydrophobicities, thus also different affinities to bind to the food of C. elegans. Measured concentrations of the dissolved aqueous and the bacterial-bound fraction allowed the calculation of binding constants (K). Experimental K were comparable to literature data of hydrophobic chemicals and correlated well with their hydrophobicity, expressed as log K. The chronic toxicity of the various compounds on C. elegans' reproduction, based on their aqueous concentration, was weakly related to their log K. Toxicity expressed based on chemical activity and comparisons with a baseline toxicity model, nevertheless, suggested a narcotic mode of action for most hydrophobic compounds (except methylisothiazolinone and trichlorocarbanilide). Although revealing a similar toxicity ranking than Daphnia magna, C. elegans was less sensitive, probably due to its ability to reduce its internal concentrations by means of its very impermeable cuticle or by efficient detoxification mechanisms. It could be shown that measured aqueous concentrations in the nematode test system corresponded well with freely dissolved concentrations that were modeled using simple mass-balance models from nominal concentrations. This offers the possibility to estimate freely dissolved concentrations of chemicals from nominal concentrations, making routine testing of chemicals and their comparison to other species more accurate.
秀丽隐杆线虫被用于评估水介质中化学物质的毒性。然而，化学物质可能会被细菌食物吸收，从而降低受试化合物的自由溶解浓度。因此，基于总浓度或名义浓度，毒性会被低估，从而导致对毒性机制的错误假设或与其他测试生物的比较。由于在小测试系统中验证自由溶解暴露浓度 (C) 具有挑战性，因此简单的分配模型可能是估计 C 的一个很好的选择。因此，将秀丽隐杆线虫暴露于七种具有不同疏水性的不同作用的有机化学物质中，从而也具有与秀丽隐杆线虫食物不同的结合亲和力。溶解水相和细菌结合相的测量浓度允许计算结合常数 (K)。实验 K 与疏水性化学物质的文献数据相当，并与它们的疏水性（表示为 log K）很好地相关。基于其水相浓度，各种化合物对秀丽隐杆线虫繁殖的慢性毒性与它们的 log K 弱相关。基于化学活性表达的毒性及其与基线毒性模型的比较，表明大多数疏水性化合物（甲基异噻唑啉酮和三氯卡班除外）具有麻醉作用模式。尽管秀丽隐杆线虫与大型蚤揭示了相似的毒性排序，但秀丽隐杆线虫的敏感性较低，这可能是由于其通过非常不渗透的角质层或通过有效的解毒机制来降低其内部浓度的能力。结果表明，在线虫测试系统中测量的水相浓度与使用名义浓度的简单质量平衡模型建模的自由溶解浓度非常吻合。这使得从名义浓度估计化学物质的自由溶解浓度成为可能，从而使化学物质的常规测试及其与其他物种的比较更加准确。
