Background

The assessment of persistence, bioaccumulation and toxicity (PBT) is part of the regulation process of ionic organic compounds (IOCs) and a major challenge, as a commonly acknowledged approach for the estimation of the bioaccumulation potential of IOCs is still missing. The goal of the present study was, therefore, to experimentally determine the bioaccumulation of fully ionized compounds and to identify screening parameters that can indicate high bioaccumulation potential of IOCs. Three feeding studies with rainbow trout (Oncorhynchus mykiss) were carried out according to OECD TG 305. Separation of liver, gastrointestinal tract (GIT) and carcass allowed to further elucidate the tissue distribution of the individual test substances. The chemicals chosen had characteristics that made them suspect for high bioaccumulation, and included two cations (tetrabutylphosphonium bromide (TBP), trimethyloctadecyl ammonium chloride (TMOA)) and four anions (benzotriazole, tecloftalam, pentachlorophenol (PCP), MEE-phosphonate). Data on the dietary biomagnification of IOCs (strong acids) were also collected from published literature.

Results

The highest distribution factors were found for the GIT, followed by liver. However, none of the tested IOCs showed a distinct biomagnification potential, as kinetic biomagnification factors (BMF_k) ranged between 0.001 and 0.05 g/g (median 0.009 g/g). Cations showed lower assimilation efficiency (α) than anions, except for tecloftalam. In contrast, anions showed a considerably faster depuration rate (half-life less than 0.5 days) compared to cations (half-life of around 5 days). Sixteen potential screening parameters for BMF were calculated with a chemical property estimation tool (ACD/i-Lab) and correlated with the BMF data from this study and from literature. The number of hydrogen bond donors (nHBD) showed the highest correlation to measured BMF, but the prediction is only based on two values (one or two nHBD), while the other descriptors were insignificantly correlated.

Conclusion

The suspected dietary bioaccumulation potential of the six IOCs could not be confirmed in the feeding studies with rainbow trout. The more than twenty screening parameters showed no particularly high correlation neither with the test results nor with the BMF values collected from literature. The results corroborate earlier findings that ionization lowers the tendency of a chemical for dietary bioaccumulation, compared to non-ionized chemicals. In addition to the lipophobicity of ionic molecule moieties, fast depuration seems to be a major reason for the observed low dietary bioaccumulation of ionic compounds, in particular anions. Fast depuration may happen due to rapid metabolism of charged compounds, and future studies should test this hypothesis.

中文翻译：

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虹鳟Onkihynchus mykiss中可电离有机化合物的生物放大作用

背景

持久性，生物蓄积性和毒性（PBT）的评估是离子有机化合物（IOC）调节过程的一部分，也是一项重大挑战，因为仍然缺少普遍公认的评估IOC潜在生物蓄积性的方法。因此，本研究的目的是通过实验确定完全电离的化合物的生物蓄积性，并确定可以表明IOC具有高生物蓄积潜力的筛选参数。虹鳟鱼（Oncorhynchus mykiss的三个喂养研究）按照OECD TG 305进行。分离肝脏，胃肠道（GIT）和屠体可进一步阐明各个测试物质的组织分布。选择的化学药品具有使它们容易被高生物蓄积的特性，包括两个阳离子（溴化四丁基phosph（TBP），三甲基十八烷基氯化铵（TMOA））和四个阴离子（苯并三唑，tecloftalam，五氯酚（PCP），MEE-膦酸酯）。还从已发表的文献中收集了IOC（强酸）的饮食生物放大数据。

结果

发现GIT的分布系数最高，其次是肝脏。但是，没有任何一种经测试的IOC作为动力生物放大因子（BMF _k）介于0.001至0.05 g / g（中位数0.009 g / g）之间。除tecloftalam外，阳离子显示的同化效率（α）比阴离子低。相反，与阳离子（半衰期约为5天）相比，阴离子显示出更快的净化速率（半衰期少于0.5天）。使用化学性质评估工具（ACD / i-Lab）计算了16种潜在的BMF筛选参数，并将其与本研究和文献中的BMF数据相关联。氢键供体（nHBD）的数量与测得的BMF具有最高的相关性，但预测仅基于两个值（一个或两个nHBD），而其他描述子则无显着相关性。

结论

在用虹鳟鱼进行的喂养研究中，无法确定这六个IOC的可疑膳食生物蓄积潜力。二十多个筛选参数与测试结果和从文献中收集的BMF值均无特别高的相关性。该结果证实了较早的发现，即与非电离的化学物质相比，电离降低了化学物质在饮食中积累生物的趋势。除了离子分子部分的疏脂性之外，快速净化似乎也是观察到的离子化合物（尤其是阴离子）的低饮食生物蓄积的主要原因。由于带电荷化合物的快速代谢，可能会发生快速净化，因此未来的研究应验证这一假设。