Biomagnification of ionizable organic compounds in rainbow trout Oncorhynchus mykiss

Abstract

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 (BMFk) 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.

Biotransformation Potential of Cationic Surfactants in Fish Assessed with Rainbow Trout Liver S9 Fractions

“…The potential for biotransformation to substantially reduce the accumulation of neutral hydrophobic organic chemicals in fish has been well documented (Arnot et al, 2008a, 2008b; De Wolf et al, 1992; Laue et al, 2014). The same effect may apply to ionizable chemicals (Mueller et al, 2020). Predicting the impact of biotransformation on bioaccumulation of ionizable chemicals is complicated, however, by uncertainty regarding other kinetic processes that control uptake, distribution, and excretion (Armitage et al, 2017).…”

Investigating the Bioaccumulation Potential of Anionic Organic Compounds Using a Permanent Rainbow Trout Liver Cell Line

“…For example, pharmaceuticals, such as the anionic diclofenac, express a low bioaccumulation in fish compared to neutral compounds despite a log K OW of > 4 (Schwaiger et al, 2004;Memmert et al, 2013). However, certain anionic surfactants, such as perfluoroalkyl substances and long chained alkyl sulfonates (alkyl chain ≥ 14) (Martin et al, 2003;Inoue et al, 2012;Ribbenstedt et al, 2022), exert a high bioaccumulation in fish relative to other anionic compounds (Könnecker et al, 2011;Tolls et al, 2000;Mueller et al, 2020). Anionic compounds that lack the typical surfactant-like structure but have a largely hydrophobic surface, such as pentachlorophenol, also show high bioaccumulation in fish (McKim et al, 1986;ECHA, 2017).…”