• A concentration dependent increase of B[ a ]P metabolites was observed • No induction of phase I or II activity was observed with increasing B[ a ]P exposure • Biotransformation of B[ a ]P was successfully implemented into in silico models • The models accurately predicted life stage-specific abundances of B[ a ]P metabolites Understanding internal dose metrics is integral to adequately assess effects environmental contaminants might have on aquatic wildlife, including fish. In silico toxicokinetic (TK) models are a leading approach for quantifying internal exposure metrics for fishes; however, they often do not adequately consider chemicals that are actively biotransformed and have not been validated against early-life stages (ELS) that are often considered the most sensitive to the exposure to contaminants. To address these uncertainties, TK models were parameterized for the rapidly biotransformed chemical benzo[ a ]pyrene (B[ a ]P) in embryo-larval and adult life stages of fathead minnows. Biotransformation of B[ a ]P was determined through measurements of in vitro clearance. Using in vitro-in vivo extrapolation, in vitro clearance was integrated into a multi-compartment TK model for adult fish and a one-compartment model for ELS. Model predictions were validated using measurements of B[ a ]P metabolites from in vivo flow-through exposures to graded concentrations of water-borne B[ a ]P. Significantly greater amounts of B[ a ]P metabolites were observed with exposure to greater concentrations of parent compound in both life stages. However, when assessing biotransformation capacity, no differences in phase I or phase II biotransformation were observed with greater exposures to B[ a ]P. Results of modelling suggested that biotransformation of B[ a ]P can be successfully implemented into in silico models to accurately predict life stage-specific abundances of B[ a ]P metabolites in either whole-body larvae or the bile of adult fish. Models developed increase the scope of applications in which TK models can be used to support environmental risk assessments.

Uptake and effects of ionizable organic chemicals (IOCs) that are weak acids in aqueous solution by fish can differ as a function of pH. While the pH-dependent behavior of select IOCs is well-understood, complex mixtures of IOCs, e.g., from oil sands process-affected water (OSPW), have not yet been studied systematically. Here, we established an in vitro screening method using the rainbow trout gill cell line, RTgill-W1, to investigate pH-dependent cytotoxicity and permeation of IOCs across cultured epithelia using ultra-high-performance liquid chromatography with high-resolution mass spectrometry (UPLC-HRMS). The assay was benchmarked using model chemicals and technical mixtures, and then used to characterize fractions and reconstituted extracts of field-collected OSPW. Significant pH-dependent cytotoxicity of individual IOCs, acidic fractions, and reconstituted extracts of OSPW was observed. In vitro data were in good agreement with data from a 96 h in vivo exposure experiment with juvenile rainbow trout. Permeation of some IOCs from OSPW was mediated by active transport, as revealed by studies in which inhibitors of these active transport mechanisms were applied. We conclude that the RTgill-W1 in vitro assay is useful for the screening of pH-dependent uptake of IOCs in fish, and has applications for in vitro-in vivo extrapolation, and prioritization of chemicals in nontarget screenings.

Brominated azo dyes (BADs) have been identified as predominant indoor brominated pollutants in daycare dust; thus, their potential health risk to children is of concern. However, the toxicities of BADs remain elusive. In this study, the toxicokinetics of two predominant BADs, Disperse Blue 373 (DB373) and Disperse Violet 93 (DV93), and their suspect metabolite 2-bromo-4,6-dinitroaniline (BDNA) was investigated in embryos of zebrafish (Danio rerio). The bioconcentration factor of DV93 at 120 hpf is 6.2-fold lower than that of DB373. The nontarget analysis revealed distinct metabolism routes between DB373 and DV93 by reducing nitro groups to nitroso (DB373) or amine (DV93), despite their similar structures. NAD(P)H quinone oxidoreductase 1 (NQO1) and pyruvate dehydrogenase were predicted as the enzymes responsible for the reduction of DB373 and DV93 by correlating time courses of the metabolites and enzyme development. Further in vitro recombinant enzyme and in vivo inhibition results validated NQO1 as the enzyme specifically reducing DB373, but not DV93. Global proteome profiling revealed that the expression levels of proteins from the "apoptosis-induced DNA fragmentation" pathway were significantly upregulated by all three BADs, supporting the bioactivation of BADs to mutagenic aromatic amines. This study discovered the bioactivation of BADs via distinct eukaryotic enzymes, implying their potential health risks.

Recent advances in mass spectrometry have facilitated chemical characterization and profiling of complex environmental mixtures such as oil sand process-affected water (OSPW) and identification of previously unresolved chemicals. However, because OSPW is a complex mixture of salts, metals, suspended particulate matter, and dissolved organics, extraction techniques are required to reduce the effects of signal suppression/enhancement. In this work, Orbitrap, ultrahigh resolution mass spectrometry was used to perform a comprehensive comparison of solid phase extraction (SPE) and liquid–liquid extraction (LLE) techniques on profiling of dissolved organic chemicals in OSPW. When operated in negative ion mode, extraction of naphthenic acid (NAs–O2) was dependent on acidification of OSPW samples for C18 and LLE techniques. However, when applying a hydrophilic lipophilic balance (HLB) sorbent (ABN) SPE technique, the extractability of NAs was independent of pH. When operated in positive ion mode, for all extracti...