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Don Mackay, a pioneer in environmental organic chemistry, passed away in 2023. He was known for his contributions to understanding and quantifying the fate and transport of contaminants in the environment. Mackay's work, which applied principles from chemical engineering and physical chemistry, simplified complex concepts and made them accessible to a wide audience. His research was widely adopted and applied in regulatory practice, demonstrating its usefulness. Mackay was dedicated to translational research and believed in collaboration among academia, government, and industry to manage chemical risks. His work focused on understanding the properties of contaminants, their behavior in the environment, and developing models to assess their effects. Mackay's legacy highlights the importance of scientific collaboration and using knowledge to address environmental challenges. [Extracted from the article]

The bioaccumulation behavior, including the uptake, internal distribution, depuration, and biotransformation rates, of three widely used linear methyl‐siloxanes was investigated in rainbow trout. Dietary uptake efficiencies of octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), and dodecamethylpentasiloxane (L5) were 15% (3.3% standard error [SE]), 8.6% (1.4% SE), and 15% (1.8% SE), respectively, and for L3 and L4 were well below those of nonmetabolizable reference chemicals with similar octanol–water partition coefficients, suggesting significant intestinal biotransformation of L3 and L4. Somatic biotransformation rate constants were 0.024 (0.003 SE) day–1 for L3 and 0.0045 (0.0053 SE) day–1 for L4 and could not be determined for L5. Lipid‐normalized biomagnification factors for L3, L4, and L5 were 0.24 (0.02 SE), 0.24 (0.01 SE), and 0.62 (0.05 SE) kg‐lipid kg‐lipid–1, respectively. Bioconcentration factors standardized to a 5% lipid content fish for water in Canadian oligotrophic lakes with a dissolved organic carbon content of 7.1 mg L–1 were 2787 (354 SE) for L3, 2689 (312 SE) for L4, and 1705 (418 SE) L kg‐wet weight–1, respectively, and 3085 (392 SE) for L3, 4227 (490 SE) for L4, and 3831 (938 SE) L kg‐wet weight–1 in water with a dissolved organic carbon content of 2.0 mg L–1. A comparison of 238 bioaccumulation profiles for 166 different chemicals shows that the bioaccumulation profiles for L3, L4, and L5 are vastly different from those of other very hydrophobic compounds found in the environment. Environ Toxicol Chem 2024;43:42–51. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

This study investigates and reviews methods for the assessment of the terrestrial bioaccumulation potential of hydrocarbons and related organic substances. The study concludes that the unitless biomagnification factor (BMF) and/or the trophic magnification factor (TMF) are appropriate, practical, and thermodynamically meaningful metrics for identifying bioaccumulative substances in terrestrial food chains. The study shows that various methods, including physical–chemical properties like the KOA and KOW, in vitro biotransformation assays, quantitative structure–activity relationships, in vivo pharmacokinetic and dietary bioaccumulation tests, and field‐based trophic magnification studies, can inform on whether a substance has the potential to biomagnify in a terrestrial food chain as defined by a unitless BMF exceeding 1. The study further illustrates how these methods can be arranged in a four‐tier evaluation scheme for the purpose of screening assessments that aim to minimize effort and costs and expediate bioaccumulation assessment of the vast numbers of organic substances in commerce, identifies knowledge gaps, and provides recommendations for further research to improve bioaccumulation assessment. Integr Environ Assess Manag 2023;19:1433–1456. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Key Points: •A four‐tier terrestrial bioaccumulation (TB) screening assessment scheme for hydrocarbons and related organic substances is presented.•The TB screening scheme makes use of various sources of information including physical–chemical properties (KOA and KOW), in vitro biotransformation assays, quantitative structure–activity relationships, in vivo tests, and field‐based trophic magnification studies. [ABSTRACT FROM AUTHOR]

To advance methods for bioaccumulation assessment of organic substances in air‐breathing organisms, the present study developed an in vitro approach for screening neutral hydrophobic organic substances for their bioaccumulation potential in air‐breathing organisms consisting of (1) depletion assays for chemicals in rat liver S9 subcellular fractions, (2) in vitro–in vivo extrapolation, and (3) whole‐organism bioaccumulation modeling to assess the biomagnification potential of neutral organic substances in the rat. Testing of the in vitro method on 14 test chemicals of potentially biomagnifying substances showed that the bioassays could be conducted with a high level of reproducibility and that in vitro–derived elimination rate constants were in good agreement with in vivo–determined elimination rate constants in the rat. Exploring the potential of the in vitro approach for screening organic chemicals for bioaccumulation in air‐breathing organisms indicated that chemical substances that exhibit a depletion rate constant in the S9 in vitro bioassay ≥0.3 h−1 are not expected to biomagnify in rats independent of their octanol–water partitioning coefficient (KOW) or octanol–air partitioning coefficient (KOA). The high level of reproducibility achieved in the test, combined with the good agreement between in vitro–derived and in vivo–determined depuration rates, suggests that the in vitro approach in combination with a KOA‐ and KOW‐based screening approach has good potential for screening chemicals in commerce for their bioaccumulation potential in air‐breathing organisms in a cost‐effective and expedient manner, especially if the bioassay can be automated. Environ Toxicol Chem 2022;41:2565–2579. © 2022 SETAC [ABSTRACT FROM AUTHOR]