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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]

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]

Abstract: To support the goals articulated in the vision for exposure and risk assessment in the twenty‐first century, we highlight the application of a thermodynamic chemical activity approach for the exposure and risk assessment of chemicals in the environment. The present article describes the chemical activity approach, its strengths and limitations, and provides examples of how this concept may be applied to the management of single chemicals and chemical mixtures. The examples demonstrate that the chemical activity approach provides a useful framework for 1) compiling and evaluating exposure and toxicity information obtained from many different sources, 2) expressing the toxicity of single and multiple chemicals, 3) conducting hazard and risk assessments of single and multiple chemicals, 4) identifying environmental exposure pathways, and 5) reducing error and characterizing uncertainty in risk assessment. The article further illustrates that the chemical activity approach can support an adaptive management strategy for environmental stewardship of chemicals where “safe” chemical activities are established based on toxicological studies and presented as guidelines for environmental quality in various environmental media that can be monitored by passive sampling and other techniques. Environ Toxicol Chem 2018;37:1235–1251. © 2018 The Authors. Published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The article focuses on investigating the sources and environmental fate of halomethoxybenzenes (HMBs), compounds with attributes of persistence and potential for long-range transport, bioaccumulation, and toxic effects. It is discussed that the study reveals the widespread atmospheric dispersal of HMBs, emphasizing their continent-scale transport primarily through evaporation from water sources, shedding light on their origins and environmental pathways.

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]

In vivo dietary bioaccumulation experiments for 85 hydrophobic organic substances were conducted to derive the in vivo gastrointestinal biotransformation rates, somatic biotransformation rates, bioconcentration factors (BCF), and biomagnification factors (BMF) for improving methods for bioaccumulation assessment and to develop an in vivo biotransformation rate database for QSAR development and in vitro to in vivo biotransformation rate extrapolation. The capacity of chemicals to be biotransformed in fish was found to be highly dependent on the route of exposure. Somatic biotransformation was the dominant pathway for most chemicals absorbed via the respiratory route. Intestinal biotransformation was the dominant metabolic pathway for most chemicals absorbed via the diet. For substances not biotransformed or transformed exclusively in the body of the fish, the BCF and BMF appeared to be closely correlated. For substances subject to intestinal biotransformation, the same correlation did not apply. We conclude that intestinal biotransformation and bioavailability in water can modulate the relationship between the BCF and BMF. This study also supports a fairly simple rule of thumb that may be useful in the interpretation of dietary bioaccumulation tests; i.e., chemicals with a BMFL of <1 tend to exhibit BCFs based on either the freely dissolved (BCFWW,fd) or the total concentration (BCFWW,t) of the chemical in the water that is less than 5000. [ABSTRACT FROM AUTHOR]