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Schmitt BG, Tobin J, McNett DA, Kim J, Durham J, Plotzke KP. Comparative pharmacokinetic studies of 14C-octamethylcyclotetrasiloxane ( 14C-D4) in Fischer 344 and Sprague Dawley CD rats after single and repeated inhalation exposure. Toxicol Lett 2022; 373:13-21. [PMID: 36332816 DOI: 10.1016/j.toxlet.2022.10.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Revised: 10/21/2022] [Accepted: 10/25/2022] [Indexed: 11/06/2022]
Abstract
Octamethylcyclotetrasiloxane (D4) is a high production volume chemical that has been subject to thorough toxicological investigations. Animal studies with the substance were conducted with either Fischer 344 or Sprague Dawley CD rats. While the pharmacokinetic fate of D4 in Fischer rats is well understood, little information exists on Sprague Dawley CD rats, where reproductive effects have been demonstrated. The objective of this study was to explore the pharmacokinetic behavior in both rats, and to identify potential strain-specific differences. Fischer and Sprague Dawley CD rats were exposed for six hours to 700 ppm of 14C-D4 vapor either with or without preceding 14-day exposure to non-radiolabeled D4. Time-course data in blood, tissues and excreta were obtained through 168 h post-exposure and analyzed for both total radioactivity and parent D4. The data confirm that repeated exposure results in increased metabolism in both rat strains, confirming the findings of earlier studies of auto-induction of CYP2B1/2 by D4. The results also indicate that D4 is subject to strain-specific pharmacokinetic behavior, and that Fischer rats appear to metabolize D4 to a greater extent than Sprague Dawley CD rats.
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Affiliation(s)
- Barbara G Schmitt
- Dow Silicones Belgium SPRL, 7170 Seneffe, Belgium; Evonik Operations GmbH, 45127 Essen, Germany.
| | - Joseph Tobin
- The Dow Chemical Company, Midland, MI 48674, United States; Du Pont, Midland, MI 48686, United States
| | - Debra A McNett
- The Dow Chemical Company, Midland, MI 48674, United States
| | - Jaeshin Kim
- The Dow Chemical Company, Midland, MI 48674, United States
| | - Jeremy Durham
- The Dow Chemical Company, Midland, MI 48674, United States
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2
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Andersen ME, Guerrero T. Assessing Modes of Action, Measures of Tissue Dose and Human Relevance of Rodent Toxicity Endpoints with Octamethylcyclotetrasiloxane (D4). Toxicol Lett 2022; 357:57-72. [PMID: 34995712 DOI: 10.1016/j.toxlet.2021.12.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 12/07/2021] [Accepted: 12/30/2021] [Indexed: 10/19/2022]
Abstract
Octamethylcyclotetrasiloxane (D4), a highly lipophilic, volatile compound with low water solubility, is metabolized to lower molecular weight, linear silanols. Toxicity has been documented in several tissues in animals following mixed vapor/aerosol exposures by inhalation at near saturating vapor concentrations or with gavage dosing in vegetable oil vehicles. These results, together with more mechanism-based studies and detailed pharmacokinetic information, were used to assess likely modes of action (MOAs) and the tissue dose measures of D4 and metabolites that would serve as key events leading to these biological responses. This MOA analysis indicates that pulmonary effects arise from direct epithelial contact with mixed vapor/aerosol atmospheres of D4; liver hypertrophy and hepatocyte proliferation arise from adaptive, rodent-specific actions of D4 with nuclear receptor signaling pathways; and, nephropathy results from silanol metabolites binding with alpha-2μ globulin (a rat specific protein). At this time, the MOAs of other liver effects - pigment accumulation and bile duct hyperplasia (BDH) preferentially observed in Sprague-Dawley (SD) rats- are not known. Hypothalamic actions of D4 delaying the rat mid-cycle gonadotrophin releasing hormone (GnRH) surge that result in reproductive effects and subsequent vaginal/uterine/ovarian tissue responses, including small increases in incidence of benign endometrial adenomas, are associated with prolongation of endogenous estrogen exposures due to delays in ovulation. Human reproduction is not controlled by a mid-cycle GnRH surge. Since the rodent-specific reproductive and the vaginal/uterine/ovarian tissue responses are not relevant for risk assessments in human populations, D4 should neither be classified as a CMR (i.e., carcinogenic, mutagenic, or toxic for reproduction) substance nor be regarded as an endocrine disruptor. Bile duct hyperplasia (BDH) and pigment accumulation in liver seen in SD rats are endpoints that could serve to define a Benchmark Dose or No-Observed-Effect-Level (NOEL) for D4.
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Affiliation(s)
- Melvin E Andersen
- Andersen ToxConsulting LLC, 424 Granite Lake Ct., Denver, NC 28037, United States.
| | - Tracy Guerrero
- American Chemistry Council Director, Silicones, Environmental, Health, and Safety Center, 700 2nd Street, NE, Washington, DC, 20002, United States.
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3
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Threshold of Toxicological Concern: Extending the chemical space by inclusion of a highly curated dataset for organosilicon compounds. Regul Toxicol Pharmacol 2021; 127:105074. [PMID: 34757112 DOI: 10.1016/j.yrtph.2021.105074] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 10/04/2021] [Accepted: 10/27/2021] [Indexed: 11/22/2022]
Abstract
The Threshold of Toxicological Concern (TTC) for non-genotoxic substances, a risk assessment tool to establish safe exposure levels for chemicals with insufficient toxicological data, is based on the 5th percentile of cumulated distributions of Point of Departures in a high amount of repeat-dose, developmental and reproductive toxicity studies, grouped by Cramer Classes. The lack of organosilicon compounds in this dataset has resulted in regulatory concerns over the applicability of the TTC concept for this chemistry. We collected publicly available, scientifically robust oral repeat-dose and DART studies for 71 organosilicon substances for inclusion in the existing TTC dataset, using criteria for evaluation of studies and derivation of points of departure analogous to the Munro and COSMOS TTC publications. The resulting 5th percentile of this dataset was 13-fold higher than the 5th percentile for Cramer Class III compounds reported by Munro (which is the default for silicon-containing substances). Both the existing TTC for Cramer Class III compounds from Munro (1.5 μg/kg bw/day) and the COSMOS TTC (2.3 μg/kg bw/day), recommended by the SCCS for cosmetics-related substances, provide a conservative and sufficiently protective approach for this class of chemistry.
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4
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Emond C, DeVito MJ, Birnbaum LS. A PBPK model describing the pharmacokinetics of γ-HBCD exposure in mice. Toxicol Appl Pharmacol 2021; 428:115678. [PMID: 34390738 PMCID: PMC8674938 DOI: 10.1016/j.taap.2021.115678] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 07/10/2021] [Accepted: 08/09/2021] [Indexed: 11/22/2022]
Abstract
The brominated flame retardant, hexabromocyclododecane (HBCD), is added-but not bound-to consumer products and is eventually found in the environment and human tissues. Commercial-grade HBCD mixtures contain three major stereoisomers, alpha (α), beta (β), and gamma (γ), that are typically at a ratio of 12%:6%:82%, respectively. Although HBCD is widely used, the toxicological effects from its exposure in humans are not clearly understood. Using a physiologically based pharmacokinetic (PBPK) model could help improve our understanding of the toxicity of HBCD. The aim of this work was to develop a PBPK model, consisting of five permeability limited compartments (i.e., brain, liver, adipose tissue, blood, and rest of the body), to evaluate the pharmacokinetics of γ-HBCD in C57BL/6 mice. Physiological parameters related to body size, organ weights, and blood flow were taken from the literature. All partition coefficients were calculated based on the log Kow. The elimination in urine and feces was optimized to reflect the percent dose eliminated, as published in the literature. Compared with data from the literature for brain, liver, blood, and adipose tissue, the model simulations accurately described the mouse data set within 1.5-fold of the data points. Also, two examples showing the utility of the PBPK model supplement the information regarding the internal dose that caused the health effects observed during these studies. Although this version of the PBPK model expressly describes γ-HBCD, more efforts are needed to clarify and improve the model to discriminate between the α, β, and γ stereoisomers.
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Affiliation(s)
- Claude Emond
- BioSimulation Consulting Inc., Newark, DE, USA; School of Public Health, Department of Environmental and Occupational Health, University of Montreal, Quebec, Canada.
| | - Michael J DeVito
- National Institute of Environmental Health Sciences, National Toxicology Program, Research Triangle Park, NC, USA
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5
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Kenyon EM, Eklund C, Pegram RA, Lipscomb JC. Comparison of in vivo derived and scaled in vitro metabolic rate constants for several volatile organic compounds (VOCs). Toxicol In Vitro 2020; 69:105002. [PMID: 32946980 DOI: 10.1016/j.tiv.2020.105002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 08/26/2020] [Accepted: 09/13/2020] [Indexed: 10/23/2022]
Abstract
Metabolic rate parameters estimation using in vitro data is necessary due to numbers of chemicals for which data are needed, trend towards minimizing laboratory animal use, and limited opportunity to collect data in human subjects. We evaluated how well metabolic rate parameters derived from in vitro data predict overall in vivo metabolism for a set of environmental chemicals for which well validated and established methods exist. We compared values of VmaxC derived from in vivo vapor uptake studies with estimates of VmaxC scaled up from in vitro hepatic microsomal metabolism studies for VOCs for which data were available in male F344 rats. For 6 of 7 VOCs, differences between the in vivo and scaled up in vitro VmaxC estimates were less than 2.6-fold. For bromodichloromethane (BDCM), the in vivo derived VmaxC was approximately 4.4-fold higher than the in vitro derived and scaled up VmaxC. The more rapid rate of BDCM metabolism estimated based in vivo studies suggests other factors such as extrahepatic metabolism, binding or other non-specific losses making a significant contribution to overall clearance. Systematic and reliable utilization of scaled up in vitro biotransformation rate parameters in PBPK models will require development of methods to predict cases in which extrahepatic metabolism and binding as well as other factors are likely to be significant contributors.
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Affiliation(s)
- Elaina M Kenyon
- Center for Computational Toxicology and Exposure, U.S. EPA, Office of Research and Development, Research Triangle Park, NC, United States.
| | - Christopher Eklund
- Center for Computational Toxicology and Exposure, U.S. EPA, Office of Research and Development, Research Triangle Park, NC, United States
| | - Rex A Pegram
- Center for Computational Toxicology and Exposure, U.S. EPA, Office of Research and Development, Research Triangle Park, NC, United States
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Moreau M, Nong A. Evaluating hexabromocyclododecane (HBCD) toxicokinetics in humans and rodents by physiologically based pharmacokinetic modeling. Food Chem Toxicol 2019; 133:110785. [DOI: 10.1016/j.fct.2019.110785] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Revised: 08/20/2019] [Accepted: 08/22/2019] [Indexed: 10/26/2022]
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7
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Metabolism and disposition of [ 14 C]-methylcyclosiloxanes in rats. Toxicol Lett 2017; 279 Suppl 1:98-114. [DOI: 10.1016/j.toxlet.2017.05.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Revised: 03/31/2017] [Accepted: 05/02/2017] [Indexed: 11/18/2022]
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Abstract
Octamethylcyclotetrasiloxane (D4) is a volatile cyclic siloxane used primarily as a monomer or intermediate in the production of some silicon-based polymers widely used in industrial and consumer applications and may be present as a residual impurity in a variety of consumer products. A robust toxicological data set exists for D4. Treatment-related results from a chronic inhalation study conducted in rats are limited to mild effects on the respiratory tract, increases in liver weight, increases in the incidence of uterine endometrial epithelial hyperplasia, and a dose-related trend in the incidence of endometrial adenomas. The observed increases in liver weight appear to be related to the induction of hepatic metabolizing enzymes, similar to those that are induced in the presence of phenobarbital. D4 is not mutagenic or genotoxic in standard in vitro and in vivo tests; therefore, the benign uterine tumors observed likely occur by a non-genotoxic mechanism. Results from mechanistic studies suggest that D4 has very weak estrogenic and antiestrogenic activity, as well as dopamine agonist-like activity. In rats, D4 exposure delays ovulation and hypothesized to prolong exposure of the uterine endometrium to endogenous estrogen. Though this mode of action may play a role in the development of benign uterine tumors in the rat, it is considered unlikely to occur in the human due to the marked differences in cycle regulatory mechanisms. Reproductive effects were observed following D4 exposure in female rats. These effects appear to be related to a delay of the luteinizing hormone (LH) surge, which fails to induce complete ovulation in the rat. However, based on differences in ovulatory control in rats and humans, it appears these effects may be species-specific with no risk or relevance to human health. Results from pharmacokinetic studies indicate that dermal absorption of D4 is limited, due to its high volatility and, if absorbed via dermal, oral or inhalation exposure, the majority of D4 is rapidly cleared from the body, indicating bioaccumulation is unlikely.
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Affiliation(s)
| | - Tracy Greene
- Ramboll Environ US Corporation, Monroe, LA, United States
| | | | - Robinan Gentry
- Ramboll Environ US Corporation, Monroe, LA, United States
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Campbell JL, Andersen ME, Van Landingham C, Gentry R, Jensen E, Domoradzki JY, Clewell HJ. Refinement of the oral exposure description in the cyclic siloxane PBPK model for rats and humans: Implications for exposure assessment. Toxicol Lett 2017; 279 Suppl 1:125-135. [PMID: 28408153 DOI: 10.1016/j.toxlet.2017.04.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Revised: 04/05/2017] [Accepted: 04/06/2017] [Indexed: 11/25/2022]
Abstract
The multi-compound, and multi-dose (MC-MD) route physiologically based pharmacokinetic (PBPK) model for cyclic siloxanes reported by McMullin et al. (2016) brought together the series of models for octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) in rat and human into a unified code structure that would allow simulation of both compounds following the inhalation and dermal routes of exposure. The refined MC-MD PBPK model presented here expands upon this effort to include representation of rat kinetic data in plasma, tissues and exhaled breath for the parent compounds after oral bolus administration. Additional refinements were made with regards to hepatic induction of metabolism in the liver and allometric scaling of rate constants for the deep tissue compartments which will allow the MC-MD model to be used in uncertainty analysis. Overall, the refined MC-MD model was able to reproduce both parent D4 and D5 kinetic data in rat and human after inhalation exposure (rat and human) or dermal exposure (human). The inclusion of sequestered (i.e., lipid associated) oral absorption into plasma after oral bolus dosing successfully described the lack of exhalation as well as the initial distribution of siloxane to the liver which was higher than simple partitioning from plasma would allow. The refined MC-MD PBPK model presented here can be incorporated into uncertainty and variability analysis and cross-species dosimetry for both D4 and D5.
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Affiliation(s)
- Jerry L Campbell
- Ramboll Environ, 6 Davis Drive, Research Triangle Park, NC 27709, United States.
| | - Melvin E Andersen
- ScitoVation, LLC, 6 Davis Drive, Research Triangle Park, NC 27709, United States
| | | | - Robinan Gentry
- Ramboll Environ, 3107 Armand St., Monroe, LA 71201, United States
| | - Elke Jensen
- Dow Corning Corporation, 2200 W. Salzburg Road, Midland, MI 48686, United States
| | - Jean Y Domoradzki
- Dow Corning Corporation, 2200 W. Salzburg Road, Midland, MI 48686, United States
| | - Harvey J Clewell
- ScitoVation, LLC, 6 Davis Drive, Research Triangle Park, NC 27709, United States
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10
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Biological relevance of effects following chronic administration of octamethylcyclotetrasiloxane (D4) in Fischer 344 rats. Toxicol Lett 2017; 279 Suppl 1:42-53. [PMID: 28109826 DOI: 10.1016/j.toxlet.2017.01.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 01/13/2017] [Accepted: 01/15/2017] [Indexed: 11/21/2022]
Abstract
Octamethylcyclotetrasiloxane (D4) is a cyclic siloxane primarily used as a monomer or intermediate in the production of silicone polymers resulting in potential exposure of workers, and potential low level inhalation or dermal exposure for consumers and the general public. Following a two-year inhalation toxicity study with D4 in rats, increases in uterine endometrial cystic hyperplasia and adenomas were observed at the highest concentration of D4 administered (700ppm). No other neoplasms were increased with D4 treatment. In addition, chronic inhalation exposure of rats to D4 induced changes in relative liver and kidney weights, and produced a chronic nephropathy. This manuscript examines the biological relevance and possible modes of action for the effects observed in the F344 rat following chronic inhalation exposure to D4. D4 is not genotoxic and appears to exert its effects through a nongenotoxic mode of action. An alteration in the estrous cycle in the aging F344 rat was the most likely mode of action for the observed uterine effects following chronic inhalation exposure. Data support the conclusion that D4 acts indirectly via a dopamine-like mechanism leading to alteration of the pituitary control of the estrous cycle in aging F344 rats with a decrease in progesterone and an increase in the estrogen/progesterone ratio most likely induced by a decrease in prolactin concentration. D4 also inhibited the pre-ovulatory LH surge causing a delay in ovulation, persistent follicles and thus a prolonged exposure to elevated estrogen in the adult Sprague Dawely rat. A lengthening of the estrous cycle in the F344 rat with an increase in endogenous estrogen was also induced by D4 inhalation. Although the mode of action responsible for induction of uterine adenomas in the female F344 rat has not been clearly confirmed, the subtlety of effects on the effects of D4 on cyclicity may prevent further assessment and definition of the mode of action. The occurrence of uterine endometrial adenoma in the rat is not relevant for human risk characterization because (1) there are differences in ovulatory cycle regulation in rats compared to humans, (2) cystic hyperplasia without atypia in women is not a cancer precursor, and (3) there is no endometrial lesion in women that is directly analogous to endometrial adenoma in the rat. The effects of D4 on liver are due to a phenobarbital-like mechanism that results in induction of cytochrome P450 and other enzymes of xenobiotic biotransformation. The liver effects are adaptive and not adverse. Kidney findings included chonic progressive nephropathy, a rat lesion that has no counterpart in the human and that should not be used in human risk assessment.
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11
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Garner CE, Liang S, Yin L, Yu X. Physiologically based pharmacokinetic modeling for 1-bromopropane in F344 rats using gas uptake inhalation experiments. Toxicol Sci 2015; 145:23-36. [PMID: 25634537 DOI: 10.1093/toxsci/kfv018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
1-Bromopropane (1-BP) was introduced into the workplace as an alternative to ozone-depleting solvents and increasingly used in manufacturing industry. The potential exposure to 1-BP and the current reports of adverse effects associated with occupational exposure to high levels of 1-BP have increased the need to understand the mechanism of 1-BP toxicity in animal models as a mean of understanding risk in workers. Physiologically based pharmacokinetic (PBPK) model for 1-BP has been developed to examine 2 metabolic pathway assumptions for gas-uptake inhalation study. Based on previous gas-uptake experiments in the Fischer 344 rat, the PBPK model was developed by simulating the 1-BP concentration in a closed chamber. In the model, we tested the hypothesis that metabolism responsibilities were shared by the p450 CYP2E1 and glutathione (GSH) conjugation. The results showed that 2 metabolic pathways adequately simulated 1-BP closed chamber concentration. Furthermore, the above model was tested by simulating the gas-uptake data of the female rats pretreated with 1-aminobenzotrizole, a general P450 suicide inhibitor, or d,l-buthionine (S,R)-sulfoximine, an inhibitor of GSH synthesis, prior to exposure to 800 ppm 1-BP. The comparative investigation on the metabolic pathway of 1-BP through the PBPK modeling in both sexes provides critical information for understanding the role of p450 and GSH in the metabolism of 1-BP and eventually helps to quantitatively extrapolate current animal studies to human.
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Affiliation(s)
- C Edwin Garner
- *Lovelace Respiratory Research Institute, Albuquerque, New Mexico 87108 and Department of Environmental Health Science, College of Public Health, University of Georgia, Athens, Georgia 30602
| | - Shenxuan Liang
- *Lovelace Respiratory Research Institute, Albuquerque, New Mexico 87108 and Department of Environmental Health Science, College of Public Health, University of Georgia, Athens, Georgia 30602
| | - Lei Yin
- *Lovelace Respiratory Research Institute, Albuquerque, New Mexico 87108 and Department of Environmental Health Science, College of Public Health, University of Georgia, Athens, Georgia 30602
| | - Xiaozhong Yu
- *Lovelace Respiratory Research Institute, Albuquerque, New Mexico 87108 and Department of Environmental Health Science, College of Public Health, University of Georgia, Athens, Georgia 30602
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Xu S, Kozerski G, Mackay D. Critical review and interpretation of environmental data for volatile methylsiloxanes: partition properties. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:11748-11759. [PMID: 25238034 DOI: 10.1021/es503465b] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Volatile methylsiloxanes (VMS) enter the environment through industrial activities and the use of various consumer products. Reliable measurements of environmental partition properties for these compounds are critical for accurate prediction of their environmental fate, distribution, transport, exposure and potential effects. In this study, the measured partition properties including air/water (K(AW)), octanol/water (K(OW)), and octanol/air partitioning coefficients (K(OA)), soil organic carbon/water distribution coefficient (K(OC)), and biological medium/fluid partition coefficients, and their temperature dependence were critically reviewed. Based on these results, organosilicon compounds such as methylsiloxanes are expected to behave differently in the environment compared to conventional hydrophobic environmental contaminants, as a result of their inherent characteristics related to molecular size and capacity for different types of molecular interactions that control partitioning. The differences are critical and need to be taken into consideration in environmental exposure and risk analyses of these compounds.
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Affiliation(s)
- Shihe Xu
- Dow Corning Corporation, Health and Environmental Sciences, Auburn, Michigan 48686, United States
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13
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Johnson W, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler DC, Marks JG, Shank RC, Slaga TJ, Snyder PW, Andersen FA. Safety Assessment of Cyclomethicone, Cyclotetrasiloxane, Cyclopentasiloxane, Cyclohexasiloxane, and Cycloheptasiloxane. Int J Toxicol 2012; 30:149S-227S. [DOI: 10.1177/1091581811428184] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Cyclomethicone (mixture) and the specific chain length cyclic siloxanes (n = 4-7) reviewed in this safety assessment are cyclic dimethyl polysiloxane compounds. These ingredients have the skin/hair conditioning agent function in common. Minimal percutaneous absorption was associated with these ingredients and the available data do not suggest skin irritation or sensitization potential. Also, it is not likely that dermal exposure to these ingredients from cosmetics would cause significant systemic exposure. The Cosmetic Ingredient Review Expert Panel concluded that these ingredients are safe in the present practices of use and concentration.
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Affiliation(s)
- Wilbur Johnson
- Senior Scientific Analyst/Writer, Cosmetic Ingredient Review
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