Uptake of 10 polar organic solvents during short-term respiration

Blood absorption toxicokinetics of glycol ethers after inhalation: A human controlled study

Glycol ethers are organic solvents present in countless products for professional and domestic use. The main toxicological concerns are hematotoxicity, respiratory and reproductive toxicity. The general population can be exposed when using products containing one or several glycol ethers that evaporate or if sprayed, generate aerosols that can be inhaled. The rate at which glycol ethers enters blood following inhalation exposure are unknown in humans, and chemical risk assessors only rely on animal and in vitro toxicity studies. Propylene glycol monomethyl ether (PGME) and propylene glycol monobutyl ether (PGBE) are two examples of glycol ethers used worldwide. Our study aimed to provide human toxicokinetic data after inhalation exposure of low PGME and PGBE concentrations tested alone or in mixture. Healthy participants (n = 28) were exposed to 35 ppm (131 mg/m³) of PGME and 15 ppm (i.e., 83 mg/m³) of PGBE for 2 or 6 h. Blood was regularly collected during the exposure sessions. PGME and PGBE were immediately bioavailable in blood during exposure, and the mean absorption rates were up to 13 μg/L/min and 2.45 μg/L/min, respectively. Maximum mean blood concentration (Cmax) was 2.91 mg/L and 0.41 mg/L for PGME and PGBE. The cumulative internal doses over time (area under the curve, AUC) were 11 mg∗h/L and 1.81 mg∗h/L for PGME and PGBE. PGME and PGBE total blood uptake could possibly be higher in physically active individuals, such as workers. We recommend that glycol ethers present on the market undergo toxicological testing with the internal doses we found in our toxicokinetic study.

Solvent-based paint and varnish removers: a focused toxicologic review of existing and alternative constituents

Paint and varnish removers constitute a major potential source of organic solvent exposure to contractors and home improvement enthusiasts. Unfortunately, the leading paint remover formulations have traditionally contained, as major ingredients, chemicals classified as probable human carcinogens (eg, methylene chloride) or reproductive toxicants (eg, N-methylpyrrolidone). In addition, because of its unique toxicology (ie, hepatic conversion to carbon monoxide compounding generic solvent narcosis and arrythmogenesis), high volatility, and rigorous requirements for personal protective equipment, methylene chloride exposures from paint removers have been linked to numerous deaths involving both occupational and consumer usage. The aim of this review is to summarize the known toxicology of solvent-based paint remover constituents (including those found in substitute formulations) in order to provide health risk information to regulators, chemical formulators, and end-users of this class of products, and to highlight any data gaps that may exist.

RIFM fragrance ingredient safety assessment, 2-decanone, CAS Registry Number 693-54-9

The existing information supports the use of this material as described in this safety assessment. 2-Decanone was evaluated for genotoxicity, repeated dose toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, and environmental safety. Data from read-across analog 2-heptanone (CAS # 110-43-0) show that 2-decanone is not expected to be genotoxic. Data on read-across analog 2-heptanone (CAS # 110-43-0) provide a calculated margin of exposure (MOE) > 100 for the repeated dose toxicity and reproductive toxicity endpoints. The skin sensitization endpoint was completed using the dermal sensitization threshold (DST) for non-reactive materials (900 μg/cm²); exposure is below the DST. The phototoxicity/photoallergenicity endpoints were evaluated based on ultraviolet (UV) spectra; 2-decanone is not expected to be phototoxic/photoallergenic. For the local respiratory endpoint, a calculated MOE >100 was provided by the read-across analog 4-methyl-2-pentanone (CAS # 108-10-1). The environmental endpoints were evaluated; for the hazard assessment based on the screening data, 2-decanone is not persistent, bioaccumulative, and toxic (PBT) as per the International Fragrance Association (IFRA) Environmental Standards. For the risk assessment, 2-decanone was not able to be risk screened as there were no reported volumes of use for either North America or Europe in the 2015 IFRA Survey.

Measuring breath acetone for monitoring fat loss: Review

OBJECTIVE

Endogenous acetone production is a by-product of the fat metabolism process. Because of its small size, acetone appears in exhaled breath. Historically, endogenous acetone has been measured in exhaled breath to monitor ketosis in healthy and diabetic subjects. Recently, breath acetone concentration (BrAce) has been shown to correlate with the rate of fat loss in healthy individuals. In this review, the measurement of breath acetone in healthy subjects is evaluated for its utility in predicting fat loss and its sensitivity to changes in physiologic parameters.

RESULTS

BrAce can range from 1 ppm in healthy non-dieting subjects to 1,250 ppm in diabetic ketoacidosis. A strong correlation exists between increased BrAce and the rate of fat loss. Multiple metabolic and respiratory factors affect the measurement of BrAce. BrAce is most affected by changes in the following factors (in descending order): dietary macronutrient composition, caloric restriction, exercise, pulmonary factors, and other assorted factors that increase fat metabolism or inhibit acetone metabolism. Pulmonary factors affecting acetone exchange in the lung should be controlled to optimize the breath sample for measurement.

CONCLUSIONS

When biologic factors are controlled, BrAce measurement provides a non-invasive tool for monitoring the rate of fat loss in healthy subjects.

Physiologically based pharmacokinetic modeling of ethyl acetate and ethanol in rodents and humans

A physiologically based pharmacokinetic (PBPK) model was developed and applied to a metabolic series approach for the ethyl series (i.e., ethyl acetate, ethanol, acetaldehyde, and acetate). This approach bases toxicity information on dosimetry analyses for metabolically linked compounds using pharmacokinetic data for each compound and toxicity data for parent or individual compounds. In vivo pharmacokinetic studies of ethyl acetate and ethanol were conducted in rats following IV and inhalation exposure. Regardless of route, ethyl acetate was rapidly converted to ethanol. Blood concentrations of ethyl acetate and ethanol following both IV bolus and infusion suggested linear kinetics across blood concentrations from 0.1 to 10 mM ethyl acetate and 0.01-0.8 mM ethanol. Metabolic parameters were optimized and evaluated based on available pharmacokinetic data. The respiratory bioavailability of ethyl acetate and ethanol were estimated from closed chamber inhalation studies and measured ventilation rates. The resulting ethyl series model successfully reproduces blood ethyl acetate and ethanol kinetics following IV administration and inhalation exposure in rats, and blood ethanol kinetics following inhalation exposure to ethanol in humans. The extrapolated human model was used to derive human equivalent concentrations for the occupational setting of 257-2120 ppm ethyl acetate and 72-517 ppm ethyl acetate for continuous exposure, corresponding to rat LOAELs of 350 and 1500 ppm.

Acute effects of exposure to vapors of 3-methyl-1-butanol in humans

The secondary alcohol 3-methyl-1-butanol (3MB, isoamyl alcohol) is used, for example, as a solvent in a variety of applications and as a fragrance ingredient. It is also one of the microbial volatile organic compounds (MVOCs) found in indoor air. There are little data on acute effects. The aim of the study was to assess the acute effects of 3MB in humans. Thirty healthy volunteers (16 men and 14 women) were exposed in random order to 1 mg/m(3) 3MB or clean air for 2 h at controlled conditions. Ratings with visual analogue scales revealed slightly increased perceptions of eye irritation (P = 0.048, Wilcoxon) and smell (P < 0.0001) compared with control exposure. The other ratings were not significantly affected (irritation in nose and throat, dyspnea, headache, fatigue, dizziness, nausea, and intoxication). No significant exposure-related effects were found in blinking frequency, tear film break-up time, vital staining of the eye, nasal lavage biomarkers, lung function, and nasal swelling. In conclusion, this study suggests that 3MB is not a causative factor for health effects in damp and moldy buildings.

PRACTICAL IMPLICATIONS

3-Methyl-1-butanol (3MB) is one of the most commonly reported MVOCs in damp and moldy buildings and in occupational settings related to agriculture and composting. Our study revealed no irritation effects at 1 mg/m3, a concentration higher than typically found in damp and moldy buildings. Our study thus suggests that 3MB is not a causative factor for health effects in damp and moldy buildings.

Exposure of German residents to ethylene and propylene glycol ethers in general and after cleaning scenarios

Glycol ethers are a class of semi-volatile substances used as solvents in a variety of consumer products like cleaning agents, paints, cosmetics as well as chemical intermediates. We determined 11 metabolites of ethylene and propylene glycol ethers in 44 urine samples of German residents (background level study) and in urine samples of individuals after exposure to glycol ethers during cleaning activities (exposure study). In the study on the background exposure, methoxyacetic acid and phenoxyacetic acid (PhAA) could be detected in each urine sample with median (95th percentile) values of 0.11 mgL(-1) (0.30 mgL(-1)) and 0.80 mgL(-1) (23.6 mgL(-1)), respectively. The other metabolites were found in a limited number of samples or in none. In the exposure study, 5-8 rooms were cleaned with a cleaner containing ethylene glycol monobutyl ether (EGBE), propylene glycol monobutyl ether (PGBE), or ethylene glycol monopropyl ether (EGPE). During cleaning the mean levels in the indoor air were 7.5 mgm(-3) (EGBE), 3.0 mgm(-3) (PGBE), and 3.3 mgm(-3) (EGPE), respectively. The related metabolite levels analysed in the urine of the residents of the rooms at the day of cleaning were 2.4 mgL(-1) for butoxyacetic acid, 0.06 mgL(-1) for 2-butoxypropionic acid, and 2.3 mgL(-1) for n-propoxyacetic acid. Overall, our study indicates that the exposure of the population to glycol ethers is generally low, with the exception of PhAA. Moreover, the results of the cleaning scenarios demonstrate that the use of indoor cleaning agents containing glycol ethers can lead to a detectable internal exposure of residents.

Final report on the safety assessment of methoxyisopropanol and methoxyisopropyl acetate as used in cosmetics

Methoxyisopropanol and Methoxyisopropyl Acetate, commonly known as propylene glycol monomethyl ether (PGME) and propylene glycol monomethyl ether acetate (PGMEA), respectively, have fragrance, solvent, and viscosity-decreasing functions in cosmetics, although only Methoxyisopropanol is in current use at concentrations ranging from 4% to 35%. Methoxyisopropanol is easily absorbed into the bloodstream upon inhalation or ingestion. The acetate ester is readily metabolized to Methoxyisopropanol in the body, which is excreted unchanged in the expired breath or in the urine as free or conjugated Methoxyisopropanol, or as the primary metabolite propylene glycol. In acute oral toxicity studies, the LD(50) values of Methoxyisopropanol were 4.6 to 9.2 g/kg in rats, with similar low acute toxicity in other animal species. Inhalation exposures of rats, mice, and rabbits to 3000 ppm Methoxyisopropanol for 6 h per day for 9 days to 13 weeks produced increased relative liver weights, signs of central nervous system (CNS) depression, and in some cases, elevated serum alkaline phosphatase, alanine aminotransferase, or hepatocellular hypertrophy, but the kidneys were unaffected. The no observed adverse effect level (NOAEL) for 13-week inhalation exposures to Methoxyisopropanol was 1000 ppm in rats and rabbits. In a 90-day dermal exposure study using rabbits, 10 ml/kg undiluted Methoxyisopropanol produced narcosis and increased kidney weights and the NOAEL was 7.0 ml/kg. Chronic (2-year) daily inhalation exposures of rats and mice to 3000 ppm Methoxyisopropanol produced signs of liver toxicity (rats and mice) and some evidence of renal toxicity in rats. The only observation at 1000 ppm was dark foci of the liver in male rats. For female rats and male and female mice, the NOAEL of this chronic inhalation study was 1000 ppm Methoxyisopropanol. Methoxyisopropanol and Methoxyisopropyl Acetate were found to be nonirritating to slightly irritating and non-sensitizing in rabbit and guinea pig skin. Repeated applications of undiluted Methoxyisopropanol to the eyes of rabbits produced transient slight to moderate irritation. Pregnant rats exposed to 200 or 600 ppm Methoxyisopropanol by inhalation on gestation days 6 to 17 had no effects on maternal health or normal fetal development. Adult male rats exposed to these concentrations had no effects on the reproductive organs. Pregnant rats and rabbits exposed to 500 to 3000 ppm Methoxyisopropanol by inhalation during gestation had no significant embryotoxic or fetotoxic effects, althougth CNS depression and reduced body weight gain were observed in the 3000 ppm group. In a two-generation inhalation study using rats, continuous inhalation of 3000 ppm Methoxyisopropanol produced CNS depression, prolonged estrous cycles, reduced fertility indices, reduced pup weights and pup survival, and delayed sexual development, with a NOAEL for reproductive and developmental effects of 1000 ppm. In a continuous breeding protocol using mice, 2.0% Methoxyisopropanol in drinking water produced reduced growth, reduced relative epididymis weight, reduced relative prostate weight, and increased liver weight (females only) in offspring, with a NOAEL at a 1% concentration. Exposure of mice or rats to 300 ppm to 3000 ppm Methoxyisopropanol by inhalation produced no signs of carcinogenicity. Methoxyisopropanol was negative for mutagenicity or genetic toxicity in the bacterial reverse mutation assay (<or= 5000 microg/plate), the unscheduled DNA synthesis (UDS) assay (<or= 0.1 M), V79 Chinese hamster lung assay (>100 mM), and in the Siberian hamster embryo assay (concentrations not reported). In other assays, 100 mM Methoxyisopropanol increased sister chromatid exchanges in V79 cells. In human inhalation exposure studies of 1 to 7 h duration, 50 to 75 ppm Methoxyisopropanol vapor had an objectionable odor; 150 ppm was slightly irritating to the eyes and throat; 250 ppm produced eye irritation, lacrimation, blinking, rhinorrhea, and headache; 300 ppm was mildly irritating to the eyes, nose, and throat; 750 ppm was extremely irritating; and 2050 ppm produced extreme discomfort with severe lacrimation, blepharospasm, and painful breathing. None of the concentrations tested impaired motor coordination or performance on neurological tests. The irritating effects subsided within 15 min to 24 h of removal from the inhalation chamber. The National Institute of Occupational Safety and Health (NIOSH) recommended an 8-h time-weighted average for occupational exposure of 100 ppm. A margin of safety of 500 was determined, based on a calculated exposure from the normal use of nail polish remover products (100% absorption) and the NOAEL for reproductive toxicity. The absorption of Methoxyisopropanol through the nail is likely to be low, suggesting this margin of safety is conservative. Because Methoxyisopropanol is volatile, exposure by inhalation is possible, but the odor becomes objectionable at 50 to 75 ppm in air. The Cosmetic Ingredient Review (CIR) Expert Panel concluded that Methoxyisopropanol and Methoxyisopropyl Acetate are safe for use in nail care products in the practices of use and concentration as described in this safety assessment.

Approaches for evaluating the relevance of multiroute exposures in establishing guideline values for drinking water contaminants

In establishing the guideline values for chemical contaminants in drinking water, the contribution of inhalation and dermal routes associated with showering/bathing needs to be evaluated. The present article reviews the current approaches available for evaluating the importance of inhalation and dermal routes of exposure to drinking water contaminants (DWCs) and integrates them within a 2-tier approach. Accordingly, tier 1 would evaluate whether the dermal or inhalation route is likely to contribute to at least 10% of the dose received from ingestion of drinking water (i.e., 0.15 L-equivalent per day based on the daily water intake rate of 1.5 L/day typically used in Health Canada assessments). Based on the route-specific exposure parameters (i.e., area of skin exposed, effective skin permeability coefficient [K(p)], and air to water concentration ratio during use conditions [F(air-water)], breathing rate, duration of contact, and fraction absorbed), it was determined that for DWCs with K(p) less than 0.024 cm/hr and F(air - water) less than 0.0063, the dermal and inhalation routes during showering or bathing are unlikely to contribute significantly to the total dose. For DWCs with K(p) value equal to or greater than 0.025 cm/hr, dermal notation is implied, and as such, tier 2 calculation of L-equivalent associated with dermal exposure needs to be performed. Similarly, for DWCs with F(air-water) greater than 0.00063, inhalation notation is implied, and detailed evaluation of the L-equivalent associated with inhalation exposure (i.e., tier 2) is suggested. In general, data from human volunteer studies, observational measurements, and targeted modeling studies are useful for deriving L-equivalents, reflective of the magnitude of dose received via dermal and inhalation routes relative to the oral route. However, in resource-limited situations, these approaches can be integrated within a 2-tier approach for prioritizing and providing quantitative evaluations of the relevance of dermal and inhalation routes for developing exposure guidelines for DWCs.

Framework for evaluation of physiologically-based pharmacokinetic models for use in safety or risk assessment

Proposed applications of increasingly sophisticated biologically-based computational models, such as physiologically-based pharmacokinetic models, raise the issue of how to evaluate whether the models are adequate for proposed uses, including safety or risk assessment. A six-step process for model evaluation is described. It relies on multidisciplinary expertise to address the biological, toxicological, mathematical, statistical, and risk assessment aspects of the modeling and its application. The first step is to have a clear definition of the purpose(s) of the model in the particular assessment; this provides critical perspectives on all subsequent steps. The second step is to evaluate the biological characterization described by the model structure based on the intended uses of the model and available information on the compound being modeled or related compounds. The next two steps review the mathematical equations used to describe the biology and their implementation in an appropriate computer program. At this point, the values selected for the model parameters (i.e., model calibration) must be evaluated. Thus, the fifth step is a combination of evaluating the model parameterization and calibration against data and evaluating the uncertainty in the model outputs. The final step is to evaluate specialized analyses that were done using the model, such as modeling of population distributions of parameters leading to population estimates for model outcomes or inclusion of early pharmacodynamic events. The process also helps to define the kinds of documentation that would be needed for a model to facilitate its evaluation and implementation.

Application of a physiologically based pharmacokinetic model for isopropanol in the derivation of a reference dose and reference concentration

An interspecies physiologically based pharmacokinetic (PBPK) model describing isopropanol (IPA) and its major metabolite, acetone, was applied to perform route-to-route and cross-species dosimetry to derive reference dose (RfD) and reference concentration (RfC) values for IPA. Adult PBPK models for rats and humans were extended to simulate exposure to IPA during pregnancy and used to estimate internal dose metrics in the mother and fetus during development. Endpoints from chronic, developmental, and reproductive toxicity studies were considered for the derivation of RfDs and RfCs. Due to uncertainties in the mode of action of toxicity for IPA and acetone, the dose metric used for most responses was the total area under the blood concentration curve (AUC) for the combination of IPA and acetone. This combined dose metric provided a more conservative estimate than those based on AUCs for IPA or acetone. Peak blood concentration of IPA was the dose metric for neurobehavioral effects. The recommended RfD and RfC for IPA are 10 mg/kg/day and 40 ppm, respectively, based on decreased fetal body weights. All of the PBPK-derived RfD or RfC values for various endpoints were similar (within a factor of 3), regardless of route of exposure in the animal study.

A lung model describing uptake of organic solvents and roles of mucosal blood flow and metabolism in the bronchioles

A simple lung model (mucosal blood flow and metabolism model, MBM model) was developed to describe the uptake of organic solvents and investigate the role of mucosal blood flow and metabolism. The model separates the lung into four compartments, the peripheral bronchial tract (gas phase), the mucus layer lining the wall surface of the tract, the alveolar space (gas phase), and the alveolar blood. Solvent molecules are absorbed in the mucus layer during inhalation and released during exhalation. The deposited solvent diffuses radially into the mucosal tissue of the respiratory tract and transfers to the mucosal blood flow. To describe this behavior, a hypothetical mucosal blood flow throughout the mucus layer was used. The solvent in the mucosal tissue may be also metabolized, and a hypothetical metabolism in the mucus layer was used. The rate of the hypothetical mucosal blood flow was determined to be 5.2 ml/min based on the best fitting of previously obtained data for seven polar organic solvents. The MBM model predicts that as the blood-air partition coefficient (lambda(B)) increases from 0.1 to 20, the relative end-exhalation (E(end)) will decrease from 0.89 to 0.07, and as lambda(B) increases to 500, E(end) will increase to 0.33. After lambda(B) = 500, E(end) is predicted to decrease again, and at lambda(B) = 10000, E(end) is 0.09. The model also predicts that as lambda(B) increases from 0.1 to 10, the relative uptake (U) increases from 0.08 to 0.61, and as lambda(B) increases to 150, U decreases to 0.50. After lambda(B) = 150, U increases again, and at lambda(B) = 10,000, U is 0.8. The predictions show good agreement with values observed in human experimental studies. The MBM model predicts that uptake by the mucosal blood (U(Al)) would be equal to uptake by the alveolar blood (U(Mu)) at lambda(B) of 1000 and U(Al) is more than 90% of total uptake at lambda(B) > 10,000. The model also shows that U is significantly increased by the mucosal metabolism at lambda(B) between 50 and 5000. Especially, U in the case of CL(Mu) = 100 ml/min is higher by 0.3 than that in the nonmucosal metabolism.