Deposition and fate of inhaled ethylene glycol vapor and condensation aerosol in the rat

A toxicological review of the ethylene glycol series: Commonalities and differences in toxicity and modes of action

This review summarizes the hazards, exposure and risk that are associated with ethylene glycols (EGs) in their intended applications. Ethylene glycol (EG; CAS RN 107-21-1) and its related oligomers include mono-, di-, tri-, tetra-, and penta-EG. All of the EGs are quickly and extensively absorbed following ingestion and inhalation, but not by the dermal route. Metabolism involves oxidation to the mono- and dicarboxylic acids. Elimination is primarily through the urine as the parent compound or the monoacid, and, in the case of EG, also as exhaled carbon dioxide. All EGs exert acute toxicity in a similar manner, characterized by CNS depression and metabolic acidosis in humans and rodents; the larger molecules being proportionally less acutely toxic on a strict mg/kg basis. Species differences exist in the metabolism and distribution of toxic metabolites, particularly with the formation of glycolic acids and oxalates (OX) from EG and diethylene glycol (DEG); OX are not formed to a significant degree in higher ethylene glycols. Among rodents, rats are more sensitive than mice, and males more sensitive than females to the acute and repeated-dose toxicity of EG. The metabolic formation of glycolic acid (GA), diglycolic acid (DGA), and OX are associated with nephrotoxicity in humans and rodents following single and repeated exposures. However, physiological and metabolic differences in the rate of formation of GA, DGA and OX and their distribution result in EG and DEG causing embryotoxicity in rats, but not rabbits. This rodent-specific sensitivity indicates that EG and its higher oligomers are not anticipated to be embryotoxic in humans at environmentally relevant doses. None of the compounds present developmental toxicity concerns at doses that do not also cause significant maternal toxicity, nor do any of the EGs cause adverse effects on fertility. The EGs are neither genotoxic nor carcinogenic. A read-across matrix is presented, which considers the common and distinct toxicological properties of each compound. It is concluded that EGs pose no risk to human health as a result of their intended use patterns.

Inhalation and epidermal exposure of volunteers to ethylene glycol: kinetics of absorption, urinary excretion, and metabolism to glycolate and oxalate

Ethylene glycol (EG) is a widely used liquid. Limited data are published regarding inhaled EG and no data regarding transdermal EG uptake in humans. In order to gain information on the quantitative fate of EG, four male volunteers inhaled between 1340 and 1610 micromol vaporous 13C-labeled EG (13C2-EG) for 4h. Separately, three of these subjects were epidermally exposed for up to 6h to liquid 13C2-EG (skin area 66 cm2). Plasma concentrations and urinary amounts of 13C2-EG were determined by gas chromatography with mass selective detection. Additionally, plasma was assayed for 13C-labeled glycolic acid 13C2-GA) and urine for 13C2-GA and 13C-labeled oxalic acid (13C2-OA). Both EG metabolites were nephrotoxic in animals and humans and embryotoxic in rodents. 13C-labels enabled to differentiate from also determined endogenous EG, glycolic acid (GA), and oxalic acid (OA). Of 13C2-EG inhaled, 5.5+/-3.0%, 0.77+/-0.15%, and 0.10+/-0.12% were detected in urine as 13C2-EG, 13C2-GA, and 13C2-OA, respectively. The skin permeability constant of liquid EG was 2.7 x 10(-5)+/-0.5 x 10(-5)cm/h. Of the dose taken up transdermally, 8.1+/-3.2% and up to 0.4% were excreted in urine as 13C2-EG and 13C2-GA, respectively. It is calculated that equally long-lasting exposure to 10 ppm vaporous EG or wetting of both hands by liquid EG leads to about the same body burden by EG and metabolites. The amounts of GA and OA excreted daily in urine as a result of exposure (8h/day) to 10 ppm EG are about 15% and 2%, respectively, of those excreted from naturally occurring endogenous GA and OA.

Development of a Physiologically Based Pharmacokinetic Model for Ethylene Glycol and Its Metabolite, Glycolic Acid, in Rats and Humans

An extensive database on the toxicity and modes of action of ethylene glycol (EG) has been developed over the past several decades. Although renal toxicity has long been recognized as a potential outcome, in recent years developmental toxicity, an effect observed only in rats and mice, has become the subject of extensive research and regulatory reviews to establish guidelines for human exposures. The developmental toxicity of EG has been attributed to the intermediate metabolite, glycolic acid (GA), which can become a major metabolite when EG is administered to rats and mice at high doses and dose rates. Therefore, a physiologically based pharmacokinetic (PBPK) model was developed to integrate the extensive mode of action and pharmacokinetic data on EG and GA for use in developmental risk assessments. The resulting PBPK model includes inhalation, oral, dermal, intravenous, and subcutaneous routes of administration. Metabolism of EG and GA were described in the liver with elimination via the kidneys. Metabolic rate constants and partition coefficients for EG and GA were estimated from in vitro studies. Other biochemical constants were optimized from appropriate in vivo pharmacokinetic studies. Several controlled rat and human metabolism studies were used to validate the resulting PBPK model. When internal dose surrogates were compared in rats and humans over a broad range of exposures, it was concluded that humans are unlikely to achieve blood levels of GA that have been associated with developmental toxicity in rats following occupational or environmental exposures.

Identification of proximate toxicant for ethylene glycol developmental toxicity using rat whole embryo culture

The effects of ethylene glycol (EG) and its metabolite, glycolic acid (GA), were compared by culturing day 10.5 rat conceptuses for 46 h in media containing 0.5, 2.5, 12.5, 25 or 50 mM EG or GA. EG up to 50 mM was essentially without effect, whereas > or = 12.5 mM GA inhibited embryo growth and development. Craniofacial dysmorphogenesis was observed in 70% of the 12.5 mM GA embryos (0% in controls). To determine if GA toxicity in vitro was an indirect effect of medium acidification, embryos were cultured in 12.5 mM GA (pH 6.7), 12.5 mM sodium glycolate (pH 7.4), or in control medium (pH 7.4 or 6.7). The percentage of dysmorphic embryos was 67% for the 12.5 mM GA (pH 6.7) group, 58% for the sodium glycolate (pH 7.4) group, 8% in the pH 6.7 controls, and 0% in the pH 7.4 controls. These results suggest that GA, not parent EG, is the active toxicant for EG-induced developmental toxicity and that acidification of culture medium pH plays only a minor role in GA's effects in vitro. The identification of GA as the active toxicant is important for the risk assessment of EG because GA exhibits dose-rate-dependent, nonlinear kinetics in vivo.