Percutaneous toxicokinetic and repeated cutaneous contact studies with ethylene glycol monohexyl ether

Ethylene oxide derived glycol ethers: A review of the alkyl glycol ethers potential to cause endocrine disruption

The 'ethylene glycol ethers' (EGE) are a broad family of solvents and hydraulic fluids produced through the reaction of ethylene oxide and a monoalcohol. Certain EGE derived from methanol and ethanol are well known to cause toxicity to the testes and fetotoxicity and that this is caused by the common metabolites methoxy and ethoxyacetic acid, respectively. There have been numerous published claims that EGE fall into the category of 'endocrine disruptors' often without substantiated evidence. This review systematically evaluates all of the available and relevant in vitro and in vivo data across this family of substances using an approach based around the EFSA/ECHA 2018 guidance for the identification of endocrine disruptors. The conclusion reached is that there is no significant evidence to show that EGE target any endocrine organs or perturb endocrine pathways and that any toxicity that is seen occurs by non-endocrine modes of action.

Disposition and metabolism of ethylene glycol 2-ethylhexyl ether in Sprague Dawley rats, B6C3F1/N mice, and in vitro in rat hepatocytes

Ethylene glycol 2-ethylhexyl ether (EGEHE) is a solvent used in a variety of applications.We report disposition and metabolism of EGEHE following a single gavage or dermal administration of 50, 150 or 500 mg/kg [¹⁴C]EGEHE in rats and mice and in vitro in rat hepatocytes.EGEHE was cleared rapidly in rat hepatocytes (half-life ∼4 min) with no sex difference.EGEHE was well- and moderately absorbed following oral administration (rats: 80-96%, mice: 91-95%) and dermal application (rats: 25-37%, mice: 22-24%), respectively, and rapidly excreted in urine.[¹⁴C]EGEHE-derived radioactivity was distributed to tissues (oral: 2.3-7.2%, dermal: 0.7-2.2%) with liver and kidney containing the highest levels in both species.EGEHE was extensively metabolised with little to no parent detected in urine. The alkoxyacetic acid metabolite, which has previously been shown to mediate toxicities of other shorter-chain ethylene glycol ethers, was not detected.There were no apparent dose, species or sex differences in disposition and metabolism of EGEHE, except that the exhaled volatile compounds were greater in mice (19-20%) compared with rats (<2%).These studies address a critical gap in the scientific literature and provide data that will inform future studies designed to evaluate toxicity of EGEHE.

Urinary excretion of toluene diisocyanates in rats following dermal exposure

Toluene diisocyanates (TDI) are commonly used in polyurethane (PU)-related products. TDIs have been documented as the leading cause of occupational asthma. Skin exposure to TDI in the workplace is common. However, no studies in the literature have investigated the exact biomarker concentration profile for skin TDI absorption through any in vivo animal studies. In this study a rat model was used to evaluate the TDI skin absorption to explore the dose-response pattern and to determine the kinetic characteristics of urinary toluene diamine (U-TDA) during skin exposure. TDIs were topically exposed on the dorsum of rat skin at 0.2%, 1% and 5%. Consecutive urine samples were collected for 6 days and U-TDA were analysed using GC/ECD. It was demonstrated in this rat study that absorption of 2,4- and 2,6-TDI through skin contact is possible. A clear dose-dependent skin absorption relationship for 2,4- and 2,6-TDI was demonstrated by the AUC, Cmax findings and accumulative amounts (r > or = 0.968). U-TDA concentration profiles in 6-day consecutive urine samples fit well in the first-order kinetics, although higher order kinetics could not be excluded for the high dose. The apparent half-lives for excretory urinary TDA were about 20 h consistent at various skin exposures. It is concluded that skin absorption of TDI was confirmed in a rat model and a clear dose-dependent skin absorption relationship for 2,4- and 2,6-TDI was demonstrated. Excretory U-TDA concentrations in 6-day consecutive urine samples via skin exposure reveal the first-order kinetics and the half-lives were about 20 h.