Cytotoxic effects of 2-butoxyethanol in vitro are related to butoxyacetaldehyde, an intermediate oxidation product

Ethylene glycol ethers belong to a group of solvents with a wide spectrum of applications, particularly because of their compatibility to both hydrophilic and lipophilic systems. Especially ethylene glycol monobutyl ether (2-butoxyethanol, BE) is widely used as a key ingredient in many industrial and consumer cleaning products. Therefore, the risk of human exposure and toxicity by BE as well as its potential for environmental contamination have to be carefully evaluated. By using an established kidney epithelial cell line from the proximal tubule (opossum kidney cells), we investigated the effects of BE on viability, proliferative activity, volume and the organization of the intracellular cytoskeleton of the cells. The experiments were performed with freshly used BE and BE that had been stored at room temperature in the original packing for 3 months after use. After this period of storage the latter BE contained-besides butyraldehyde and n-butanol-0.5 vol% butoxyacetaldehyde (BAL) as measured by capillary gas chromatography and mass spectrometry. Freshly used BE did not cause a toxic effect in the in vitro assays at all concentrations tested (up to 1 mg/ml). In contrast, stored BE which contained BAL reduced cell viability and mitotic activity in a dose-dependent manner. The effective concentration of stored BE causing a 50% loss in cell viability (EC(50/24h)) was calculated to be 1 mg/ml. The toxic effect of stored BE also resulted in alterations of cell morphology and a depolymerization of actin-containing stress fibers. Moreover, administration of stored BE also caused a dose-dependent cell volume increase by the uptake of water, pointing to a necrotic process. In addition, synthesized BAL with a purity of 73.5% (gas chromatography) was also tested and caused an EC(50/24h) of 15 μg/ml, which is a 70-fold lower concentration when compared with stored BE. The present study provides evidence that BE possesses only a low cytotoxic potential in vitro, whereas the corresponding BAL, an intermediate in the oxidation process of BE to butoxyacetic acid, has marked toxic effects. The occurrence of the aldehyde might explain the predominant hematological effects of BE observed in vivo.