2-(propyloxy)ethanol

Endpoint summary

Description of key information

Only minimal hematological effects were noted in rats administered the subject chemical by gavage for 6 weeks at 195 mg/kg bw/day.  Sub-chronic inhalation toxicity studies in rats indicated a clear NOAEL of 100 ppm (433 mg/m3).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

LOAEL

195 mg/kg bw/day

Study duration:

subacute

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

433 mg/m³

Study duration:

subchronic

Species:

rat

Additional information

Oral

Groups of male rats were administered the subject chemical by gavage for 5 days/week for 6 weeks at dose levels of 195, 390, 780 and 1560 mg/kg bw/day. Clinical signs of toxicity present at all dose levels included hemoglobinuria, with the frequency of observation decreasing as the study progressed suggesting acclimation to the dosing. At the two higher dose levels signs of toxicity included weakness, labored breathing, prostration and rales. Dose-dependent decreases in hemoglobin concentration and red blood cell counts were seen at all dose levels. Histologic analysis revealed congestion of the spleen at the three highest dose levels. Histologic changes in the kidney included proteinaceous casts (high dose) and hemosiderin deposition (all dose levels). Focal hemosiderin deposition was present in the liver at the highest dose level. No testicular effects were noted at any dose level tested. The primary site of toxicity in the rat was identified as the red blood cell with secondary effects noted in the spleen, kidney and liver.

Inhalation

In a key study, male and female rats were exposed by inhalation 6 hours/day, 5 days/week for 14 weeks to concentrations of 0, 100, 200 or 400 ppm of the subject chemical. Body weight gains for males at the highest dose level were slightly reduced. At the two highest dose levels, transient hemoglobinuria was observed in both sexes, with effects more pronounced in males. Reduced red blood cell counts, hemoglobin concentration and hematocrit were all indicative red blood cell hemolysis. Absolute and relative spleen weights were increased in males at the highest concentration and in females at the 200 and 400 ppm concentrations. Other than pignment deposits in the kidneys and spleen, no other gross or histopathological effects were observed. There were no effects noted on reproductive tissues from exposed rats. The NOEL in this latter study was assigned as 100 ppm. In another subchronic inahalation toxicity study in rats conducted at equivalent exposure concentrations and durations as those described above, similar toxicological effects were noted. In addition, a Functional Observational Battery, forelimb and hindlimb grip strength and histological analysis of both central and peripheral neurological tissue indicated no significant neurological effects. The NOEL for neurological effects was reported as > 400 ppm.

In supporting studies, only slight hematological changes were noted in male and female rats exposed by inhalation to the subject chemical at vapor concentrations as high as 800 ppm for 6 hours/day, 5/days/week for 2 weeks. Hematological effects noted that were concentration dependent included decreased red blood cell counts (highest dose). Changes in red blood cell morphology were noted in both sexes of rat and these changes were concentration dependent. Absolute and relative liver, kidney, brain, heart and gonad weights were normal. In another study, 12, 6 -hour exposures of male rats at 100 ppm produced no significant hematologic changes.

Relevance of Hemolytic Effects in Rodents to Humans

The hemolytic activity in certain animal species of ethylene glycol ethers such as ethylene glycol monopropyl ether and ethylene glycol monobutyl ether (2 -butoxyethanol; CAS No. 111 -76 -2) have been shown to be due to the alkoxyacetic acid metabolites, 2 -propoxyacetic acid and 2 -butoxyacetic acid (Ghanayem et al., 1987 and 1989; Foster et al., 1987; Ghanayem and Sullivan, 1993; Boatman et al., 1993). The red blood cell hemolysis seen in sensitive species such as rats and mice produces secondary effects in the liver, kidney and spleen. In the case of the most well studied of these glycol ethers, 2 -butoxyethanol, blood from humans, including the elderly and those with blood disorders, has been shown to be far less susceptible to this hemolytic effect, with human sensitivity estimated to be 150x less than that seen in the rat (Udden and Patton, 1994; Udden, 1996).

Ghanayem, B.I., Burka, L.T., and Mathews, H.B. (1987). Metabolic basis of ethylene glycol monobutyl ether (2 -butoxyethanol toxicity: Role of alcohol and aldehyde dehydrogenass. J. Pharmacol. Exp. Ther. 242:222 -231.

Ghanayem, B.I., Burka, L.T., and Mathews, H.B. (1989). Structure-activity relationships for the in vitro hematoxicity of N-alkoxyacetic acids, the toxic metabolites of glycol ethers. Chem.-Biol. Inter. 70:339 -352.

Foster, P.M.D., Lloyd, S.C. and Blackburn, D.M. (1987). Comparison of the in vivo and in vitro testicular effects produced by methoxy-, ethoxy- and n-butoxyacetic acids in the rat. Toxicology 43:17 -30.

Ghanayem, B.I. and Sullivan, C.A. (1993). Assessment of the haemolytic activity of 2 -butoxyethanol and its major metabolite, butoxyacetic acid, in various mammals including humans. Hum. Exp. Toxicol. 12:305 -311.

Boatman, R.J., Perry, L.G. and Bialecki, V.E. (1993). The in vitro hemolytic activity of propoxyacetic acid in both rat and human blood. The Toxicologist 13, 364 (Abstract 1424).

Udden, M.M. and Patton, C.S. (1994). Hemolysis and decreased deformability of erythrocytes exposed to butoxyacetic acid, a metabolite of 2 -butoxyethanol. I. Sensitivity in rats and resistance in normal humans. J. Appl. Toxicol. 14:91 -96.

Udden, M.M. (1996). Effects of butoxyacetic acid on human red blood cells. Occup. Hygiene 2:283 -290.

Justification for classification or non-classification

The primary site of toxicity in the rat, a sensitive rodent species, is the red blood cell. Effects in other organs are considered secondary to this hemolytic effect and include the spleen, kidneys and liver. It has been demonstrated that red blood cells from humans are relatively insensitive to this hemolytic effect. Thus, for purposes of classification, the subject chemical would not be classified under the EU Directive 67/548/EEC (R48, danger of serious damage to health by prolonged exposure). Similarly, the test material would not be rated for “Specific Target Organ Toxicity – Repeated Exposure” according to the EU CLP (Regulation (EC) No. 1272/2008), and UN GHS.