Abstract
Sulfur mustard (HD) undergoes hydrolysis to form various products such as thiodiglycol (TG) in biological and environmental systems. TG is a precursor in the production of HD and it is also considered as a “Schedule 2” compound (dual-use chemicals with low to moderate commercial use and high-risk precursors). Several toxicological studies on TG were conducted to assess environmental and health effects. The oral LD50 values were >5000 mg/kg in rats. It was a mild skin and moderate ocular irritant and was not a skin sensitizer in animals. It was not mutagenic in Ames Salmonella, Escherichia coli, mouse lymphoma, and in vivo mouse micronucleus assays, but it induced chromosomal aberrations in Chinese hamster ovarian (CHO) cells. A 90-day oral subchronic toxicity study with neat TG at doses of 0, 50, 500, and 5000 mg/kg/day (5 days/week) in Sprague-Dawley rats results show that there are no treatment-related changes in food consumption, hematology, and clinical chemistry in rats of either sex. The body weights of both sexes were significantly lower than controls at 5000 mg/kg/day. Significant changes were also noted in both sexes in absolute weights of kidneys, kidney to body weight ratios, and kidney to brain weight ratios, in the high-dose group. The no-observed-adverse-effect level (NOAEL) for oral toxicity was 500 mg/kg/day. The developmental toxicity conducted at 0, 430, 1290, and 3870 mg/kg by oral gavage showed maternal toxicity in dams receiving 3870 mg/kg. TG was not a developmental toxicant. The NOAEL for the developmental toxicity in rats was 1290 mg/kg. The provisional oral reference dose (RfD) of 0.4 mg/kg/day was calculated for health risk assessments. The fate of TG in the environment and soil showed biological formation of thiodiglycalic acid with formation of an intermediate ((2-hydroxyethyl)thio)acetic acid. It was slowly biodegraded under anaerobic conditions. It was not toxic to bluegill sunfish at 1000 mg/L and its metabolism and environmental and biochemical effects are summarized.
Under multinational agreements, the United States and other countries are demilitarizing their stockpiles of chemical warfare agents, including sulfur mustard (2,2′-dichlorodiethyl sulfide, HD). Sulfur mustard undergoes hydrolysis to form various products such as thiodiglycol (TG), 1,4-oxathiane, 1,4-dithiane, 2-vinylthionethanol, and mustard chlorohydrin in biological or environmental systems (D’Agostino and Provost 1988; Rosenblatt et al. 1996). Thiodiglycol has been detected as a contaminant of soil and water at certain Army installations. The U.S. Army has proposed to neutralize HD through a hydrolysis process to convert it to a biodegradable compound, TG (Lee et al. 1996). Stockpiles of HD have been disposed through the hydrolysis process (National Research Council [NRC] 1996). Thiodiglycol is a precursor in the production of HD and it is also considered as a “Schedule 2” compound (dual-use chemicals with low to moderate commercial use and high-risk precursors) within the terms of the Chemical Weapons Convention treaty (Ember 1993, 1996). It is prepared from ethylene oxide and hydrogen sulfide. It is a water-soluble liquid of low vapor pressure and has industrial use as a solvent for vat, basic, and acid dye stuff. The toxicity data on TG are limited. Therefore the U.S. Army conducted several studies to develop a toxicity data base for the evaluation of its environmental and health effects. These are mostly in reports. In this review we summarized the toxicity information on TG that we developed and from published work as well as a proposed provisional oral reference dose (RfD) (Reddy, Major, and Leach 2004).
The chemical and physical properties of TG are given here (Sax and Lewis 1989; RTECS 1991; Budavari et al. 1996; Lewis 1992; University of Oxford 2002; Von Bramer and Davis 1981).
CHEMISTRY
ENVIRONMENTAL FATE
The information on the fate of thiodiglycol in the environment is limited to a few reports. The source, fate, and toxicity of chemical warfare agent degradation products were described (Munro et al. 1999.) However, several studies were conducted in developing alternative technology to dispose of neutralized products of HD. TG was detected as a major product in environmental samples contaminated by HD. It is also detected in the soils and in ground water at certain Army installations where HD production, storage, or disposal activities were performed (Rosenblatt et al. 1996). Lee and Allen (1998) studied the environmental fate of TG and its sorption to soils. They showed the sorption was less than 10 mg/kg whereas its degradation product thiodiglycolic acid (TGA) had a maximum sorption capacity of 19.9 to 427.4 mg/kg with the different soils types studied. The fate of TG and TGA at concentrations of 20 and 50 mg/L were also studied under different conditions. Photolysis, hydrolysis, and the presence of iron oxide and aluminum oxide had little effect on the fate of TG and TGA. However, they showed biological transformation of TG to TGA with formation of an intermediate, ((2-hydroxyethyl)thio)acetic acid. This biological transformation was inhibited by an anionic poison, sodium azide, and a cationic poison, mercuric chloride. Thiodiglycol was slowly biodegraded under anaerobic conditions. The biodegradation reached 42% after 185 days (Sklyar et al. 1999). There were no reports available on TG effects in ecosystems or in plants, but some studies were conducted with HD degradation products or the neutralized products of bioreactor effluent in fish and Daphnia. These effluents were not toxic at the concentration tested (Haley et al. 1998). TG was not toxic to small bluegill sunfish at a concentration of 1000 mg/L during a 42-day observation period (Inamori et al. 1990). It also showed no effect on several crop species including beans, oats, rice, soybeans, radishes and morning glories on aerial application at 1 lb/acre (Wiswesser and Frank 1975, cited in Rosenblatt et al. 1975).
ANIMAL TOXICITY
Acute Toxicity
Acute toxicity data on thiodiglycol are limited. Smyth, Seaton, and Fischer (1941) reported oral LD50 values for male Wistar rats, 6610 mg/kg, and guinea pigs of mixed sexes, 3960 mg/kg. The toxic effects reported were similar to those of other glycols, i.e., at higher doses animals displayed sluggish depressed function, digestive tract irritation, and damage to kidneys and the liver. Angerhofer, Michie, and Leach (1998), while studying approximate lethal dose, administered neat thiodiglycol by oral gavage at a dose of 9900 mg/kg to male and female Sprague-Dawley rats and found no toxic effects or deaths, except slight lethargic symptoms in males after 1 h of dosing, which recovered within 4 h. A subcutaneous LD50 of 4 g/kg for rats and mice and an intravenous LD50 of 3 g/kg for rabbits were also reported (Anslow et al. 1948).
The dermal LD50 value of TG for rabbits was 20 ml/kg (Union Carbide 1971). Thiodiglycol produced mild irritation to skin (500 mg) and moderate irritation to eyes (500 mg) of rabbits (Carpenter and Smyth 1946; Union Carbide 1971). Manthei et al. (1997) studied the dermal irritation potentials of HD decontamination products and neat TG (98%) and HD in New Zealand white (NZW) rabbits at a concentration of 1.0 ml/kg. Samples of decontamination water byproducts showed no dermal irritation potential, whereas neat TG (98% pure), at 1 ml/kg as a control, produced mild dermal irritation in rabbits that lasted for <48 h. The positive-control HD/PE-200 (1%) samples at 1 ml/kg produced severe dermal irritation in all rabbits tested. Skin sensitizing of thiodiglycol (glyecine A) on the skin of the guinea pigs was conducted in the maximization test based on the method of Magnusson and Kligman (1969). Thiodiglycol (glycerin A, 98.4% pure), at 75% in aqueous solution, when challenged to guinea pigs after 21 days of intradermal induction showed no skin reactions in test and control animals. Based on these results, it is not considered as a skin sensitizer (BASF AG 2004).
Acute inhalation toxicity tests were conducted on neutralized HD solution for the Department of Transportation (DOT) (Mouse et al. 1977). In these experiments, HD was neutralized by hot water (90°C) hydrolysis to produce a less toxic water stream product solution, which contained mostly thiodiglycol. Rats were exposed (nose only) to this hydrolysis product (aerosol) at a concentration of 5.4 mg/L for 4 h. No overt toxicity or deaths attributed to this hydrolysis product were observed during or after the post exposure period of 14 days. The analysis of the HD hydrolysis product showed only a trace amount of HD remained after treatment. These results show that exposure to TG aerosols at 5.4 mg/L for 4 h do not appear to pose an acute inhalation hazard to rats.
Subacute and Subchronic Toxicities
Angerhofer, Michie, and Leach (1998,1999) conducted subacute (14-day) and subchronic (90-day) toxicity studies with thiodiglycol (99.9% pure) in male and female Sprague-Dawley rats. In the 14-day oral toxicity study, 48 male and 48 female rats (8 to 9 weeks old) were used. There were eight treatment groups (randomly distributed) consisting of six male and six female rats for each group. The dose levels were selected on the basis of approximate lethal dose. The doses used were 0 (negative control), 157, 313, 625, 1250, 2500, 5000, and 9999 mg/kg/day. Rats were dosed orally with neat thiodiglycol 5 days per week for 2 weeks using a stainless steel gavage needle. During the 14-day study, food consumption and body weights and any clinical signs were recorded. At the end of the 14-day period, rats were euthanized using CO2 and blood samples were collected for hematology and clinical chemistry. Gross necropsies were performed and various organs were removed at necropsy for weighing. Thiodiglycol at 9999 mg/kg produced 66% (4/6) and 83% (5/6) deaths in males and females, respectively, within 1 to 3 days, of dosing. Clinical signs observed were lethargy followed by death. Male and female rat body weights were decreased at 14-days in the high dose 9999 mg/kg/day group. Absolute kidney weights were higher than controls in the 5000 and 9999 mg/kg/day groups. In males kidney/body weight ratio in the 5000 and 9999 mg/kg/day dose groups and kidney/brain weight ratio in the 9999 mg/kg/day group were significantly higher than in controls. In females these kidney/body and kidney/brain weight ratios were higher but not significant in the 2500, 5000, and 9999 mg/kg/day dose groups. There were no meaningful changes in hematological or clinical parameters between treated and control groups. No histopathology was performed on any tissues. Based on these studies, the low-observed-adverse-effect level (LOAEL) was 5000 mg/kg/day in the 14-day study, and this dose was selected as the highest dose for the 90-day study.
A 90-day oral toxicity study of thiodiglycol was conducted in male and female Sprague-Dawley rats. Rats were randomly distributed into four groups consisting of 10 males and 10 females for each group. The dose levels were 0, 50, 500, and 5000 mg/kg/day. Rats were gavaged with neat test compound using a stainless steel feeding needle 5 days per week (excluding weekends) for 91 to 92 days. Control rats were sham treated with an empty needle. Body weights and food consumption were recorded prior to dosing and during dosing days 1, 3, 7, and thereafter weekly for the remainder of the study. Doses were adjusted weekly to reflect the changes in individual body weights. Animals were observed daily for any clinical signs. Ophthalmic examination was performed prior to dosing and a few days before termination in control and high (5000 mg/kg/day) dose groups. Urine samples also were collected from all rats at the end of the in-life study for routine and microscopic analysis. At the end of the study, blood samples were collected and various tissues (brain, liver, kidneys, spleen, adrenals, and testes/ovaries) were removed for organ weights and histopathological evaluation. There were no consistent signs of toxicity noted during daily observation. Deaths occurred during the study in control and treatment groups, but were not considered treatment related. There were no significant differences in food consumption in either sex. The body weights of both sexes were significantly lower (p < .05) than control in the 5000 mg/kg/day dose group (Tables 1 and 2).
There were no treatment-related changes in hematological and clinical chemistry parameters in rats of either sex when compared to controls. There were no gross pathological or histopathological changes in test and control. Analysis of urine collected at the end of the study revealed lower pH and higher specific gravity in males (50 and 5000 mg/kg/day) and females (500 and 5000 mg/kg/day). Microscopic examination revealed granular casts in the urine of rats receiving 5000 mg/kg/day. Significant increase or decreases were noted in males and females in absolute weights of kidneys, kidney to body weight ratio, and kidney to brain weight ratio in the highest dose group, 5000 mg/kg/day. Liver, testes, and brain to body weight ratios, in males and adrenals to body weight ratios in females of the 5000 mg/kg/day dose group were also significantly (p < .01) higher when compared to controls.
The no-observed-adverse-effect level (NOAEL) determined for oral toxicity in this study was 500 mg/kg/day and the LOAEL was determined to be 5000 mg/kg/day for the toxic effects observed in body weights and certain organ weights in both sexes.
Reproductive Toxicity
There is no reproductive toxicity studies reported.
Developmental Toxicity
Houpt, Crouse, and Angerhofer (2001,2003) studied developmental toxicity of thiodiglycol in Sprague-Dawley rats. An initial range-finding study was conducted to select suitable doses for the main developmental toxicity study. In the range-finding study, 36 positively mated female rats were randomly placed into six groups of six animals each, and one group served as a sham-negative control. The remaining five groups received neat thiodiglycol orally at dose level 0, 250, 500, 1000, 2000, 5000 mg/kg/day with gavage needle during the 5th through19th day of gestation. Cesarean sections were performed on day 20, and litters were examined. The results of this study showed that there were no consistent dose-related lesions at the necropsies. Rats receiving the high dose (5000 mg/kg/day) had lower food consumption during gestation days 5 to 9, but the body weight gains were not affected. However, the body weights of fetuses from females receiving 5000 mg/kg were significantly (p < .05) lower than any other group mean fetal weight.
On the basis of the range finding study, doses were selected for a subsequent definitive study. The doses were 0 (control), 430, 1290, and 3870 mg/kg/day. The results of this study showed that TG produced maternal toxicity in dams receiving 3870 mg/kg. At this dose body weights and food consumption were negatively affected during a certain period of gestation. Fetuses derived from those dams exhibited an increase in incidence of variations when compared to controls. However, the increase in variation was not significant. Fetal body weights at 3870 mg/kg were significantly (p < .05) lower than control. There was no increase in anomalies in all TG treated fetuses when compared to controls. It was concluded that TG is not teratogenic at the dose levels tested. The NOAEL for developmental oral toxicity in rats is 1290 mg/kg/day when administered during the major period of organ genesis. The LOAEL for developmental toxicity is 3870 mg/kg. The NOAEL for developmental toxicity is about two and a half times higher than the 90-day oral NOAEL (500 mg/kg/day) derived from the Angerhofer, Michie, and Leach (1998) study.
Chronic Toxicity
No chronic toxicity studies have been reported.
Genotoxicity
Stankowski (2001) conducted a mutagenicity assay with Salmonella typhimurium strains (TA98, TA100, TA1535, and TA1537) and Escherichia coli strain (WP2uvrA). The doses used were 33.3, 100, 333, 1000, 3330, and 5000 μg per plate with and without S9, along with concurrent vehicle and positive controls. The results showed that TG did not produce mutagenic effects at any doses up to 5000 μg per plate in any of the tester strains with or without a metabolic activation.
Erexson (2001) performed an in vivo mouse micronucleus assay with TG. In these studies, five mice were gavaged with TG in sterile water at doses of 500, 1000, and 2000 mg/kg. Then he analyzed clastogenic activity and/or disruption of mitotic activity in the micronuclei in the bone marrow. The test article TG showed no signs of clinical toxicity and no cytotoxic effects to bone marrow. This test showed that TG is not mutagenic in the mouse bone marrow micronucleus assay under the conditions studied.
Tice et al. (1997) evaluated the effects of thiodiglycol on in vitro chromosomal aberrations in Chinese hamster ovary (CHO) cells at various concentrations with and without a metabolic activation system. The test substance was dissolved in sterile water. The clastogenic activity evaluated at 3, 4, and 5 mg/ml concentrations showed a significant increase in the percentage of metaphase cells containing chromosomal aberrations. These induced chromosomal aberrations consisted of chromatid and chromosomal breaks and chromatid type rearrangements. These chromosomal aberrations also were observed without a metabolic activation system. Based on these results, the lowest effective dose was 5000 μg/ml in the absence of metabolic activation and 4000 μg/ml in the presence of S9 metabolic activation system.
Clark and Donner (1998) conducted mammalian mutagenesis assays with thiodiglycol in cultured mouse lymphoma L5178Ytk+/−cells in the presence and absence of metabolic activation. The test substance was prepared freshly in distilled water on the day of treatment. Five concentrations at 0, 50, 158, 500, 1580, and 5000 μg/ml were tested. Thiodiglycol did not induce a significant increase in mutant frequency in the presence or absence of metabolic activation.
These genotoxicity tests were conducted in accordance with the Environmental Protection Agency (EPA) Health Effects Test Guidelines in compliance with Good Laboratory Practices. These studies revealed that TG is negative in three assays (Ames test, mouse lymphoma and mouse micronucleus assay) and positive in vitro in chromosomal CHO cells. This positive response in vitro may not correspond to any change in the in vivo system.
CARCINOGENICITY
No carcinogenicity studies were reported.
TOXICOKINETICS AND METABOLISM
The toxicokinetics studies of TG were conducted by Black et al. (1993). They administered labeled TG dissolved in propylene glycol-ethanol (1:1 v/v) at doses of 0.2, 1, 5, and 328 μmol/kg (40 mg/kg) intraperitoneally to male Porton strain rats. The injection volumes were typically 1 ml/kg. Four rats per dose group were used. They found about 90% of the administered dose was excreted in urine in 0 to 24 h. There was about 3% to 4% excreted during the next 24 h and by day 8 virtually the entire dose was excreted in the urine. There was no significant excretion in the feces. The primary metabolite was thiodiglycol sulfoxide (90% of excreted activity); minor metabolites included thiodiglycol sulfone, S-(2-hydroxyethylthio)acetic acid, and S-(2-hydroxyethylsulphinyl)acetic acid. Approximately 0.5% to 1% of the original TG dose was excreted as free TG. Black et al. (1992b) studied the biological fate of sulphur mustard following intraperitoneal administration to rats and found approximately 60% of the initial dose was excreted in urine (24 h). The primary metabolites were thiodiglycol sulfoxide, 1,1′-sulfonylbis (2-S-(N-acetylcysteinyl)ethane), 1,1′-sulfonylbis(2-methylsulfinyl ethane), and/or 1-methylsulfinyl-2-(2-(methioethyl sulfonyl) ethane. Thiodiglycol was a minor metabolite. They proposed that the majority of thiodiglycol undergoes biotransformation through conjugation with glutathione and part of it undergoes hydrolysis. In another study TG was detected as a minor metabolite of sulfur mustard metabolism in male Wistar rats, where it was excreted in both free and conjugated form within 1 to 24 hrs after intravenous (i.v.) or intraperitoneal (i.p.) administration (Davison, Rozman, and Smith 1961; Roberts and Warwick 1963). Thiodiglycol has been found as a urinary metabolite in humans either accidentally or occupationally exposed to sulfur mustard (Black and Reed 1995) and from intentional exposure during the Iran-Iraq war (Wils, Hulst, and Van Laar 1985, 1988).
BIOCHEMICAL EFFECTS
Brimfield (1995) showed that TG at concentrations from 30 to 300 mM inhibited the hydrolysis of p-nitrophenol in mouse liver cytosol. He concluded that this measured effect indicates inhibition of protein serine/threonine phosphates. It has been reported that TG is oxidized by alcohol dehydrogenase (ADH) purified from horse liver or in mouse liver and human skin. They also showed different specific catalytic activities of TG with human skin ADH (classes I, II, III, and IV) (Dudley, Brimfield, and Winston 2000). Vodela et al. (1999a), studied the effect of TG on the glutathione antioxidant system in rat erythrocytes obtained from 14-day and 90-day toxicity studies (Angerhofer, Michie, and Leach 1998). In these studies neat TG (99.0%) was given orally to rats at dose 1250, 2500, and 5000 mg/kg for 14 days and 50, 500, and 5000 mg/kg for 90 days. The results of the 14 day study showed an increase (not dose related) in glutathione transferase (GSH-T) activity in male and female rats and a decrease in oxidized glutathione in female and male rats. The reduced glutathione content also showed a decrease trend in both sexes. The glutathione reductase levels were decreased in females and increased in males at 5000 mg/kg. However, there was no significant difference in the glutathione antioxidant system in rats exposed at up to 5000 mg/kg/day for 90 days. These results show that the rat erythrocyte glutathione antioxidant system is not a highly sensitive indicator for TG subchronic exposure. Vodela et al. (1999b) also studied the effects of TG on the hepatic mixed function oxidase (MFO) system and cytosolic glutathione antioxidant system in male and female rats gavaged with TG at 50, 500, and 5000 mg/kg/day for 90 days. The exposure to TG for 90 days resulted in an increase in petoxyresorufin O-dealkylation (CYP2B1/B2) activity (5000 mg/kg/day and a significant decrease in cytochrome b5 (500 and 5000 mg/kg), glutathione (500 and 5000 mg/kg), and glutathione S-transferases in all doses and glutathione peroxidase in males (5000 mg/kg). There were no significant differences in any of the parameters in female rats. These effects in MFO and glutathione antioxidant systems occurred at high dose, indicating that these parameters are not highly responsive to TG subchronic exposure.
Reiss et al. (1985) have shown that TG strongly stimulates differentiation of chick embryo myogenic cells. The myofibers formed in the presence of 0.1% of TG morphologically resemble myogenic fibers formed in vivo. Detheux, Jijakli, and Lison (1997), while studying the effect of HD on the expression of urokinase in 3T3 fibroblasts, showed that HD at 100 μM increased expression of urokinase, whereas while its degradation product TG (100 μM) did not influence the expression of urokinase (plasminogen activator), which is associated with inflammatory reactions, cell migration, tissue destruction, and remodeling.
DERMAL ABSORPTION
Dermal exposure may occur during occupational use or in use of consumer products associated with thiodiglycol. There is no information on dermal absorption of TG. Percutaneous absorption of 14C-thiodiglycol in vitro was studied, using freshly isolated pig skin in a flow-through cell system (Reifenrath and Kammen 1998; Reifenrath et al. 2002). They studied absorption of pure TG and TG contaminated or spiked into two types of soils, Yolow soil (1.9% carbon) and Tinker soil (9.5% carbon). They applied approximately 10 μg/cm2 of TG in 5 μl of acetone or 5 mg of soil spiked with an equivalent amount of TG to the excised skin mounted on a cell chamber. The radiochemical recovered from the dermis and receptor fluid was considered to be absorption of the chemical. The results show the percent absorption of TG from Yolo soil as 0.9% ± 0.8% and Tinker soils as 0.5% ± 0.5%. The absorption of TG in acetone was 20% ± 9%. In these experiments TG spiked soils were wetted with 5 μl of artificial sweat to facilitate partition of TG from soil to skin. These results demonstrate that absorption of TG from soil to skin is very low. They also measured biochemical parameters by lactate dehydrogenase profile of RNA metabolites in the dermis and mutagenic activity of receptor fluid. TG application to skin did not show significant changes in production of LDH or alteration of RNA metabolites. Thiodiglycol seems to be not hazardous to humans when exposed to skin, as very low levels of TG were absorbed from contaminated soils.
STRUCTURE-ACTIVITY RELATIONSHIP
Bausum (1998) and Bausum, Reddy, and Leach (1999) estimated toxicity values for TG on the basis of quantitative structure-activity relationships (QSARs) by employing the software package TOPKAT (Accelrys Inc., San Diego, CA). The estimated values were found to be negative for Ames mutagenicity and rodent carcinogenicity but positive for developmental toxicity potentials. Bausum (1998) also estimated a rat oral LD50 value of 2,700 mg/kg and a rat chronic oral low lethal dose (LD10) of 1700 mg/kg for TG. He also estimated acute toxicity end points for TG for skin and eye irritation potentials which were found to be negative.
HUMAN EXPOSURE
No reports were located on human exposure in the occupational environment. Consumers may be exposed through use of thiodiglycol containing products or through inhalation or dermal or oral exposure as TG may be used as an antioxidant in cosmetics (INCI 2004).
DERIVATION OF ORAL REFERENCE DOSE
The review of toxicity data available on TG indicates that this compound is not likely to pose a risk to human health and the environment. This compound is likely to be confined only to the area where HD will be neutralized and disposed. It is a water-soluble compound and has low vapor pressure. The aquatic toxicity of discharged effluent showed relatively less toxicity at tested concentration levels. TG in soil transforms rapidly to oxidative products thiodiglycolic acid. The acute toxicity data show that LD50 values are high. The oral LD50 value for male rats was 6610 mg/kg and for guinea pigs of mixed sexes was 3960 mg/kg (Smyth, Seaton, and Fischer 1941). Toxicokinetic studies showed that TG is rapidly metabolized and eliminated in 8 days. The major metabolite identified was thiodiglycol sulfoxide (Black et al. 1993). The subchronic toxicity and developmental toxicity studies were conducted in compliance with Good Laboratory Practices (GLP). There are no reports pertaining to reproductive toxicity of TG in animals. However, considerable toxicity data are available on ethylene glycol (EG) and propylene glycol (PG) (ATSDR 1997, LaKind et al. 1999). EG is used in coolants and on an airplane de-icier. Propylene glycol has been certified as GRAS (generally recognized as safe) by U.S. Food and Drug Administration and is used in a variety of cosmetics and foods. An oral reproductive NOAEL of EG at 0.5% (approximately 840 mg/kg/day), with minimal maternal toxicity, was observed in CD mice with administered in drinking water. The LOAEL of EG was approximately 1640 mg/kg/day for mice (Lamb et al. 1985). In a three-generation reproductive toxicity study in rats, the NOAEL of EG was found to be 1000 mg/kg/day (DePass et al. 1986). EG appears not to be a reproductive toxicant in rats. PG was also found not to be a reproductive toxicant. The NOAEL of PG for CD-1 mice in drinking water (at 5%) was 10, 100 mg/kg/day (Gulati, Barnes, and Welch 1985). It appears TG may be not a reproductive toxicant, as seen with other glycols. It has been reported that the developmental oral toxicity NOAEL for rats are 1290 mg/kg/day (Houpt, Crouse, and Angerhofer 2001). In subchronic study (Angerhofer, Michie, and Leach 1998), the only effects observed were on body weight and certain organ weights at the high dose, 5000 mg/kg, this is the LOAEL. There were no effects observed on female gonads in this study at the doses up to 5000 mg/kg/day; in males the ratio of testis weight to body weight was significantly reduced at this dose group. However, the body weight of male rats was significantly reduced. The absolute testes weight was not changed in any treatment group (Tables 1 and 2). Further, no changes of gonads of males and females were observed in histopathological examination. The NOAEL from subchronic oral toxicity studies (Angerhofer, Michie, and Leach 1998) 500 mg/kg is considered for the derivation of the provisional oral reference dose (RfD).
NOAEL = 500 mg/kg/day (oral subchronic toxicity studies).
The NOAEL is based on a 5-day exposure regimen per week, extrapolated to a 7-day
exposure:
An uncertainty factor of 1000 was used (10 for subchronic to chronic, 10 for animal to human extrapolation, and 10 for human sensitive populations). No modifying factors used as these studies are conducted according to Health Effects Testing Guidelines in compliance with GLP. A no reproductive potentials for propylene and ethylene glycols were reported. No effects on gonads were found in male and female rats in subchronic study at this dose (500 mg/kg) and considered it may not reproductive toxicant. Therefore, the proposed oral chronic RfD = 0.4 mg/kg/day or 400 μg/day.
Footnotes
Tables
Acknowledgements
The authors thank Dr. Howard Bausum for a critical review of the manuscript.
Disclaimer: The views, opinions, and/or findings should not be construed as official Department of Army position, policy, or decision unless designated by other official documentation.