Butoxyacetic Acid Research Articles

Occupational chronic exposure to organic solvents

Seventeen persons (2 women and 15 men), who were exposed to glycolethers in a varnish production plant, were examined according to their external and internal solvent exposure. The workers in the production plant (n = 12) were exposed to average concentrations of ethoxyethanol, ethoxyethyl acetate, butoxyethanol, 1-methoxypropanol-2, 2-methoxypropyl-1-acetate and xylene of 2.8; 2.7; 1.1; 7.0; 2.8 and 1.7 ppm. In the air of the store (n = 3) and in the laboratory (n = 2) only minor concentrations of xylene respectively xylene and ethoxyethyl acetate could be measured. Internal exposure was estimated by measuring butoxyethanol (BE) in blood as well as ethoxyacetic acid (EAA) and butoxyacetic acid (BAA) in urine samples. Urine samples were taken pre- and post-shift. As expected, the highest values were found in the varnish production. The average post shift concentrations of BE, EAA and BAA were 121.3 micrograms/l; 167.8 and 10.5 mg/l. The relatively high concentrations of EAA and BAA in pre-shift samples can be explained by the long half-lives of these metabolites. According to our findings most of the glycolethers were taken up through the skin. Comparing our results with those reported in the literature we think that a future tolerable limit value for the concentration of ethoxyacetic acid in urine should be in the order of 100 to 200 mg/l.

Metabolic and cellular basis of 2-butoxyethanol-induced hemolytic anemia in rats and assessment of human risk in vitro

Recent work in this laboratory indicated that 2-butoxyethanol (BE) causes acute hemolytic anemia in rats, and activation of BE to butoxyacetic acid (BAA), presumably through the intermediate 2-butoxyacetaldehyde (BAL), is a prerequisite for development of hematotoxicity. In the present studies, the effects of BE and its metabolites, BAL and BAA, on erythrocytes from rats and humans were investigated in vitro. Incubation of BE (up to 10 mM) with blood from male F344 rats caused no hemolysis and resulted in no metabolic alteration of BE. Further, addition of alcohol and aldehyde dehydrogenases, with their co-factors, to the incubation mixture failed to alter BE or its effect. At 20 mM, BE caused significant (P ⩽ 0.05) hemolysis of rat erythrocytes accompanied by a significant (P ⩽ 0.05) decrease in hematocrit (HCT). In contrast, incubation of BAL or BAA with rat blood caused time- and concentration-dependent swelling of red blood cells followed by hemolysis; however, BAA was significantly more efficacious than BAL. Addition of aldehyde dehydrogenase and its co-factors significantly (P ⩽ 0.05) potentiated the effect of BAL on rat erythrocytes. Further in vitro investigation of the cellular mechanisms involved in the hemolytic effect revealed that incubation of rat blood with BAA or BAL caused a time- and concentration-dependent decrease in blood ATP concentration. As observed with the hemolytic effects, the decrease in blood ATP was significantly (P ⩽ 0.05) greater with BAA than with BAL and was not induced by BE. Further, BAA caused no significant changes in the concentration of reduced glutathione and glucose-6-phosphate dehydrogenase in rat erythrocytes. Assessment of human sensitivity by incubation of human blood with BAA showed minimal swelling or hemolysis of erythrocytes with minimal decline in blood ATP levels at BAA concentrations several-fold higher than required to cause complete hemolysis of rat erythrocytes. In summary, the current studies confirm that the hemolytic effect of BE can be attributed primarily to its metabolite BAA, that hemolysis of rat erythrocytes by BAA or BAL is preceded by swelling and ATP depletion, suggesting that the erythrocyte membrane is the most likely target, and, finally, that human erythrocytes are comparatively insensitive to the hemolytic effects of BAA in vitro.

Analysis of ethylene glycol ether metabolites in urine by extractive alkylation and electron-capture gas chromatography.

Alkoxyacetic acids are metabolically formed and excreted in urine after exposure to ethylene glycol monoalkyl ethers (alkoxyethanols) or their acetate esters. This paper presents a sensitive method based on extractive alkylation for determination of alkoxyacetic acids in urine. Alkoxyacetate ions were extracted from 200 microliters urine into methylene chloride, with tetrabutylammonium acting as counter ion, and derivatized with pentafluorobenzyl bromide in a single step. After separation of the methylene chloride phase, evaporation, and dissolution of the residues in hexane the esters were analyzed by fused silica capillary column gas chromatography and electron capture detection. The esters formed were stable for at least 2 weeks at room temperature. The limit of quantification was estimated to 2 microM (corresponding to an injected amount of 2 pg) for methoxyacetic (MAA) and ethoxyacetic acid (EAA) in urine. The corresponding values for butoxyacetic acid (BAA) were 4 microM and 5 pg, respectively. The detector response was linear up to 80 microM and the formation of derivative at least up to 1 mM. The method error may be reduced by using a second alkoxyacetic acid derivative, EAA, BAA or 2-pentoxyacetic acid (PAA), as an internal standard. The sensitivity, stability, reduced number of extractions, and small volumes of reagents and sample needed make the present method useful in biomonitoring of occupational exposure to ethylene glycol ethers.

Structure-activity relationships for the in vitro hematotoxicity of N-alkoxyacetic acids, the toxic metabolites of glycol ethers

Ethylene glycol mono- n-alkyl ethers are a major class of industrial chemicals which cause a wide range of toxic effects in laboratory animals including reproductive and developmental toxicity, as well as hematotoxicity. Alkoxyacetic acids are the major metabolites of ethylene glycol ethers and are considered to be the proximate toxic metabolites. The structure-toxicity relationships of these acids are well documented in the reproductive and developmental systems. Therefore, current studies were conducted to investigate the structure-activity relationships of these acids for hematotoxicity in rat blood in vitro. Results presented here indicate that the effects of various alkoxyacetic acids on rat erythrocytes are qualitatively similar and comprise early swelling followed by hemolysis. The ranking of the activity of these acids was as follows: butoxyacetic acid (BAA)>propoxyacetic acid ≅ pentoxyacetic acid > ethoxyacetic acid>methoxyacetic acid. Furthermore, this effect of alkoxyacetic acids was associated with a parallel decrease in blood ATP levels. It is currently unknown if swelling or ATP depletion is the primary effect of these acids. In addition, at equimolar concentrations neither heptanoic, butoxypropionic, nor propoxypropionic acids caused any significant effect on rat erythrocytes in vitro. This suggests that the presence and position of the ether linkage, as it is in BAA, are critical for the development of hematotoxicity. Studies of the relationship between the toxic effect of BAA and its partitioning between erythrocytes and plasma showed that the concentration of [ 14C]BAA in plasma remained relatively constant while that in the erythrocytes increased as a function of time. This pattern of BAA distribution between plasma and erythrocytes was parallel to erythrocyte swelling. Incubation of BAA with rat blood for 30 min followed by removal of BAA by washing the erythrocytes twice and then continuing the incubation revealed that erythrocyte swelling was not reversible, however, the rate of swelling declined significantly.

Metabolic studies with diethylene glycol monobutyl ether acetate (DGBA) in the rat

1. The in vitro hydrolysis of DGBA in rat blood and its in vivo metabolism and disposition in male Sprague-Dawley rats were studied. 2. DGBA (5 mM) was hydrolysed in rat blood to diethylene glycol monobutyl ether (DGBE) with a half-life of less than 3 min. 3. 14C-DGBA was rapidly absorbed from the gastrointestinal tract and eliminated predominantly in rat urine within 24 h following oral administration at 200 or 2000 mg/kg. The major urinary metabolite was 2-(2-butoxyethoxy)acetic acid. No unchanged DGBA or DGBE was detected in rat urine at either dose level. 4. No evidence was found for excretion of 2-butoxyacetic acid, which has been shown to exert haematological effects in rats.

Aspects of biological monitoring of exposure to glycol ethers

Glycol ethers are frequently used as solvents, detergents, and emulsifiers alone or as components in industrial and consumer products. The monomethyl and monoethyl ethers of ethylene glycol, and their acetate esters, are teratogenic and embryotoxic and cause testicular damage in laboratory animals, while the monobutyl ether causes hemolysis of the red blood cells. The adverse effects are attributed to the acid metabolites methoxy-, ethoxy- and butoxyacetic acid, respectively. The glycol ethers may readily enter the body by inhalation as well as dermal uptake. Biological monitoring of exposure to glycol ethers has therefore been suggested. This paper reviews physical properties, occurrence, analysis, toxicity, and toxicokinetics of the most common glycol ethers and then discusses toxicokinetic aspects of biological monitoring. The effect of physical exercise and the relative importance of respiratory and percutaneous absorption on the internal exposure to glycol ethers are illustrated. Monitoring the acid metabolite in urine is suggested as the best index of exposure. Intra- and inter-individual variability, dose-dependent toxicokinetics, and metabolic induction and inhibition are examples of possible sources of error in the estimation of internal exposure from the urinary excretion of acid metabolite.

Percutaneous absorption of 2-butoxyethanol in man.

The percutaneous absorption of the commonly used glycol ether 2-butoxyethanol (ethylene glycol monobutyl ether) was investigated in 12 exposure experiments with five men. The subject kept two or four fingers immersed in neat butoxyethanol for 2 h. Arterialized capillary blood samples were collected from the other hand before, during, and up to 4 h after the exposure and analyzed for butoxyethanol by gas chromatography. Urine was collected for 24 h and analyzed for the metabolite butoxyacetic acid, also by gas chromatography. The presence of butoxyethanol in blood and of butoxyacetic acid in urine confirmed that butoxyethanol enters the systemic circulation in man in vivo during dermal exposure. Percutaneous uptake rates were calculated from measured blood levels of butoxyethanol with the use of kinetic parameters (clearance and volume of distribution) obtained in earlier experiments with the same subjects. The uptake rates ranged from 7 to 96 nmol.min-1.cm-2. The results indicate that persons exposing large portions of their skin to butoxyethanol are at risk of absorbing acutely toxic doses.

Determination of Urinary 2-Ethoxyacetic Acid as an Indicator of Occupational Exposure to 2-Ethoxyethanol

Abstract A biological monitoring method which can detect human exposure to glycol ethers is described. A procedure for measurement of 2-ethoxyacetic acid (EAA), a urinary metabolite of 2-ethoxyethanol (EE), has been validated. EAA is removed from the urine specimen by a methylene chloride extraction of an EAA-tetrabutyl ammonium hydrogen sulfate ion pair. The ion pair subsequently reacts with pentafluorobenzyl bromide to produce the pentafluorobenzyl derivative of EAA. The EAA derivative is separated from other co-extracted urinary constituents by packed column gas chromatography and quantitated with flame ionization detection. 2-Butoxyacetic acid and 2-methoxyacetic acid can also be separated by this procedure. The analytical range for EAA is 5 to 100 μg/ml of urine; the limit of detection is 4 μg/ml, while the limit of quantitation is 7 μg/ml. The day-to-day relative standard deviation (Sr) was better than 4.7 percent; the corresponding within-day Sr was less than 2.0 percent. The procedure has been app...

Determination of butoxyacetic acid in urine by capillary gas chromatography

A simple, rapid and reliable method is presented for the determination of butoxyacetic acid (BAA), the main metabolite of ethylene glycol monobutyl ether (Butyl Cellosolve). The urine is acidified with hydrochloric acid and passed through a cation-exchange column. BAA which is quantitatively found in the filtrate is subsequently adsorbed on XAD-4 resin. After desorption with diethyl ether an aliquot of the eluate is evaporated in a nitrogen stream and methylated with diazomethane in diethyl ether. A forty-fold enrichment is achieved by this procedure. The gas-chromatographic separation is performed on a 60 m fused silica capillary column DB-1 (100% dimethyl-polysiloxane). Flame ionization is used for detection. Pentoxyacetic acid (PAA) serves as internal standard. The detection limit of BAA in urine is 0.02 mg/l. Linearity has been tested up to 50 mg/l. The losses by the clean-up steps are between 10.0% and 22.7%. The average recovery is 100.9%. Within-series imprecision (n=10) has been determined for three concentrations and ranges between 4.8% and 12.6%.

Effect of age on the toxicity and metabolism of ethylene glycol monobutyl ether (2-butoxyethanol) in rats

Heavy production as well as the diversity of 2-butoxyethanol (BE) uses, which include preparation of products intended for household uses, pose a high risk of human exposure to BE. The current studies were designed to investigate the acute toxicity of BE and to evaluate the effect of age on BE-induced toxicity in F344 male rats. Data presented in this report show that BE causes severe acute hemolytic anemia resulting in significant increases in the concentration of free plasma hemoglobin. Secondary to the hemolytic effects, BE also caused hemoglobinuria as well as histopathologic changes in the liver and kidney. These effects of BE were dose- and time-dependent. Further, both the hemolytic effects and the secondary effects of BE were age dependent with older rats being more sensitive than younger rats. The metabolic basis of the greater susceptibility of older rats to BE-induced toxicity was investigated by comparing BE metabolism in adult (9- to 13-week-old) and young (4- to 5-week-old) rats. These studies revealed that there was a significantly higher portion of the administered dose eliminated by young rats as CO2 as compared to that eliminated by older rats. Similarly, a significantly higher portion of the administered dose was excreted in the urine of young rats. HPLC analysis of the urinary metabolites of BE in adult and young rats showed that the ratio of butoxyacetic acid (BAA)/BE-glucuronide + BE — sulfate (previously thought to reflect an activation/detoxification index of BE; see text) was significantly higher in older rats. We currently believe that the increase in the activation/detoxification index in older rats is caused by decreased degradation of BAA to CO2 (as evident by the lower percentage of the dose excreted as CO2 by older rats) and by depressed urinary excretion of BAA (as evident from the lower percentage of the dose excreted in the urine of older rats).

Percutaneous absorption, metabolism, and hemolytic activity of n-butoxyethanol

A series of studies was conducted to examine the percutaneous absorption, distribution, excretion, and hemolytic activity of n-butoxyethanol (BE). Rats receiving a subcutaneous dose of 14C-labeled BE excreted the radioactivity in the urine (79%), expired air (10%), and feces (0.5%) within 72 hr. Of the organs analyzed, thymus and spleen showed elevated specific radioactivities as compared with blood. A percutaneous application of BE on rats, under nonocclusive conditions, showed 25–29% absorption within 48 hr. Peak blook levels of BE occurred at 2 hr after application; butoxyacetic acid (BAA) was found to be the major metabolite. Comparison of in vitro skin penetration data showed the following absorption pattern of BE: hairless rat ⪢ pig > human skin. Hemolysis and associated hematological changes were noted in the rats which received single dermal applications of 260–500 mg/kg of BE. In vitro, BAA showed markedly greater hemolytic ability on rat erythrocytes than did BE. Human erythrocytes showed no hemolysis when incubated with BE or BAA at concentrations that are hemolytic to rat erythrocytes. An intravenous dose of 62.5 mg/kg of BE does not result in hemolysis or hemoglobinuria in the rat. The rat may be an animal model with increased susceptibility to the effects of BE compared with hjmans because of its rapid percutaneous absorptive ability and its greater hemolytic sensitivity.

Toxicokinetics of inhaled 2-butoxyethanol (ethylene glycol monobutyl ether) in man.

Seven male volunteers were exposed to 2-butoxyethanol at the Swedish occupational exposure limit (20 ppm or 0.85 mmol/m3) during light physical exercise (50 W) on a bicycle ergometer. The exposure took place in an exposure chamber and lasted 2 h. Expired air was collected at regular time intervals for estimation of the respiratory uptake of the solvent. Arterialized capillary blood and urine were sampled during and after the exposure period and analyzed for 2-butoxyethanol and its metabolite butoxyacetic acid. A new sensitive method for analyzing 2-butoxyethanol in biological specimens is described. 2-Butoxyethanol was derivatized with pentafluorobenzoyl chloride and analyzed by gas chromatography with electron capture detection. The respiratory uptake of 2-butoxyethanol averaged 10.1 mumol/min or 57% of the inspired amount. The concentration in blood reached a plateau level of 7.4 mumol/l. The apparent values of elimination half-time, mean residence time, total blood clearance, and steady-state volume of distribution were 40 min, 42 min, 1.2 1/min and 54 l, respectively. The amount of 2-butoxyethanol excreted in urine was less than 0.03% of the total uptake, while that of butoxyacetic acid ranged from 17 to 55%.

The metabolism of n-butyl glycidyl ether in the rat and rabbit.

[1-14C]Butyl glycidyl ether administered orally to male rats and rabbits (20 mg/kg) is rapidly absorbed and metabolized. Most of the administered compound, 87% (rat) and 78% (rabbit), is eliminated in the 0-24 urine. Major metabolites in the rat include 3-butoxy-2-hydroxypropionic acid (9%), 3-butoxy-2-acetylaminopropionic acid (23%) and butoxyacetic acid (10%). 3-Butoxy-2-hydroxypropionic acid (35%) and butoxyacetic acid (5%) are also major metabolites in the rabbit. Biotransformations of the glycidyl ether and their likely biochemical mechanisms are discussed.

Occupational chronic exposure to organic solvents

Seventeen persons (2 women and 15 men), who were exposed to glycolethers in a varnish production plant, were examined according to their external and internal solvent exposure. The workers in the production plant (n =12) were exposed to average concentrations of ethoxyethanol, ethoxyethyl acetate, butoxyethanol, 1-methoxypropanol-2, 2-methoxypropyl-1-acetate and xylene of 2.8; 2.7; 1.1; 7.0; 2.8 and 1.7 ppm. In the air of the store (n = 3) and in the laboratory (n = 2) only minor concentrations of xylene respectively xylene and ethoxyethyl acetate could be measured. Internal exposure was estimated by measuring butoxyethanol (BE) in blood as well as ethoxyacetic acid (EAA) and butoxyacetic acid (BAA) in urine samples. Urine samples were taken pre- and post-shift. As expected, the highest values were found in the varnish production. The average post shift concentrations of BE, EAA and BAA were 121.3 μg/l; 167.8 and 10.5 mg/l. The relatively high concentrations of EAA and BAA in pre-shift samples can be explained by the long half-lives of these metabolites. According to our findings most of the glycolethers were taken up through the skin. Comparing our results with those reported in the literature we think that a future tolerable limit value for the concentration of ethoxyacetic acid in urine should be in the order of 100 to 200 mg/l.