formic acid ethyl ester

Formic acid ethyl ester MAK value (1961) 100 ml/m 3 (ppm) 3.10 mg/m 3 Peak limitation (2000) Category I, excursion factor 1 Absorption through the skin (1997) H Sensitization Carcinogenicity Prenatal toxicity (1997) Pregnancy risk group C Germ cell mutagenicity BAT value Synonyms ethyl formate Chemical name (CAS) formic acid ethyl ester CAS number 109-94-4 Structural formula HCOO CH 2 CH 3 Molecular formula C 3 H 6 O 2 Molecular weight 74.08 Melting point 80 C Boiling point 54.3 C Density at 20 C 0.917 g/cm 3 Vapour pressure at 20 C 256 hpa logp ow * not specified 1 ml/m 3 (ppm) 3.07 mg/m 3 1mg/m 3 0.325 ml/m 3 (ppm) The MAK value for formic acid ethyl ester of 100 ml/m 3 was established in 1961 in analogy to the TLV value at the time. In the meantime studies have appeared which make it necessary to re-evaluate the substance. The present document is based on documentation of the American Conference of Governmental Industrial Hygienists on formic acid ethyl ester (ACGIH 1991) and an evaluation by the Food and Drug Administration (FDA 1976). * n-octanol/water distribution coefficient

182 Formic acid ethyl ester Volume 19 1 Toxic Effects and Mode of Action Formic acid ethyl ester is a liquid with a pleasant odour. The odour threshold is 31 ml/m 3. Formic acid ethyl ester in concentrations of 330 ml/m 3 caused slight irritation of the eyes of test persons, and rapidly increasing irritation of the nose, which was still severe after 4 hours (no other details, Flury and Zernik 1931). Compared with formic acid methyl ester, formic acid ethyl ester produces less pronounced irritative effects, but more pronounced narcotic effects. Formic acid ethyl ester is metabolized to ethanol and formic acid. After repeated exposure, these two substances are thought to be mainly responsible for the systemic effects. In persons who have absorbed large amounts of formic acid ethyl ester, metabolic acidosis can result from formation of formic acid and acetic acid. Formic acid ethyl ester was not found to be mutagenic in bacteria and yeasts. 2 Mechanism of Action Formic acid ethyl ester causes irritation which is attributed to the hydrolysis product formic acid. The metabolic acidosis is caused by the lowering of the ph value in blood by the formation of formic acid and acetic acid. 3 Toxicokinetics and Metabolism Formic acid ethyl ester is enzymatically hydrolysed to formic acid and ethanol. Formic acid is oxidized via the tetrahydrofolate system to form carbon dioxide which is exhaled. As a result of the lower (50 75 %) tetrahydrofolate level, in primates this oxidation process is saturated more rapidly than in rodents (Johlin et al. 1987, Kavet and Nauss 1990) so that formic acid can accumulate. Ethanol is oxidized in the liver by alcohol dehydrogenase to form acetaldehyde and by aldehyde dehydrogenase to form acetic acid. The acetic acid is oxidized via the tricarboxylic acid cycle to form mainly carbon dioxide. To a lesser extent acetic acid can also enter intermediary metabolism.

Volume 19 Formic acid ethyl ester 183 4 Effects in Man In man, formic acid ethyl ester in a concentration of 330 ml/m 3 caused slight irritation of the eyes and rapidly increasing irritation of the nose which was still present to a marked degree after 4 hours (Flury and Zernik 1931). Concentrations of 10500 ml/m 3 caused moderate, yet progressive irritation of the eyes and nose. The occlusive application of 4 % formic acid ethyl ester to the skin of volunteers did not produce visible irritation (Snyder 1992). There is no information available about the exposure concentrations which can lead to metabolic acidosis via the metabolites formic acid and acetic acid in man. It is estimated below whether accumulation of metabolites and metabolic acidosis can occur when the MAK value is observed. With formic acid ethyl ester concentrations of 100 ml/m 3 (300 mg/m 3 )andarespiratory volume of about 1.25 m 3 per hour, assuming 100 % absorption, 3000 mg formic acid ethyl ester (40.5 mmol) per 8 hours or 375 mg (5.06 mmol) per hour is absorbed. For a person of 70 kg body weight, the amount absorbed is 5.4 mg/kg body weight and hour (0.072 mmol/kg body weight and hour). Assuming complete hydrolysis, this corresponds to the same molar amounts of formic acid and ethanol. For formic acid, the metabolic rate in primates to form carbon dioxide is given as 34 mg/kg body weight (0.75 mmol/kg body weight) and hour (Johlin et al. 1987, Kavet and Nauss 1990). The rate of elimination of ethanol for women is 85 mg/kg body weight (1.15 mmol/kg body weight) and hour and for men 100 mg/kg body weight (1.35 mmol/kg body weight) and hour (Forth et al. 1992). Accumulation of the substances or their metabolites is therefore not to be expected. With a blood volume in man of 4.5 l and amounts of formic acid ethyl ester of 375 mg (5.06 mmol) absorbed per hour, the concentrations of formic acid and acetic acid formed are each 1.12 mmol/l blood. Assuming 100 % dissociation of the formic and acetic acids, 2.24 mmol H + ions per litre blood causes a decrease in the bicarbonate concentration from 24 to 21.76 mmol/l blood. A ph value of 7.38 is calculated according to the Henderson-Hasselbalch equation (pk value of bicarbonate 6.1; concentration of the undissociated acid in an open system 1.2 mmol/l), which is at the lower end of the physiological range of the blood ph value of 7.37 to 7.46 (Lentner 1984). Overloading of the body s buffer systems is, however, not to be expected as the extracellular space and other physiological buffer systems were not taken into consideration in the above calculation and an hourly bolus uptake was assumed. Therefore in persons exposed to formic acid ethyl ester concentrations of 100 ml/m 3 metabolic acidosis is not to be expected. 5 Animal experiments and in vitro Studies There are no data available on the allergenic effects of formic acid ethyl ester.

184 Formic acid ethyl ester Volume 19 5.1 Acute toxicity Exposure of mice and cats for 20 minutes to formic acid ethyl ester concentrations of 5000 ml/m 3 and more led to eye irritation. Exposure of cats to 10000 ml/m 3 for 75 minutes caused deep narcosis and, after 90 minutes, death. Exposure to 8000 ml/m 3 for 4 hours was lethal for rats (Smyth et al. 1954), and 10000 ml/m 3 was lethal for dogs (Flury and Zernik 1931). The oral LD 50 for rats was 1850 mg/kg body weight, for guinea pigs 1110 mg/kg body weight and for rabbits 2075 mg/kg body weight (FDA 1976, Sandmeyer and Kirwin 1981). In rabbits the LD 50 after dermal application was found to be over 20 ml/kg body weight (> 18000 mg/kg body weight) (Smyth et al. 1954). 5.2 Subacute, subchronic and chronic toxicity After administration of formic acid ethyl ester for 17 weeks to groups of 10 male and 10 female Osborne-Mendel rats in concentrations of 1000, 2500 or 10000 ppm with the diet, corresponding to 100, 250 or 1000 mg/kg body weight and day, adverse effects were not reported (FDA 1976). Because formic acid ethyl ester is volatile, however, administration with the diet is not a suitable method. 5.3 Local effects on skin and mucous membranes Formic acid ethyl ester was not found to cause irritation of rabbit skin (a score of 1 on a scale up to 10); in the rabbit eye, however, inflammation of the cornea was observed (4 points on a scale up to 10) (Smyth et al. 1954). 5.4 Reproductive toxicity There are no studies available of the reproductive toxicity of formic acid ethyl ester. Formic acid ethyl ester was previously classified in Pregnancy risk group D, in analogy to methanol (Henschler 1989). Methanol was re-classified in 1995 in Pregnancy risk group C (see MAK documentation for Methanol in Volume 16 of the present series). 5.5 Genotoxicity Formic acid ethyl ester was not found to be mutagenic in plate tests or suspension tests with Saccharomyces cerevisiae D4 or Salmonella typhimurium TA1535, TA1537 and TA1538 in concentrations up to 5 % with and without the addition of a metabolic activation system made from mouse, rat or monkey liver homogenates (FDA 1976).

Volume 19 Formic acid ethyl ester 185 5.6 Carcinogenicity In a short-term carcinogenicity test, two groups of 15 male and 15 female strain A mice were given a total dose of formic acid ethyl ester of 2400 or 12000 mg/kg body weight 3 times per week for 8 weeks by intraperitoneal injection. This corresponded to formic acid ethyl ester doses per injection of 100 or 500 mg/kg body weight and formic acid doses of 66 or 330 mg/kg body weight (Stoner et al. 1973). No effects on survival or the incidence of lung adenomas were detected. Other organs were not investigated. Valid long-term studies of the carcinogenicity of formic acid ethyl ester are not available. 6 Manifesto (MAK value/classification) Formic acid ethyl ester in concentrations of 330 ml/m 3 caused slight irritation of the eyes of test persons, and rapidly increasing irritation of the nose, which was still severe after 4 hours. After brief exposures to 200 ml/m 3 systemic effects (acidosis) are not to be expected. The previous MAK value of 100 ml/m 3 can, therefore, be retained. No NOEL for the irritant effects has been determined. On the basis of these data, formic acid ethyl ester is classified in Peak limitation category I and an excursion factor of 1 is established provisionally. In view of the fact that the MAK value for ethanol is 1000 ml/m 3 and the substance is classified in Pregnancy risk group C, provided the MAK value for formic acid ethyl ester of 100 ml/m 3 is observed, no danger to reproduction is to be expected from the ethanol formed from formic acid ethyl ester. Also the concentration of formic acid formed given observation of the MAK value (see Section 4; 1.12 mmol/l blood) is not expected to lead to toxic effects on reproduction as in vitro effects were first observed after formic acid concentrations of 11.8 mmol/l had been achieved (see MAK documentation for formic acid in this volume). Therefore, provided the MAK value for formic acid ethyl ester of 100 ml/m 3 is observed, toxic effects on reproduction are not to be expected. Formic acid ethyl ester is therefore classified in Pregnancy risk group C. Data for the dermal absorption of formic acid ethyl ester are not available. In analogy to formic acid methyl ester, formic acid ethyl ester is also designated with an H. Studies of the allergenic effects of formic acid ethyl ester are not available; for this reason no decision can be made on the designation of the substance with an S.

186 Formic acid ethyl ester Volume 19 7 References ACGIH (American Conference of Governmental Industrial Hygienists) (1991) Documentation of the threshold limit values and biological exposure indices, ethyl formate, ACGIH, Cincinnati, Ohio FDA (Food and Drug Administration) (1976) Evaluation of the health aspects of formic acid, sodium formate, and ethyl formate as food ingredients, FDA, Washington, DC, NTIS PB-266 282 Flury F, Zernik F (1931) Schädliche Gase (Hazardous gases) (German), J Springer, Berlin, 375 376 Forth W, Henschler D, Rummel W, Starke K (Eds) (1992) Allgemeine und spezielle Pharmakologie und Toxikologie (German), 6th edition, Wissenschaftsverlag, Mannheim, Wien, Zürich, 795 800 Henschler D (1989) Methanol, Methylacetat, Methylformiat, Ethylformiat (MAK-Werte und Schwangerschaft). Toxikologisch-arbeitsmedizinische Begründungen von MAK-Werten, 15th issue, VCH-Verlagsgesellschaft mbh, Weinheim Johlin FC, Fortman CS, Nghiem DD, Tephly TR (1987) Studies on the role of folic acid and folate-dependent enzymes in human methanol poisoning. MolPharmacol31: 557 561 Kavet R, Nauss KM (1990) The toxicity of inhaled methanol vapors. Crit Rev Toxicol 21: 21 50 Lentner (Ed.) (1984) Geigy Scientific Tables. Vol. 3, Physical chemistry, composition of blood, hematology, somatometric data. CIBA-GEIGY, Basel, 70 71 Sandmeyer EE, Kirwin Jr CJ (1981) Esters. in: Clayton GD, Clayton FE (Eds) Patty s Industrial Hygiene and Toxicology, Vol. 2A, John Wiley & Sons, New York, NY, 2263 2267 Smyth HF, Carpenter CP, Weil CS, Pozzani UC (1954) Range-finding toxicity data. List V. Arch Ind Hyg Occup Med 10: 61 68 Snyder (Ed.) (1992) Ethel Browning s Toxicity and Metabolism of Industrial Solvents. 2nd ed, Vol. 3: Alcohols and Esters, Elsevier, New York, NY Stoner GD, Shimkin MB, Kniazeff AJ, Weisburger JH, Weisburger EK, Gori GB (1973) Test for carcinogenicity of food additives and chemotherapeutic agents by the pulmonary tumor response in strain A mice. Cancer Res 33: 3069 3085 completed 07.04.1997; peak limitation category completed 25.04.00