Occupational Exposure Limit Proposal for Ethyl Lactate
(University of Texas at Houston)
Ethyl lactate (CAS Registry Number 97-64-3), a member of the lactate esters class, is used in food additives, in biochemicals, pharmaceuticals, cosmetics, and as a high purity liquid solvent in the semiconductor industry. Ethyl Lactate conforms to the formula CH3CH(OH)COOCH2CH3 and has a molecular weight of 118.3. At room temperature it is a clear, colorless liquid with low volatility, having a mild, characteristic odor (MSDS, 2002). Conventional solvents used in positive photoresist are predominantly ethylene glycol derived ethers. A number of photoresist formulations using "less toxic" solvents are available today for use in semiconductor manufacture. Ethyl lactate is one of the solvents being used as a replacement for the conventional solvents, principally 2-ethoxyethyl acetate (Boggs, 1989).
Ethyl lactate is a widely used chemical in the semiconductor industry (Vaughn, 2002). Its popularity, as well as its chemical properties make it a potential toxicant in the occupational setting. This group of chemicals has been studied extensively in standard toxicity tests. Many lactate esters (including ethyl lactate) are moderate to severe eye irritants and may also be mild skin irritants. "At high doses (2500 mg/m3) a decrease in body weight, a decrease in food consumption, a decrease in blood glucose in males, decrease in urea levels, decrease in liver weight, and an increase in testes weight were observed in rats" (Clary, Feron, and van Velthuijsen, 1998). The calculated RDso (RDso is the dose that causes a 50 percent reduction in respiratory rate) for mice is 750 - 800 mg/m for ethyl lactate (Montelius, 1999). Lactate esters are metabolized to form lactic acid in humans. "As an industrial chernical, lactic acid toxicity is related primarily to its acidity. Concentrated lactic acid is a potential eye and skin irritant" (Clary, Feron, and van Velthuijsen, 2001).
Even though ethyl lactate is used in well ventilated and well enclosed processes, new employees who are not familiar with this chemical, tend to be apprehensive. Certain tasks, such as changing out bottles, can result in exposure via the inhalation route (Vaughn, 2002).
Although it is extensively used in industry, the Occupational Safety and Health Administration (OSHA) has not established an Occupational Exposure Limit (OEL) for ethyl lactate. While industrial hygienists continue to monitor potential occupational exposures to this chemical, having no industry wide OEL makes quantification of exposures difficult. In the absence of a formal OEL from a regulatory or authoritative source it becomes necessary to identify an "internal OEL" to differentiate acceptable from unacceptable exposures (Mulhausen and Damiano, 1998).
The purpose of this paper will be to do a detailed occupational health and toxicology review of the relevant literature published on this ethyl lactate,, and propose a internal OEL to be potentially used for ethyl lactate. The end result of this research will be of value to health and safety professionals in the semiconductor manufacturing sector. Besides being useful in the industry, the effort of making a toxicologic review and proposing an OEL is a very valuable educational exercise for me as a graduate student. In order to successfully address this issue, it will be important for me to familiarize myself with the semiconductor industry and the processes involving the use of ethyl lactate, as well as procedures commonly used to set OELs.. References
Boggs, A. A Comparative Risk Assessment of Casting Solvents for Positive Photoresist. Applied Industrial Hygiene, vol. 4, no.4, 81-87. (1989).
Clary, J. J., Feron, V. J.,van Velthuijsen, J. A. Safety Assessment of Lactate Esters. Regulatory Toxicology and Pharmacology 27, 88-97. (1998).
Clary, J. J., Feron, V. J.,van Velthuijsen, J. A. Evaluation of Potential Neurotoxic. Effects of Occupational Exposure to (L)-Lactates. Regulatory Toxicology and Pharmacology 33, 21-28. (2001).
Material Safety Data Sheet (MSDS). Ethyl lactate.
Montelius. J./editor. Scientific basis for Swedish Occupational Standards: XX (Arbete och Halso; 1999:26) Stockholm: National Institute for Working Life, 75-82. ( 1 999)
Mulhausen, J. R., Damiano, J. Mulhausen J.R.;Damiano J.: A Strategy for Assessing and Managing Occupational Exposures. American Industrial Hygiene Association, Fairfax, VA (1998).
Vaughn, M. Personal communication. (7 Nov. 2002).
[abstract as .pdf]