Ethylene

JCHAS-892; No of Pages 3

Ethylene Toxic Tips

INTRODUCTION Chemical and Physical Description

Ethylene, C2H4, also known as ethene, is a colorless organic gas with a sweet odor composed of two double bonded carbons with two hydrogens attached to each carbon. It is a plant hormone that occurs in ripening fruit.1 Ethylene is also known as ‘‘acetene; olefiant gas; and bicarburretted hydrogen. At low temperatures it is a liquid’’.2 It is partially soluble in water with a concentration of 130 mg/L. Ethylene is an extremely flammable gas that ‘‘forms explosive mixtures with air’’.3 It is a simple asphyxiant and common air contaminant.4 The CAS registry number is 74-85-1. Its molecular weight is 28.05.5 The vapor density of ethylene is 0.978 (air = 1.00).1 Its vapor pressure is 40 mm Hg at 20 8C. The flash point of ethylene is approximately 136 8C.2 Uses and Typical Exposure Situations

Ethylene is used in the ‘‘manufacture of alcohol, mustard gas, petrochemicals, polymers, and resins’’.1,6 It is a ‘‘plant growth regulator and used commercially to accelerate the ripening of various fruits’’.1 Ethylene was formerly used as an anesthetic which may have resulted in its direct release into the environment.7 It is used frequently in ‘‘oxyethylene welding and cutting metals’’.1 Ethylene is used as a refrigerant. It is a natural product released by plants and ‘‘it is also produced by soil microorganisms ’’.6 This compound is not persistent in the environment because it has a half-life of only 1.9 days and is easily dispersed in air. ‘‘Occupational exposure to ethylene may occur through inhalation of the compound in workplaces where ethylene is produced or used’’.7 It is released from ‘‘acrylonitrile, chemical and petroleum manufacture, automotive and diesel exhaust, foundries, turbine engines, veneer drying, and tobacco smoke’’.6 ‘‘Based on its estimated bioaccumulation factor, it is expected to have a low bioaccumulation potential’’.8 Metabolism and Pharmacokinetics

‘‘The main route of exposure for ethylene is via the respiratory tract’’.3 In general, ‘‘uptake of ethylene into the body is low."9 ‘‘The majority of ethylene inhaled into the lungs is exhaled again without becoming systemically available via the blood stream. For a substance with a low solubility ratio such as ethylene, only a small percentage of the total gas is removed

1871-5532 http://dx.doi.org/10.1016/j.jchas.2016.04.006

by blood during each circulation."6 ‘‘Approximately 2% of the ethylene absorbed in the lungs is finally metabolized by the cytochrome P450 system to 2% ethylene oxide that is hydrated to glycol or conjugated to cysteine derivatives and thioesters"3, which are eliminated in the urine. ‘‘Liver microsomal mono-oxygenases transform ethylene to oxirane in rats."6 ‘‘Information on skin absorption is not available."3

PATHOPHYSIOLOGY Determinants of Toxicity

The airborne concentration of ethylene, the respiratory rate of the individual, and time of exposure to the contaminated air will determine the amount of toxicant in contact with the respiratory system. The amount of liquid ethylene in contact with the skin and length of time will determine skin exposure, although it is not absorbed through the skin readily. Mechanism of Action

Ethylene functions as a simple asphyxiant in the body.4 ‘‘Simple asphyxiants act mainly by displacing oxygen from the atmosphere which leads to decreased alveolar partial oxygen pressure and hypoxemia."10 It is ‘‘thought to act by fluidizing lipids in membranes of nerve cells, which interferes with normal physiological functions of membranes".11

CLINICAL PRESENTATION Effects Following Inhalation

Humans exposed to ethylene for short periods of time may show ‘‘signs of intoxication, including prolonged reaction time".6 ‘‘In severe cases, respiratory tract irritation can progress to acute respiratory distress syndrome (ARDS)/acute lung injury, which may be delayed in onset for up to 24 to 72 h in some cases. Ethylene is a known irritant to the respiratory tract."10 Excessive inhalation, however, impairs the nervous system.3 ‘‘Exposure to high concentrations may cause CNS depression and unconsciousness."1 In general, at lower concentrations, ethylene ‘‘exhibits only minor toxic effects and is to be considered chiefly an asphyxiant".3 Effects Following Skin and Eye Exposure

Ethylene can irritate the skin if it is in liquid form. ‘‘Local frostbite occurs after direct contact

ß Division of Chemical Health and Safety of the American Chemical Society Elsevier Inc. All rights reserved.

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with liquid ethylene." Serious health problems have not occurred from skin contact with ethylene. Ethylene can irritate the eyes and cause redness and burning. Untreated exposure to the eyes can cause eye problems.3 Effects Following Ingestion

Although irritation can occur in the gastrointestinal tract, it is ‘‘assumed that toxicologically relevant amounts of the gaseous ethylene cannot be absorbed via the digestive tract".3 Carcinogenicity

There is inadequate evidence in humans and experimental animals to classify ethylene as a carcinogen. However, ‘‘there are grounds for suspecting carcinogenic potential".3 When it is ‘‘metabolized to ethylene oxide, a known carcinogen, it forms 2-hydroxyethyl adducts with hemoglobin and DNA".12 In certain species, notably rats and mice, experiments proved ethylene to be converted into ethylene oxide. Ethylene is not classified as a human carcinogen.5 However, in a ‘‘case–control study of brain cancer among petrochemical workers, an increased risk associated with exposure to multiple chemicals, including ethylene", was reported.6

FIRST AID AND CLINICAL MANAGEMENT

‘‘In the case of local frostbite in the eye after the direct contact with the liquid form of ethylene, have the individual remove contact lens and rinse the affected eye with widely spread lids for 10 min under running water. If vision disorders occur after exposure, transport the individual to an opthamologist or hospital. In the case of local frostbite on the skin after contact with liquid ethylene, relocate the individual away from the source of danger and defrost clothes frozen to the individual’s body with lukewarm or cold water. In the case of excessive inhalation, move the individual away from the hazardous area to fresh air. Warm the individual to protect from hypothermia. If breathing difficulties ensue, administer oxygen. If the individual stops breathing, give mouth to nose resuscitation. If this is not possible, give the individual mouth to mouth resuscitation. In all cases of exposure, after administering first aid, arrange for medical evaluation’’.3

‘‘Rats were exposed to ethylene for two weeks up to 5000 ppm for 6 h/day prior to pairing, during pairing, and until the day prior to necropsy for males or until day 20 of gestation. There were no deaths, no affect on weight gain or food intake, and no evidence of adverse effects on fertility, litter size, pup weight or growth, or clinical condition."6 However, ‘‘certain findings in appropriate mutagenicity tests give ground for concern because of possible mutagenic action in human germ cells. Exposure of mice to 0.25–11 ppm over a 6–10 h period entailed an alkylation of the hemoglobin and an alkylation of the DNA in several organs."3 ‘‘Sequelae of oxygen deprivation in the unborn are controversial. Cerebral palsy, for example, previously thought to be due to acute hypoxia during labor and/or childbirth, remains poorly understood’’.10

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Reactivities and Incompatibilities

‘‘Mixtures of ethylene and aluminum chloride explode in the presence of nickel catalysts, methyl chloride, or nitromethane. Ethylene forms an explosive reaction with bromotrichloromethane. It also forms an explosive reaction with chlorine catalyzed by sunlight or UV light or in the presence of mercury(I) oxide, mercury(II) oxide, or silver oxide. Violent polymerization of ethylene is catalyzed by cooper above 400 8C/54 bar. Ethylene is incompatible with AlCl3; (CCl4 + benzoyl peroxide); (bromotrichloromethane + AlCl3); O3; CCl4; Cl2; NOx; tetrafluoroethylene; and trifluorohypofluorite. When heated to decomposition, ethylene emits acrid smoke and irritating fumes."4

EXPOSURE CONTROLS Sampling and Analysis

HANDLING AND STORAGE Accidental Release Measures

Reproductive Effects

falling over. Ethylene should be stored below 50 8C in a well-ventilated place. Ethylene should not be stored in escape routes, work rooms, or in direct proximity to these locations."3

To prevent the build-up of explosive concentrations, ‘‘keep ethylene out of a confined space. If ethylene is accidentally released, ventilate the area of the leak to disperse the gas. Stop the flow of gas. If the ethylene is from a cylinder and the leak cannot be stopped in place, remove the leaking cylinder to a safe place in the open air, and repair the leak or allow the cylinder to empty. It may be necessary to contain and dispose of ethylene as a hazardous waste."2 ‘‘Wear respiratory protection and use nonsparking tools when stopping a leak. Shut off all sources of ignition and evacuate the area. People in affected surroundings should be warned of the leak. After the leak is contained, the area should be ventilated."3 Storage Guidelines

Ethylene should be stored in a container ‘‘labeled clearly and permanently. The container should be secured in an upright position to protect against

There are no specific sampling methods for ethylene published by the Occupational Safety and Health Administration (OSHA) or the National Institute for Occupational Safety and Health (NIOSH). Ethylene can be detected in air using ‘‘gas chromatography with electron capture detection", and gas chromatography with mass spectrometry (GC–MS).6 A novel sampling technique for ethylene was reported that combines sorption tube sampling and thermal desorption. Once the samples are collected, analysis can be conducted by detection of the trace ethylene by ‘‘HWG-FT-IR (hollow waveguide Fourier transform infrared spectroscopy)".13 Exposure Guidelines

The American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value–time weighted average (TLV–TWA) is 200 ppm.5 There is no permissible exposure limit (PEL) set by OSHA for ethylene. However, OSHA says that available oxygen

Journal of Chemical Health & Safety, May/June 2016

shall be at least 19.5% of the air by volume. There is no specific NIOSH recommended exposure limit (REL) for ethylene. Since there is some concern that ethylene could be a suspected carcinogen, exposure by all routes should be carefully controlled to levels as low as possible. Since the odor of ethylene is detected between 260 and 4000 ppm, odor is not an adequate warning property to prevent over exposure to ethylene.6

PERSONAL PROTECTION

When working in areas where one has the potential to be exposed to ethylene, workplace controls are preferred over the use of personal protective equipment. ‘‘However, for some jobs, such as outside work, confined space entry, jobs done only once in a while, or jobs done while workplace controls are being installed, personal protective equipment may be appropriate."2 To protect the body, ‘‘wear flameproof, antistatic protective clothing and wear protective boots while handling gas cylinders. In an emergency respiratory protection such as a self-contained breathing apparatus must be worn. When handling the compressed gas, at least eyeglasses with side protection must be worn. When handling the liquid gas, chemical safety goggles must

be worn as well as a protective shield. Wear leather gloves to prevent frostbite injuries to the hands."3

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REFERENCES 1. O’Neil, M. J.; Heckelman, P. E.; Koch, C. B.; Roman, K. J. The Merck Index, 14th ed. Merck & Co.: Whitehouse Station, NJ, 2006, p. 649. 2. New Jersey Department of Health and Senior Services. Hazardous Substance Fact Sheet: Ethylene. Available from: http://nj.gov/health/eoh/rtkweb/documents/ fs/0878.pdf [accessed 2.09.15]. 3. GESTIS Substance Database. Ethylene. Available from: http://gestis-en. itrust.de/nxt/gateway.dll/gestis_en% 2F012710.xml?=templates&fn=print. htm&GLOBAL= G_&G_DIEXSL=GESTISPRINT.XSL [assessed 2.11.15]. 4. Lewis, R. J. Sr. Sax’s Dangerous Properties of Industrial Materials. 8th ed. Volume II; VanNostrand Reinhold: New York, NY, 1992, p. 1597. 5. American Conference of Governmental Industrial Hygienists (ACGIH). TLVs and BEIs Based on the Documentation of the Threshold Limit Values for Chemical Substances and Physical Agents & Biological Exposure Indices; ACGIH: Cincinnati, OH, 2015, p. 30. 6. Bingham, E.; Cohrssen, B. Patty’s Toxicology. 6th ed. Volume 2; John Wiley & Sons: New York, NY, 2012, pp. 49–53. 7. National Library of Medicine (NLM). Hazardous Substance Database

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(HSDB): Ethylene. http://toxnet.nlm.nih. gov/cgi-bin/sis/search2/f?./tempPewa1W:1 [accessed 2.09.15]. Environmental Protection Agency. ChemView: Ethylene. Available from: http://java.epa.gov/chemview# [accessed 2.11.15]. IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT (Multivolume work). Available at: http://monographs.iarc.fr/ENG/ Classification/index.php. p. 60–64 (1994). Hall, A. H.; Rumack, B. H. CCIS Volume 167; TOMES(R) Information System Micromedex, Inc.: Englewood, CO, 2016. American Medical Association, AMA Department of Drugs. AMA Drug Evaluations, 4th ed.; American Medical Association: Chicago, IL, 1980, p. 307. Occupational Safety and Health Administration (OSHA). Chemical Sampling Information: Ethylene. Available from: https://www.osha.gov/dts/ chemicalsampling/data/CH_240380.html [accessed 11.09.15]. Pogodina, O. A.; Pustogov, V. V.; de Melas, F.; Haberhauer-Troyer, C.; Rosenberg, E.; Puxbaum, H.; Inberg, A.; Croitoru, N.; Mizaikoff, B. Combination of sorption tube sampling and thermal desorption with hollow waveguide FT-IR spectroscopy for atmospheric trace gas analysis: Determination of atmospheric ethene at the lower ppb level. Anal Chem, 2004, 76(2), 464–468.

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