Methyl ethyl ketone
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INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 143
METHYL ETHYL KETONE
This report contains the collective views of an international group of experts and does not necessarily represent the decisions or the stated policy of the United Nations Environment Programme, the International Labour Organisation, or the World Health Organization.
Published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organisation, and the World Health Organization
First draft prepared by Dr R.B. Williams, United States Environmental Protection Agency World Health Orgnization
Geneva, 1993
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coordination of laboratory testing and epidemiological studies, and promotion of research on the mechanisms of the biological action of chemicals.
WHO Library Cataloguing in Publication Data Methyl ethyl ketone.
(Environmental health criteria ; 143)
1.Butanones - adverse effects 2.Butanones - toxicity 3.Occupational exposure I.Series
ISBN 92 4 157143 8 (NLM Classification: QV 633) ISSN 0250-863X
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR METHYL ETHYL KETONE 1. SUMMARY
1.1. Properties and analytical methods 1.2. Sources of exposure and uses
1.2.1. Production and other sources 1.2.2. Uses and loss to the environment 1.3. Environmental transport and distribution 1.4. Environmental levels and human exposure 1.5. Kinetics and metabolism
1.6. Effects on experimental species 1.7. Effects on humans
1.7.1. MEK alone
1.7.2. MEK in solvent mixtures
1.8. Enhancement of the toxicity of other solvents
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES AND ANALYTICAL METHODS 2.1. Identity
2.2. Chemical and physical properties 2.3. Conversion factors
2.4. Sampling and analytical methods 2.4.1. General considerations 2.4.2. Air
2.4.3. Water
2.4.4. Solids
2.4.5. Biological materials
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE 3.1. Natural occurrence
3.2. Production levels, processes and uses 3.2.1. World production
3.2.2. Production processes 3.2.3. Other sources
3.2.4. Uses
3.3. Release into the environment
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION 4.1. Transport in the environment
4.2. Bioaccumulation and biodegradation 5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels 5.1.1. Air
5.1.2. Water 5.1.3. Foodstuffs
5.2. General population exposure 5.3. Occupational exposure
5.4. Peri-occupational exposure 6. KINETICS AND METABOLISM
6.1. Absorption
6.1.1. Percutaneous absorption 6.1.2. Inhalation absorption 6.1.3. Ingestion absorption
6.1.4. Intraperitoneal absorption 6.2. Distribution
6.3. Metabolic transformation 6.3.1. Animal studies 6.3.2. Human studies 6.4. Elimination and excretion 6.5. Turnover
6.6. Metabolic interactions 6.7. Mechanisms of action
7. EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS 7.1. Acute exposure
7.1.1. Lethal doses 7.1.2. Non-lethal doses
7.1.3. Skin and eye irritation 7.2. Repeated exposures
7.3. Neurotoxicity
7.3.1. Behavioural testing 7.3.2. Histopathology 7.4. Developmental toxicity
7.5. Mutagenicity and related end-points 7.6. Carcinogenicity
8. EFFECTS ON HUMANS
8.1. General population exposure 8.2. Effects of short-term exposure 8.3. Skin irritation and sensitization 8.4. Occupational exposure
8.4.1. MEK alone
8.4.2. MEK in solvent mixtures 8.5. Carcinogenicity
9. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD 9.1. Microorganisms
9.2. Aquatic organisms 9.3. Terrestrial organisms
9.3.1. Animals 9.3.2. Plants
10. ENHANCEMENT OF THE TOXICITY OF OTHER SOLVENTS BY MEK 10.1. Hexacarbon neuropathy
10.1.1. Introduction 10.1.2. Animal studies 10.1.3. Human studies
10.1.3.1 Solvent abuse
10.1.3.2 Occupational exposure 10.2. Haloalkane solvents
10.2.1. Studies in animals
10.2.2. Potentiation of haloalkane toxicity in humans 11. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT
11.1. Human health risks
11.1.1. Non-occupational exposure 11.1.2. Occupational exposure 11.1.3. Relevant animals studies 11.2. Effects on the environment
12. RECOMMENDATIONS FOR THE PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
12.1. Human heath protection 12.2. Environmental protection 13. FURTHER RESEARCH
REFERENCES
APPENDIX 1. Conversion factors for various solvents RESUME
RESUMEN
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR METHYL ETHYL KETONE
Members
Professor E.A. Bababunmi, Postgraduate Institute for Medical Research and Training, College of Medicine, Ibadan, Nigeria
Dr P.E.T. Douben, Department of Ecotoxicology, Institute for Forestry and Nature Research, Arnhem, The Netherlands
Professor C.L. Galli, Toxicology Laboratory, Institute of
Pharmacological Sciences, University of Milan, Milan, Italy (Chairman)
Dr R.F. Hertel, Fraunhofer Institute of Toxicology and Aerosol Research, Hanover, Germany
Dr H.P.A. Illing, Head of Toxicology, Health and Safety Executive, Bootle, United Kingdom
Professor A. Massoud, Department of Community, Environmental &
Occupational Health, Faculty of Medicine, Ain Shams University, Abbassia, Egypt (Joint Rapporteur)
Dr K. Morimoto, Division of Chem-Bio Informatics, National Institute of Hygienic Sciences, Setagaya-ku, Tokyo, Japan
Dr V. Riihimäki, Institute of Occupational Health, Helsinki, Finland Dr E. de Souza Nascimento, University of Sao Paulo, Sao Paulo, Brazil Dr H. Tilson, Neurotoxicology Division, Health Effects Research
Laboratory, US Environmental Protection Agency, Research Triangle Park, USA
Dr R.B. Williams, Office of Research and Development, US Environmental Protection Agency, Washington D.C., USA (Joint Rapporteur)
Secretariat
Dr P.G. Jenkins, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland
Dr E. Smith, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland
NOTE TO READERS OF THE CRITERIA MONOGRAPHS
Every effort has been made to present information in the criteria monographs as accurately as possible without unduly delaying their publication. In the interest of all users of the Environmental Health Criteria monographs, readers are kindly requested to communicate any errors that may have occurred to the Director of the International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland, in order that they may be included in corrigenda.
* * *
A detailed data profile and a legal file can be obtained from the International Register of Potentially Toxic Chemicals, Palais des Nations, 1211 Geneva 10, Switzerland (Telephone No. 7988400 or 7985850).
ENVIRONMENTAL HEALTH CRITERIA FOR METHYL ETHYL KETONE
A WHO Task Group on Environmental Health Criteria for Methyl Ethyl Ketone (MEK) met at the World Health Organization, Geneva, from 9 to 13 September 1991. Dr E. Smith welcomed the participants on
behalf of Dr M. Mercier, Director, IPCS, and on behalf of the heads of the three IPCS cooperating organizations (UNEP/ILO/WHO). The Task Group reviewed and revised the draft monograph and made an evaluation of the risks for human health and the environment from exposure to MEK.
The first draft of this monograph was prepared by Dr R.B.
Williams, Office of Research and Development, US Environmental Protection Agency. Dr E. Smith and Dr P.G. Jenkins, both members of the IPCS Central Unit, were responsible for the scientific content and technical editing, respectively.
The efforts of all who helped in the preparation and finalization of the monograph are gratefully acknowledged.
ABBREVIATIONS
ALT alanine transferase
BEI biological exposure index DCB dichlorobenzene
DMA dimethylamine DMF dimethylformamide
DNPH 2,4-dinitrophenyl hydrazine EBK ethyl n-butyl ketone
ECD electron-capture detection FID flame ionization detection FT-IR Fourier transform infrared GC gas chromatography
GLDH glutamate dehydrogenase
GPT glutamic-pyruvic transaminase GST glutathione-S-transferase 2,5-HD 2,5-hexanedione
2,5-Hpdn 2,5-heptanedione
HPLC high-performance liquid chromatography HS headspace
IR infrared
LC50 median lethal concentration LDQ lowest detectable quantity MAC maximum allowable concentration MBK methyl n-butyl ketone
MEK methyl ethyl ketone MIBK methyl isobutyl ketone MS mass spectrometry
NADPH reduced nicotinamide adenine dinucleotide phosphate
OCT ornithine carbamyl transferase PID photo-ionization detection SRT simple reaction time
STEL short-term exposure limit TLV threshold limit value TWA time-weighted average UV ultraviolet
1. SUMMARY
1.1 Properties and analytical methods
Methyl ethyl ketone (MEK) is a clear, colourless, volatile,
highly flammable liquid with an acetone-like odour. It is stable under ordinary conditions but can form peroxides on prolonged storage; these may be explosive. MEK can also form explosive mixtures with air. It is very soluble in water, miscible with many organic solvents, and forms azeotropes with water and many organic liquids. In the atmosphere MEK produces free radicals, which may lead to the formation of
photochemical smog.
Several analytical methods exist for the measurement of MEK at environmental levels in air, water, biological samples, waste and other materials. In the more sensitive methods, MEK is trapped and concentrated either on a solid sorbant or as a derivative of
2,4-dinitrophenylhydrazine (DNPH). Absorbed MEK and other volatile organic compounds are desorbed, separated by gas chromatography and measured with a mass spectrometer or flame ionization detector.
Derivatized MEK is separated from related compounds by high performance liquid chromatography and measured by ultraviolet
absorption. In media such as solid waste and biological materials, MEK must first be separated from the substrate by methods such as solvent extraction or steam distillation. High concentrations of MEK in air can be monitored continuously by infrared absorption. Detection limits are 3 µg/m3 in air, 0.05 µg/litre in drinking-water, 1.0 µg/litre in other types of water, 20 µg/litre in whole blood and 100 µg/litre in urine.
1.2 Sources of exposure and uses
1.2.1 Production and other sources
Recent values for annual industrial manufacture (in thousands of tonnes) are: USA, 212 to 305; western Europe, 215; Japan, 139. In addition to its manufacture, sources of MEK in the environment are exhaust from jet and internal combustion engines, and industrial activities such as gasification of coal. It is found in substantial amounts in tobacco smoke. In the USA, production of MEK by engines is no more than 1% of its deliberate manufacture. In smog episodes,
photochemical production of MEK and other carbonyls from free radicals can be far greater than direct anthropogenic emission. MEK is produced biologically and has been identified as a product of microbial
metabolism. It has also been detected in a wide diversity of natural products including higher plants, insect pheromones, animal tissues, and human blood, urine and exhaled air. It is probably a minor product of normal mammalian metabolism.
1.2.2 Uses and loss to the environment
The major use of MEK, application of protective coatings and adhesives, reflects its excellent characteristics as a solvent. It also is used as a chemical intermediate, as a solvent in magnetic tape production and the dewaxing of lubricating oil, and in food
processing. In addition to industrial applications, it is a common ingredient in consumer products such as varnishes and glues. In most applications MEK is a component of a mixture of organic solvents.
Losses to the environment are mainly to the air and result principally from solvent evaporation from coated surfaces. MEK is released into water as a component of the waste from its manufacture and from a variety of industrial operations. It has been detected in natural waters and could have originated from microbial activities and from atmospheric input, as well as from anthropogenic pollution.
1.3 Environmental transport and distribution
MEK is highly mobile in the natural environment and subject to rapid turnover. It is very soluble in water and evaporates readily into the atmosphere. In air MEK is subject to rapid photochemical decomposition and is also synthesized by photochemical processes. In water containing free halogens or hypohalites, it reacts to form a haloform that is more toxic than the original compound. MEK is distributed by both air and water, but does not accumulate in any individual compartment, and does not persist long where there is
microbial activity. It is rapidly metabolized by microbes and mammals.
There is no evidence of bioaccumulation. MEK occurs naturally in some clover species and is produced by fungi to concentrations that affect the germination of some plants.
1.4 Environmental levels and human exposure
General population exposure to low levels of MEK is widespread.
In minimally polluted air, the concentration is less than 3 µg/m3 (< 1 ppb), but a level of 131 µg/m3 (44.5 ppb) has been measured under conditions of heavy air pollution. Away from industrial areas where MEK is manufactured or used, major sources may be vehicle
exhaust and photochemical reactions in the atmosphere. Cigarettes and other tobacco products that are burned contribute to individual
exposure (20 cigarettes contain up to 1.6 mg). Volatilization of MEK from building materials and consumer products can pollute indoor air to levels far above adjacent outdoor air. MEK concentrations in
exposed natural waters are rarely above 100 µg/litre (100 ppb) and are usually below a detectable level. Trace amounts of MEK, however, have been detected widely in drinking-water (approximately 2 µg/litre) and presumably originated as solvent leached from cemented joints of plastic pipe. Although MEK is a normal component of many foods, concentrations are low and food consumption cannot be considered a significant source of population exposure. Average daily per capita intake in the USA via foodstuffs is estimated to be 1.6 mg, most coming from white bread, tomatoes and Cheddar cheese. In addition to MEK present naturally, foods may contain MEK from cheese ripening, aging of poultry meat, cooking or food processing, or by absorption from plastic packaging materials.
Industrial exposure to moderate levels of MEK is widespread.
However, in some regions workers in small factories (e.g., shoe factories, printing plants and painting operations) are exposed to much higher concentrations due to inadequate ventilation. In these factories, exposure is usually to a mixture of solvents including
n-hexane.
1.5 Kinetics and metabolism
Absorption of MEK is rapid via dermal contact, inhalation, ingestion and intraperitoneal injection. It is rapidly transferred into the blood and thence to other tissues. The solubility of MEK appears similar for all tissues. The clearance of MEK and its metabolites in mammals is essentially complete in 24 h. It is metabolized in the liver where it is mainly oxidized to
3-hydroxy-2-butanone and subsequently reduced to 2,3-butanediol. A small portion may be reduced to 2-butanol, but 2-butanol is rapidly oxidized back to MEK. The bulk of MEK taken into the mammalian body enters the general metabolism and/or is eliminated as simple compounds such as carbon dioxide and water. Excretion of MEK and its
recognizable metabolites is mainly through the lungs, although small amounts are excreted via the kidneys.
MEK increases microsomal cytochrome P-450 enzyme activities. This enhancement of enzymatic activity and thus of the body's potential for metabolic transformation may well be the mechanism by which MEK
potentiates the toxicity of haloalkane and aliphatic hexacarbon solvents.
1.6 Effects on experimental species
MEK has low to moderate acute, short-term and chronic toxicity for mammals. LD50 values for adult mice and rats are 2 to 6 g/kg body weight, death occurring within 1 to 14 days following a single oral dose. Average vapour concentrations producing lethality in rats following a single exposure are around 29 400 mg/m3 (10 000 ppm), although guinea-pigs survived a 4-h exposure to this concentration.
The lowest acute oral dose modifying body structure is 1 g/kg body weight, which damaged kidney tubules in the rat. Inhalation by rats of 74 mg/m3 (25 ppm) for 6 h produced measurable changes in behaviour which persisted for several days. Repeated exposure of rats to 14 750 mg/m3 (5000 ppm) (6 h/day, 5 days/week) produced no lethality, had only minor effects on growth and structure, and there were no neuropathological changes. There was no evidence that MEK produced neuropathological changes in chickens, cats or mice exposed to 3975 mg/m3 (1500 ppm) for periods of up to 12 weeks. Transient effects on behaviour or neurophysiology were detected following repeated exposure of rats and baboons to concentrations as low as 295-590 mg/m3 (100 to 200 ppm).
There is evidence for a low level of fetotoxicity without any maternal toxicity at 8825 mg/m3 (3000 ppm), but no evidence for
embryotoxic or teratogenic effects at lower exposure levels. Repeated exposure of pregnant rats to 8825 mg/m3 induced in their offspring a small but significant increase in skeletal abnormalities of types that occurred at low incidences among the unexposed population.
Although examined in a number of conventional mutagenicity test systems, the only evidence of mutagenicity was provided by a study on aneuploidy in the yeast Saccharomyces cerevisiae.
MEK is not acutely toxic to fish or aquatic invertebrates and LC50 values range from 1382 to 8890 mg/litre.
MEK has an inhibiting effect on the germination of several plant species, even at levels occurring naturally. The growth of aquatic algae is inhibited.
Compared with natural background levels, relatively high
concentrations of MEK have been used for fumigation under experimental conditions. It is moderately effective as a fumigant against the
Caribbean fruit fly and is a very effective attractant for tsetse flies. Levels of MEK up to 20 mg/litre retard biodegradation but do not stop the process entirely. At levels of up to 100 mg/litre, MEK is biostatic to a variety of bacteria. At higher concentrations (1000 mg/litre or more) inhibition of the growth of bacteria and protozoa occurs.
1.7 Effects on humans
1.7.1 MEK alone
Exposure to 590 mg/m3 (200 ppm) had no significant effect in a variety of behavioural and psychological tests. Short-term exposure to MEK alone does not appear to be a significant hazard, either
occupationally or for the general public. Experimental exposure to a concentration of 794 mg/m3 (270 ppm) for 4 h/day had little or no effect on behaviour, and a 5-min contact with liquid MEK produced no more than a temporary whitening of the skin. There is only one
non-occupational report of acute toxicity to MEK. This resulted from accidental ingestion and appeared to produce no lasting harm. There is no evidence that occupational MEK exposure has resulted in death.
There have been two reports of chronic occupational poisoning and one questionable report of acute occupational poisoning. In one of the chronic cases, exposure to 880-1770 mg/m3 (300-600 ppm) resulted in dermatoses, numbness of fingers and arms, and various symptoms such as headache, dizziness, gastrointestinal upset, and loss of appetite and weight. This paucity of incidents of reputed poisoning by MEK alone reflects both the low toxicity of MEK and the fact that it is most commonly used not on its own but as a component of solvent mixtures.
1.7.2 MEK in solvent mixtures
Exposure to solvent mixtures containing MEK has been associated with some reduction in nerve conduction velocity, memory and motor alterations, dermatoses and vomiting. In one longitudinal study,
consecutive measurements of simple reaction time showed an improvement in performance in parallel with decreasing concentrations of MEK to one tenth the original values (which were up to 4000 mg/m3 for certain routine tasks).
1.8 Enhancement of the toxicity of other solvents
MEK potentiates the neurotoxicity of hexacarbon compounds
( n-hexane, methyl- n-butylketone and 2,5-hexanedione) and the liver and kidney toxicity of haloalkane (carbon tetrachloride and
trichloromethane) solvents.
The potentiation of the neurotoxic effects of hexacarbons has been demonstrated for all three hexacarbons in animals. The peripheral neuropathies observed in humans followed changes in the formulations of solvents to which they had been exposed, either voluntarily or occupationally. The mechanism by which this potentiation occurs is unclear.
Evidence for potentiation of the liver and kidney toxicity of haloalkanes comes from animal studies. MEK probably activates the haloalkane metabolism to tissue-damaging species as a result of induction of the relevant oxidation enzymes.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES AND ANALYTICAL METHODS
2.1 Identity
H H O H | | || | Chemical structure: H - C - C - C - C - H | | | H H H Chemical formula: C4H8O
Synonyms: Butanone, 2-butanone, butane-2-one, ethyl methyl ketone, MEK, MEETCO, methyl acetone, methylpropanone CAS registry number: 78-93-3
RTECS registry number: EL 6475000 UN registry number: 1193
EC registry number: 606-002-00-3 Relative molecular mass: 72.10
2.2 Chemical and physical properties
Methyl ethyl ketone (MEK) is an important synthetic organic
chemical. The physical properties of MEK are summarized in Table 1. It is a highly flammable, volatile, clear, colourless liquid that is stable under ordinary conditions. The vapour forms explosive mixtures with air over a range of approximately 2% to 12% (vol./vol.). The odour is acetone-like and variously described as sharp, fresh or sweet. The odour threshold appears to be around 5.9 mg/m3 (2 ppm) although a range between 0.74 and 147.5 mg/m3 has been reported (Ruth, 1986). MEK is moderately soluble in water; the solubility decreases with increasing temperature. It is miscible with organic solvents such as alcohol, ether and benzene, and forms azeotropes with water and many organic liquids.
The value in Table 1 for log Po/w (logarithm of the octanol/
water partition ratio) of 0.26 is taken from Verschuren (1983).
Banergee & Howard (1988) quoted a slightly higher value of 0.29. Other partition values for MEK (at 37 °C) are: water/air = 254; blood/air = 202; olive oil/air = 263; olive oil/water = 1.0; and olive oil/blood = 1.3 (Sato & Nakajima, 1979). Perbellini et al. (1984), however, determined partition values for saline solution/air and olive oil/air of 193 and 191 respectively.
Table 1. Physical properties of MEK
Reference Appearance colourless liquid
Relative molecular mass 72.10 Papa & Sherman (1978 Specific gravity (liquid density)
(at 20 °/4 °C)a 0.805 Krasavage et al. (19 Vapour density (air = 1.00) 2.41 Verschuren (1983) Vapour pressure at 20 °C (torr) 77.5 Weast (1986)
Boiling point (°C) 79.6 Weast (1986) Melting point (°C) -86 Weast (1986) Water solubility at 20 °C (g/litre) 275 Windholz (1983) Refractive index 1.3788 Krasavage et al. (19 Flash point (closed cup) (°C) -6 Papa & Sherman (1978 Log Po/w 0.26 Verschuren (1983) 0.29 Banergee & Howard (1 Saturation concentration in
air (g/m3 at 20 °C) 301 Krasavage et al. (19
a Specific gravity at 20 °C relative to the density of water at 4 °C The physical and chemical properties of MEK are determined largely by its carbonyl group. MEK engages in reactions typical of saturated aliphatic ketones. These include condensations with amines, aldehydes and many other organic compounds, hydrolysis (catalysed with acid or base), oxidation via concentrated oxidizing acids or acidic peroxides, and reduction with hydrogen and metal catalysts. None of these reactions is likely to be important in nature. On the other hand, MEK and other methyl ketones will react with halogens and hypohalides in aqueous solution to form a carboxylic acid and a haloform. The reaction provides a specific test for methyl ketones, and may produce chloroform in chlorinated water supplies contaminated with methyl ketones. MEK and other ketones are photochemically
reactive when excited by wavelengths occurring in the atmosphere and produce free radicals which lead to the formation of photochemical smog (Grosjean et al., 1983).
2.3 Conversion factors
1 ppm = 2.95 mg/m3; 1 mg/m3 = 0.34 ppm (at 25 °C and 101.3 kPa)
2.4 Sampling and analytical methods
2.4.1 General considerations
Analytical methods for MEK depend on the matrix. They are summarized in Table 2.
Where MEK is present in a substantial concentration and is known to be the only or the dominant organic contaminant, simplified
methodology is feasible. The occupational atmospheric exposure limits, currently in the range 295-590 mg/m3 (100-200 ppm), permit
monitoring in the workplace with less sensitive procedures.
The precise determination of MEK when present in the environment at low concentrations is a complex task because of the wide variety of other organic compounds that may be present and the many possibilities for error, interference and contamination. MEK, other ketones and other interfering substances are so prevalent in laboratory and industrial air that care must be taken in all determinations to minimize the possibility of contamination of samples, equipment and reagents. Care must be taken to avoid contamination in sampling since, for example, easily unnoticed sources like PVC (polyvinyl chloride) glue in collection equipment may leach a significant amount of MEK into water samples (Kent et al., 1985).
Table 2. Some analytical techniques for determining MEK concentrations i Methods Detection Comments limits
Air
Trapping in solid sorbant tube (Tenax(R)); 200 µg/m3 working range is thermal desorption: separation-detection; be automated GC-FID
Trapping in DNPH; separation: HPLC 3-6 µg/m3 general method (reverse phase); detection: UV air; some isome absorption not well separa Trapping in solid sorbant tube 0.15 mg per working range i (Ambersorb XE-347(R)); desorption: sample isopropanol inte CS2; separation-detection: GC-FID
Absorption of specific IR wavelengths 3 mg/m3 can measure sev from CO2 laser; automated, computer- vapours simulta controlled system
Trapping in DNPH; colour matching 300 mg/m3 working range i against standards aldehydes and k requires no spe
Water
Separation from water sample by heated 0.05-1.0 water samples m gas purge; trapping on Tenax(R); thermal µg/litreb action with meth desorption; separation-detection: GC/MS removed with th of detection re distillation; n
Table 2 (contd.)
Methods Detection Comments limits
Concentration on zeolite (ZSM-5); 2 µg/litre developed for d elution with acetonitrile; derivatization interference re with DNPH; separation-detection: HPLC/UV
Direct injection of aqueous sample; 40 µg/litre developed for i separation-detection: GC/FID no interference
Solids
Solvent extraction with tetraethylene 0.5-5 µg/g tetraglyme must glycoldimethyl ether (tetraglyme); purge (wet weight) prevent peroxid and trap; separation-detection: GC/MS reported
Heated purge of sample/water slurry or 10 µg/kg method develope of methanol extract of sample; trap; (wet weight) at concentratio desorption; separation-detection: GC/MS reported
Biological Materials
Mixture with dextrose and heating; 20 µg/litre method develope HS analysis; GC/FID of MEK, toluene rates 90-98%
Incubation in sealed vial; HS 100 µg/litre method develope analysis; separation-detection: applicable to u GC/FID and ECD reported
Concentration by reverse-phase 100-150 method develope extraction column; separation- µg/litre in urine; no in detection: GC/FID
Table 2 (contd.)
Methods Detection Comments limits
Derivatized with o-nitrophenylhydrazine 100 µg/litre method develop and reacted with cyclohexane; in human urine centrifuge separation; reversed-
phase HPLC; UV (254 nm)
Steam distillation of slurry; HS 20 µg/litre method develope analysis; separation-detection: widely applicab GC/FID
Homogenization; HS analysis; 6 mg/litre method develope GC/FT-IR solvents of abu
a Abbreviations used in the table
DNPH 2,4-dinitrophenylhydrazine ECD electron-capture detector FID flame ionization detector FT Fourier transformed
GC gas chromatograph
HPLC high performance liquid chromatograph HS headspace
IR infrared
MS mass spectrometer UV ultraviolet
b 0.05 µg/litre for drinking-water; 1.0 µg/litre for all other types of wa
The general procedure for analysis of MEK is summarized below:
a) collect the sample, and if necessary, chemically stabilize it;
b) separate MEK (and other volatile organic compounds) from the substrate;
c) trap and concentrate MEK (plus other organic compounds);
d) recover the trapped material;
e) separate MEK and other organic compounds;
f) detect and identify MEK;
g) determine the quantity recovered;
h) calculate the concentration present in the sample.
In actual practice the procedure may be simplified by combining or omitting certain steps, or it may contain an additional step, i.e. the preparation of 2,4-dinitrophenylhydrazine (DNPH) derivatives of MEK and other aldehydes and ketones. The formation of DNPH derivatives quantitatively captures both aldehydes and ketones, and facilitates their subsequent separation with either gas or liquid chromatography.
The preparation of DNPH derivatives also forms the basis for a
simplified, non-specific method for roughly measuring high levels of ketones and aldehydes without the use of sophisticated laboratory equipment (Smith & Wood, 1972). The use of other derivatives, such as imines via phenylmethylamine (Hoshika et al., 1976), azines via
3-methyl-2-benzothiazolone (Chiavari et al., 1987), and O-(2,3,4,5,6-pentafluorobenzyl) oximes via
pentafluorophenylhydrazine and pentafluorobenzyloxyamine (Kobayashi et al., 1980) has also been proposed.
2.4.2 Air
A general methodology for determining MEK in air consists of trapping and concentrating MEK and other volatile organic compounds in sampling devices containing an absorbent material, charcoal
(carbopack) or an artificial resin (Tenax GC(R), Ambersorb XE(R), Amberlites XAD(R)), followed by desorption and analysis.
MEK decomposes when absorbed on charcoal and sample loss may occur after a few days (Elskamp & Schultz, 1983; Levin & Carleborg, 1987). Ambersorb XE(R) showed good capacity, and decomposition was insignificant (Levin & Carleborg, 1987). Kenny & Stratton (1989) evaluated various mixtures to find a solvent that would provide optimum desorption efficiency. For samples of MEK collected on charcoal tubes, a mixture of carbon disulfide with 10% amyl alcohol was found to be an effective desorption solvent. The substitution of hexyl for amyl alcohol gave comparable recovery but slower GC/FID analysis. Both thermal desorption and solvent desorption have been used to release the MEK from the trapping column.
Collectors may be passive and dependent on diffusion or a packed tube through which a known volume of air is drawn. Passive collectors, often in the form of badges, avoid the need for specialized sampling equipment and are convenient for monitoring individual exposure.
However, the results of several studies suggest that passive
(diffusive) collectors not only show significant individual and brand variability but also variability in their speed of uptake of different solvent vapours (Hickey & Bishop, 1981; Feigley & Chastain, 1982), and thus may require calibration against a more quantitative method. The trapped organic compounds are desorbed either thermally by application of heat or microwave radiation, or by solution in carbon disulfide, and are separated with gas chromatography. A wide diversity of columns and packings have been found satisfactory for this separation.
Using gas chromatography with a flame ionization detector, an overall precision (Sr) of 0.069 with a limit of detection of 0.004 mg/sample was achieved (US NIOSH, 1984a).
Methodology for analysing air samples recommended by the United States Environmental Protection Agency (US EPA) can detect MEK and most other mono-functional aldehydes and ketones at the 3-6 µg/m3 (1-2 ppb) level (Riggin, 1984). Air is drawn through a mixture of isooctane and an acidified solution of 2,4-dinitrophenylhydrazine (DNPH), which reacts chemically with MEK. DNPH derivatives of
aldehydes and ketones are extracted from the aqueous layer, separated with high performance liquid chromatography (HPLC) and detected by
ultraviolet absorption.
MEK vapour can also be detected and measured directly and
instantaneously by absorption of infrared light. The method (detection limit, 3 mg/m3) appears suitable for use in the workplace where only a limited number of solvent vapours are present (Persson et al., 1984) but may not reliably detect MEK in the presence of a diverse mixture of organic vapours, due to overlapping of infrared absorption peaks (Puskar et al., 1986). Ying & Levine (1989) used Fourier
transform-infrared spectrometry (FT-IR) to determine the concentration of MEK in mixtures of vapours in ambient air and obtained a detection limit of 1 mg/m3. Surface acoustic wave devices have been tested experimentally for the detection of MEK and other vapours
(Rose-Pehrsson et al., 1988) and show promise for the development of electronic devices that can continuously monitor and analyse vapour mixtures at concentrations likely to be present in the work
environment.
2.4.3 Water
Water samples containing high levels of MEK (e.g., industrial waste water) can be analysed by direct injection of the sample into a gas chromatograph; the detection limit is 40 µg/litre (Middleditch et al., 1987). Samples with low levels of MEK (e.g., drinking-water) require some form of concentration such as distillation (Pellizzari et al., 1985) or adsorption on a hydrophobic zeolite (Ogawa & Fritz, 1985). GC/MS analysis gives a detection limit of 0.05 µg/litre (Pellizzari et al., 1985) whereas HPLC with UV detection has a detection limit of 2 µg/litre (Ogawa & Fritz, 1985).
2.4.4 Solids
Analysis of solid and semisolid materials such as industrial wastes for MEK presents special difficulties in terms of both sampling and analysis. The sample must be representative and of adequate size, since substrates such as waste tend to be very non-homogeneous and MEK must be completely removed from both solid and liquid components. One method accomplishes this by extracting the sample with an appropriate solvent (tetraglyme) and purging MEK and other volatile organics from the tetraglyme with an inert gas (Gurka et al., 1984). Another method (Fisk, 1986) either directly purges MEK and other organic compounds from a water/solid material slurry held at an elevated temperature or purges a methanol extract of the solid material at an elevated
temperature.
2.4.5 Biological materials
Biological materials offer the same analytical problems as solid waste: MEK must be completely removed from both solid and liquid components of the sample. This can be accomplished by headspace analysis (Ramsey & Flanagan, 1982; US NIOSH, 1984b), steam distillation of a sample slurry followed by headspace analysis (Bassette & Ward, 1975; Lin & Jeon, 1985), derivation with
o-nitrophenylhydrazine (Van Doorn et al., 1989) and, in the case of an entirely liquid substrate, separation and concentration by
reverse-phase extraction (Kezic & Monster, 1988).
For MEK in blood the United States National Institute of
Occupational Safety and Health method (US NIOSH, 1984b), using GC/FID, has a detection limit of 20 µg/litre and the Ramsey & Flanagan (1982) method has a detection limit of 100 µg/litre. The latter method can also be used for the analysis of MEK in urine with the same limit of detection. Other methods for analysis in urine are those of Kezic &
Monster (1988), using GC/FID, and Van Doorn et al. (1989) using
HPLC/UV; both methods have limits of detection of 100 µg/litre.
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE 3.1 Natural occurrence
MEK occurs naturally at low concentrations. It has been
identified in cigarette smoke (Osborne et al., 1956; Hoshika et al., 1976; Higgins et al., 1983). It also has been reported in chicken breast muscle (Grey & Shrimpton, 1967), weed residues (Bradow &
Connick, 1988), southern pea seeds (Fisher et al., 1979), insect pheromones (Cammaerts et al., 1978; Attygalle et al., 1983), juniper leaves (Khasanov et al., 1982); marine macroalgae (seaweeds) (Whelan et al., 1982) and as a product of microbial metabolism (Patel et al., 1982; Mohren & Juttner, 1983; Zechman et al., 1986), including
cultures isolated from fresh water and soil (Hou et al., 1983; Patel et al., 1983). Berseem clover, hairy vetch and crimson clover emitted volatile compounds including MEK (Bradow & Connick, 1990). Six
amaranth species emit MEK which has been shown to cause significant inhibition of tomato and onion seed germination (Connick et al., 1989). Some bacteria (e.g., thermophilic obligate methane-oxidizing bacteria) can oxidise 2-butanol to produce MEK (Imai et al., 1986).
Studies have shown that MEK is a normal component of flavour and odour in a wide range of foods, especially cheese and other fermented
products (Zakhari et al., 1977), often as a result of bacterial
activity (Lin & Jeon, 1985). Seven types of fish contain MEK, although reported levels were low relative to other compounds (Sakakibara et al., 1990). MEK has been detected in coyote urine (Schultz et al., 1988), in the urine of non-occupationally exposed humans (Tsao &
Pfeiffer, 1957; Mabuchi, 1969), in human blood (Mabuchi, 1969) and in exhaled air (Conkle et al., 1975). The MEK in exhaled air may have been derived from food, but the observations of Poli et al. (1985) and other researchers (see section 6) strongly suggest that MEK and
similar carbonyl compounds are minor products of normal mammalian metabolism.
3.2 Production levels, processes and uses
3.2.1 World production
Although MEK is an important industrial chemical, world
production figures are not available. Annual production in the USA, reported by the US International Trade Commission, ranged from 212 to 305 thousand tonnes over the period 1980-1987 and averaged 258
thousand tonnes (USITC, 1981-1988). Current (1987) annual capacity and production values for western Europe are 308 and 215 thousand tonnes, respectively (Chemical Business Newsbase, 1988). Japanese annual capacity and production figures in 1986 were 180 and 139 thousand tonnes, respectively (Chemical Business Newsbase, 1987). Argentinean annual capacity was 15 thousand tonnes in 1985 (Chemical Business Newsbase, 1986). A production plant opened in Brazil in 1991 but information on capacity and production is not available (personal communication from E. de S. Nascimento).
3.2.2 Production processes
MEK is produced mainly by dehydrogenation of sec-butyl alcohol (Liepins et al., 1977; SRI International, 1985, 1988). In the USA, one process uses sec-butyl alcohol vapour at 400 to 550 °C oxidized with a zinc oxide catalyst. Reaction gases are condensed and the condensate fractionated in a distillation column. The yield of MEK is 85 to 90%
(Lowenheim & Moran, 1975). Any uncondensed reaction gases are scrubbed with water or a non-aqueous solvent and the waste stream from the scrubber, which contains MEK and reaction by-products, is either
recycled or discarded (Liepins et al., 1977). In Europe, sec-butyl alcohol is dehydrogenated over Rainey nickel or copper chromite catalyst at 150 °C (Papa & Sherman, 1978)
MEK is also produced by the oxidation of n-butane, either as the main product or as a by-product in the manufacture of acetic acid (Liepins et al., 1977; Papa & Sherman, 1978). Liquid butane reacts with compressed air in the presence of a transition metal acetate catalyst, normally cobalt acetate, and the reaction product phase is separated. The hydrocarbon-rich phase is recycled to the reactor and the aqueous phase with MEK is withdrawn and purified. MEK and other organic compounds with low boiling points are separated from acetic acid by distillation. Reaction conditions determine whether MEK or acetic acid is the principal product (Lowenheim & Moran, 1975). Butane oxidation accounted for about 13% of the 1987 MEK production capacity in the USA (SRI International, 1988) but for none of the 1984
production capacity in western Europe (SRI International, 1985). Other methods exist for the commercial manufacture of MEK (Papa & Sherman, 1978), but there is no evidence that any of these alternatives are of current importance.
3.2.3 Other sources
In addition to manufacture by the chemical industry, MEK and other carbonyls are incidentally produced as components of exhaust from jet (Miyamoto, 1986) and internal combustion engines (Seizinger & Dimitriades, 1972; Creech et al., 1982; Hampton et al., 1982) and from industrial activities such as retort distillation of oil shale (Hawthorne et al., 1985) and gasification of coal (Pellizzari et al., 1979). MEK comprises about 0.05% of the hydrocarbon exhaust gases of motor vehicles, and in 1987 the vehicle emission of MEK in the USA was estimated to be 1909 tonnes (Somers, 1989). Thus its anthropogenic production by vehicles plus an additional amount by stationary engines was no more than 0.1% of the industrial production in the USA.
Grosjean et al. (1983) concluded, however, that during smog episodes in the Los Angeles basin much of the ambient level of MEK was produced photochemically.
3.2.4 Uses
The major uses of MEK reflect its excellent characteristics as a solvent (Table 3). Its high solvency for gums, resins and many
synthetic polymers permits formulations with high solid content and low viscosity. It is also inert to metal, evaporates rapidly, and is relatively low in toxicity compared with solvents like benzene which MEK replaced (Zakhari et al., 1977; Basu et al., 1981).
Table 3. Major uses of MEK in the USAa
End use %
Solvent - protective coatings 65
Solvent - adhesives 15
Solvent - magnetic tape production 8
Lubricating oil dewaxing 5
Chemical intermediate 4
Miscellaneous 3
a From: Manville Chemical Products Corp. (1988)
The largest single use of MEK is as a solvent for vinyl plastic used in coatings and moulded articles. Other important uses are as a solvent for lacquers and for cellulose nitrate, cellulose acetate, acrylics, and adhesive coatings. Its properties as a selective solvent make it ideal for dewaxing lubricating oils. MEK is also used for degreasing metals, in the manufacture of magnetic tapes, inks and smokeless powder, and as a chemical intermediate in the production of methyl ethyl ketoxime, MEK peroxide, methyl isopropyl ketone and many other compounds.
In addition to industrial uses, MEK is an ingredient in a variety of consumer products such as lacquers, varnishes, spray paints, paint removers, sealers and glues (Zakhari et al., 1977). In both consumer products and industrial applications, MEK is frequently only one of several components in a mixture of organic solvents.
MEK is also used as an extraction solvent in the processing of foodstuffs and food ingredients, e.g., in fractionation of fats and oils, decaffeination of tea and coffee, and extraction of flavourings.
3.3 Release into the environment
Releases of MEK are mainly into the atmosphere (Reilly, 1988).
These can result from: spillage; venting of gases and fugitive emissions during manufacture, transfer and use; solvent evaporation from coated surfaces; loss from landfills and waste dumps; and engine exhaust (Basu et al., 1981; LaRegina & Bozzelli, 1986). Relatively little MEK is lost during manufacture when the process is enclosed.
The average annual release from four manufacturing plants in the USA was estimated to be 82 tonnes per site, equal to a total of 328 tonnes or about 0.1% of their annual production (Reilly, 1988).
The bulk of MEK eventually evaporates to the atmosphere, since the major use of MEK is as a solvent for coatings and adhesives. In industry, some of the MEK evaporated from surface coatings or lost during cooking and thinning of resin is removed from the ventilation exhaust by absorption on charcoal filters or by incineration of the exhaust stream. The latter method can reduce emission by up to 97%
(Gadomski et al., 1974), and removal is accomplished in a single step without generating a residue for subsequent disposal (DiGiacomo, 1973).
The waste stream from MEK production contains acetic acid and a variety of alcohols, aldehydes, ketones and other organic compounds.
It is likely that butane and other organic compounds are discharged into the atmosphere from the reaction section, but no specific information is available (Liepins et al., 1977).
MEK is released from other industrial operations involving its use, and from activities such as retort distillation of oil shale and gasification of coal (Pellizzari et al., 1979; Hawthorne et al., 1985).
It has been detected in drinking-water (Ogawa & Fritz, 1985), in well water (Jacot, 1983), in ground water (Botta et al., 1984) and in leachate from a hazardous waste site (Jacot, 1983). MEK occurs in water often as a result of natural processes (section 3.1).
Atmospheric input and direct anthropogenic pollution contribute significantly to elevated levels (Grosjean & Wright, 1983).
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION 4.1 Transport in the environment
MEK appears to be highly mobile in the natural environment (Lande et al., 1976). It is water soluble (Windholz, 1983) and evaporates rapidly in air. The generally low values for MEK in outdoor air probably stem mainly from its rapid removal by photodecompo-sition.
Scavenging by aqueous droplets and dry deposition, which also
represent potential routes of loss from the atmosphere, are balanced to an unknown extent by evaporation of MEK from water and soil. There is no specific information on partitioning of MEK in the environment.
Although Basu et al. (1981) estimated from its physical properties that MEK will "exhibit low sediment-water and soil-water partitioning and be susceptible to substantial leaching from soils to which it is not extensively chemically bound", there is no information on chemical binding of MEK to sediment particles. As mentioned above, MEK has, however, been detected in ground water and the leachate from hazardous waste sites (section 3.3).
4.2 Bioaccumulation and biodegradation
On the basis of its octanol/water partition and water solubility, bioconcentration factors (BCF) of approximately 1 and 0.5,
respectively, have been calculated for MEK (US EPA, 1985b). In view of its high water solubility, ecosystem modelling (Metcalf et al., 1973;
Chiou et al., 1977) indicates that it is unlikely that MEK will accumulate in food webs. It is absorbed and metabolized by organisms present in the environment, e.g., in waste water (Dore et al., 1975;
Bridie et al., 1979a) and in soil (Perry, 1968). It is rapidly
metabolized by mammals (Di Vincenzo et al., 1976, 1978; Dietz et al., 1981; Miyasaka et al., 1982) and by many microbes (Gerhold & Malaney, 1966; Dojlido, 1977; Urano & Kato, 1986). MEK is nearly completely degradable at concentrations up to 800 mg/litre on the basis of
biochemical oxygen demand (BOD), and the rate of degradation decreases with increasing concentration of MEK. Using activated sludge there was complete degradation of MEK in 8 days at a concentration of 200
mg/litre (200 ppm) and in 9 days at a concentration of 400 mg/litre (400 ppm) (Dojlido, 1979). At a concentration of 20 mg/litre in river water containing preadapted microbes, MEK was completely degraded in 2.5 days (Dojlido, 1977). Delfino & Miles (1985) reported a slower rate of decomposition in aerobic ground water; 1 mg/litre was fully degraded in 14 days. However, a bacterial species (Alcaligenes
faecalis) found in sewage sludge metabolized MEK slowly if at all (Marion & Malaney, 1963). The data on mammals and microbes suggest that MEK is rapidly absorbed and metabolized by most living organisms (Basu et al., 1981).
MEK in air is rapidly decomposed by photochemical processes, mainly through oxidation by hydroxyl free radicals as well as some decomposition by direct photolysis (Levy, 1973; Laity et al., 1973;
Dilling et al., 1976; Grosjean, 1982; Seinfeld, 1989). Basu et al.
(1981) estimated a half-life of 5.4 h for photochemical decomposition in urban atmospheres. They further concluded that the lower
concentration of photochemically produced oxidants in rural air will lead to a substantially lower rate of photochemical decomposition in these areas. The concentration of MEK and other carbonyls is higher in urban air (Grosjean & Wright, 1983; Snider & Dawson, 1985). Greater anthropogenic emissions and photochemical synthesis of carbonyls from free radicals (Grosjean et al., 1983) may overwhelm the more rapid photochemical decomposition in urban atmospheres. Scavenging by
aqueous droplets and dry deposition may also be important processes in
the removal of atmospheric MEK (Grosjean & Wright, 1983).
MEK (and other saturated aliphatic carbonyls) is not chemically reactive under conditions found in most natural waters and in general will not degrade rapidly from physical causes once deposited in water (US EPA, 1985b). The exception is water containing free halogens (such as chlorine) or hypohalides. MEK reacts with these to form a haloform and propionic acid (Basu et al., 1981). This can be a cause for
concern in chlorinated waste water and water supplies, since the chloroform thus produced is more toxic than the original MEK (US EPA, 1985a).
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE 5.1 Environmental levels
5.1.1 Air
Although MEK is widely present in the natural environment, concentrations are always low even under conditions of pollution (Table 4). In minimally polluted outdoor air, the level is less than 3 µg/m3 (1 ppb), but 131 µg/m3 (44.5 ppb) has been measured under conditions of heavy air pollution in the Los Angeles basin.
Volatilization of MEK from building materials and consumer products can pollute indoor air to levels above adjacent outside air. In a study of 15 Italian urban homes, De Bortoli et al. (1985, 1986) reported 8 µg/m3 as a mean indoor air value and 38 µg/m3 as a maximum value. Maximum and average values for MEK in outdoor air adjacent to these homes were 12 and 3.8 µg/m3 respectively. Shah &
Singh (1988) reported four observations of MEK in indoor air in the USA; the median and mean values were 21 and 27 µg/m3 (7.1 and 9.2 ppb), respectively. In a confined and tightly sealed space, however, MEK concentrations can be much higher. Liebich et al. (1975) measured 1.9 to 4.4 mg/m3 (665 to 1505 ppb) in Space Lab IV.
Human activities, other than the deliberate manufacture and use of MEK, may in some circumstances contribute significantly to
environmental levels. MEK is a minor component, < 2.95 mg/m3 (1.0 ppm), of gasoline engine exhaust and also has been detected in the exhaust from diesel engines and jet aircraft. The US Environmental Protection Agency estimated that 1909 tonnes of MEK was emitted in motor vehicle exhaust in the USA in 1987 ("Mobile source estimates for methyl ethyl ketone"; personal communication by J.H. Somers, 1989). In addition, Grosjean et al. (1983) concluded that synthesis of MEK and other carbonyls from hydrocarbons in vehicle exhaust by photochemical reactions in the atmosphere may greatly exceed their direct production by motor vehicles. Thus, away from industrial areas where MEK is
manufactured or used, it is likely that motor vehicles are an
important and possibly major source of atmospheric pollution by MEK.
Smoking cigarettes and other tobacco products contributes slightly to individual exposure. Although the concentration of MEK in cigarette smoke (Table 4) may exceed recommended levels of permissible
occupational exposure (Table 5) by several a Assuming a respiratory volume of 20 m3 per day times, the total amount of MEK generated by smoking a single cigarette is about 1/74th of the acceptable human daily chronic intake in the USA (15.43 mg/day) (US EPA, 1986). MEK also has been detected in the gases from structural (building) fires (Lowry et al., 1981).
5.1.2 Water
MEK concentrations in exposed natural waters are less than 0.1 mg/litre (0.1 ppm) and are usually below the level of detection. Ewing
et al. (l977) analysed 204 samples from rivers with industrialized basins; only one sample contained MEK (0.023 mg/litre). Jungclaus et al. (1978) measured significant levels of MEK in waste water from a chemical plant but could not detect it in either water or sediment of the brackish Delaware River receiving this waste. Despite its rapid disappearance from water, trace amounts of MEK have been detected widely in drinking-water (US EPA, 1985b). A potential source is solvent leached from the cemented joints of plastic pipe (Wang &
Bricker, 1979; Boettner et al., 1981). A single unexpectedly high value of 0.47 mg/litre (0.47 ppm) in mist from the landward edge of the Los Angeles basin probably resulted from scavenging of heavily polluted air (Grosjean & Wright, 1983). Data on MEK in sediment (US EPA, 1985b) were based on four samples and are difficult to interpret.
Sawhney & Kozloski (1984) studied organic pollution of leachates from municipal landfill sites in Connecticut, USA. MEK concentrations ranging between 4.8 and 8.2 mg/litre were measured over a two-year period at one site. This high value may have resulted not only from a substantial input but also from reduced microbial activity and no evaporative loss to the air.
Environmental concentrations in a number of media are shown in Table 4.
Table 4. Concentrations of MEK in the environment
Source Concentration Reference Air (rural)
South-western USA 1.77 µg/m3 Snider & Dawson (1985) (0.6 ppb)
Air (urban)
South-western USA, Tucson 7.1 µg/m3 Snider & Dawson (1985) (2.4 ppb)
USA, Los Angeles basin 0-131.3 µg/m3 Grosjean et al. (1983) (0-44.5 ppb)
Sweden, traffic areas 7.7-94 µg/m3 Jonsson et al. (1985) (2.6-32 ppb)
Italy < 2.1-12.1 µg/m3 De Bortoli et al. (198 (< 0.7-4.1 ppb)
Japan (air pollution) 12.7 µg/m3 Anonymous (1978) (4.3 ppb)
Air (indoor)
Italy (homes) < 2.1-38.1 µg/m3 De Bortoli et al. (198 (< 0.7-12.9 ppb)
USA (homes) detected in 3 out of Jarke et al. (1981) 87 samples
Space Lab IV 1.96-4.44 mg/m3 Liebich et al. (1975) (0.665-1.505 ppm)
Water
Sea water (Gulf Stream) < 0.022 mg/litre Corwin (1969)
Sea water (Mediterranean) < 0.008 mg/litre Corwin (1969)
Mist (California, USA) < 0.47 mg/litre Grosjean & Wright (198 Drinking-water (USA) < 0.0016 mg/litre Ogawa & Fritz (1985) Ground water (hazardous 4.8-8.2 mg/litre Sawhney & Kozloski (19 waste landfill sites, USA)
Table 4 (contd.)
Source Concentration Reference
Rivers (industrialized 0.023 mg/litrea Ewing et al. (1977) areas, USA)
Waste water (oil well, USA) 1.5 mg/litre Sauer (1981)
Waste water (Chemical plant, 8-20 mg/litre Jungclaus et al. (1978 USA)
Waste water (plant, Poland) > 100 mg/litre Dojlido (1977) Sediment
USA 0.050-23 mg/kg US EPA (1985b) Anthropogenic sources
Automobile exhaust < 0.3-2.95 mg/m3 Seizinger & Dimitriade (0.1-1.0 ppm) (1972)
Cigarette smoke 80-207 µg/cigarette Higgins et al. (1983)
a MEK was detected in only one of 204 samples.
Table 5. Levels of estimated daily MEK intake from different sources/routes of exposure
Type/route of exposure Daily intake
Foodstuffs 1590 µg Drinking-water (2 litres) 3.2 µg Ambient aira
outdoor, rural 36 µg outdoor, urban < 2620 µg indoor < 760 µg Tobacco smoking (20 cigarettes) < 1620 µg
a Assuming a respiratory volume of 20 m3 per day 5.1.3 Foodstuffs
MEK is produced in small amounts by animals, higher plants, algae
and microbes, and is a widespread, although generally minor, component of taste and odour in foods (Zakhari et al., 1977). It has been
identified in some foodstuffs and beverages. Using the DNPH method with column or paper chromatography, it has been identified (but not quantified) in white bread (Ng et al., 1960), tomatoes (Schormüller &
Grosch, 1964), cooked turkey meat (but not in raw meat and with more MEK in roasted than in boiled meat, the level increasing with roasting time) (Hrdlicka & Kuca, 1965), and in egg white (Sato et al., 1968).
Using gas chromatography, traces of MEK were found in fresh chicken meat (pectoral muscle) with a marked increase in samples kept for 4 days at room temperature. It was not found in caecal gas from living chickens but was detected in the gas 18 and 24 h after death (Grey &
Shrimpton, 1967). MEK has also been detected in cottonseed oil (Dornseifer et al., 1965), honey (Cremer & Riedmann, 1964), coffee (Gianturco et. al., 1966), roast barley (Shimizu et al., 1969), and in the mushroom Agaricus bisporus (Staüble & Rast, 1971). By means of GC/MS, Wong et al. (1967) detected MEK in codfish and Kahn et al.
(1968) reported its presence in a low-boiling distillation fraction of Canadian whisky.
In a study of compounds related to milk flavour, Wong & Patton (1962) determined MEK concentrations using the DNPH method with column separation and paper chromatography. The concentrations in two samples of untreated milk were 0.77 and 0.79 mg/litre and in two samples of cream were 0.154 and 0.177 mg/litre. Gordon & Morgan (1972) examined the influence of volatile compounds in milk on "feed" flavour and reported MEK concentrations of 0.25-0.35 mg/litre in moderately "feed"
flavoured milk and 0.50-1.0 mg/litre in strongly flavoured milk, with a highest concentration detection of 1.4 mg/litre. They concluded that MEK is one of the compounds responsible for producing the unpleasant "feed" flavour in milk. Using the DNPH method and paper
chromatography, Harvey & Walker (1960) detected MEK in New Zealand cheddar cheese one day after manufacture. The concentration increased during ripening, reaching 0.9 mg/kg at 40 weeks, and was related to the development of typical Cheddar cheese flavour. In another study of the chemical nature of USA Cheddar cheese flavour, Day et al. (1960) analysed the volatile flavour fraction of cheeses over 1 year old using DNPH and column partition chromatography, and reported approximate MEK concentrations of 12.5 mg/kg. Keen et al. (1974) postulated that the formation of MEK in New Zealand Cheddar cheese, for which levels as high as 19 mg/kg had been reported, occurred in steps carried out by different microbial species including
Streptococcus cremaris, Pediococcus cerevisiae, Lactobacillus plantarum and Lactobacillus brevis. They considered that MEK was an important flavour constituent in the cheese.
In another investigation of monocarbonyl compounds as flavour components, Mookherjee et al. (1965) measured MEK in fresh and stale (8 weeks old) potato chips with the DNPH method and liquid-liquid chromatography. In fresh potato chips the concentration of MEK was 1.8 µmoles/kg, and this increased to 2.2 µmoles/kg in stale chips.
Amylomaize starches are heat treated in the production of films and fibres to concentrate the amylose. Bryce & Greenwood (1963) used gas chromatography to measure pyrolysis products (including MEK) of potato starch, potato amylose and amylopectin, maltose, isomaltose and glucose. MEK was not detected in untreated starch nor in starch
pyrolysed in vacuo for 20 min at 200 and 220 °C. With increasing temperatures the concentration of MEK increased; at 230, 250, 300, 350 and 400 °C the MEK concentrations were 10, 15, 50, 65 and 70 moles x 107/g starch, respectively.
Small quantities (up to 2 ng/1.5 g bean) were found in soybeans
