Brief (3-5 minute) exposures to methyl ethyl ketone (MEK) vapours produced slight nose and throat irritation at 100 ppm and definite nose and throat irritation at 350 ppm in approximately 10 people. 143 volunteers exposed to 200 ppm for 4 hours reported throat irritation, unpleasant odour, nausea, and headache (in order of frequency reported). Higher exposures are expected to cause central nervous system depression with symptoms such as headache, nausea, dizziness, drowsiness, and confusion. Extremely high concentrations may cause loss of consciousness and possibly death.

Neurobehavioural effects of exposures to MEK (200 ppm for 4 hours) were studied with 137 volunteers. There were no statistically significant effects observed in biochemical, psychomotor, sensorimotor and psychological tests. Similar findings have been reported in other studies. Four volunteers were exposed to 90 to 270 ppm MEK for 4 hours/day for 4 days. Minor disturbances in time perception were observed.

MEK is expected to cause no or mild irritation. No irritation was produced when 20% MEK in petrolatum was applied to volunteers for 48 hours in a closed patch test. Animal studies indicate that MEK is a mild skin irritant.

Animal evidence suggests that MEK is a moderate to severe eye irritant. There is one human case report of an industrial splash of MEK into the eye. The next day there was only slight eye irritation with no permanent injury. Later, severe inflammation of the eye developed which required intensive treatment. The author of the case study speculated that the delayed irritation may have been triggered by slight trauma. MEK vapour is irritating to the eyes. Brief (3-5 minutes) exposure to MEK vapours produced mild eye irritation in some people at 200 ppm, while the majority experienced eye irritation at 350 ppm. Momentary exposure to 3,300 and approximately 10,000 ppm produced intolerable eye irritation in men. 100 ppm was intolerable after "several inhalations" and 330 ppm was moderately irritating.

Unintentional, non-occupational ingestion of MEK produced unconsciousness and hyperventilation in a woman. Severe lactic acidosis was apparent upon admission to hospital but the authors were not certain whether MEK or circulatory insufficiency caused this effect. Ingestion of MEK is expected to cause central nervous system depression with symptoms such as headache, nausea, dizziness, drowsiness, and confusion. Extremely high concentrations may cause loss of consciousness and possibly death. Animal evidence suggests that MEK can be aspirated (inhaled) into the lungs during ingestion or vomiting. Aspiration of even a small amount of liquid could result in a life threatening accumulation of fluid in the lungs. Severe lung damage (edema), respiratory failure, cardiac arrest and death may result.

SKIN EFFECTS: Repeated or prolonged contact can produce dermatitis (red, dry, itchy skin) and whitening of the skin.

NERVOUS SYSTEM EFFECTS: Epidemiological studies and case reports have shown nervous system effects in workers exposed to solvents, including MEK, over a prolonged period of time. It is not possible to associate the observed effects with any particular chemical.

SKIN SENSITIZATION: Despite extensive industrial use, there is only one case report of sensitization in a painter which was confirmed by positive response to standard patch testing with MEK. A maximization test using 20% MEK in petrolatum produced no sensitization in 24 volunteers.

A mortality study of 446 people who had worked at MEK dewaxing plants concluded that there was no evidence of a cancer hazard. The average follow-up was 14 years. This study is limited by the small size of the cohort and the relatively short follow-up period. Therefore, it is does not necessarily prove that MEK is not a carcinogen. There is no other information available.

No human or animal information available

Some researchers have pointed to a concern that solvent exposure may have led to congenital defects in children born to female workers. One of the solvents mentioned is MEK, but is it not possible to implicate any particular solvent due to the extent of combined exposure. Three animal studies have shown fetotoxicity (skeletal anomalies) at doses which did not produce any or only very slight maternal toxicity.

There are several human case reports of neurological effects resulting from high exposure to MEK in combination with other solvents. Animal studies have confirmed synergism between MEK and ethyl n-butyl ketone; methyl n-butyl ketone; n-hexane; carbon tetrachloride; 2,5- hexanedione and chloroform. Principal target organs involved in toxicological interactions are the nervous system and liver, although the lung has also been implicated.

MEK does not accumulate in the body. It is rapidly absorbed by inhalation, skin contact and ingestion and transferred into the blood and other tissues. MEK is metabolized in the liver, mainly to 3-hydroxy-2-butanone and 2,3-butanediol which are eliminated in urine. Most MEK probably enters the general metabolism in the body and is converted to acetate which is eventually broken down to carbon dioxide and water which are then eliminated in exhaled air and urine. Small amounts of MEK itself are also eliminated in exhaled air and urine. MEK and its metabolites are mostly cleared from the body within 24 hours.