It is estimated that up to 700,000 workers in the EU are exposed to oximes. Oximes are used in liquid paints and coatings (where they act as anti-skinning agents) and in some types of silane-based sealants. Because they are volatile, the main route of exposure is inhalation.
Oximes describe a substance family. The oximes Methylethylketoxime or 2-butanone oxime (MEKO) and acetone oxime used in paints, varnishes and sealants are classified to as carcinogens category 1B according to CLP regulation. MEKO is further classified for specific target organ toxicity with effects on the upper respiratory tract (STOT SE 1, H370) and the blood system (STOT RE 2, H373) by prolonged or repeated exposure. Similar effects on the blood system have been observed for acetone oxime and other oximes.
Where risks occur
Occupational exposure mainly occurs during the application phase of liquid paints and coatings when the solvents evaporate. Typically, the application of paints and coatings takes place in the worker’s visual field, which is in the breathing zone, so that the exposure to vapours is high. In case of oxime-releasing silanes, oximes are released continuously during the curing phase until the sealants are completely cured. High exposures can be expected in the painting and varnishing sector and in the spraying and painting of motor vehicles. Consequently, the occupations at high risk of exposure to oximes are painters, motor vehicle refinishers (when painting), but also plumbers and fitters when using oxime-releasing sealants. Furthermore, other occupations might be at risk when they enter work areas in which oxime-containing products have previously been used and are still evaporating.
More about the substance
Oximes are colourless, volatile liquids with an aromatic odour. The most commonly used oximes are 2-butanone oxime (MEKO), acetone oxime, 2-pentanone oxime (MPKO) and 4-methypentanone oxime (MIBKO). However, they are almost never used in pure form, but in low concentrations (usually < 1%) as anti-skinning agents in (mostly alkyl) paints and coatings, or in bound form in oxime-releasing silane sealants.
Hazards that may occur
There is no human epidemiological data available concerning toxicological effects of any oximes, so far. In animal studies, the main target organs are the liver, spleen and blood system, after oral or inhalation exposure to oximes. Additionally, for MEKO transient narcotic effects and irritation of the skin were observed. It should be noted that after dermal exposure to MEKO, allergic skin reactions are possible. To date, only MEKO and acetone oxime are harmonized as Carc. 1B (presumed carcinogenic to humans). For MPKO, MIBKO and cyclohexanone oxime, which are used as alternative oximes for MEKO and acetone oxime, there is no corresponding data that would justify a CLH classification as carcinogenic up to present. After inhalation of MEKO, animals developed liver cancer and the enzymatic pathway can be assumed in humans as well.
Currently, evidence on liver cancer in humans based on MEKO exposure and a possible latency period is lacking.
What you can do
The most effective way to prevent exposure and potential liver cancer is substitution by safer, oxime-free alternatives. For oximes in paints and varnishes, alternative paint systems might be an option, such as water-based paints and acrylic or polyurethane (PU) systems. Alternative anti-skinning agents for solvent-based paints are on the market and contain amine-compounds. For silicone sealants, oxime-free alternatives are available as acetoxy-, benzamide-, amine-, alkoxy-and lactate ester systems. Silicone sealants with alternative bases (e.g., polyurethane or Silane Terminated Polymer (STP)) are also applicable. Where substitution of oximes is not possible and use of oximes cannot be avoided, measures to reduce exposure must be taken. The most effective way to avoid exposure is to develop and use closed systems. Where this is not possible, technical measures such as effective local exhaust ventilation, or good ventilation of the workplace as well as checking their effectiveness should be implemented to ensure that exposure to vapours with oximes from paints or sealants is minimised as much as technically possible.
Implement regular exposure assessments to check if your protective measures in place are effective or whether further actions need to be taken. Workers need to be aware of the potential effects of exposure and should be trained regularly on the control measures necessary for working safely with oximes to prevent exposure. They should be encouraged to report early symptoms such as dizziness, skin irritation and skin allergies. Involving an occupational physician is recommended. In addition, train workers on effective hygiene measures.
Ensure that workers have adequate personal protective equipment, such as protective clothing and gloves, if necessary. Personal protective equipment (PPE) should only be used as a last resort and only considered temporarily, after the possible technical solutions have been exhausted. If reusable PPE is used, take care that it is removed in the foreseen (respiratory equipment at last) manner, cleaned regularly and stored in a way that contamination is prevented.
References: BAuA, CLP, BG BAU
