Ethylene oxide

Exposure

Exposure to ethylene oxide has been reported predominantly in workers in sterilization units, and should be kept as low as feasible. Health personnel working in close proximity to ethylene oxide should be given information about its dangers, and should be informed of the known and uncertain risks of exposure. Sterilizing equipment should be regularly checked, proper ventilation established, and alarm systems installed. These procedures must guarantee that the content of ethylene oxide is lower than 1 ppm, and that the content of halogenated ethylene hydrines is lower than 150 ppm on materials that have been sterilized by ethylene oxide at the time of use. The manufacturer of each device or instrument that should be sterilized by ethylene oxide must declare the conditions necessary for sterilization and decontamination [ ].

Occupational exposure of sterilizing staff to ethylene oxide in hospitals, tissue banks, and research facilities can result during any of the following operations and conditions [ ]:

• Changing pressurized ethylene oxide gas cylinders;

• Leaking valves, firings, and piping;

• Leaking sterilizer-door gaskets;

• Opening sterilizer doors at the end of a cycle;

• Improper ventilation at the sterilizer door;

• Improperly ventilated or unventilated air gap between the discharge line and the sewer drain;

• Removal of items from sterilizers and transfer of sterilized loads to aerators;

• Improper ventilation of aerators and aeration areas;

• Incomplete aeration items;

• Inadequate general room ventilation;

• Passing near sterilizers and aerators during operation.

In most studies, exposure appears to result mostly from peak emissions during such operations as opening the door of a sterilizer and unloading and transferring sterilized material. Although much smaller amounts are used in sterilizing medicinal instruments and supplies in hospitals and industrially, it is during these uses that the highest occupational exposures have been measured. On the other hand, proper engineering controls and work practices are reported to result in full-shift exposure of less than 0.1 ppm (0.18 mg/m ³ ) and short-term exposure of less than 2 ppm (3.6 mg/m ³ ) [ ]. Regular medical follow-up is advisable for sterilizing staff.

Monitoring exposure

Measurement of the concentration of ethylene oxide in workplace air is commonly used for exposure control. A standard of 1 ppm for workplace air is currently accepted as a threshold limit [ ].

In 12 workers who were occupationally exposed to ethylene oxide during the sterilization of medical equipment, concentrations of 0.2–8.5 ppm were detected [ ]. This study also confirmed the relation between the ethylene oxide concentration in ambient air and the amount of N-2-hydroxyethylvaline in human globin, which has been used as a biological marker of carcinogenicity.

Disposition

Ethylene oxide is readily taken up by the lung. At steady state, 20–25% of inhaled ethylene oxide reaching the alveolar space is exhaled as unchanged compound and 75–80% is taken up by the body and metabolized. Aqueous ethylene oxide solutions can penetrate human skin.

Ethylene oxide is rapidly and uniformly distributed throughout the body. It is eliminated metabolically by hydrolysis and by conjugation with glutathione and glycol. The half-life has been estimated at 14 minutes to 3.3 hours [ ]. It is excreted mainly in the urine as thioethers; at higher doses, the proportion of thioethers is reduced, while the proportion of ethylene glycol increases.

Ethylene oxide alkylates nucleophilic groups in biological macromolecules. Hemoglobin adducts have been used to monitor tissue doses of ethylene oxide [ ].

Local irritant effects

Some communications report irritating effects caused by liberation of residue of ethylene oxide and its reaction products in industrial materials, for example [ , , ]:

• Tracheal stenosis by tracheotomy cannulae;

• Severe bronchospasm and asthmatic attacks after endotracheal anesthesia by endotracheal tubes;

• Anaphylaxis in a hemodialysis patient from plastic and rubber connecting tubes in an arteriovenous shunt;

• Postoperative inflammatory reactions to intraocular lenses;

• Allergic contact dermatitis;

• Hemolysis after exposure to plastic tubing sterilized with ethylene oxide.