What you need to know about Ethylene oxide

What is ethylene oxide?

Ethylene oxide (EtO or EO for short) is a manmade chemical, which is colorless and exists as a gas at room temperature (a gas above 10 °C). It is a cyclic ether and the simplest epoxide: a three-membered ring consisting of one oxygen atom and two carbon atoms (see table below). It is highly unstable and is rapidly converted in the environment to 2-chloroethanol, among other things. Owing to its instability it does not persist for long in the environment. As the conversion of ETO to 2-chloroethanol (2-CE) takes place relatively quickly only 2-CE is usually detected. Small amounts of ETO are also produced when tobacco is burned.

Very small amounts of ETO can be found in nature. ETO is produced in the human body from oxidation of ethylene, and biological processes producing endogenous ethylene have been identified, such as lipid peroxidation, methionine and heme oxidation, and metabolic activity of intestinal bacteria. The contribution of these processes to internal levels of ethylene or ethylene oxide has not been directly quantified.

Where and why is EtO used?

The primary use of EtO is as an intermediate ingredient in the manufacture of industrial products (e.g. polyester). ETO is a surface disinfectant that is widely used in hospitals and the medical equipment industry to replace steam in the sterilization of heat-sensitive medical tools and equipment, such as disposable plastic syringes. ETO is capable of killing bacteria, viruses, and fungi. Due to this property, ETO is also often used in cold sterilisation to reduce the microbial contamination of heat-sensitive food products like spices, herbs and sesame seeds. When spice/seeds etc are is fumigated with ETO, but the aeration step is not properly carried out, the residue of the ETO gas reacts with chlorine ions always present in the matrix to form 2-CE which can be found in the treated matrix at higher levels. Because of its volatility, ETO residues in food post-treatment will fully dissipate with time and the residue left is 2-chloroethanol.

EtO as a processing aid/fumigant pesticide, is not an accepted biocidal treatment for herbs, spices or any food sold in India, (Food Safety and Standard (Contaminants, Toxins and Residues) Regulations, 2011Appendix C of Food Safety and Standard (Food Products and Food Additives) Regulations, 2011). Singapore Food Agency, Singapore’s food regulations, ETO can be “used to sterilise spices.

Safety assessment of ETO

United States Environmental Protection Agency (USEPA) and the International Agency for Research on Cancer (IARC), based on environmental risk assessment data, have designated ETO as a human carcinogen by the inhalation route of exposure.

Carcinogenicity is associated with long environmental exposure to EtO gas. Furthermore, ETO gas exposure affects the nervous system, causing symptoms like headache, dizziness, and nausea. All the health effects (reported incidence of cancer) associated with EtO are based on inhalation route exposure studies where there is a continual exposure over a long period.

Most of the available information on the adverse effects of ETO in humans comes from occupational studies of workers exposed during ETO production and/or related to its uses in sterilization and not due to oral consumption.

A study on dominant lethal tests of spices (onion and paprika) treated with EtO demonstrate, that ETO-treated ground paprika or dried onion have no genotoxic effect (Barna 1982). Given orally in water or corn oil, EtO is only slightly toxic with an LD50 of 250-350 mg/kg, (rats and mice). By the inhalation route, EtO is moderately toxic with an LC50 (1 hr) of 1460 ppm in rats and 835 ppm in mice.

International Regulations: Maximum Residue Level (MRLs) vary.

A maximum residue level (MRL) is the highest level of a pesticide residue that is legally tolerated in or on food or feed when pesticides are applied correctly (Good Agricultural Practice). Some countries rely on the Codex Alimentarius Committee on Pesticide Residues to establish MRLs, whereas others set their own. MRLs have been recommended by the Joint Food and Agricultural Organization/World Health Organization Meeting on Pesticide Residues (JMPR).

No international MRL is available for EtO and 2-CE residues in food products, each country has its own policy in regard to this matter. Various countries regulate EtO and 2-CE within the scope of pesticide regulations. For instance, U.S (40 Code of Federal Regulations (CFR) part 180: Tolerances and exemptions for pesticide chemical residues in food) and Canada (Canada MRL search engine) have set the MRLs of ETO and 2-CE at 7 mg/kg (ppm) and 960 mg/kg ppm respectively. On the other hand, some countries like the EU and UK have established a uniform MRL 0.1 mg/kg (0.1 ppm, sum of ethylene oxide and 2-chloro-ethanol expressed as ETO). MRLs for nuts, oil fruits, and oil seeds were set at 0.05 mg/kg (Regulation (EU) 2015/868). As a result, several trade problems related to EtO and its metabolites have been identified in instant noodle products, ice cream, sesame seeds, spices and several food additives such as locust bean gum. Singapore Foods Agency has an MRL of 50 mg/Kg for spices, whereas Honkong has zero tolerance. The SFA MRL is 500-fold higher than EU. USA and Canada have 70 fold higher.

Analysis of ETO and 2-Chloroethanol in food products is an analytical challenge?

The analysis of ETO at trace levels in foods is not straightforward and the approaches used by enforcement agencies and countries are quite diverse. In the absence of certified reference materials available for all food items including masala/spice powders, accuracy remains uncertain, and discrepancies in the amounts of Total ETO reported between laboratories underscores the analytical challenges (Bessaire et al., 2023).
Various analytical approaches to quantify ETO, ideally simultaneously with 2-CE have been reported. Due to the high volatility of ETO, confirmatory analysis usually entails gas chromatography coupled to mass spectrometry (GC-MS). Sample preparation involves converting ETO to 2-CE before GC-MS analysis (Bessaire et al. 2023). The direct measurement of ETO with solid-phase microextraction (Du et al. 2019) or by the QuEChERS procedure is also feasible (Jensen,1988). Other methods are based on the conversion of the ETO to 2-CE under acidic conditions, followed by extraction of 2-CE with ethyl acetate and analysis by gas chromatography–mass spectrometry (GC–MS).

Recently Bessaire et al., (2023) demonstrate that not ETO, but 2-CE is the predominant analyte detected in the different processed ingredients suspected to have been previously treated with ETO. Additionally, they show that results of free ETO from methods based on conversion may lead to artefactual detection of native ETO (false positive). They re-enforce the fact that in absence of native ETO in food items (n=146), risk assessment of ETO in foodstuffs should consider the predominance of 2-CE. German Federal Institute for Risk Assessment (BfR 2020, 2021) and other laboratories (EURL SRM 2020, Nawaz 2022, Stupak et al. 2021, Bessaire et al., 2023) document the detection of only 2-CE and not ETO in items (e.g. seeds and spices) apparently treated with ETO.

Bessaire et al., 2023 recommend that an official method from standardization bodies (e.g. CEN, AOAC, ISO, etc.) for the analysis of ETO in different food matrices would be useful to avoid false positive results as evidenced in their study.

Does ETO affect health?

Those who work where ethylene oxide is made or used (such as in hospitals or facilities processing certain herbs and spices), are exposed to it by breathing it in or getting it on your skin. These workers generally have a higher exposure to EtO than the common man.

The prevailing view among the United States Environmental Protection Agency (US EPA) and the World Health Organization (WHO) has been that the contribution to cancer risk from the consumption of low levels of ETO residues in spices is unlikely to be significant due to the relatively low levels of exposure involved (WHO, 1985; US EPA, 1996

Levels of ETO decrease with time as ETO evaporates or breaks down into other substances, and thus, little or none may remain when the food is eaten.? The boiling point of ETO is very low (10–11 °C at 760 mm Hg), so ETO will not persist when applied to produce at the farm or in storage facilities.
United States Environment Protection Agency (EPA) (US EPA 2012), and EFSA (EFSA 2022) reported the conflicting results on the genotoxicity of 2-CE

How much ETO do you ingest from consuming spices

Fowles, et al., (2001) in a conservative estimate of potential cancer risks from consuming ETO in uncooked spices in New Zealand indicated no significant risk but as the breakdown products, remain at considerable concentrations in spices for a relatively long time. These risks are practically negligible considering the spice consumption of 2.8 kg spices per year and the inconclusive toxicological picture of 2-CE. An oral carcinogenicity study is needed to ascertain whether 2-CE is a potential carcinogen when spices are eaten, and to obtain an estimate of any dose–response relationship.

Disparity in the scientific information on ETO.

Several questions related to risk assessment arise based on the 1) exclusive finding of 2-CE and not ETO in a large range of fumigated samples (Bessaire et al., 2023) 2) the toxicological profile of 2-CE is less severe than that of ETO (Allemang et al. 2022). In addition, 1) harmonised analytical methods are not used for analysis of ETO by different regulatory agencies, 2) there is a wide disparity in the MRLs for ETO globally, 5) if the MRL for 2-CE is 150-fold higher it is less toxic, 6) certified reference materials are not available for ETO or 2-CE e for different spices. In view of the current scenario of ETO the significance & regulatory implications of the above disparities must be addressed by international regulatory bodies.

References

Allemang et al. 2022. Food Chem Toxicol. 168: 113290. doi:10.1016/j.fct.2022.113290
Bessaire et al., 2023 Food Additives & Contaminants: Part A, 40:1, 81-95, DOI: 10.1080/19440049.2022.2143909
Fowles et al., 2001 Food and Chemical Toxicology 39 1055–1062
Jensen K.G., (1988) Z. Lebensm. Unters Forsch 187, 535–540
U.S. Environmental Protection Agency. Evaluation of the Inhalation Carcinogenicity of Ethylene Oxide (CASRN 75-21-8) In Support of Summary Information on the Integrated Risk Information System (IRIS). National Center for Environmental Assessment, Office of Research and Development. Washington, DC. EPA/635/R-16/350Fa. 2016. https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/1025tr.pdf 2. 2.
Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Ethylene Oxide. U.S. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. 1990. https://www.atsdr.cdc.gov/toxprofiles/tp137.pdf
Barna, J. (1982). Mutation Research/Environmental Mutagenesis and Related Subjects, 97(3), 170. doi:10.1016/0165-1161(82)90072-3
US EPA (United States Environmental Protection Agency), 1996.mMemorandum from Leung Cheng, Health Effects Division, to Vivian Prunier Special Review Branch: Ethylene Oxide. Case No. 2275. Analytical Method, Residue Persistence in Herbs and Spices and Walnuts, and Cooking study. Dated 28 March 1996.
WHO, 1985. (World Health Organization). Environmental Health Criteria 55: Ethylene Oxide. International Programme on Chemical Safety. WHO, Geneva