EURL-SRM - Analytical Observations Report
Concerning the following…
ooooCompound(s): Ethylene oxide (EO), 2-Chloroethanol (2CE)
Commodities: Sesame seeds
Extraction Method(s): QuOil, QuECHERS
Instrumental analysis: GC-MS/MS

Analysis of Ethylene Oxide and its Metabolite 2-Chloroethanolby the QuOil or the QuEChERS Method and GC-MS/MS
Version 1.1 (December 2020)

Background information / Initial Observations:
In late August 2020, Belgium initiated a RASFF notification concerning residues of the unauthorized
substance ethylene oxide (EO) in various lots of sesame seeds from India at levels up to 186 mg/kg.
On 9 September 2020, a notification this concerning was published in the RASFF portal (2020.3678).
The affected products were delivered to several member states and were used for the production ofvarious processed foodstuffs. Until 20 November 2020, roughly 140 notifications concerning EO insesame from India were notified within the RASFF portal with two of them being border rejections.
These notifications originated from 17 different EU-Member states and 2 EFTA countries1. The EOlevels encountered in the sesame samples mostly ranged between 0.1 and 10 mg/kg, all exceeding
the EU-MRL (maximum residue limit) of 0.05 mg/kg.
For how long EO-fumigation has been in use or increasingly applied to sesame seeds in India willneed to be investigated. In a review paper from 2004 concerning fumigation of oily seeds with focus
on India2, methyl bromide and phosphine are reported as the main fumigants used in India for oilseeds.
The alternatives discussed in this review do not include EO. Given the strong antibacterial properties
of EO (reportedly 10-fold more effective than methyl bromide3), it is conceivable that EO-fumigations
may have been initiated in India as a counter-measure for reducing the incidences of sesame seedcontaminations with salmonella and other fecal bacteria. These contaminations have led to numerous
border rejections of sesame seeds from India by EU Member States in the past two decades. Looking
at the RASFF portal,4 the first three notifications on salmonella in sesame seeds were launched by

1

Austria, Belgium, Croatia, Czech Republic, Finland, France, Italy, Germany, Latvia, Luxemburg, Poland, Slovenia, Spain, Sweden, The
Netherlands, Norway Switzerland.
2
Somiahnadar Rajendran, Chayadevi HS; Oilseeds -Storage and Insect Pest Control, JFST (2004); 41(4):359-367
3
L.T. Richardson and H. A. U. Monro; Fumigation of jute bags with ethylene oxide and methyl bromide to eradicate potato ring rot bacteria.
Appl. Microbiol.l0: 448451 (1962)4https://webgate.ec.europa.eu/rasff-window/portal/?event=SearchForm&cleanSearch=1

Community Reference Laboratory for Single Residue Methods
CVUA Stuttgart, Schaflandstr. 3/2, 70736 Fellbach, Germany
CRL@cvuas.bwl.de

Page 1- 2 -Germany in 2001. The first border rejections were reported by Greece in 2007. By 20 November 2020
most RASFF-notifications concerning salmonella and other bacteria in sesame seeds were notified
by Greece (60) followed by Italy and Poland (45 each), Germany (34) and The Netherlands (23).
On 1 October 2014, a modification of Regulation (EC) No 669/2009 came into force requiring an increased level of import controls on sesame seeds from India with 20% of lots being required to bechecked for salmonella. Thereafter, the number of notifications peaked but started falling again from2016 onwards. In an FVO-inspection report from mid-2015, concerning a visit to India in 20145, theauditors did not report about EO-fumigations, but reported that, according to the local authorities,
fumigations with phosphine (alumina phosphide) were taking place, where pests were observed. In
February 2017, a new EU-Regulation was implemented6 requiring that a health certificate, as well asa laboratory report verifying the absence of Salmonella spp. shall accompany each consignment of
sesame seeds. In 2018, a follow-up FVO-mission to India was undertaken, but fumigations are notmentioned in the respective mission report7.
Problems with salmonella in sesame are not just limited to India. Over the years, salmonella was also
encountered in sesame seeds from various African countries. This resulted in the implementation of
EU regulations requiring increased import controls of sesame originating from Uganda (Dec. 2016),
Nigeria and Sudan (Jun. 2017) and Ethiopia (Jan. 2019). The frequency of controls was initially set at
50% and was subsequently dropped to 20% in the case of Sudan and Uganda (May 2020 onwards).
In 2016-17, a salmonellosis outbreak with a novel salmonella subspecies was reported by five EU
countries (Greece, Germany, Czech Republic, Luxembourg and the United Kingdom) that could betraced back to the consumption of contaminated sesame from Nigeria and Sudan 8.
Around 70% of the world’s sesame production comes from Asia (mainly India, China and Myanmar)and 26% from Africa (mainly Sierra Leone, Sudan, Nigeria and Uganda)9. Europe’s own sesame production is limited to less than one thousand tons, mainly from Greece and Italy. In 2019, the sesame
import into the European Union was 132 thousand tones10. More than half of the import volume (ca.
70,000 tons annually) originate from India. Thereof 80-90% are hulled. It is estimated that ca. 1.5 Miopeople are involved in sesame production within India. India also imports large quantities of sesame
seeds from Africa, which are processed and partly re-exported. According to the Indian plant quarantine (Regulation of Import into India)11, sesame imported to India from African countries such as Somalia, Sudan, Senegal as well as from Pakistan, Bangladesh and Mexico needs to undergo fumigation
with methyl bromide or an equivalent treatment prior to entering India.

DG(SANTE) 2014-7170 – MR: Final report of an audit carried out in India from 09 December 2014 to 17 December 2014 in order to assess the control systems in place to control microbiological contamination in seeds for human consumption intended for export to the European Union
6
Commission Implementing Regulation (EU) 2017/186, amending Regulation (EC) No 669/2009
7
Final report of an audit carried out in India from 23 October 2017 to 27 October 2017 in order to evaluate the control systems in place tocontrol microbiological contamination in seeds for human consumption intended for export to the European Union
8
A. Meinen et al.; Salmonellosis outbreak with novel Salmonella enterica subspecies enterica serotype (11:z41:e,n,z15) attributable tosesame products in five European countries, 2016 to 2017, Euro Surveill. 2019 Sep 5; 24(36): 1800543.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6737830/
9H.A. Abou-Gharbia, A.A.Y. Shehata and F. Shahidi; Effect of processing on oxidative stability and lipid classes of sesame oil; Food Res.
Int., 33: 331-340 (2000).
10
https://www.cbi.eu/market-information/grains-pulses-oilseeds/sesame-seeds/market-potential
11
https://plantquarantineindia.nic.in/PQISPub/pdffiles/pqorder2015.pdf
5

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 2Ethylene oxide uses beyond fumigation:
EO is one of the most widely produced chemicals worldwide. It is mainly used as a chemical intermediate in the manufacture of numerous important chemicals such as mono-, di-, tri- and polyethylene
glycols as well as various ethanol-amines and glycol-ethers. These chemicals are either used directly12, or as intermediates for the fabrication of other important products, such as polymers (e.g.
PET) and surfactants (e.g. ethanol-amines and ethanol-amides). Other important products derived
from EO are modified polysaccharides (e.g. hydroxyethyl cellulose13) and TCEP14.
Ethylene oxide uses as a fumigant:
Only 0.05% of the global EO production is used for fumigation purposes including the sterilization of
medical equipment15 and the control of insects and microorganisms (fungi and bacteria) in dry foodproducts, such as herbs, spices, nuts and oily seeds. The use of EO for controlling diseases in honeycombs has also been reported16. Empty storage facilities, wood, wool and furs are also fumigatedwith EO. In the EU, the use of EO for the disinfection of foodstuffs, e.g. in storage areas, is not permitted (ECHA, 2020).
EO inactivates bacterial spores and viruses by reacting with DNA and proteins such as enzymes. Dueto its small size, EO shows a high diffusivity and strong penetrating properties and is thus very effectivein the disinfestation or disinfection of dry food commodities. Owing to its high flammability, EO is usually mixed 1:9 with carbon dioxide. For sterilization, higher EO concentrations and prolonged treatment
times are required compared to conditions for insect control. In an FAO manual from 201317, the recommended doses for EO-fumigation are as follows: Nuts / nuts with shell (560 / 640 g/m³ for min. 3 h at 20°C);
 Dates and raisins (640 g/m³ for min. 3 h at 20°C);
 Spices (640 g/m³ for min. 3 h at 20°C);
 Milk powder (720 g/m³ for min. 3 h at 20°C);
 Milled cereals and feed (800 g/m³ for min. 6 h at 25°C).
No recommendation is given for oily seeds.
Residues following fumigation:
Evaporation and reactions with matrix constituents are the main dissipation pathways of EO in food.
Following EO-fumigation, the EO levels in fumigated goods decrease rapidly if products are aerated.
Typically, EO levels fall below 1 ppm within 2 weeks following fumigation18. With no aeration, or if thesamples are sealed, the EO levels decrease more slowly. The removal of EO from food products issometimes assisted by applying vacuum or higher temperatures. The latter sometimes negatively affects the sensory properties of the food products.

12

e.g. ethylene glycol is used as an antifreeze agent and various glycol-ethers are used as additives to cosmetics and water-based paints
Hydroxyethyl cellulose is used in cosmetics, drug capsules, toys and construction materials
14
TCEP stands for tris-(2-chlorethyl)-phosphate. It is used as a plasticizer (e.g. in PVC and polyurethanes) and as a flame retardant invarious plastics and fabrics, It is a chemical of high toxicological concern as regards indoor air contamination (https://www.umweltbundesamt.de/sites/default/files/medien/pdfs/Tris-chlorethylphosphat.pdf)
15
E.g. catheters, blood conserve bags, dialysis membranes, surgical implants; endoscopes, dentist equipment
16
G W Bruns, R A Currie; Determination of 2-chloroethanol in honey, beeswax, and pollen; J Assoc. Off. Anal. Chem. 1983 May;66(3):65962
17
http://www.fao.org/3/x5042e/x5042E00.htm
18
http://www.inchem.org/documents/jmpr/jmpmono/v071pr15.htm
13

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 3Once in contact with the food EO undergoes various reactions within the matrix. Reaction products
include ethylene glycol, 2-chloroethanol (2-CE)19 and 2-bromoethanol20. The latter two are formed inpresence of chloride and bromide ions, respectively. Diethylene glycol and dioxane are also formed
to some extent. Where fumigation with methyl bromide preceded the fumigation with EO, leaving highresidues of bromide, the levels of 2-bromoethanol formation can be very high21. EO furthermore directly reacts with matrix components, such as amino acids, purines and fatty acids forming hydroxyethyl adducts. 2-CE also undergoes reactions with fatty acids forming 2-CE esters. 2-CE and thevarious reaction products of EO and 2-CE are only removed at a limited extend during aeration andmany of them can serve as markers for EO-fumigations.
Legal situation in the EU
The use of EO for food fumigation has been phased out in many countries worldwide, due to toxicological concerns. In Germany, fumigation of food with EO was prohibited already in 1981 due to concerns as regards the toxicological properties of the residues remaining in food. In 1985, China restricted the use of EO only to empty warehouses. In 1986, the EEC prohibited marketing and use of
EO as plant protection product with certain small-scale temporary exemptions still applying at national
level22. In 1991, the EEC fully prohibited all plant protection products containing EO as active ingredient due to health concerns as it was classified as a Category 2 carcinogen and mutagen23.
In 1994, EO was included in a list of high priority compounds for which EC-harmonized MRLs wereneeded24. Thereafter, separate MRLs were proposed for EO and its primary metabolite 2-CE at 0.05*
and 0.01* mg/kg, respectively. These MRL-levels were applying to all commodities. In 2008,25 it was
decided to introduce a joint residue definition for the two components: “Sum of ethylene oxide and 2chloroethanol expressed as ethylene oxide”. This residue definition is still valid today The MRLs forEO (sum) were set at 0.2* mg/kg for oilseeds, teas, cocoa and spices; at 0.1* mg/kg for fruits, vegetables, sugar plants, fungi and oil fruits; and at 0.02* mg/kg for cereals and food of animal origin. In
201526 the EU-MRLs for teas, cocoa and spices were lowered to 0.1* mg/kg; the MRLs for nuts, oilfruits and oilseeds were lowered to 0.05* mg/kg and for fruits, vegetables, sugar plants, fungi andpulses they were lowered to 0.02* mg/kg. The MRLs for cereals and products of animal origin were
kept at 0.02* mg/kg. For apicultural products, the MRLs were newly set at 0.05* mg/kg. These MRLvalues are still valid today.
(*=MRL set at LOQ)

Legal situation elsewhere
Internationally, many countries (e.g. Australia27, Japan28, Korea, and Thailand) do not have explicit
MRLs for EO implemented. In Canada, EO has long been classified as food additive for whole or
ground spices. The permitted concentration of EO during fumigation was set at 500 mg/L and theresidues of 2-CE were limited at 1500 mg/kg. In 2017, it was decided to change the status of EO from

19

Also known as ethylene chlorohydrin (ECH)
Also known as ethylene bromohydrin (EBH)21
http://www.inchem.org/documents/jmpr/jmpmono/v071pr15.htm
22
Directive 86/355/EEC
23
Currently classified as Category 1B (Reg. 1223/2009/EC)24
http://aei.pitt.edu/46684/1/COM_(94)_482_final.pdf
25Regulation 149/2008/EC
26
Regulation 868/2015/EU27
https://apvma.gov.au/sites/default/files/gazette_17112020.pdf
28
https://db.ffcr.or.jp/front/
20

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 4

additive to pesticide29. Nowadays, USA and Canada have common MRLs for EO and 2-CE in spices,
dried herbs, dried vegetables and oily seeds (including sesame seeds) at 7 and 940 ppm, respectively30. In USA EO residues in walnuts are additionally regulated with a tolerance at 50 ppm31. In
Australia and New Zealand the Food Standards Australia New Zealand (FSANZ), following an industry request to extend the MRLs of 20 mg/kg applying for EO till 2001, thoroughly evaluated the EO
residues checking toxicological and microbiological risks as well as the actual residue situation intreated products. Finally, it was decided to phase-out EO-treatments, and only to grant a limited extension for EO-treatments to give industry time to develop alternative techniques for removing humanpathogens from herbs and spices32. This temporary provision only applied to Australia and treatedproducts were only allowed to be sold or imported 21 days after treatment with EO.
Other legal aspects
Apart from food products, EU-limits for EO also exist for certain food additives involving the use of
EO in their production. Regulation 231/2012/EU, laying down the specifications of food additives, setsa maximum limit of 0.2 mg/kg for polyoxyethylene stearate (E 431); a number of polyoxyethylene
sorbitan fatty acids (E 432, E 433, E 434, E 435, E 436); polyvinyl alcohol PEG copolymer (E 1209);and PEG (E 1521). For the byproduct dioxane, the respective limit in E 431-436 was set at 5 mg/kg
and for E 1209 and E 1521 at 10 mg/kg. This regulation additionally states that EO may not be used
for sterilizing food additives.
In the non-food area, EO is included in a list of prohibited substances within the cosmetics regulation33. In the Plastics Food Contact Regulation34, EO is listed in Annex I (Authorized substances) withrestrictions as regards the maximum amount allowed to be contained in the plastic (1 mg/kg) and as
regards the Specific Migration Limit (SML) which was set at 0.01 mg/kg.
On the ECHA website35, EO is categorized as a biocide falling under product type category PT2(“Disinfectants and algaecides not intended for direct application to humans or animals”)36. The initial
application for approval is still in progress.
Toxicity, Exposure and Metabolism of EO and its reaction products:
Compared to other fumigants, EO shows a relatively moderate acute toxicity to humans. Short-term
effects of EO in humans consist mainly of depression of the central nervous system and irritation of
mucous membranes such as the conjunctiva of the eyes. Chronic exposure to EO in humans is reported to cause neurological disorders through damage to brain and the nervous system, even at low
exposure doses.
The ability of EO to react with and damage DNA explains its sterilizing properties but it also accounts
for its genotoxic, mutagenic and carcinogenic potential. Evidence in humans indicates that exposure
to EO increases the risk of lymphoid and breast cancer. There is also some evidence linking EO

29https://www.canada.ca/en/health-canada/services/food-nutrition/food-safety/food-additives/lists-permitted/8-other-accepted-uses.html
Health Canada - MRL Database (choose: Ethylene Oxide & Sesame seeds); http://oasdmz01.hc-sc.gc.ca/mrl-lrm/index-eng.php, extracted on 25.11.2020
and https://www.ecfr.gov/cgi-bin/text-idx?SID=f944ee5791ae8ffd2915f089996c105b&mc=true&node=se40.26.180_1151&rgn=div8
31
https://www.law.cornell.edu/cfr/text/40/180.151
32
https://foodregulation.gov.au/internet/fr/publishing.nsf/Content/forum-communique-2001-September
33
Regulation 1223/2009/EC
34
Regulation 10/2011/EU
35
ECHA: https://echa.europa.eu/de/substance-information/-/substanceinfo/100.000.773
36
Annex V to Reg. 528/2012/EU (Biocide Product Regulation - BPR)
30

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 5

exposure to reprotoxic effects. ECHA has classified ethylene oxide in category 1B as regards carcinogenicity, mutagenicity and reproductive toxicity respectively, and in category 3 as regards the acutetoxicity37. The US National Institute of Health (NIH)38 classified EO as “known to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in humans, including epidemiologicalstudies and studies on mechanisms of carcinogenesis.” The US Environmental Protection Agency(EPA)39 has concluded that EO is carcinogenic to humans by the inhalation route of exposure. Being
considered a genotoxic carcinogen and as there is no acceptable threshold for exposure, no ADI wasestablished for EO.
The pathway of EO exposure can influence its metabolism within the body. EO is readily absorbed via
inhalation or dermal contact and distributes within the body via the blood stream. Available data indicate that parts of the EO taken up through inhalation are exhaled (ca. 20-25%), parts are hydrolyzed
to ethylene glycol (ca. 50%) and parts are conjugated to glutathione (ca. 20%). Other parts of EO bindto various reaction partners within the body, such as amino acids (and proteins), purine bases (andDNA / RNA), fatty acids and other.
EO quickly disappears in food through evaporation or reactions, so the exposure of consumers to
EO-related residues through food consumption will mainly concern EO reaction products, themost prominent of which being 2-CE. 2-CE is also legally relevant as it is included in the current MRL
residue definition. Ingested 2-CE will be oxidized by alcohol dehydrogenase to 2-chloroacetaaldehyde, and finally to 2-chloroacetic acid. Both 2-chloroacetaaldehyde, and 2-chloroacetic acid are detoxified through glutahion conjugation40. 2-chloroacetaldehyde is toxicologically more critical than 2CE41,42,43 and is classified as Category 2 carcinogen by ECHA44. 2-CE and 2-bromoethanol are considered weakly genotoxic and potentially carcinogenic45. A thorough overview on the toxicology of 2chloroethanol is presented by Hartwig et al. (2019)46. The German Risk Assessment Authority (BfR)
recently evaluated the toxicity of 2-CE. Given the inconclusive toxicological picture of 2-CE, it was
decided to follow the precaution approach and consider 2-CE equally toxic to EO47.
Any intact EO remaining in food and thus orally ingested is expected to partly transform to 2-CE within
the stomach, where acidic conditions and high concentrations of chloride occur.
Consumer exposure to EO-related residues in sesame (mainly 2-CE), will strongly depend on thesesame consumption, which can be very different from country to country. According to FAOSTATin the decade 2004-2013, the average annual consumption of sesame seeds in the EU countries was37

https://echa.europa.eu/de/regulations/clp/classificationhttps://echa.europa.eu/en/regulations/clp/classification
https://ntp.niehs.nih.gov/ntp/roc/content/profiles/ethyleneoxide.pdf
39
https://www.epa.gov/sites/production/files/2016-09/documents/ethylene-oxide.pdf
40
W. Grunow, H.J. Altmann Toxicokinetics of chloroethanol in the rat after single oral administration. Arch Toxicol 49: 275–284 (1982)41
https://www.foodstandards.gov.au/code/applications/documents/A445_FARs37.pdf
42
J. McCann,V. Simmon,D. Treitwieser, and B.N. Ames; Mutagenicity of chloroacetaldehyde,a possible metabolic product of 1,2-dichloroethane (ethylene dichloride), chloroethanol (ethylene chlorohydrin), vinylchloride, and cyclophosphamide; Proc. Nat. Acad. Scd. USA Vol.
72, No.8, pp.3190-3193 (1975) Genetics
43
J Fowles, J Mitchell, H McGrath; Assessment of cancer risk from ethylene oxide residues in spices imported into New Zealand.; Food andchemical toxicology 39 (2001) 1055-1062
44
https://echa.europa.eu/information-on-chemicals/cl-inventory-database/-/discli/details/53634
45
https://www.foodstandards.gov.au/code/applications/documents/A445_FAR_091002.pdf
46
A. Hartwig, MAK Commission; 2‐Chlorethanol [MAK Value Documentation in German language, 2019]; Volume 4; Issue (2019);
https://onlinelibrary.wiley.com/doi/full/10.1002/3527600418.mb10707d0067
47
BfR-Stellungnahme zur Toxizität von Ethylenoxid und 2-Chlorethanol, hier: Funde in Sesamsamen und in hieraus hergestellten Erzeugnissen vom 20.11.2020, Az. 30-0202-01-11345065
38

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 6

0.07 kg per person48. Looking at individual countries, the highest sesame consumption in the EU isobserved in Cyprus (1.3 kg per person annually) followed by Greece (1.1 kg), Malta and Austria (0.3
kg each). In most EU countries, annual sesame consumption is below 0.1 kg per person. Considerably
higher consumption figures are encountered in the Middle East (e.g. Israel 4.7 kg; Lebanon 2.5 kg).
These consumption differences between EU-countries will need to be taken into account in dietaryintake and risk assessment calculations as well as in MRL-setting. Individual population groups withhigh consumption of sesame products (e.g. immigrants from the Middle East) may also need to beconsidered. Beyond the average consumption figures, short-term consumptions are also of interestas high-dose exposures (especially if repetitive) increase the risk of a mutation incidence within the
body and therefore the risk of developing follow-up effects such as cancer.
Alternative sources of human exposure to EO and its reaction products:
It could be shown that EO can be formed naturally through enzymatically catalyzed oxidation of ethylene; involving CYP-450 oxidases. This was demonstrated for both bacteria49 and plants50. Endogenous oxidation of ethylene to EO in the human body through bacterial activity within the intestinal
tract was reported by Ehrenberg et al. (1977)51 and many other authors. Tornqvist (1996)52 indicatedthat the transformation of ethylene to EO explains the background levels of EO-adducts with DNA andproteins, such as hemoglobin. They have also demonstrated that EO-adduct formation is linked to themetabolism of unsaturated fatty acids via ethylene by the intestinal flora. An additional ethylene precursor is the amino acid methionine, which is also metabolized to ethylene53. Another source of EO
formation and uptake is the inhalation of combustion gases including cigarette smoke and car
exhaust gasses54. Kirman (2017)55 discusses the risks originating from endogenous and exogenous(occupational and cigarette smoke) exposure to EO.
Possible sources of background levels in food
It is always of interest to check whether food may be contaminated with regulated pesticides andmetabolites (i.e. EO and 2-CE) through pathways going beyond direct pesticide use on the product.
From a purely theoretical perspective EO and 2-CE may end up in food when ethylene, which isendogenously produced within the plants, is enzymatically oxidized to EO and further transformed to2-CE within the plant. Ethylene could theoretically also react with hypochlorite (contained in chlorinated water) to form 2-CE. This could take place during sesame processing (soaking, washing) or in
the field during (irrigation). A minor contamination with EO and 2-CE could take place when combustion gasses containing EO contaminate the samples during the drying or roasting process. Less likely,
but theoretically conceivable as sources of 2-CE, would be vinyl chloride (chloroethene) and dichloroethane (ethylene chloride), that are both well-known 2-CE precursors. See also discussion under“Residues in real samples”.
48

http://www.fao.org/faostat/en/#home
De Bont JAM. 1975. Oxidation of ethylene by bacteria. Ann. Appl. Biol. 81:119–121.
50
Dodds JH, Musa SK, Jerie PH, Hall MA. 1979. Metabolism of ethylene to ethylene oxide by cell-free preparations from Vicia faba L. Plant
Sci. Letts. 17:109–114.
51
Enrenberg L, Osterman-Golkar S, Segerback D, Svensson K, Calleman CG. 1977. Evaluation of genetic risks of alkylating agents. III
Alkylation of hemoglobin after metabolic conversion of ethene to ethylene oxide in vivo. Mutation Res. 45:175–184.
52
Tornqvist M.: Ethylene oxide as a biological reactive intermediate of endogenous origin; Adv Exp Med Biol (1996) 387: 275-283.
53
Lieberman, M. and Mapson, L.W. Genesis and biogenesis of ethylene Nature, 204, 343-345 (1964)
54
Törnqvist, M., Osterman-Golkar, S., Kautiainen, A., Jensen, S., Farmer, P.B., Ehrenberg,L., 1986. Tissue doses of ethylene oxide incigarette smokers determined from adductlevels in hemoglobin. Carcinogenesis 7 (9), 1519–1521.
55
C.R. Kirman, S.M. Hays; Derivation of endogenous equivalent values to support risk assessment and risk management decisions for an
endogenous carcinogen: Ethylene oxide; Regulatory Toxicology and Pharmacology; Volume 91, December 2017, Pages 165-172
49

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 7

Analytical procedures
Various methods for the analysis of EO, or the sum of EO and 2-CE have been presented in literature.
In 1988, K.G. Jensen56 published a method involving conversion of 2CE to EO under alkaline conditions. The produced EO (consisting of any EO originally present in the sample and the EO formed
from 2-CE) is purged using a nitrogen flow into an aqueous reservoir containing sodium iodide andsulfuric acid. There, EO is converted to iodoethanol, which is subsequently partitioned into ethyl acetate and measured via GC-ECD. The method was adapted in a modified form and extensively validated in an inter-laboratory study by Gilsbach et al.57 ultimately becoming an official standard in Germany58. The method also foresees the analysis of intact EO, originally present in the sample. This isachieved by purging EO from the sample without any alkaline treatment at the initial step. The 2-CElevels can then be determined through difference calculation between intact EO and EO (sum).
In 1988, Aitkenhead et al.59 presented a method for the analysis of 2-CE (and 2-bromoethanol) in
spices. The analytes are extracted from the sample using a mixture of acetonitrile and methanol andthen determined by GC-FID. In 1995, Woodrow et al.60 published a method involving direct headspace
sampling for the analysis of EO in spices. In 2002, Ayoub et al.61 published a method involving headspace sampling or direct immersion SPME to determine EO from medical devices. In 2006, Tadeo
and Bononi62 published a method for the analysis of 2-CE in pepper. The method involved conversionof any residual EO into 2-CE, using sulfuric acid and sodium chloride, followed by an extraction of thetotal 2-CE with ethyl acetate, an evaporation step for enrichment and GC-MS analysis.
Analyte properties and analytical strategies
The choice of the analytical approach depends on both the analytes and the matrix to be analyzed.
The available equipment and the methods already routinely employed in a lab also need to be considered. When following a single-residue analysis approach, the procedure can be optimized towards
better analytical performance (sensitivity, recovery rates etc.) by taking advantage of the specific physicochemical properties of the analytes (e.g. polarity, volatility). Some methods focusing only on EO
and/or 2-CE were described above. When trying to integrate those two analytes into an existing multiresidue procedure, there are more restrictions when it comes to optimization possibilities, but at thesame time, this approach it is more efficient for the labs.
Tables 1 and 2 give an overview of the physicochemical properties of 2-CE and EO. The logKow
values of EO (-0.3) and 2-CE (0.24) suggest a decent partitioning of both analytes from an aqueous
phase into an organic solvent if not too non-polar. Satisfactory recovery rates by the QuEChERS
approach are thus expected. The volatility and reactivity of EO raise concerns as regards the handlingof standard solutions and the possibility of losses due to evaporation or interactions with the matrix.
The chromatographic separation of EO and its isomer acetaldehyde is an additional important aspect
56

K.G. Jensen; Determination of ethylene oxide residues in processed food products by gas-liquid chromatography after derivatization. Z.
Lebensm Unters Forsch 187, 535–540 (1988)
57
W. Gilsbach, R.D. Weeren; Ringuntersuchungen zur Validierung einer gaschromatographischen Methode zur Bestimmung von Rücksänden an Ethylenoxid und 2-Chloroethanol in Gewürzen aus Paprika und Chili, Dtsch. Lebensm. Rundsch. 95, 83–90 (1999).
58
Amtliche Sammlung von Untersuchungsverfahren nach § 64 LFGB, L53.00-1 (formerly ASU §35 LMBG L53.00-1)
59
P. Aitkenhead and A. Vidnes;. Simple and accurate method for determination of ethylene chlorohydrin in dried spices and condiments. J.
Assoc. Off. Anal. Chem. 71, 729–731 (1988).
60
J. E. Woodrow, M. M. McChesney, and J. N. Seiber; Determination of Ethylene Oxide in Spices Using Headspace Gas Chromatography;
J. Agric. Food Chem., 43, 8, 2126–2129 (1995)
61
K. Ayoub, L. Harris, B. Thompson; Determination of low-level residual ethylene oxide by using solid-phase microextraction and gas
chromatography. J. AOAC Int. 85 (6), 1205–1209 (2002)
62
F. Tateo, M. Bononi: Determination of ethylene chlorohydrin as marker of spices fumigation with ethylene oxide; Journal of Food Composition and Analysis 19, 83–87 (2006)

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 8to consider in GC analysis60;63.. 2-CE, the main analyte expected to be present as residue in samples,shows a remarkably low volatility for its size, which is attributed to strong intramolecular hydrogenbonds64. It also appears to be quite stable in the matrix and during GC analysis. The non-amenabilityof 2-CE and EO to standard LC-ESI-MS/MS measurement65 and the amenability of both compounds
to GC-MS(/MS) makes the latter approach the first choice to focus on. In the case of GC-analysis, theremoval of matrix co-extractives of low volatility is needed. Fortunately, lipid removal in QuEChERS
or QuOil is easily achieved by C18 sorbents or by a freeze-out step.
Table 1: Comparison of physicochemical properties of EO and 2-CE compared to common solvents

Compound

LogKow

Ethylene oxide
Acetonitrile
Ethanol
Water
2-Chloroethanol

-0.3
-0.34
-0.3
--0.14

Molecular
weight
44.05
41.05
46.07
18.02
80.52

Vapour pressure at
20 °C
1,45 bar
0.1 bar0.06 bar0.02 bar
0.007 bar

Boiling point
10.4 °C
80.2 °C
78.5 °C
100 °C
129 °C

Commodities relevant for residues of EO/2-CE are primarily spices, oily seeds and nuts. Nuts and oily
seeds (including some oily spices, such as cumin seeds) contain lipids in the range between 20 and
70%. The lipid content of sesame (currently in the focus), ranges between 42 and 56% according toGirmay (2018)66 and between 53 and 67%, with an average at 60%, according to Hanine et al.
(2019)67. Processed products derived from sesame, such as oils, tahini, halva and bakery goods arealso of relevance. When it comes to such commodities (high lipid content, low water content), manylabs nowadays employ the QuOil method. This method involves extraction with acetonitrile (in thecase of oils) or acetonitrile containing 5% of water (in the case of oily seeds and nuts). Co-extracted
lipids and fatty acids are removed by dSPE with C18 and PSA sorbent respectively. MgSO4 can reduce
the water content in the acetonitrile extract of QuEChERS and QuOil extracts from 7-8% and 5%
respectively, down to 2-3%.
Direct GC-analysis of the QuEChERS or QuOil extracts, can be problematic due to the large expansion volume of acetonitrile and the negative impact of acetonitrile and the residual water contained in
extracts to the column and the filaments. A way out is split-injection and in case of PTV-injectors, theevaporation of the solvent in the in the liner by a gentle nitrogen stream. In the latter case, evaporation
losses of EO during purging would be expected to a certain extent.
Based on all above considerations, it was decided to target EO and 2-CE by QuOil, in the case of dryhigh oil content commodities, and by QuEChERS when dealing with other commodities and to analyze
the extract directly by GC-MS/MS following the removal of the lipids. Both QuEChERS and QuOil areroutinely employed in many labs for multiresidue analysis.

63

https://www.agilent.com/cs/library/applications/A01291.pdf
Microwave Spectra and Intramolecular Hydrogen Bonding in the 2‐Haloethanols: Molecular Structure and Quadrupole Coupling Constantsfor 2‐Chloroethanol and 2‐Bromoethanol J. Chem. Phys. 52, 5299 (1970)
65
According to pre-experiments of the EURL-SRM
66
A. B. Girmay; Sesame Production, Challenges and Opportunitiesin Ethiopia; Agri Res & Tech: Open Access J 15(5):ARTOAJ.MS.ID.555972 (2018); https://juniperpublishers.com/artoaj/pdf/ARTOAJ.MS.ID.555972.pdf
67
M. El Harfi, A. Nabloussi, H. Rizki, S. Ennahli and H. Hanine; Proximate Composition and Fatty Acid Composition, Phytochemical Content
of Sesame (Sesamum indicum L.) Seeds Landrace from Morocco; Adv Crop Sci Tech 2019, 7:3
64

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 9

Table 2: Compound details at a glance
Ethylene oxide (CAS: 75-21-8),
Other names: Oxiran, Epoxyethane, Oxacyclopropane; Abbreviations: EO, EtO, ETO
Parameter

Value

Molecular Mass

44.052 g/mol

Notes

FormulaC2H4O

Boiling point

10.4°C

pKa

No dissociation in water

LogD-0.0568

pH independent; LogKow -0.3 (WHO); computed by Chemicalize.com

Water solubility

infinite

pH independent

Stability

The main route of losses is evaporation. In neutral water at 25 °C, ethylene oxide is hydrolyzed to glycol with ahalf-life of 14 days (at 0 °C, half-life is 309 d). In presence of halide ions (chloride, bromide, iodide), 2-haloethanol
is formed next to glycol and half-life is shortened (Conway et al., 1983).
When heated, EO isomerizes to acetaldehyde through surface catalyzed rearrangement69

Residue definition EU

Ethylene oxide (sum of ethylene oxide and 2-chloro-ethanol expressed as ethylene oxide) (F)(Note by EURL-SRM: the (F) attribute is questionable given the LogD value and the lack of bioaccumulation properties)

Approved in…

No authorization in place within the EU

Properties of concern

Being an electrophilic agent, EO reacts with nucleophilic groups (e.g. amino, thiol, hydroxyl). 2-hydroxyethyl adducts are formed with amino acids within proteins (e.g. with cysteine, histidine and N-terminal valine) and bases
within DNA and RNA (e.g. adenine, guanine). Shown to be mutagenic, carcinogenic and reprotoxic in animals.
Endocrine Disruption properties are being assessed (ECHA). IARC70 classified EO as carcinogenic to humans(Group 1). Certain plastics are permeable by ethylene oxide, so not all cloves offer full protection.

Other sources

Naturally developed at very low levels in plants and animals as a metabolite of the growth hormone ethylene.
Formed during combustion of organic material (e.g. 2-7 µg per cigarette)
Diethylene glycol and polyurethanes produced thereof may contain residues of EO
Polyethylene glycol-based detergents (used in cosmetics) may contain residues (Legal limits established).

2-Chloroethanol (CAS: 107-07-3)
Other names: 2-Chloroethan-1-ol; Ethylene chlorhydrin; Glycol chlorohydrin; Abbreviations: 2-CE; 2CE; CE; ECH
Parameter

Value

Molecular Mass

80.51 g/mol

FormulaC2H5ClO

Boiling point

129°C (due to intramolecular hydrogen bonding, the boiling point is comparablyhigh and volatility low)71

pKa

Strongest acidic pKa: 14.86

LogD

0.15

pH independent

Water solubility

misciblepH independent

Stability

Hydrolyzed to ethylene glycol, Oxidized via chloroacetaldehyde to chloroacetic acidAt high temperatures acetaldehyde is formed though HCl elimination72

Residue definition EU

Ethylene oxide (sum of ethylene oxide and 2-chloroethanol expressed as ethylene oxide)

Properties of concern

Forms phosgene upon combustion, Reported to have a moderate mutagenic potential

Acute toxicity

Fatal if swallowed, in contact with skin and if inhaled (ECHA)Classified as an extremely hazardous substance in the United States

Other sources

Notes

Metabolite in the degradation of 1,2-dichloroethane (widely used in the production of vinyl chloride) and also metabolite of vinyl chloride. Furthermore formed when ethylene interacts with hypochlorite

68

Computed by Chemicalize.com
M.L. Neufeld and A.T. Blades; The kinetics of the thermal reactions of ethylene oxide; Canadian Journal of Chemistry; Volume 41, Number
12, December 1963 (https://cdnsciencepub.com/doi/pdf/10.1139/v63-434)
70
IARC: International Agency for Research on Cancer (2008 report)
71
Microwave Spectra and Intramolecular Hydrogen Bonding in the 2‐Haloethanols: Molecular Structure and Quadrupole Coupling Constantsfor 2‐Chloroethanol and 2‐Bromoethanol J. Chem. Phys. 52, 5299 (1970)
72
The thermal decomposition of 2-chloroethanol; DC Skingle and VR Stimson Australian Journal of Chemistry 29(3) 609 – 615(1976)
69

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 10

Chemicals and Materials
The materials needed can be found under EN-15662 (QuEChERS) or CEN/TS 17062:2019 (QuOil)with the exception of the grinding balls that are needed to improve residue accessibility and reduce
extraction time (e.g. SPEX 2155 (9.5 mm)).
Analytical Standards:
Table 3 gives an overview of the analytical standards used for this study.
Table 3: Analytical standards73
Compounds74
Details on standards used

ProviderOther providers, notes

Ethylene oxide

Both by Merck

Temperate the purchased 1 mL ampulecontaining EO solution in the refrigerator. Open it while still cold and quickly
transfer its content into a sealable container (e.g. a GC-Vial) and store at 18°C.
In lecture bottle.
Difficult to handle
LGC (Dr. Ehrenstorfer);
HPC Standards GmbH

50 mg/mL in methanol(code: CRM48838)

or
50 mg/mL in dichloromethane(code: CRM48891)

Ethylene oxide D4≥98 atom % D, ≥99% (CP)Merck(code: 457833)

2-Chloroethanol

Pure substance >99%

Both by Merck(code: 23000-50ML)

or
2000 µg/mL solution in MeOH
(code: CRM48085)

2-Chloroethanol D4

98 atom%(code: DLM-1928-PK)

Cambridge
Isotopes

HPC Standards GmbH;
TRC
Merck (delays)
LGC: soon available

Stock and working solutions of analytes and ILISs
IMPORTANT SAFETY REMARKS: Ethylene oxide and, to a lesser extent, 2-chloroethanol areconsidered dangerous to health (see introductory text). The use of a fume hood and wearing cloves
is recommended to minimize exposure (Note: some clove materials can be penetrated by EO overtime and should be avoided75).
2-chloroethanol (density 1.21 g/cm3): A stock solution at 5 mg/mL may be prepared as follows:
Pipette 83 µL of 2-chloroethanol (tempered to room temperature) into a reservoir of 20 mL acetonitrile76. This solution is diluted with acetonitrile to prepare various working solutions as required by eachexperiment. Alternative ready to use solutions may be purchased.
2-chloroethanol-D4: A stock solution at 5 mg/mL is prepared by pipetting 41 µL of 2-chloroethanol(tempered to room temperature) into a reservoir of 10 mL acetonitrile. This solution is diluted withacetonitrile to prepare working solutions (at e.g. 40 µg/mL for use during sample preparation and ate.g. 4 µg/mL for calibration solutions 77.
73

Disclaimer: Names of companies are given for the convenience of the reader and do not indicate any preference by the EURL-SRM
towards these companies and their products
74
Under IATA regulations, EO and 2-CE are not allowed to be transported by air.
75
https://www.lyondellbasell.com/globalassets/documents/chemicals-technical-literature/ethylene-oxide-manual.pdf (page 78 ff)
76
82.64 µL 2-CE and 19,92 mL ACN would be more precise figures, assuming 100% purity of 2-CE
77
Spiking 100 µL of this standard to a 2 g sample portion will correspond to 2 mg/kg

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 11Ethylene oxide: Commercial certified ethylene oxide solutions, as those listed above, can be considered as stock solutions. Prepare the necessary working solutions by dilution with acetonitrile. Overall,
it is preferable to handle EO-solutions at low temperatures to reduce evaporation losses. Open cold
vessels only for a short time to reduce water-condensation. As the density of methanol, dichloromethane and acetonitrile shifts similarly when moving from room- (~ 22°C) to refrigerator- (~ 4°C) andfreezer- (~ -18°C) temperatures78, volumetric errors become negligible, if the standard solutions to bediluted and the solvents used for dilution have similar temperatures. You may also pipette the acetonitrile reservoir at room temperature and place it in the fridge or freezer afterwards, but in this case,the volume contraction needs to be considered79.
For the preparation of further diluted working solution, follow the same principles. If these solutions
are used in cold condition for spiking, volume contraction must be considered80.
Ethylene oxide D4: As soon as commercial EO-D4 solutions become available (as in the case ofnative EO), working solutions may be prepared in the same way as described above for EO81.
For the purpose of the experiments shown in the following, the EURL-SRM has prepared EO-D4 solutions in two different ways:a) by carefully trapping gaseous EO-D4 into a cold methanol reservoir. The concentration of the solution prepared in this way was estimated at ~20 mg/mL82. This solution was stepwise diluted with acetonitrile to obtain a working solution at ~10 µg/mL, which was for spiking the analytical portions prior
to extraction. A 10-fold dilution thereof in acetonitrile, was prepared freshly before each experimentday and used for the preparation of calibration standards.
b) by chemically transforming 2-CE-D4 to EO-D4 under alkaline conditions and partitioning the latter
into acetonitrile83. The final EO-D4 concentration in the prepared solution was expected to be around
120 µg /mL and this was confirmed by a measurement against a native standard. Residual levels of
2-CE-D4 in the final solution were checked and found being negligible. This solution was further diluted
with acetonitrile to a working solution containing ~5 µg/mL, which was used for spiking analytical portions during analysis. For calibration purposes, a 10-fold diluted working solution of this standard was
freshly prepared on each experiment day.

78

Density figures and density ratios at 22°C, 4°C and -18°C, respectively- ACN: Density: 782.2, 801.8, 825.2 (mg/mL);- MeOH: Density: 790.5, 806.7, 825.7 (mg/mL); density ratio MeOH/ACN: abs.: 1.010; 1.006; 1.001; normalized: 1.000; 0.995; 0,990- DCM: Density: 1324.4, 1356.1, 1393.8 (mg/mL); density ratio DCM/ACN: abs. 1.693; 1.691; 1.689; normalized: 1.000; 0.999; 0,998
The density figures for DCM were calculated by http://www.ethermo.us using the “Antoine” approach and for ACN and MeOH they wereretrieved from Dortmund Database (http://ddbonline.ddbst.com/DIPPR105DensityCalculation/DIPPR105CalculationCGI.exe).
The small of error <1% can be considered acceptable considering that working at RT increases the risk of larger errors through evaporation.
79
Pipette 2.5% ACN more at room temperature if the EO standard you would like to dilute is tempered in the fridge (~4°C) and 5.5% more
ACN if the EO-solution is tempered in the freezer (~-18°C). Examples: 10,19 mL ACN at room temperature corresponds to 9.9 mL at 4°C
and 10.45 mL ACN at room temperature corresponds to 9.9 mL at -18°C.
80
When working at refrigerator temperature increase the volume of acetonitrile-based solutions by 2.5% (e.g. 102.5 µL corresponds to 100µL at room temperature) and when working at freezer temperature by 5.5% (e.g. 105.5 µL corresponds to 100 µL at room temperature)81
The concentrations of ILIS solutions do not have to be exactly known (unlike native EO). It is, however, important that the amount of ILIS
added to the analytical portion and the amount of ILIS added to the calibration solutions is at an exactly known proportion (e.g. 10:1). Thismeans that only the last dilution step will need to be conducted in a way ensuring exactness.
82
Approximate concentration was estimated by comparing the GC-MS signals against those of native EO solutions
83
Procedure followed: Add 2 mL 5N NaOH + 3 mL ACN + 1 mL 2CE-D4 (1000 µg/mL ACN) into a 50 mL PP falcon tube. Close the trube
and let it react for 2 h at room temperature, occasional shaking. Cool down in the freezer. Neutralize with 2 mL 5N H 2SO4, add partitioning
salt (1.5 g MgSO4), + Buffer mix (200 mg NaAc + 20µL HAc) centrifuge shortly, cool down in the freezer and transfer 3,5 mL of the ACNPhase into a 15 mL PP centrifuge tube containing 300 mg MgSO4. Shake, centrifuge shortly, and cool down. Transfer twice 1.3 mL into two
GC-Vials with screw caps. Assuming full transformation and partitioning of ca. 80% of EO-D4 into the ACN phase the expected EO-D4
concentration was ~120 µg/mL. A signal comparison against native EO confirmed this.

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 12Remarks on stability of EO / EO-D4 solutions: To minimize evaporation losses the EO-solution should
be preferably added to the acetonitrile reservoir rather than into an empty vessel. Screw-caped bottles
are preferable to bottles with fitting glass stoppers. Stock and working solutions of EO in screw-cap
glass bottles with Teflon seals can be stored in the refrigerator for at least a month and for longer
periods in the freezer. Chemical degradation does not seem to contribute significantly to ethyleneoxide losses, but evaporation losses can be critical and should be minimized (i.e. avoid large headspace, repeated tempering of working standards to room temperature and frequent opening of vessels). Diluted EO and EO-D4 working solutions used for the preparation of calibration solution arerecommended to be prepared freshly on the day of the experiment.

Sample Preparation
Homogenization: For oily seeds, it is recommended to pre-cool the knife mill84 by grinding a small
portion of dry ice. Reopen the mill; add the material to be homogenized (oily seeds, nuts or spices)
and if no dry ice is left in the mill add a small amount of dry ice (sample to dry ice ratio ca. 5:1) and
grind for a few seconds at high speed to obtain fine free-flowing grit85.
When dealing with very small oily seeds, such as sesame seeds (ca. 3 mg per seed) or poppy seeds(ca. 0.3 mg per seed), intact seeds may also be employed for analysis, but the whole sample should
be mixed thoroughly before withdrawing the analytical portion. In this case, the use of extraction aids,
such as stainless steel balls, will be needed to ensure good residue accessibility.´
Tahini should be thoroughly mixed to ensure a homogeneous distribution of the solids. Experiments
by the EURL-SRM have shown that no significant losses of 2-CE occur when the sample is milled86.

QuOil-Method (CEN/TS 17062:2019 modified)87
Weigh 2 g ± 0.02 g88 of sample homogenates (oil, nuts, or oily seeds89) and add 10 mL of acetonitrile
containing 5% v/v of water. Optionally add ILIS-solution(s)90, add extraction aids (e.g. 3-4 9.5 mm
stainless steel balls), close the vessel and extract by a mechanical shaker for 5 minutes in the caseof oils, 15 minutes in the case of finely comminuted material (e.g. tahini) and for 15-30 min in the caseof intact seeds or laboratory-homogenized material91. Centrifuge at >3000 g92 and then subject the84

The mill should have a hole to allow the evaporated dry ice to escape. Mill at high speed for a short time. If dry ice is left in the material
after milling, mill further until the dry ice is evaporated.
85
Homogenizations of high oil content commodities for extended periods or without cooling often lead to pasty material sometimes stillcontaining larger insufficiently comminuted pieces.
86
The impact of milling on EO concentrations needs to be checked on samples containing incurred EO-levels. Such samples were notavailable to the EURL.
87
QuOil is a multiresidue method for pesticides in commodities of high lipid and low water content such as oils, oily seeds and nuts. In
such matrices, the method achieves higher recoveries for lipophilic pesticides compared to QuEChERS. The current version of CEN/TS
17062:2019 only includes the module for pure oils in which pure acetonitrile is used as extraction solvent. The module for oily seeds
and nuts is currently in the implementation process and foresees acetonitrile containing 5% v/v of water as extraction solvent. For labs
already employing the QuOil method routinely, the inclusion of EO and 2-CE in the analyte scope would be a convenient and efficient step.
88
2 g are used within the multiresidue approach to keep the overall lipid amount small and reduce losses of lipophilic compounds. Where
this method will only target EO and 2CE, which are polar enough not to partition into the lipid phase, the sample weight may be increased from 2g to 5 g. This improves method sensitivity without negatively influencing recoveries.
89
Seed spices can be also regarded as oily seeds, e.g. nutmeg (25-40%, mace 20-30%); cumin seeds (22%) and coriander seeds (18%)
90e.g. 50 or 100 µL of appropriately concentrated ILIS solutions 2-CE-D4 and EO-D4. Conduct pre-experiments to determine the appropriate
amount of 2-CE. If EO-D4 is used as ILIS, it should be spiked to the vessel after adding the acetonitrile to minimize evaporation losses.
91
Intact seeds can only be extracted properly when adding grinding aids (e.g. metal balls) during extraction. Adding extraction aids,
such as stainless steel balls to the extraction vessels, improve residue accessibility and extractability, thus allowing for shorter extraction
times. EURL-SRM experiments have shown that without extraction aids extraction times of 15 min (typical with QuOil) are barely sufficientfor very finely milled material (e.g. tahini) but insufficient for laboratory milled material (here, 45-60 min extraction times are recommended).
92
Cold centrifugation at -10°C for 10 minutes will also remove certain amounts of lipids and fatty acids

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 13

extract to dispersive SPE cleanup with C18/PSA/MgSO4 (25/25/150 mg/mL extract) to remove lipids
and fatty acids93. The extract is filled into GC-vials for GC-MS/MS measurement.

QuEChERS-Method (EN 15662)94
For cereals, spices and other dry commodities of low lipid content the procedure described in
EN-15662 is followed but extraction time is prolonged to 15 min in case extraction aids are used andto 45 min if they are not used.
Nuts and oily seeds (such as sesame) are actually not included in the scope of EN 15662. Still, thisprocedure is suitable for the analysis of EO and 2-CE as these compounds are polar and show only
little tendency to partition into a separated lipid phase. Weigh 2 g ± 0.02 g95 of sample homogenates(nuts, or oily seeds89) and add 10 mL of acetonitrile. Optionally add ILIS-solution(s)90, add extraction
aids (e.g. 3-4 9.5 mm stainless steel balls), close the vessel and extract by a mechanical shaker for 5
minutes in the case of oils, 15 minutes in the case of finely comminuted material (e.g. tahini) and for
15-30 min in the case of intact seeds or laboratory-homogenized material91. Add the QuEChERS
buffer-partitioning salts mixture and shake for 1-2 minutes. Centrifuge at >3000 g92 and then subject
the extract to dispersive SPE cleanup with C18/PSA/MgSO4 (25/25/150 mg/mL extract) to remove
lipids and fatty acids. The extract is filled into GC-vials for GC-MS/MS measurement.

Figure 1: Overview of QuEChERS and QuOil as regards the role of lipids and the partitioning of pesticides
between the phases depending on their polarity (see also comments under Note 94)93

This mixture corresponds to the standard mixture used in the QuEChERS procedure (EN-15662)
QuEChERS is a multiresidue method for the analysis of pesticides in commodities of low lipid content. At high lipid content, the lipids
not dissolven in CAN will form a separate phase into which lipophilic compounds will partly partition. When targeting lipophilic compounds
the amount of the lipid phase should be kept low to minimize the partitioning losses of lipophilic pesticides. Typically the amount of lipids
within the analytical portion is kept < 0.35 g (i.e. < 7% lipids in sample if 5 g analytical portions are employed (e.g. cereals) and < 18% lipids
in samples where 2 g portions are employed (e.g. spices).
95
Increasing the sample weight from 2g to 5 g improves method sensitivity without negatively influencing recoveries.
94

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 14

Measurement:
The cleaned-up extract is directly measured by GC-MS/MS. Exemplary measurement conditions are
given in Table 4 and Table 5.
Table 4: Instrumentation details

GC
Injector
MS/MS
ColumnPre-column
Mobile Phase / Flow
Injection mode
Injection volume
Injection temp. program
Oven temp. program
MS Parameters

Thermo Trace 1310 with TriPlusRSH Autosampler
Gerstel KAS 6
Thermo TSQ 8000
J&W HP-VOC GC Column, 30 m, 0.20 mm, 1.10 µm, Part Number:19091R-303
Fused Silica Tubing, Deactivated, Diameter: 0.25 mm, Agilent J&W,
Length: 3 m
Helium, 1 mL constant flow
Split 1:4
2 µL
Start at 90°C and hold for 0.8 min, ramp with 12°C/s to 250°C, hold
10 min,Start: 45 °C, hold 2 min, ramp to 150°C reached at 4.1 min; ramp to
280°C reached at 5.1 min, hold till 16 min
Mass axis tune mode: LowMass
Ionisation mode: EITransfer line temperature: 250°C; Ion source temperature: 270°C

Table 5: MRM Details of EO, 2-CE and their respective ILISs

Name of Compound

Retention timemin

Ethylene oxide

2.57

Ethylene oxide D4

2.57

2-Chloroethanol

4.61

2-Chloroethanol D4

4.61

Parent
(m/z)
44
44
44
48
48
80
80
82
84
86

Daughter
(m/z)
14
28
29
16
30
31
43
31
33
33

CE
20
5
5
20
5
5
5
5
5
5

Calibration and Matrix Effects
Both EO and 2-CE show moderate matrix effects (ME) in GC. Unlike the general trend in GC, in whichanalyte signals increase in presence of matrix, in the case of EI and 2-CE signals are slightly larger inabsence of matrix. Matrix components, however, improve the peak shape of 2-CE which shows slightly

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 15

better peak shapes in QuEChERS compared to QuPPe extracts. For improving the peak-shape of 2CE96 analyte protectants (APs)97 may be added to sample extracts and calibration solutions alike.
All available options for dealing with ME may be used including external matrix-matched calibration,
standard addition to extract aliquots, standard addition to sample portions, and procedural calibration.
The later two options will also correct for recovery, although recovery rates are generally satisfactorywith both QuPPe and QuEChERS. The use of ILISs (2-CE-D4 and EO-D4) can be combined with anyof the above approaches and it will correct for recovery if added at the beginning of the procedure. In
the case of matrix-matched and external calibration, make sure to select a blank matrix showing insignificant background levels. This is of high importance when dealing with low levels.

µg/mL
Figure 2: Exemplary calibration curves of EO and 2CE without AP. Matrix effects at the 5 µg/mL level were 12% for EO and -17% for 2CE. No use of AP

96

In general, the 2-CE peak form when injecting QuEChERS extracts is narrower than when injecting QuOil extracts, which is attributed tothe presence of polar co-extractives in QuEChERS extracts, that interact with active sites in the GC-system thus protecting the analytes.
97
https://www.eurl-pesticides.eu/library/docs/srm/EURL_Observation-APs.pdf

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 16

Experiments and observations:
GC-Analysis:Some exemplary chromatograms of EO in sesame extracts (at 0.2 g sesame/mL) are shown in Figure
3. Peak shape is overall satisfactory and matrix interference moderate. At the low level, the second
transition is interfered.

Figure 3: Exemplary chromatograms for EO spiked on QuOil extracts of blank sesame at levels corresponding
to 0.025 mg/kg; 0.25 mg/kg and 0.5 mg/kg. Matrix Concentration: 0.2 g/mL.

Some exemplary chromatograms of 2-CE in sesame extracts (at 0.2 g sesame/mL) are shown in
Figure 4. Peak shape is overall satisfactory and matrix interferences moderate.

Figure 4: Exemplary chromatograms for 2-CE spiked on QuOil extracts of blank sesame at levels corresponding
to 0.12 mg/kg and 0.5 mg/kg. Matrix Concentration: 0.2 g/mL

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 17

Dealing with acetaldehyde: Some sesame samples contain high levels of acetaldehyde (AA). AA canbe of natural origin, but it may be also be formed at high temperatures from EO (through thermal
rearrangement) or from 2-CE (through HCl elimination, see more on this below). As AA is an isomerof EO with which it shares several MRM transitions, a chromatographic separation between EO and
AA is paramount. Fortunately, the two compounds are sufficiently separated under the presented
chromatographic conditions. Figure 5 gives an example of a sesame extract containing AA that wasoverspiked with AA or EO. Experiments to check whether AA is formed at the high temperatures, towhich the compounds are exposed during GC analysis, have shown that, under the GC conditions
employed, the transformation of EO and 2-CE to AA in the injector is negligible.

Figure 5: Chromatographic separation between EO and acetaldehyde. Extracts of sesame were overspiked withacetaldehyde (center) or ethylene oxide (right).

Recovery experiments:
Results of recovery experiments using QuOil or QuEChERS are shown in Table 6. Absolute recovery
rates are satisfactory, but EO shows tentatively a bit lower recoveries compared to 2-CE. Based onthese results the use of ILIS to correct for recover is not paramount.
Table 6: Recovery figures obtained using QuOil and QuEChERS method
CompoundEthylene oxide

2-Chloroethanol

MethodPortion[g]n

Spiking Level[mg/kg]

QuOil

2

5

0.04

QuOil

2

5

0.5

QuEChERS

2

5

0.5

ILIS

Mean Rec.
[%]

RSD
[%]

Yes

90%

12.9%

No

92%

8.1%

Yes

94%

3.6%

No

83%

7.8%

Yes

91%

11.5%

No

93%

9.8%

QuOil

2

5

0.12 (expr. as EO: 0.066)

QuOil

5

5

0.05 (expr. as EO: 0.0275)

Yes

95%

2,5%

QuEChERS

2

5

0.08 (expr. as EO: 0.044)

Yes

102%

7,4%

QuEChERS25

0.5 (expr. as EO: 0.275)

Yes

102%

8.1%

No

91%

7.1%

QuEChERS

5

5

0.05 (expr. as EO: 0.0275)

Yes

97%

13.7%

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 18

Impact of comminution on extraction of incurred residues
Experiments on sesame samples containing incurred 2-CE residues have revealed a delay in theextraction of incurred residues from both intact and homogenized seeds.
Figure 6 shows the extraction yields from a sesame sample prepared in two different ways:a) milled shortly at cryogenic conditions (dry ice) to a fine grit andb) milled further for 3 minutes at room temperature to a paste.
As can be seen in the figure comminution to a fine paste accelerates extraction but still 15 min extractions (typical for QuOil) were not sufficient to reach the plateau, whereas 30 min extractions were justsufficient. It seems that the plateau is only reached somewhere between 30 and 45 min. It seems that
ethylene oxide penetrates deep into the sesame corn where is converts to 2-CE which is then difficult
to extract. Another important conclusion from this experiment was that 2-CE was not noticeably affected by the longer comminution at higher temperatures.

Figure 6: Impact of milling on extraction yields of incurred 2-CE from sesame at different extraction times (average of n=3). The average 2-CE yield obtained when extracting the paste for 45 min was set at 100%.

In a subsequent experiment, intact sesame seeds were extracted with and without stainless steel
grinding balls. As shown in Figure 7, without these extraction aids 2-CE yields were very low evenafter 45 min extraction. The stainless steel balls crush the sesame seeds thus accelerating the extraction and shortening the soaking period. Using extraction aids, satisfactory 2-CE yields were already achieved at 15 min extraction times onwards. A 15 min extraction of intact seeds with balls
seems to provide equivalent yields as 15 min extraction of a milled material. Furthermore, theseresults confirm that milling does negatively affect 2-CE residues.
Sesame seeds weigh around 3 mg on average, which means that in 2 g sample there is around 600700 units. In theory, it should be possible to obtain a representative 2 g subsamples if the entire
sample is mixed well. To check how homogeneous the residues are distributed when the sesame
seeds are not milled and whether milling would improve homogeneity of the material, six replicate
extractions were conducted on milled and non-milled sesame seeds. The intact sesame seeds were
thoroughly mixed before withdrawing the analytical portions. Milling was conducted cryogenically withthe help of dry ice. In both cases the analytical portion size was 2g and the extraction time was 15 minwith balls being added to assist extraction. The RSD of the six replicate extractions was at 6.1% in thecase of the non-milled material and at 3.3% for the milled material, which is in both cases within the

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 19

normal analytical variability range. It can thus be concluded, that intact sesame seeds may be extracted from the portion-to-portion variability point of view, but extraction will need to be assisted byextraction aids, such as grinding balls, for achieving satisfactory extraction yields. Even when using
extraction aids the duration of the extraction should be at least 15 min, preferably 30 min.

Figure 7: Impact of stainless steel balls as extraction aids to accelerate the extraction of incurred 2-CE residues
from intact sesame seeds (n=3 each and in some cases n=6; see text).Yield obtained at 45 min extractions withextraction aids was set at 100%.

When extracting tahini, 2-CE extractions are less retarded. In tahini production, sesame seeds areindustrially milled with very small particle sizes being obtained. This results in a larger surface area, abetter accessibility of the residues and consequently a faster extraction. As can be seen in Figure 8,
satisfactory yields of 2-CE were already obtained at 15 min extractions, without the addition of stainless steel balls.

Figure 8: Extraction of incurred 2-CE residues from tahini (n=2 each).The average yield obtained at 45 min
extraction was set at 100%.

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 20

In another experiment it was further observed that in the case of tahini, soaking of the sample in theextraction solvent for 20 min (without shaking), followed by a 1 min extraction, will also lead to quantitative extraction yields. This approach is interesting for labs that do not possess any mechanicalshaker.
Overall extraction aids (stainless steel balls) clearly helped to reduce extraction times significantly,
also enabling the extraction of intact sesame seeds. This may be of advantage when dealing with EO
or other fumigants that are by far more volatile than 2-CE. Without extraction aids extraction times of45-60 min were required to reach the plateau even for samples that were previously homogenized.

Impact of cleanup on removal of co-extractives
To minimize contamination of the GC-system a cleanup step is needed. dSPE with ODS and PSA
sorbents (25 mg /mL extract each) removes considerable amounts of co-extractives.
Table 7 shows the dry residue of extracts that were cleaned-up by different procedures.
It was furthermore observed, that PSA considerably reduces the signals of acetaldehyde. This may
be due to the interaction between the amine groups of the sorbent and the aldehyde group of acetaldehyde, that possibly result in the formation of covalent imine bonds.
Table 7: Dry residues obtained when applying different cleanup procedures.

Extract

Dry residue [mg/mL]

Raw extract

4.0

Raw extract +dSPE C18 (25 mg/mL)

3.1

Raw extract +dSPE PSA (25 mg/mL)

2.2

Raw extract + dSPE with C18/PSA (25/25 mg/mL)

1.7

Raw extract + dSPE with C18/PSA (25/50 mg/mL)

1.4

Cold centrifugation (-10°C) 10 min

3.7

Cold centrifugation (-10°C) 10 min + dSPE with C18 (25 mg/mL)

3

Cold centrifugation (-10°C) 10 min + dSPE with C18/PSA (25 mg/mL)

1.4

Freezer (-18°C) 2h

3.3

Freezer (-80°C) 30 min

2.9

Impact of Processing on 2-CE concentrations
To estimate the impact of processing on the concentration of 2-CE in sesame, intact sesame kernels
containing incurred 2-CE were processed in two ways. A). Roasting in a pan until golden color (ca. 5min); b) Baking, following attachment of the seeds on the surface of a flat dough and baking at 180°C
for 30 min followed by a drying period of 3h at 40°C.
In the roasting experiment 2-CE concentration dropped dramatically to ca 7% of the original value.
At the same time it was observed that the acetaldehyde peak areas increased by more than 80 fold(not quantified). This indicates that at high temperature 2-CE converts to acetaldehyde possibly following elimination of hydrochloric acid (HCl) to form vinylalkohol and a subsequent keto/enol tautomerism.

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 21

In the baking experiment, the dry bread was homogenized and analyzed via QuEChERS. Considering the original amount of sesame attached to the dough surface and the final weight of the driedbread the 2-CE loss following baking was calculated at 61% (39% loss). The peak area of acetaldehyde increased 8-fold.
To estimate the processing factor when producing sesame oil from EO-treated sesame seeds, atahini sample with incurred 2-CE residues was analyzed both in its entirety (following a thorough mixing) and then additionally only the oil phase (separated through centrifugation). The 2-CE residue inthe tahini was 5.1 mg/kg and in the oil only 0.85 mg/kg. Considering the oil content of 60%, andassuming that the oil-solids ratio roughly corresponds to the original ration in the seeds, it can becalculated that only ca. 10% of the original 2-CE residues end up in the raw sesame oil fraction.
Further experiments on tahini will follow.

Analysis of real samples
20 official sesame samples (14 conventional and 6 organic) from the market were analyzed for 2-CE
and EO residues. Five of these samples contained residues exceeding the MRL of 0.05 mg/kg (expressed as EO). Table 8 gives an overview of samples exceeding the MRL of 0.05 mg/kg for EO (sum)and Figure 9 shows the distribution of the residues in conventional and organic samples. Most samples with high levels originated from India or Africa. The levels below the LOQ of 0.05 mg/kg are to beconsidered as semi-quantitative and are only reported with one significant figure.
Table 8: Samples containing EO/2-CE residues exceeding the MRL.

Description of Sample

OriginSesame seeds, hulled
Sesame seeds, hulled
Sesame seeds, hulled
Sesame seeds, hulled
Sesame seeds, black

India
India
Africa (unspecified)
India
India

2-CE
mg/kg
19.1
14.8
12.4
9.6
0.23

EO (sum)
mg/kg
10.5
8.1
6.8
5.3
0.13

Assessment
>MRL
>MRL
>MRL
>MRL
>MRL

Figure 9: Findings of 2-CE residues in conventional and organic sesame samples.

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 22

Various additional sesame or sesame-containing products from local groceries originating from othercountries (e.g. Turkey, Egypt, Greece, and Cyprus) were also analyzed showing either 2-CE residues
at low levels between 0.01 (semi quantitative) and 0.1 mg/kg, or no detectable residues.
None of the official samples analyzed contained any measurable residues of EO. Samples received
from another laboratory, containing very high 2-CE levels, showed EO residues at trace levels below
the limit of quantification. These findings need to be verified. Also, none of the samples analyzed so
far was found to contain any measureable levels of 2-bromoethanol or dioxin, which can be potentiallygenerated during fumigations with EO.
Some exemplary chromatograms of extracts derived from samples from the market are shown in Figure 10.

Figure 10: Peaks of 2-CE obtained from the extraction of three samples containing incurred residues.

The frequency with which 2-chloroethanol is encountered in sesame samples at low levels (< 0.1
mg/kg), raises the question whether there are alternative sources (unrelated to direct EO-fumigations)leading to 2-CE background levels. This aspect needs to be investigated further and, if verified, itwould need to be considered in MRL-setting and the judgement of residue levels. The existence ofsamples with no detectable 2-CE levels, suggests that these low 2-CE levels, encountered in many
samples, are more likely related to exogenous factors, rather than to purely natural processes within
the sesame plant. The behavior of conjugated 2-CE residues, e.g. to fatty acids, during analysis willneed to be studied, as these are not part of the residue definition. Also the possibility of cross-contaminations between lots, during processing, storage or transport will need to be checked.

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 23

Conclusions and Outlook:
Two methods, one based on QuEChERS and one on QuOil, are presented allowing the simultaneous
analysis of ethylene oxide (EO) and its reaction product 2-chloroethanol (2-CE) in sesame. Following
a standard dSPE cleanup the samples are measured by GC-MS/MS
The extraction of 2-CE from sesame, was found to be considerably delayed compared to other analytes. It is thus of high importance to use extraction aids (e.g. stainless steel balls) during extraction
to disintegrate the sample and improve the accessibility of the residues.
For labs routinely applying these methods for multiresidue analysis of pesticides, the inclusion of theseanalytes into their scope is convenient. Still, an extra GC-run is required for measurement, due to thehigh volatility of the two analytes compared to typical multiresidue compounds. Expanding the methodwith further fumigants is planned to increase the efficiency and attractiveness of this approach. Efforts
will be furthermore undertaken to increase the sensitivity of the method, which currently just sufficientfor controlling the existing MRLs for EO.
An ad-hoc proficiency test on 3 sesame samples, containing incurred residues, has been initiated toenable a first comparison of results obtained by various methods.
Sesame samples from the market almost exclusively contained 2-CE. Next to samples with relatively
high levels (>5 mg/kg), there were also numerous samples with findings in the lower range (<0.1mg/kg), which are not likely to be a result of proper fumigation. Further investigations are required to
study the origins of background levels including mixing of lots, cross-contaminations during processing, transport or storage as well as the possibility that low 2-CE levels end up in plants or foodproducts through alternative pathways that go beyond fumigation.
Expanding and validating the method on other types of dry commodities, beyond sesame, is alsoplanned as well as a random analysis of various products to localize other hotspots of ethylene oxide
fumigations.

History
ActionWhen

Experiments

October-December 2020

Observation document placed online

December 2020

 Title amended to include QuEChERS
 Typos corrected (incl. US-MRL 970->940 ppm)
 Corrected conc. of 2-CE and 2-CE-D4 stock solutions, now 5 mg/mL
Updated document placed online

Document
VersionV1
V1.1

December 2020

EU Reference Laboratory for Pesticides Requiring Single Residue Methods

Page 24