ARCHIVED - Evaluation of the Significance of 2-Dodecylcyclobutanone and other Alkylcyclobutanones - Food Irradiation - Health Canada

• Irradiation of fat-containing food generates minute quantities of a family of compounds derived from fat known as 2-alkylcyclobutanones, including 2-dodecylcyclobutanone or "2-DCB." These compounds (molecules) are found exclusively in irradiated fat-containing food and are thus considered as unique markers for food irradiation. The fact that there is a linear relationship between the radiation dose absorbed by the food and the concentration of these compounds can form the basis of an analytical method to determine whether or not a food has been irradiated. The European Committee for Standardization (CEN) has published a method for the identification of irradiated foods based on this principle.¹
  
• For chicken, an amount of about 0.342µg 2-DCB / g lipid / kGy has been reported.² The raw flesh and skin of roasters is about 12.6% fat and therefore 100 g of the edible flesh/skin of a roasting chicken would contain about 4.3µ g (millionths of a gram) of 2-DCB / kGy. At a total overall average absorbed dose of 3 kGy, this translates to about 12.9µ g for 100 g chicken. Based on the actual mean intake of poultry by Canadians of about 62.1 g/day³, the intake of 2-DCB would be approximately 0.13µ g/kg b.w./day.⁴
  
• For hamburger, an amount of 0.409µ g 2-DCB / g lipid / kGy has been reported.⁵ Medium ground beef in Canada can contain no more than 23% beef fat (Section B.14.015A, Canadian Food and Drug Regulations) and therefore 100 g of medium ground beef would contain about 9.407µ g (millionths of a gram) of 2-DCB / kGy. At a total overall average absorbed dose of 3 kGy, this translates to about 28.2µ g for 100 g of medium ground beef. Based on the actual mean consumption of ground beef by Canadians of about 23.2 g/day⁶, the intake of 2-DCB would be approximately 0.11µ g/kg b.w./day.
  
• Despite the usefulness of 2-DCB to analytical chemists charged with enforcement of regulations, its very presence has raised questions about its safety. Recently, German researchers (Delincée et al.) at the Federal Research Centre for Nutrition at Karlsruhe, Germany, reported results that they interpreted as indicating genotoxic activity from this compound when tested in vitro using the "Comet Assay," a novel technique to detect the genotoxic effects of chemicals. The Comet Assay is not validated or adequately standardized and while it works well for strongly positive genotoxic agents, it does not perform well for weak agents. The Comet assay has as its endpoint DNA strand breaks, that can be repaired and thus may not lead to formation of a permanent genetic change.
  
• The authors stated that the concentrations of 2-DCB tested in the assay (1.12 mg/kg b.w. and 14.9 mg/kg b.w.) were very high⁷ compared with actual human intake. Based on Canadian exposure data, the amount of 2-DCB ingested via chicken would be 8,500 times lower than the lowest dose that was deemed by the German researchers to produce a comet effect. The amount of 2-DCB ingested via hamburger would be 10,000 times lower than the lowest dose that was deemed by the German researchers to produce a comet effect.
  
• The German researchers also pointed out that a major toxicological study (the "Raltech" study; discussed in Health Protection Branch Information Letter No. 746, June 4, 1988), involving the feeding of high-dose (~56 kGy) irradiated chicken to mice, revealed no adverse effects attributed to irradiation treatment. Furthermore, all cyclobutanones tested, including 2-DCB, produced negative results in the Ames Test, a bacterial gene mutation assay. The conclusion of a toxicological evaluation of the German studies and others, including background literature on the Comet Assay, is that the data do not demonstrate positive genotoxic activity by cyclobutanones, including 2-DCB, when tested in vitro or in vivo.
  
• The 34th Session of the Codex Committee on Food Additives and Contaminants (CCFAC) (March, 2002) considered removing the upper limit for the total overall average absorbed dose of 10 kGy (i.e., allowing any dose) in the Codex General Standard for Irradiated Foods. CCFAC decided to retain the upper dose in the light of concerns about the potential toxicity of alkylcyclobutanones. (The basis for removal of the 10 kGy upper limit is that a recent FAO/IAEA/WHO Study Group concluded that food irradiated to any dose appropriate to achieve the intended technical objective was both safe to consume and nutritionally adequate and that this conclusion was still valid insofar as no credible evidence has been provided to the contrary.)
  
• All of Canada's existing listings for foods that may be irradiated are below the 10 kGy limit and no listings are foreseen future that would exceed this total overall average absorbed dose.
  
• Health Canada scientists have considered the alkylcyclobutanone issue. The fact that other toxicological / feeding studies on entire irradiated foods were available and deemed acceptable, they believed that it would be inappropriate to incur further delays, particularly considering that the stated and well-publicized concerns of the EC were based on the use of an invalidated and unstandardized test, the results of which are equivocal and difficult to interpret.
  
• On July 3rd, 2002, the EC's Scientific Committee on Food issued a statement as follows:
  
  "In summary, as the adverse effects noted refer almost entirely to in vitro studies, it is not appropriate, on the basis of these results, to make a risk assessment for human health associated with the consumption of 2-ACBs present in irradiated fat-containing foods."
  
• The Committee indicated that reassurance as to the safety of irradiated fat-containing foods can be based on the results of the large number of feeding studies carried out with irradiated foods which formed the basis for the wholesomeness assessments of irradiated foods published hitherto by WHO/FAO/IAEA and the acceptance of the safety of the technology under appropriate conditions by the [EU Scientific] Committee in its Report on Food Irradiation [13 March 1986].⁸

¹ Foodstuffs - Detection of irradiated food containing fat - Gas chromatographic/Mass spectrometric analysis of alkylcyclobutanones, EN 1785:1996, CEN Publication Date: 1996-12-11.

² Bournouf, D., Delincée, H., Hartwig, A., Marchioni, E., Miesch, M., Raul, F. and Werner, D. 2002. Toxikologische Untersuchung zur Risikobewertung beim Verzehr von bestrahlten fetthaltigen Lebensmitteln. (Eine französisch-deutsche Studie im Grenzraum Oberrhein). Schlussbericht INTERREG II, Projekt No 3.171) Eds. Eric Marchioni and Henry Delincée. Bundesforschungsanstalt für Ernährung Karlsruhe. ISSN 0933-5463.

³ Derived from a consumption of 22.66 kg/person/year (Statistics Canada, 1993, Publication #32-229) and an average human body weight of 67.2 kg [average weight of 12 males + 12 females between the ages of 18 and 68 years {from Tables 5 and 7; Nutrition Canada Survey; Health and Welfare Canada; 1970-1972)].

⁴ b.w. = body weight

⁵ Bournouf et al., 2002. Op. cit.

⁶ Nutrition Canada. 1972, All Persons daily mean consumption figure.

⁷ The high dose tested was equivalent to a human consuming 800 chickens that had been irradiated at 60 kGy.

⁸ European Commission, Scientific Committee on Food (SCF), Reports of the SCF, Eighteenth Series (1986)(1989). Irradiated Foods (Opinion expressed on 13 March 1986). Cat. N EUR 10840-DA-DE-EN-ES-GR-FR-IT-NL-PT. The English version of 1989 of this publication replaces the published version of 1986.

Studies Considered in the Evaluation of 2-Dodecylcyclobutanone and Alkylcyclobutanones

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Delincée, H., Soika, C., Horvatovich, P., Rechkemmer, G., Marchioni, E., (in press) Radiat Phys Chem. Genotoxicity of 2-alkylcyclobutanones, markers for an irradiation treatment in fat- containing food-Part I: cyto- and genotoxic potential of 2-tetradecylcyclobutanone

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