Evaluation of the Significance of
2-Dodecylcyclobutanone and other Alkylcyclobutanones
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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
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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
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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.
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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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