background image
25/27
approach by intervals can be easily implemented, it is progressively introduced in the EU
regulation, to which one of us is participating.
In addition, this chapter outlines some more sophisticated approaches based on probabilistic
modeling. Previous intervals on input parameters and predictions are replaced by continuous
distributions. Assessments may always begin by treating all uncertainties qualitatively by
intervals, but when those uncertainties appear critical for the outcome they may be analyzed
quantitatively. Such refinements make it possible to generate overestimates of the contamination
of food products with a controlled risk to be exceeded. The applications are tremendous:
prediction of the contamination by a ubiquitous contaminant, by a group of homologous
molecules, non by intentionally added molecules, for several thermodynamical or geometrical
conditions... As an original illustration, this work illustrates how the combined effects of
uncertainty on all transport properties involved in the modeling of the contamination from
monolayer materials can be assessed.

As a rule of thumb, the amount of effort and detail devoted to analyzing uncertainties should be
proportionate to the needs of the problem. A tiered approach as detailed here is recommended.
Assessments may begin by point estimates for common values and subsequently using ranges,
confidence intervals and distributions. Besides, the user of such methods is encouraged to
differentiate variability and uncertainty. Variability refers to variation that exists in the real
world, e.g. varying concentrations of substances in packaging materials. Uncertainty is often
reducible through research, whereas variability is not. As a result, if a physico-chemical property
has a drastic effect on the prediction of the contamination, it may be appropriate to measure it and
to share its knowledge in anonymized databases of properties. A EU database of transport
properties is available on our server: Safe Food Packaging Portal (Vitrac, 2006).

7 References

Codex, 2005. Codex Alimentarius Commission Procedural Manual, 15
th
Edition.
http://www.codexalimentarius.net/procedural_manual.stm.
EC (2005), Substances listed in EU directives on plastics in contact with food. Updated to 26
September 2005EC (2004), Regulation (EC) No 1935/2004 of the European Parliament and of
the Council of 27 October 2004 on materials and articles intended to come into contact with food
and repealing Directives 80/590/EEC and 89/109/EEC/ Official Journal, L 338 of 13.11.2004, 4-
14
EC (2002), EU directive 2002/72/EC relating to plastics materials and articles intended to come
into contact with foodstuffs. Official Journal, L220 of 15.08.2002, 18-55.
EC-DG SANCO-D3 (2002). Conclusions of the thematic network "Evaluation of migration
models
to
be
used
under
directive
90/128/EEC":
SMT­CT98­
7513.
http://ec.europa.eu/food/food/chemicalsafety/foodcontact/eu_substances_en.pdf
.
Fytas G., Rizos A., Floudas G., Lodge T. P. (1990). Solvent mobility in polystyrene/Aroclor
solutions by depolarized Rayleigh scattering. J. Chem. Phys. 93, 5096-5104.
Glasstone S., Laidler K.J., Eyring H. (1941). Theory of rate processes. McGraw-Hill: NewYork,
US, 195-197.