Possibilities and limitations of migration modeling

Johannes Brandsch, Peter Mercea, Otto Piringer 

One of the principal aims of regulations for food contact materials and articles is the protection of consumer health. World-wide investigations over the last 20 years have demonstrated that interactions between polymers and foodstuffs occur under foreseeable physical processes (Chapter 11). Standardization of migration measurements is based on this knowledge. However, with regard to consumer safety it has to be pointed out that it is not possible to carry out all desirable tests. The reasons for this are the variety of substances to control and the necessary time and cost requirements to carry out the analysis (Chapter 10). 

As a consequence of this generally agreed principle, the Commission intends to insert a clause which could appear in a future Amendment of Directive 90/128/EEC  

The text of this clause is yet provisional and will be improved later. To develop and validate a migration estimation model for the above purpose, the Commission approved a project entitled Evaluation of Migration Models to be Used under Directive 90/128/EEC . A final objective of this project is a proposal of a validated migration model to the European Committee of Standards (CEN) for standardization. 

The following discussion summarizes the current state of knowledge regarding migration modeling. 

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BRANDSCH, J., MERCEA, p. and PiRiNGER o., 2000, Possibilities and limitations of migration modelling, in Piringer, O.-G. and Baner, A. L., Plastic Packaging Materials for Food, Wiley-VCH, Weinheim, New York. 

A generic problem with profile methods that iterate is the possibility of profile wander (also called matrix migration). This occurs when sequences found in early rounds of the iterative search are not found in later rounds of the search. This problem affects both PSI-BLAST and HMMER. This means that one should record all the intermediate steps so that these lost members of the family can be recovered. Profile wander only becomes a problem for large protein families, and therefore the cause of the profile wander may be related to the limits of modeling using profiles. 

Models of biosphere transport have been developed. 5,6) As is the case for geosphere transport models, the data base for parameters in the biosphere models is limited. The scope of available data is being expanded, (7-9) but careful assessment is needed of the validity of the data, the validity of the models, and the need for the data and models to be site-specific. One site-specific factor to consider is the possibility that geosphere migration could extend for considerable distances from the repository radioactivity might therefore enter the biosphere in an environment different from that of the repository site. 

Recent work demonstrates that chemokines are not limited in their function to their ability to attract cells and initiate cell mobility, but have multiple other functions (58-64). The possibility that C-C chemokines may directly affect (via autocrine action) pleural mesothelial cells was not recognized until recently (65). Pleural injury results in the death of mesothelial cells and denudation of the mesothelial basement membrane. Repair of the mesothelium without fibrosis requires local proliferation and migration of mesothelial cells into the injured area. In a model of mechanical pleural injury, the C-C chemokine MCP-1 was found to play a central role in the repair process. MCP-1 induces proliferative and haptotactic responses in pleural mesothelial cells. 

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