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DIN Standards Committee Water Practice

Procedure

Technical Report

Overview

During the last two decades, several scientific investigations have demonstrated that migration from organic materials into liquid simulants is a physical process that can be modelled successfully. Mass transfer from an organic material into a liquid simulant is predictable because in many cases it follows Fick's law of diffusion, that is, the diffusion process is the rate determining step. To predict migration from organic materials into contacting media a corresponding diffusion model was established on the basis of this legality. This Technical Report describes the application of predictive diffusion modelling to the estimation of the migration of a substance from a product intended for contact with water intended for human consumption. The application applies to organic materials, such as polymers, used to make such products. Substances applied externally to a product made of an organic material, for example, antistatic agents, lubricants, etcetera, are excluded from the diffusion modelling approach, as are electrolytes, salts, oxides and metals. Only organic substances with well-defined molecular weight or mixtures with well-defined ranges of molecular weights are amenable to the diffusion modelling approach. The diffusion modelling approach is readily applicable to amenable organic materials in the form of a pipe or a sheet, where data such as material thickness is readily calculable. More complicated product shapes, such as fittings, require assumptions to be made. The purpose of the report is to stimulate the use of such techniques in member states such that sufficient experience is generated to enable the value of such modelling to be assessed in relation to complementing or substituting the conventional approach. Normally in member states the estimation of such migration is performed by standardised procedures based on laboratory testing and analysis, that is an experimental approach. Migration modelling is an alternative to this type of experimental testing. The experimental determination of the specific migration of substances into test water (simulated drinking water) often requires a considerable amount of time and it can be costly. This conventional approach has worked well and, of course, it generates data on the actual concentration of a substance in test water. However, in some cases the analysis is difficult or even impossible due to problems caused, for example, by chemical degradation, volatilisation of the substance. In addition, the substance may not be amenable to, or the target concentration of interest may be too low for, available analytical techniques. Therefore, the application of a mathematical model could have considerable benefits for industry and regulators, as experience has shown in the control of migration from plastic materials in contact with foodstuffs. The modelling approach is attractive because, in principle, it is quicker and more flexible than the conventional testing approach, in that different exposure conditions can be readily and more cost-efficiently investigated. However, it should be understood that, like the experimental approach, the mathematical approach also has its limitations. An accurate prediction of the migration of a substance from an organic material to water requires detailed knowledge of the diffusion behaviour of the materials and substances under investigation. This level of information may well require extensive experimental studies - more than the experimental/ analytical approach would require. An important feature of the mathematical approach is the possibility of generalisation. This Technical Report has been prepared by CEN/TC 164/WG 3 with significant participation of German experts of NA 119-04-14 AA "Werkstoffe in Kontakt mit Trinkwasser" ("Materials and products in contact with drinking water").

Document: references other documents

Responsible national committee

NA 119-07-09 AA - Materials in contact with drinking water  

Responsible european committee

CEN/TC 164/WG 3 - Effects of materials in contact with drinking water