Comparing relative release potential
To fulfil their specific functions, additives should stay in the plastics they have been added to. They may nevertheless be released from plastic products during their use, which can result in potential risks to human health and the environment.
The release of an additive depends on some properties of the substance itself (e.g. the molecular weight), its concentration in the plastic material, the diffusivity of the polymer matrix, the dimensions of the article (e.g. the size of surface) and the conditions of use of the article (e.g. temperature). Producers of high quality plastic materials and articles will normally aim to optimise the combination of these parameters to limit release.
Whether the released amount of an additive is of concern for human health and the environment depends on its toxicological and eco-toxicological properties, and how it behaves in water, on skin and in air after release. For confirming or ruling out a concern usually a more in depth- assessment is needed.
Under the joint project, ECHA and industry developed a screening method based on the comparison of relative release potential, to enable the identification of plastic additives that should be prioritised for assessment in the light of available hazard data.
The method enables the comparison of the relative release potential of different additives used in plastics. It is meant for screening purposes among those substances not yet under regulatory scrutiny. It therefore makes use of information inputs expected to be readily available for the majority of additives, including substance properties, concentrations, and types of plastic materials they are found in. The tonnage of the additive on the market and its breakdown by article type are is not taken into account, as available data are scarce.
The method is based on existing models for plastic articles. More details on the modelling approaches and how they were used within the framework of the joint initiative are provided in the Supplementary Information on Scope and Methods .
The relative release potential among a set of additives is described by two indicator values, one for the dermal route (covering also oral contact and release to water) and one for the inhalation route.
Based on the available models, it is not possible to derive indicator values for all substance types, and thus more qualitative considerations were applied in the comparison. For pigments with very low solubility in water and octanol, for example, a low release potential is assumed by default. Additives where the release behaviour is very uncertain, such as those with charged migrants, are excluded from the comparison at all.
How it works
Where more than one function or polymer type is relevant, the type leading to the higher release is used as a reference. Where industry could not provide information on the typical concentration in plastic material, a default concentration for the function is used. Where information on the function and/or the polymer matrix was not available, a high default concentration (35 %) and a high diffusivity polymer matrix (polyethylene or soft PVC) is used as the default.
Table 1: Examples for comparing the release potential for organic plastic additives
Substances D, G and M have the highest potentials for release, while substances B, H, I and S have the lowest. This illustrates how the release potential of additives belonging to the same functional group may differ by various orders of magnitude.
|Substance name||Molecular weight (Da)||Vapour pressure (Pa)||Water solubility (mg/L)||log Kow (-)||Technical function||Polymeer Matrix||Conc. nn polymer (%)||Release indicator (dermal)||Release indicator (inhalation)|
|Q||224.0||6.28E-03||2.33E+02||2.51||Other stabiliser||PVC (soft)||2||-2||-2|
Table 2: Release potential comparison for different constituents in the same substance
A comparison is made between the intrinsic properties of constituents contained in a single additive and the resulting release potential. The concentrations of the constituents in the substance have not been taken into account, as this information is usually not publicly available. The example shows how the release potential of different constituents in the same substance may differ by various orders of magnitude. This illustrates that proper judgements on the release behaviour of such substances depend on identifying the constituents that best represent the hazard and the release behaviour of the substance.
|Name||Molecular weight (Da)||Vapour pressure (Pa)||Water solubility (mg/L)||log Kow (-)||Technical function||Polymer matrix||Conc. in polymer (%)||Release indicator (dermal)||Release indicator (inhalation)|