In vitro testing of the skin sensitizing potency of ingredients from epoxy resin systems with focus on the testing of so-called prepolymers

Status:

completed 12/2020

Aims:

Ingredients of epoxy resin systems are often triggers of allergic skin diseases (allergic contact dermatitis) in employees of different industries. For this reason, the strategy of characterising these ingredients according to their sensitising potency and establishing a ranking for sensitising potency has been pursued for several years. This approach is intended to provide the basis for substitution decisions. Highly sensitising ingredients should – if technically possible – be replaced by less sensitising ones.

Activities/Methods:

The first task in the research project was to close data gaps for the evaluation of so-called prepolymers. The prepolymers represent a promising technical innovation for reducing the sensitising potency of epoxy resin systems. Basically, they are composed of an adducted amine portion ("Amineadduct"), a free amine ("Aminefree") and solvent, in different proportions. The materials were tested using an in vitro test system, the "Genomic Allergen Rapid Detection" (GARD) test. The in vitro test system used is adequate for the ingredients tested. Factors that may influence the measurement, such as solubility and cytotoxicity, were adequately controlled in the tests. Three test materials are assigned to the category Skin Sens 1B (substances with low sensitising potency). These are

1. tetraethylenepentamine (TEPA; monomeric amine),
2. a prepolymer (TEPA- bisphenol A resin adduct (DGEBA) in benzyl alcohol) and
3. a polyamidoamine (epamide 405, < 2 % free amine).

Two other prepolymers were classified as Skin Sens. 1A (strong potency). The results are mechanistically plausible.

Results:

Combining the results from in vitro testing in this research project with results from previous projects and confidential industry data allows the derivation of pragmatic rules for the improved evaluation of untested prepolymers. The second objective of the research project has been met accordingly. While untested prepolymers are rated HS (high potency) in default, it can now be assumed that the corresponding prepolymers have a low to moderate potency (GMS) without substance-specific data, if the following rules are met:

I. > 30% Amineadduct and < 10% Aminefree of the potency HS ("strongly sensitising")

II. > 30% Amineadduct and <30% Aminefree of potency GMS ("low to moderate sensitising").

Both rules assume that the solvent in the prepolymer has no sensitising effect.

The rules are to be applied for the evaluation of DGEBA prepolymers and polyamidoamines. In all other cases, a strong potency is to be assumed unless data are available showing the contrary. A statement whether these rules can be extended to other prepolymer types (with other resin base) requires the evaluation of additional experimental data and was not within the scope of the present project.

The experimental results on the hardener mixtures and on the prepolymers confirm the basic assumptions in the "EIS mixture calculator", a software application developed in previous projects and in the epoxy resin ingredients working group ("Arbeitskreis Epoxidharz- Inhaltsstoffe", AK EIS). If the exact prepolymer composition is known, these pragmatic rules can be integrated into the "EIS mixture calculator" and used for a differentiated assessment of products with regard to their sensitising effect. The accident insurance institutions can use the new rules to identify substitution possibilities and make appropriate recommendations. For manufacturers of the formulators of epoxy resin systems the results of this project in conjunction with the "EIS mixture calculator" can serve as a tool for developing less sensitising systems. Differentiated assessments of products provide an incentive for the developers of epoxy resin systems to design and market improved formulations that are less sensitising which is in favour of occupational safety. By incorporating the data into such an assessment, the third research objective, the input of the results into practice-oriented decision-making aids, is also fulfilled.

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