Skin sensitization and possible groupings for 'read across' for rosin based substances.

A series of chemically modified rosin resins have been tested for their potential to cause skin sensitization using the mouse LLNA. Where direct comparative evidence is available, the results of the mouse LLNA are consistent with previously obtained data using the GPMT. Reactions with sufficient fumaric acid or maleic anhydride lead to maleopimaric acid anhydride (an acid anhydride), and give a clear response of a strong sensitizer that definitely requires classification. This sensitization is probably immunologically distinct from that claimed for oxidized rosin. Esterification will deactivate acid anhydrides formed from reacting rosin with maleic anhydride or fumaric acid. However, with maleic anhydride, there remains material capable of inducing a marginal (but classifiable under current criteria) immune response after the rosin had been maleinated and esterified. If proposed potency criteria are used these substances would not be considered 'strong sensitizers'. This response may be a function of a greater solubility in vehicle of the esterified maleinated (or fumarated) rosin over directly esterified material. Solubility limitations in the case of gum rosin directly esterified with pentaerythritol mean that it is not classifiable. Decarboxylated rosin and the glycerol ester of tall oil rosin are adequately soluble, and are not classifiable according to EU criteria. Polymers formed from rosin are also not classifiable as sensitizers. These studies confirm the value of grouping substances for 'read across' and the groupings chosen under the US EPA High Production Volume (HPV) Challenge Program. They also confirm the difficulties involved in dealing scientifically when examining the problem of skin sensitization associated with rosin related substances whilst still meeting current EU regulatory criteria.