Accelerated ageing systems developed for application to samples in the laboratory prior to biological tests, should reflect those natural deterioration processes that are likely to occur in the hazard classes defined in EN 335-1. Losses through evaporation or the effects of leaching have been recognised, however their importance, relative to other mechanisms has not been quantified. Degradation mechanisms including photolysis, thermolysis and hydrolysis have largely been ignored. This paper presents information from a study, conducted as part of a project supported by the European Commission (SMT4-CT96-2135), on the relative importance of these different mechanisms through a series of experiments using model compounds. These model compounds were selected because they have known susceptibility to one of the identified degradative mechanisms. TnBTO has been used to monitor photolysis, trihexylene glycol biborate to examine the effects of hydrolysis and lindane to monitor evaporation. The experimental data are compared to semi-natural exposure data. Support for ensuring that the various degradative mechanisms occur in the accelerated ageing systems is recommended.

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