Photolysis of the resin acid dehydroabietic acid in water

The effects of UV254-radiation and artificial solar radiation on the degradation of dehydroabietic acid (DHAA) in humic water and in humus-free control water were examined. The reaction rates were determined, the degradation products were tentatively identified, and the toxicity changes of the solutions were monitored. Our results demonstrate that the presence of dissolved organic matter (DOM) in water affects the light-induced degradation rate of DHAA. In the UV-experiments, the degradation was substantially slower in humic water than in humus-free control water, whereas the degradation rate was accelerated by the presence of DOM in the simulated sunlight-experiments. These differences are obviously due to different reaction pathways in the experiments. Irradiation of the aqueous DHAA solutions gave rise to a great number of degradation products of which e.g. 7-oxodehydroabietic acid and 7-oxodehydroabietin were formed in high amounts. During photolysis of DHAA in humic water, decarboxylation of DHAA to dehydroabietin (18-norabieta-8,11,13-triene) seemed to be one of the main reactions. The bacterial toxicity of the aqueous DHAA solutions decreased with increasing irradiation time. Consequently, the photolysis of DHAA did not generate any notable amounts of toxic intermediates, or the intermediates formed were rapidly further degraded into compounds of lower toxicity than the parent compound.