Photochemical fate of a mixture of emerging pollutants in the presence of humic substances.

The photodegradation of a mixture of the emerging pollutants (EPs) clofibric acid, amoxicillin, acetamiprid, acetaminophen, carbamazepine, and caffeine was studied under irradiation with a xenon lamp. The quantum efficiencies of the EPs were determined when irradiated individually. Experiments with the mixture of the EPs showed that indirect photoprocesses attributable to interaction between EPs can either enhance the photodegradation rate by photosensitization or decrease it by quenching processes. The addition of humic substances (HS) to the solutions resulted in an increase of indirect photoprocesses with higher effects on acetaminophen and carbamazepine; this was more remarkable when a filter was used to cut off radiation in the range 280-295 nm. Experiments carried out with chemical probes indicated that the triplet excited states of HS play a major role in the photosensitization process, although the contribution of other species cannot be completely ruled out. Additionally, V. fischeri toxicity tests showed a synergistic effect produced by the mixture of EPs before irradiation. Photodegradation resulted in an enhanced toxicity of the solution at the initial steps of the process, which was associated both with synergistic effects and with the formation of toxic photodegradation by-products of clofibric acid.