A new approach to assess biocompatibility of an effluent, based on combination of different bioassays and chemical analyses, has been tested using a mixture of four commercial pesticides treated by a solar photo-Fenton as target effluent. A very fast elimination of the pesticides occurred (all of them were below detection limit at t_30W=36min), but mineralisation was a more time-consuming process, due to the formation of organic intermediates and to the presence of solvents, as shown by GC–MS analysis. Measurements based on activated sludge indicated that detoxification was coincident with the removal of the active ingredients, while more sensitive Vibrio fischeri bacterium showed significant toxicity until the end of the experiment, although the effluent might be compatible with biological processes. Biodegradability of the solutions was enhanced by the photochemical process, to reach BOD₅/COD ratios above 0.8. Longer time bioassays, such as the Zahn–Wellens' test, support the applicability of coupling photochemical with activated sludge-based biological processes to deal with these effluents.