Aquatic toxicity of dyes before and after photo-Fenton treatment

•Food and textile dyes can be toxic to aquatic organisms in mgL−1 levels.•Vat Green 3 presented the highest acute and chronic toxicity.•Partial mineralization of dyes may generate more toxic degradation products.•Photo-Fenton process was effective for the degradation of 4 of the 5 tested dyes.•Toxicity tests are important parameters in dye treatment evaluation. This study evaluated the ecotoxicity of five dyes to freshwater organisms before and during their photo-Fenton degradation. EC50 (48h) of the five tested dyes ranged from of 6.9 to >1000mgL−1 for Daphnia similis. In the chronic tests IC50 (72h) varied from 65 to >100mgL−1 for Pseudokirchneriella subcapitata and IC50 (8 days) from 0.5 to 410mgL−1 for Ceriodaphnia dubia. Toxicity tests revealed that although the applied treatment was effective for decolorization of the dye, the partial mineralization may be responsible for the presence of degradation products which can be either more toxic than the original dye, as is the case of Vat Green 3 and Reactive Black 5, lead to initially toxic products which may be further degraded to non toxic products (acid Orange 7 and Food Red 17), or generate non toxic products as in the case of Food Yellow 3. The results highlighted the importance of assessing both acute and chronic toxicity tests of treated sample before effluent discharge.