Study of isoniazid degradation by Fenton and photo-Fenton processes, by-products analysis and toxicity evaluation

•High degradation of antibiotic isoniazid used for tuberculosis treatment Fenton-based processes.•Photo-Fenton by artificial and solar radiation achieves high mineralization of isoniazid.•Fenton and photo-Fenton processes generate isonicotinic acid, isonicotinamide,N'-(pyridyl-4-carbonyl)-hydrazide and four new by-products in the first 10 minutes of treatment.•Fenton reaction reduces acute toxicity in D. magna yet inhibits seeds growth in L. sativa, and photo-Fenton performed by artificial radiation reduces toxicity in both test organisms.•Solar photo-Fenton needs prolonged time to generate non-toxic results.