This is a comparative study of photolytic degradation under exposure to UV254 nm and solar-simulator irradiation of a mixture of eight equally concentrated relevant micropollutants in the presence of H2O2 and Fe(II) in ultrapure water, Lake Geneva water, and effluent from a wastewater treatment plant (WWTP). The electron-spin resonance (ESR) experiments point to a low efficiency of singlet oxygen formation by the mixture of micropollutants. This finding corroborates with the chemical stability of the micropollutants under UVC irradiation (in decreasing order: gabapentin, metformin, metoprolol, atenolol, clarithromycin, primidone, methylbenzotriazole, and benzotriazole). The oxidation rate increased in the presence of low-concentration H2O2 and Fe(II), except for metformin and gabapentin. Gabapentin and metformin were the most persistent compounds, less than 24% were removed after 60 minutes of UV254/H2O2/Fe(II) treatment. The low micropollutant removal rates were observed in WWTP effluent and lake water, and using sunlight simulation. Guanylurea, phenol, oxalic acid, tartronic acid, glycolic acid, oxamic acid, and maleic acid, could also be detected as fragmental oxidation products. Furthermore, up to 300 µg/L of nitrate and ammonia were identified as final degradation products. Ecotoxicological tests showed that the degradation products are more toxic for algae Chlamydomonas reinhardtii than the parent compounds themselves.