Photocatalysis offers low cost and durable treatment to dyes polluted effluent. But sometimes photocatalyzed dye intermediates appear to be more toxic than parent dye molecule. Present investigation uses suspended TiO2 nanoparticles and sunlight irradiation for photocatalytic treatment of Giemsa dye at optimum pH. Giemsa dye has wide applications in molecular biology, cytology and histology laboratories across the world. Surplus and used dye is discharged in sink drain which is likely to cause hazardous concerns to environment. Paper analyzes toxicity concerns of treated and untreated Giemsa dye. Bioassays incorporating agar well diffusion assay and seed germination were employed to check the toxicity of water. Significant changes were noted in alkalinity, BOD, COD, Ca2+ , Mg2+, NO3-, SO42- ion concentration, hardness, temperature, turbidity and pH; and compared with standards for drinking water, World Health Organization. HPTLC of treated waste water confirmed that photocatalyzed dye intermediates exhibited increased absorbance in visible range of spectrum. At pH 2 various investigated parameters were found to match WHO standards for drinking water. Environmental risk assessment reveals that treated water possessed toxicity at pH 7 and was not found suitable for irrigation and potable purposes. Beside photocatalytic treatment, waste disposal methodology still needs to be accompanied with secondary treatment of water.