Horseradish peroxidase (HRP) was immobilized on the poly(2-hydroxyethyl methacrylateglycidyl methacrylate) [p(HEMA-GMA)] cryogel and used for the degradation of a benzidine containing azo dye (i.e., Direct Blue-6). The maximum amount of HRP loading was found to be 87.6 mg g(-1) cryogel, and the retained immobilized HRP activity was 67% with respect to the same quantity of the free enzyme. Biochemical properties of the HRP preparations were also evaluated along with the stability studied under various denaturizing conditions. The toxicity of the Direct Blue-6 and its degradation products was tested using Daphnia magna. Decrease in the absorbance of the blue color of dye at 590 nm was observed during enzymatic degradation studies. Additionally, Chlorella vulgaris was used as a test organism in the algal growth inhibition studies. After 60 min reaction time, the Direct Blue-6 dye and its degradation product were enzymatically removed from the medium. Thus, after treatment with HRP approximately 60-min, the medium was non-toxic for both D. magna and C. vulgaris. The Direct Blue-6 dye and its degradation product toxicities were reduced after enzymatic treatment from 99.6 to 7.3%. It should be noted that the initial degradation products appeared to be extra toxic compared to the pristine dye. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.