Abstract: Natural steroid estrogens（SEs）can be classified into free（FEs）and conjugated（CEs）ones in the environment. These ubiquitous SEs in the environment have caused damages to the diversity and stability of ecosystem due to the recognized varied interfering effects on human and wildlife endocrine systems. At present,multiple enzymes play an important role in the catalytic removal of both FEs and CEs in the environment. This review summarizes the removal mechanisms of FEs and CEs by oxidoreductases and hydrolases,respectively,and elucidates the main proposed enzymatic degradation and transformation pathways of both FEs and CEs. Oxidoreductases catalyze FEs to generate radicals and subsequently form poly-products by covalent bond（C-O-C and C-C）self- and cross-coupling;meanwhile,the catalytic process is easily affected by organic compounds in the environment. As for CEs,these compounds can be deconjugated into their corresponding FEs by deconjugating sulfate or glucuronide groups via hydrolases;additionally,CSEs are recalcitrant to be deconjugated and more stable in the environment compared to CGEs. This review also discusses and highlights the further application of enzymes for removing SEs in wastewater and soil,combined use of enzymes,immobilization of enzymes,enzyme engineering,and so on,aiming at providing a theoretical reference for the degradation and transformation of FEs and CEs by enzymatic catalysis in the environment.

Key words: free estrogens, conjugated estrogens, enzymatic catalysis, coupling reaction, deconjugation