Changes in microbial communities during the removal of natural and synthetic glucocorticoids in three types of river-based aquifer media.

Glucocorticoids in sewage treatment plant effluent discharged into rivers could influence microbial community structure in river-based aquifer media and affect groundwater quality. The effect of representative natural and synthetic glucocorticoids, namely, hydrocortisone (CRL) and dexamethasone (DEX), on the microbial communities in three types of river-based aquifer media was evaluated. The aquifer media was taken from the Beijing Chaobai River (BJ), Hebei Hutuo River (HB), and Tianjin Duliujian River (TJ) and they exhibited different physicochemical and biological properties. The attenuation rates of CRL were 0.175, 0.119, and 0.096 day-1 and for DEX were 0.222, 0.151, and 0.113 day-1 in the media from BJ, HB, and TJ, respectively. All the attenuation rates followed first-order kinetics. The biodiversity decreased significantly with CRL and DEX amendment. The microbial community composition differed in relation to the type of aquifer media and glucocorticoids, especially for BJ at the phylum level. In BJ, the major bacterial genus was Bacillus and in HB it was Rhodobacter. However, in TJ, three bacterial genera (Methylophilus, Methylobacillus, and Methylotenera) and Candidatus_Nitrososphaera were predominant in the microflora. All these genera were able to degrade both CRL and DEX. Distance-based redundancy analysis revealed that total organic carbon (TOC), the type of glucocorticoid, and the pH were the main factors explaining the variations in microbial community composition.