The microbial transformation of 17β‑estradiol in an anaerobic aqueous environment is mediated by changes in the biological properties of natural dissolved organic matter.

Dissolved organic matter (DOM) is shown to act as an electron shuttle mediator which enhances the microbial degradation of steroid estrogens in natural water. Batch studies were conducted with 17β‑estradiol (E2), quinone-reducing bacteria, DOM, and Fe(III) as a terminal electron acceptor. The results show that anthraquinone‑2‑disulfonate (AQS) approximately doubles the microbial degradation of E2 by DOM alone. The effect decreases sharply at AQS concentrations above 1.0mmol·L-1. Over three oxidation-reduction cycles, the electron-shuttling ability of AQS and the E2 biodegradation rate decreased step by step. Changes in the biological properties of the dissolved organic matter increased its aromaticity, its quinone content, and its fulvic-like fluorescence while significantly improving the electron transfer between DOM and the microbes, which made the degradation more effective. This explains why steroid estrogens do not accumulate in natural aqueous environments. Moreover, the estrogenic activity of steroid estrogens is inhibited at low concentrations through the activity of DOM.