Add time:08/03/2019         Source:sciencedirect.com

Laboratory degradation tests with two model estrogen conjugates, 17ß-estradiol-3-glucuronide (E2-3G) and 17ß-estradiol-3-sulphate (E2-3S), using river water and sediment as inoculum under aerobic conditions were investigated. Throughout the 14-day incubation, degradation of E2-3G in river water, at environmentally-relevant level (25 ng/L), obeyed first-order kinetics with the formation of 17-ß estradiol and estrone; in contrast, E2-3S was slowly converted to estrone-3-sulphate stoichiometrically. Degradation of the two conjugates across the spiking concentrations (0.01–1 μg/g) was much faster in sediment than in river water where 25 ng/L of conjugate standards were spiked, possibly due to relatively high population densities of microorganisms in sediment. De-conjugation of the thio-ester bond at C-3 position and oxidation at C-17 position were the predominant degradation mechanisms for E2-3G and E2-3S, respectively, with negligible presence of metabolites estrone-3-glucuronide for E2-3G and 17ß-estradiol for E2-3S. In addition, delta-9(11)-dehydroestrone and 6-ketoestrone were determined as new metabolites of the two conjugates. Also, a lactone compound, hydroxylated estrone and a few sulfate conjugates were tentatively identified. With the observation of new metabolites, biodegradation pathways of E2-3G and E2-3S were proposed. The formation of new metabolites may pose unknown risks to aquatic biota.

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