Seasonal variations of fluorescent dissolved organic matter control estrone biodegradation potential in eutrophic waters affected by allochthonous and autochthonous sources

The spatial–temporal variation of dissolved organic matter (DOM) influences contaminant biodegradation in natural water systems. This study explored seasonal patterns of DOM concentration and composition and the consequent effect on estrone (E1) biodegradation in water columns at the northern bays of Lake Taihu. During bloom seasons, the increased concentration of autochthonous DOM (autoDOM) with higher Fresh/Humic ratios, lower aromatics, molecular weights, and humification degrees exhibited a more substantial promotion on E1 biodegradation than the processed autoDOM after algal bloom. Meanwhile, the inflow rivers imported high-molecular-weight humic-like substances with strong aromaticity in flood seasons, impairing the E1 biodegradation of affected regions. End-member mixing experiments further confirmed that the mixing of algal-derived DOM facilitated the mediation of river water-derived DOM in E1 biodegradation, but microbial ageing reduced the promotive effect of autoDOM and resulted in a weak relationship between DOM source indicators and E1 biodegradation. A significant and positive correlation was further found between E1 biodegradation and DOM bioreactivity (P < 0.001), both of which were well predicted by DOM optical properties as predictor variables in partial least squares regression (PLS-R) modelling (R2 values of 0.78 and 0.90, respectively). The ratio of fluorescence peak T and C was identified as the most effective predictor, and SUVA254 and slope ratio (SR) were moderately influential factors controlling carbon-normalized E1 biodegradation potential. These results suggested that while algal blooms would likely cause enhanced biotransformation of estrogens in freshwater lakes, the import of allochthonous DOM or the microbially aged autoDOM with high-molecular-weight may lead to higher estrogen concentrations in post-bloom seasons.