Fluorescence of sediment humic substance and its effect on the sorption of selected endocrine disruptors

Humic substances (HS) have a critical influence on the sorption of organic contaminants by soils and sediments. This paper describes investigations into the sorption behavior of three representative endocrine disruptors, bisphenol A (BPA), 17β-estradiol (E2), and 17α-ethynylestradiol (EE2), onto sediments and HS extracted sediments using a batch technique. The organic carbon-normalized partition coefficients (Koc) for the extracted HS (Koc(hs)) were calculated, and the fluorescence spectra of the HS extraced from different sediment samples were gained using excitation/emission matrix (EEM). Particular attention was paid to the correlations between the fluorescence characteristics of HS and the log Koc(hs) of selected endocrine disruptors. The results show that the log Koc(hs) values range from 3.14 to 4.09 for BPA, from 3.47 to 4.33 for E2, and from 3.65 to 4.32 for EE2. Two characteristic excitation–emission peaks were observed for HS samples extracted from sediments. They are located at Ex/Em = 250–260 nm/400–450 nm (peak α′) and Ex/Em = 310–330 nm/390–400 nm (peak α) respectively. The α′ and α peak relative intensities (Iα′/Iα)(Iα′/Iα) vary from 0.46 to 1.64 for different extracted HS samples. The similarity between fulvic acids (FA) Ex/Em pairs and those observed for HS indicates that FA is the predominant fraction of HS extracted from sediments. Moreover, the log Koc(hs) values of BPA, E2, and EE2 have a negative linear correlation to Iα′/Iα values. Peak α is often attributed to relatively stable and high molecular weight aromatic fulvic-like matter. Therefore, the result presented here reveals that the abundance of aromatic rings in HS molecular structure plays a critical role in the sorption of selected endocrine disruptors.