SORPTION OF 17B-ESTRADIOL (E2) AND BISPHENOL A (BPA) ONTO COLLOIDAL PARTICLES IN AQUATIC SYSTEM

The natural aquatic colloids play a crucial role as an intermediary in environmental behavior and ecotoxicology of endocrine disrupting chemicals (EDCs), which result from entirely different migration pathways and bioavailability of colloid-bound EDCs in multiple phases. This study attempted to investigate sorption ability of 17 beta-estradiol (E2) and bisphenol A (BPA) onto colloidal humic acid (HA), nano-Fe2O3 and nano-MnO2 that were major components of natural aquatic colloids. A stirred ultrafiltration system was firstly validated using colloidal standard molecules 0.5-kDa rhodamine 6G and 3-kDa dextran, with a satisfactory retention of 3-kDa dextran and low retention of 0.5-kDa rhodamine 6G at concentration factors (cf(s)) higher than 4, implying efficient enrichment of colloidal particles associated with target pollutants. The sorption experiment was conducted under isolated colloids (nano-HA, -Fe2O3 and -MnO2) and composite colloidal systems (nano-HA + nano-Fe2O3 and nano-HA + nano-MnO2), as well as at different HA concentration, pH value and ionic strength. The results showed that the sorption of BPA onto HA slightly enhanced with increased HA concentration, which was likely attributed to an increased strength of pi-pi bonding between pi electron donors in BPA and pi electron acceptor in HA. The higher pH value improved sorption properties of both BPA and E2 onto HA by creating more dissociated carboxyl groups on HA at high pH values, hence leading to more activated sites. The reduced sorption of E2 and BPA on HA were observed at higher concentration of Ca2+, owing to the occupation of sorption sites by Ca2+ on HA. The sorption capacities of target pollutants onto composite colloids were greatly enlarged by comparison to isolated ones. These findings suggested that the main sorption mechanisms of E2 and BPA onto HA were hydrogen bonding and pi-pi bonding, while the interaction between metal nano-oxides and pollutants was regulated by ionic exchange, cation bridge and hydrogen bonding.