Suspended particulate matter-associated environmental corticosteroids in the Pearl River, China: Occurrence, distribution, and partitioning

Suspended particulate matter (SPM) plays an important role in the geochemical behavior and fate of organic micropollutants in aquatic environments. However, the presence of trace emerging endocrine disruptors such as envi-ronmental corticosteroids (ECs) in SPM is less well understood. This study focused on the occurrence, distribution, and partitioning of SPM-associated ECs in the Pearl River system, China. Ubiquitous particulate ECs were found in the sur-face water of the rivers at average concentrations (dry weight) between 0.46 ng/g (flumethasone) and 8.83 ng/g (clobetasone butyrate). The total EC ( n-ary sumation ECs) concentrations of the 24 selected target compounds varied from <1.03 ng/g to 62.3 ng/g, with an average and median of 17.6 ng/g and 13.7 ng/g, respectively. Higher SPM-bound EC levels were commonly observed in winter (dry season), and spatially, their relatively high contamination in urban tributary networks decreased while flowing to mainstreams and then gradually attenuated from upstream to the estuary. Despite the approximately 90 % mass distribution of n-ary sumation ECs in the aqueous phase, approximately 50 % of their effect burden was derived from the suspended particulate fractions. For the first time, in situ SPM-water partitioning coefficients (Kp) and their organic carbon-normalized ones (Koc) of ECs were determined in surface wa-ters, and a field-derived preliminary linear equation was proposed to estimate Koc for ECs using basic physicochemical parameters n-octanol/water partitioning coefficient (Kow), which is of importance with regard to the assessment of transport, fate, and risk of these emerging hazardous chemicals. Furthermore, the significant logKoc-logKowrelation-ship for ECs reveals that nonspecific hydrophobic partitioning is a major association mechanism between SPM and ECs. Moreover, hydrogen bonding is suggested to be a prevailing specific binding mechanism and provides more con-tribution to nonhydrophobic interactions between ECs and particulate organic matter than environmental estrogens.