Steroid metabolites as overlooked emerging contaminants: Insights from multimedia partitioning and source–sink simulation in an estuarine environment.

Steroids have been attracting global attention given potential carcinogenic and endocrine-disrupting effects, yet the environmental status of steroids, especially their metabolites, in estuarine environment remain largely unexplored. This study investigated 31 steroids and metabolites in suspended particulate matter (SPM), water phase and sediments of the Pearl River Estuary (PRE) during the dry and wet seasons to elucidate their spatiotemporal patterning, partitioning behavior, and environmental fate. The results showed that natural steroids predominated in SPM and sediments while the metabolites predominated in water. The spatial distribution of steroids and metabolites varied seasonally, with hydrophobicity and environmental factors influencing phase partitioning in the estuary. Furthermore, a natural steroid, progesterone (P) could serve as a trustworthy chemical indicator to estimate the concentrations of steroids and metabolites in the PRE. Importantly, the mass budget of P was estimated using an improved multi-box mass balance model, revealing that outflow to the South China Sea was the primary sink of P in water (∼87%) and degradation was the primary sink of P in sediments (∼68%) of the PRE. Overall, this study offers insightful information about the distribution and environmental fate of steroids and metabolites in estuarine environment, with implications for future management strategies. Due to strong endocrine disrupting effects and potential carcinogenicity, steroids in the environment have attracted substantial attention, with studies mostly focusing on the parent steroids. Steroid metabolites often have high biological activity, while their fate in the environment remains largely unknown. This work provides new insights regarding the multimedia partitioning and source–sink relationships of steroids and their metabolites in an estuary based on field investigation and model simulation. These results underscore that substantial steroids and metabolites in the estuary eventually migrated to the open ocean, inevitably increasing the risk to marine organisms. [Display omitted] • Multimedia partitioning of steroid metabolites was elucidated for the first time. • Hydrophobicity and environmental factors influence the partitioning of steroids. • Natural steroid progesterone was a reliable indicator of steroids. • Most progesterone migrated to the open ocean, endangering marine organismal health. [ABSTRACT FROM AUTHOR]