Prevalence, distribution, accumulation, and risk of environmental corticosteroids and estrogens in biofilms from the Pearl River Delta.

Biofilms play a significant role in the biogeochemical processing of organic matter and the environmental fate of emerging pollutants. In this study, we investigated the occurrence and distribution of 32 endocrine-disrupting chemicals (EDCs), including 24 environmental corticosteroids (ECs) and 8 environmental estrogens (EEs), in natural biofilms from the Pearl River system. Their association between biofilms and water and environmental risk were assessed. The ECs and EEs ubiquitously occurred in the biofilms, ranging from <0.61-6.57 ng/g and <0.8-2535 ng/g, respectively. Temporally, there was no obvious variance in either ECs or EEs in the biofilms during the winter and summer, and their concentrations exhibited a spatial trend of upward to midstream, descending downstream, and then seaward attenuation at the estuary. For ECs and EEs, the similar levels of field-derived bioconcentration factors (BCFs) (logarithm values: 2.42-2.86 and 2.72-2.98, respectively) and biofilm organic carbon-normalized partitioning coefficients (K) (3.39-3.69 and 3.35-3.95) suggest the comparable potential of accumulation and sorption by biofilms between these two classes of EDCs. In addition, higher values of BCF and K for the EEs were found in winter and were correspondingly comparable to their distribution coefficients (K) and K derived from suspended particles and sediment, revealing that biofilms are a competitive environmental compartment for capturing EDCs, particularly during the mature period. A positive logK-logK relationship suggests hydrophobic partitioning as a primary interaction mechanism between the biofilm and EEs. Moreover, high risks from biofilm-associated ECs and EEs might have posed to the fluvial ecosystem. This study provides original insights into the occurrence, fate, and risk of ECs in natural biofilms for the first time and demonstrates that biofilms may not only serve as reservoirs but also serve as sentinels for fluvial EDC contamination. These results contribute to the further understanding of the behavior and fate of EDCs in aquatic environments.