Root accumulation and efficient translocation of steroids in mangrove plants: Implications for an overlooked coastal...

Steroid hormones are potent endocrine disruptors with profound effects on aquatic organisms, yet their environmental fate in mangrove ecosystems remains poorly understood. Here, we present the first systematic investigation of the occurrence, bioaccumulation, and translocation of 24 steroids in a subtropical mangrove ecosystem in Kaozhou Bay, South China. Steroids were ubiquitously detected in water (0.52-627 ng/L) and sediments (1.5-5.3 ng/g dw), with contamination hotspots located near sewage discharge outlets. Eleven steroids were further detected across mangrove plant tissues, with total concentrations ranging from not detected (ND) to 285 ng/g dw, showing distinct tissue-specific accumulation in the order root (22.8-285 ng/g dw) > leaf (ND-91.9 ng/g dw) > stem (6.3-65.5 ng/g dw). Root concentration factor (RCF) and transfer factor (TF) analyses of synthetic steroids revealed high root accumulation capacity, with RCFs up to 2602, and efficient root-to-stem translocation. Substantial interspecies variation was observed, with steroids preferentially accumulated in stems of Avicennia marina (Forsk.) Vierh and Kandelia obovata Sheue, but predominantly retained in roots of other mangrove species. By integrating field measurements with provincial-scale biomass data, we estimated a total steroid inventory of approximately 102 kg in mangroves across Guangdong Province. Collectively, these findings identify mangroves as major and dynamic reservoirs of steroid contaminants, redefining their role in coastal contaminant cycling from passive filters to significant storage sinks, with critical implications for regional ecological risk assessment.