Abstract
Cyclic and linear siloxanes are widely used in personal care, industrial, and consumer products. Despite their widespread use, ecological risks remain uncertain due to limited availability of data on wildlife, particularly in marine mammals. This study investigated the occurrence, accumulation profiles, temporal trends, and preliminary ecotoxicological implications of cyclic and linear siloxanes in blubber samples from common dolphins (Delphinus delphis) collected from Korean coastal waters between 2002 and 2023.
Siloxane concentrations were quantified using gas chromatography–mass spectrometry (GC–MS). The analytes comprised cyclic siloxanes from D3 to D7 and linear siloxanes from L3 to L11.  Concentrations were evaluated on a lipid-weight basis, and temporal trends were assessed across the monitoring period. Differences in contamination patterns among sex and maturity groups were also examined. A screening-level ecological risk assessment was conducted using estimated toxicity thresholds derived from surrogate mammalian data, given the absence of dolphin-specific toxicological benchmarks.
Cyclic siloxanes dominated the contamination profile and generally occurred at higher concentrations than linear siloxanes. D5 was the predominant congener, followed by D6 and D7, consistent with the widespread occurrence and bioaccumulation potential of cyclic siloxanes. No consistent sex- or maturity-related differences were observed for most cyclic compounds. Temporal analysis revealed an overall upward trend in siloxane concentrations. D4 increased significantly among cyclic siloxanes, whereas several linear siloxanes showed more pronounced increases, indicating that exposure to linear siloxanes may be becoming increasingly important in common dolphins over time.
The screening-level assessment indicated potential health concerns for some individuals whose concentrations exceeded estimated toxicity thresholds. Although these findings do not establish direct adverse effects, they highlight the need for toxicity data, toxicokinetic information, and risk assessment approaches relevant to marine mammals. To our knowledge, this study provides the first baseline dataset on siloxane contamination and long-term variation in a marine mammal species from Korean coastal waters. These results establish an important foundation for continued monitoring and the development of marine mammal-specific ecological risk assessment frameworks.

Acknowledgement: This study was supported by the Korea Institute of Marine Science and Technology Promotion, funded by the Ministry of Oceans and Fisheries, Korea (RS-2024-00417889), and by the National Research Foundation of Korea grant funded by the Korea government (MSIT) (RS-2025-02263830).

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