Tracking Contaminant Trends: PFAS, Metals and Metalloids in Indo-Pacific Bottlenose (Tursiops aduncus) and Common Dolphins (Delphinus delphis) from South Australia

Per- and polyfluorinated alkyl substances (PFAS), metals, and metalloids were analysed in liver of 42 Indo-Pacific bottlenose dolphins (Tursiops aduncus) and 28 common dolphins (Delphinus delphis) from South Australia (SA). Dolphins sampled between 1993 and 2015 (20 T. aduncus) were screened for eleven PFAS, while those sampled between 2021 and 2023 (22 T. aduncus and 28 D. delphis) were analysed for twenty-nine PFAS, and eighteen metals and metalloids. Twenty-one PFAS were identified overall, with PFOS comprising ~ 80% of ∑PFAS. Average ∑PFAS concentrations were similar among T. aduncus and D. delphis during 2021-2023. ∑PFAS was significantly higher in Adelaide Dolphin Sanctuary (ADS) T. aduncus (0.4-5.2 compared to < 2.7 mg/kg ww elsewhere). A decreasing trend in ∑PFAS, primarily driven by PFOS, was observed over time. A preliminary risk assessment based on tentative critical concentrations and hazard quotients indicated a reduced potential risk of adverse effects from PFOS exposure over time. Reductions may be due to regulatory efforts. ADS T. aduncus also exhibited significantly higher lead (0.13-1.9 mg/kg dw) and tin (0.15-1.1 mg/kg dw). In other SA regions, a low Selenium: Mercury ratio in 50% of T. aduncus, alongside Hg concentrations up to 2350 mg/kg dw, highlights a toxicity concern. This study is unique in being the first in Australia to report changes in hepatic PFAS in dolphins over time. It underscores the importance of contaminant load reassessments to understand bioaccumulation. Findings will help to understand contaminant threats to human, wildlife, and environmental health.