Thyroid hormones in coastal fish species: Associations with PFAS and multi-elemental burdens

While the endocrine-disrupting potential of heavy metals and per- and polyfluoroalkyl substances (PFAS) is well-documented in laboratory settings, evidence from wild populations remains sparse. This study investigated the impact of a suite of legacy and emerging contaminants, including five heavy metals, four mineral elements, and eleven PFAS, on the thyroid hormone (TH) levels of three wild fish species inhabiting the coastal waters of Qingdao, China. The results showed that three PFAS, including perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUdA), and 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA), were significantly positively correlated with free (FT3), total triiodothyronine (TT3), or the free triiodothyronine/thyroxine ratio (FT3:FT4), indicating a stimulatory or compensatory TH response. In contrast, heavy metals exhibited divergent effects: chromium (Cr) showed a significant negative correlation with FT3 and TT3, whereas total mercury (THg) was positively associated with TT3. Furthermore, increasing phosphorus (P) and calcium (Ca) were linked to a decrease in the FT3:FT4 ratio. Partial least square analysis identified a statistically supported association between TT3 and a co-varying exposure pattern, with PFDA, PFUdA, 6:2 Cl-PFESA, MeHg, Cr, and Zn having the highest VIP values within the identified pattern. Notably, several contaminant-TH interactions were species-specific, suggesting varying sensitivity to chemical stress among marine teleosts. Our findings underscore the potent thyroid-disrupting potential of PFAS and heavy metals in natural ecosystems, and highlight the complex, multi-contaminant exposure profiles encountered by wild fish populations.