Per- and polyfluoroalkyl substances (PFAS) pose a significant threat to aquatic ecosystems due to their persistence, bioaccumulation potential, and capacity for biomagnification. While interspecific differences are often considered, intraspecific variation—driven by individual physiological and trophic differences—remains a critical but understudied factor in accurate ecological risk assessment. This study investigated the influence of intraspecific variation on PFAS bioaccumulation in the three-line tongue sole (Cynoglossus browni) from the coastal waters of Shenzhen, a rapidly developing megacity in China. We analyzed 40 PFAS compounds and stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) in 43 fish specimens. Our results revealed a complex bioaccumulation pattern strongly linked to individual traits. A significant positive relationship was found between body length and the concentrations of several long-chain PFAS, including PFOS (R² = 0.198, p < 0.01) and PFHxS (R² = 0.094, p < 0.05), confirming their strong biomagnification potential. In contrast, short- and medium-chain carboxylic acids (e.g., PFHxA, PFOA) exhibited a negative correlation with body length, indicating growth dilution. Stable isotope analysis further uncovered substantial intraspecific trophic variation (TL range: 1.6–2.9), which was positively correlated with body length (R² = 0.175, p = 0.003). Bayesian mixing model (SIAR) analysis delineated three distinct dietary groups with varying reliance on benthic and pelagic carbon sources. Crucially, we found that dietary source independently influenced PFAS body burdens; individuals with pelagic-dominated or mixed diets accumulated significantly higher PFAS concentrations than those with benthic-dominated diets, even after accounting for trophic level. This study demonstrates that PFAS accumulation in wild fish populations is not homogeneous but is shaped by the interplay of individual growth, trophic ecology, and foraging behavior. Ignoring such intraspecific variability can lead to substantial underestimation or overestimation of exposure risks for specific subpopulations. Our findings underscore the necessity of incorporating individual-level ecological traits into bioaccumulation models and environmental monitoring strategies for a more accurate and precise risk assessment of PFAS.

PFAS; Intraspecific variation; Bioaccumulation; Stable isotopes; Tongue sole