Levels of selected carnitine-related metabolite in CHDS subjects categorized by quartile 1, 2, 3 and 4 of PFOS serum levels. A: Protein N6,N6-dimethyl-lysine; B: carnitine; C: clupanodonyl carnitine; D: tetracosapentaenyl carnitine. The metabolites here are annotated by accurate mass (5 ppm, details in Supplemental Table S2), and carnitine was further confirmed by authentic chemical standards. *P < 0.05, #P =0.07, by student’s t test compared to quartile 1 (Q1).