2.2. Serum PFAS concentrations

Laboratory analyses of serum PFASs were conducted by Exygen, State College, PA, USA (a commercial laboratory) in 2005–2006 and by the Centers for Disease Control and Prevention (CDC) in Atlanta, GA, USA in 2010. The analytical (Flaherty et al., 2005, Frisbee et al., 2009, Kato et al., 2011) and quality control (Van Leeuwen et al., 2006) procedures employed by both laboratories have been described elsewhere. Briefly, laboratory analyses of PFASs used online solid phase extraction coupled with reversed-phase high-performance liquid chromatography separation and detection by isotope-dilution tandem mass spectrometry. The limits of detection (LODs) in 2005–2006 were 0.5 ng/mL for all PFASs. In 2010, LODs were 0.1 ng/mL for PFNA and PFHxS, 0.2 ng/mL for PFOS, and 0.5 ng/mL for PFOA.