Table 5.

Population average constant elimination rate (yearly) and half-life (year) for each PFAS.

PFAS	Model with original serum levelsa			Model with serum levels after subtraction of background exposureb
	Constant elimination rate (95% CI)	Half-life (95% CI)	$p$-Value	Constant elimination rate (95% CI)	Half-life (95% CI)	$p$-Value
PFHxA	0.43 ($-0.25$, 1.1)	1.63 (NA)	0.2	NAc	NA
PFHpA	4.11 (3.13, 5.09)	0.17 (0.14, 0.22)d	$<0.001$	NA	NA
PFOA	0.39 (0.3, 0.49)	1.77 (1.43, 2.31)	0.002	0.47 (0.35, 0.58)	1.48 (1.19, 1.96)	$<0.001$
PFBS	5.96 (4.65, 7.27)	0.12 (0.1, 0.15)d	0.003	NA	NA
PFPeS	1.1 (0.68, 1.51)	0.63 (0.46, 1.01)	0.004	1.1 (0.68, 1.52)	0.63 (0.46, 1.01)	$<0.001$
PFHxS	0.24 (0.16, 0.33)	2.86 (2.1, 4.47)	0.005	0.24 (0.16, 0.33)	2.84 (2.08, 4.43)	0.002
PFHpS	0.48 (0.11, 0.84)	1.46 (0.83, 6.25)	0.014	0.51 (0.12, 0.9)	1.35 (0.77, 5.71)	0.014
L-PFOS	0.24 (0.07, 0.4)	2.91 (1.71, 9.63)	0.007	0.41 (0.11, 0.71)	1.69 (0.98, 6.04)	0.010
1m-PFOS	0.55 (0.09, 1.01)	1.27 (0.69, 7.64)	0.022	0.75 (0.15, 1.36)	0.92 (0.51, 4.77)	0.018
3/4/5m-PFOS	0.64 (0.18, 1.1)	1.09 (0.63, 3.96)	0.011	0.83 (0.24, 1.42)	0.83 (0.49, 2.84)	0.011
2/6m-PFOS	0.66 (0.29, 1.04)	1.04 (0.67, 2.42)	0.001	0.95 (0.39, 1.5)	0.73 (0.46, 1.76)	0.002

Note: CI, confidence interval; L-PFOS, linear perfluorooctane sulfonic acid; NA, not applicable; PFAS, perfluoroalkyl substances; PFBS, perfluorobutane sulfonic acid; PFHpA, perfluoroheptanoic acid; PFHpS, perfluoroheptane sulfonic acid; PFHxA, perfluorohexanoic acid; PFHxS, perfluorohexane sulfonic acid; PFOA, perfluorooctanoic acid; PFPeS, perfluoropentane sulfonic acid; 1m-PFOS, branched, perfluoro-1-methylheptanesulfonate; 2/6m-PFOS, branched, sum of perfluoro-2/6-methylheptanesulfonate; 3/4/5m-PFOS, branched, sum of perfluoro-3/4/5-methylheptanesulfonate.

^aLinear mixed model with age and sex as covariates. Serum PFAS levels were log-transformed. The constant elimination rate denotes the negative value of the slope ($-\mathrm{\beta }$) from the model, and half-life is calculated as $\text{ln}2/k$.

^bSensitivity analysis using same linear mixed model. Serum PFAS levels were first subtracted with the median levels from the reference population (background exposure levels, presented in Table 2). If the levels after subtraction were lower than half of the corresponding background levels, they were replaced with half of the background levels.

^cNo background serum PFAS levels available.

^dHalf-life and 95% CI in days: PFHpA: 62 d (95% CI: 51–80 d); PFBS: 44 d (95% CI: 37–55 d).