Table 1.

Comparison of serum PFAS concentrations of the NHANES participants (1999–2014, $n=\mathrm{11,747}$) among three subgroups divided by k-means method.

PFAS mixtures		Serum concentrations ($\text{GM}\pm \text{SE}$ and medians and quartiles) of PFAS in subgroups divided by k-means method (ng/mL)			$p$-Value (medium vs. low)	$p$-Value (high vs. medium)
		Low	Medium	High
Total PFAS	$n$	3,913	5,491	2,343	—	—
	MPAH	$0.118\pm 0.002$ 0.100 (0.070, 0.200)	$0.253\pm 0.006$ 0.300 (0.120, 0.400)	$0.385\pm 0.006$ 0.300 (0.300, 0.700)	$<0.001$	$<0.001$
	PFDE	$0.159\pm 0.002$ 0.180 (0.100, 0.200)	$0.241\pm 0.002$ 0.200 (0.200, 0.300)	$0.701\pm 0.010$ 0.600 (0.500, 0.900)	$<0.001$	$<0.001$
	PFHS	$0.781\pm 0.014$ 0.900 (0.500, 1.400)	$2.193\pm 0.029$ 2.100 (1.300, 3.400)	$2.554\pm 0.052$ 2.500 (1.520, 4.100)	$<0.001$	$<0.001$
	PFNA	$0.605\pm 0.008$ 0.656 (0.440, 0.900)	$0.956\pm 0.008$ 1.000 (0.738, 1.312)	$2.301\pm 0.031$ 2.132 (1.640, 3.000)	$<0.001$	$<0.001$
	PFOA	$1.607\pm 0.020$ 1.770 (1.200, 2.400)	$3.920\pm 0.033$ 3.900 (2.900, 5.300)	$5.324\pm 0.083$ 5.400 (3.700, 7.700)	$<0.001$	$<0.001$
	PFOS	$4.293\pm 0.064$ 4.860 (3.080, 6.890)	$15.609\pm 0.157$ 15.200 (10.500, 22.700)	$23.134\pm 0.398$ 22.600 (14.600, 35.400)	$<0.001$	$<0.001$
	PFUA	$0.113\pm 0.001$ 0.100 (0.070, 0.160)	$0.158\pm 0.001$ 0.140 (0.140, 0.200)	$0.423\pm 0.008$ 0.400 (0.270, 0.600)	$<0.001$	$<0.001$
PFAS excluding PFOA	$n$	4,160	5,327	2,260	—	—
	MPAH	$0.117\pm 0.002$ 0.100 (0.070, 0.200)	$0.234\pm 0.006$ 0.300 (0.120, 0.400)	$0.427\pm 0.006$ 0.300 (0.300, 0.700)	$<0.001$	$<0.001$
	PFDE	$0.163\pm 0.002$ 0.190 (0.100, 0.200)	$0.246\pm 0.002$ 0.200 (0.200, 0.300)	$0.709\pm 0.011$ 0.640 (0.500, 0.900)	$<0.001$	$<0.001$
	PFHS	$0.835\pm 0.015$ 0.910 (0.500, 1.500)	$2.244\pm 0.030$ 2.120 (1.370, 3.500)	$2.471\pm 0.052$ 2.400 (1.500, 3.960)	$<0.001$	$<0.001$
	PFNA	$0.633\pm 0.008$ 0.700 (0.492, 0.920)	$0.965\pm 0.009$ 1.000 (0.710, 1.340)	$2.282\pm 0.032$ 2.110 (1.600, 3.034)	$<0.001$	$<0.001$
	PFOS	$4.522\pm 0.065$ 5.100 (3.200, 7.300)	$16.532\pm 0.170$ 16.200 (11.200, 24.100)	$22.319\pm 0.392$ 21.900 (14.000, 34.300)	$<0.001$	$<0.001$
	PFUA	$0.112\pm 0.001$ 0.100 (0.070, 0.150)	$0.157\pm 0.002$ 0.180 (0.140, 0.200)	$0.444\pm 0.008$ 0.400 (0.300, 0.700)	$<0.001$	$<0.001$
PFAS excluding PFOS	$n$	4,133	5,180	2,434	—	—
	MPAH	$0.117\pm 0.001$ 0.100 (0.070, 0.200)	$0.222\pm 0.005$ 0.300 (0.1100, 0.300)	$0.442\pm 0.006$ 0.400 (0.300, 0.710)	$<0.001$	$<0.001$
	PFDE	$0.161\pm 0.002$ 0.190 (0.100, 0.200)	$0.241\pm 0.002$ 0.200 (0.200, 0.300)	$0.668\pm 0.010$ 0.600 (0.400, 0.900)	$<0.001$	$<0.001$
	PFHS	$0.807\pm 0.014$ 0.900 (0.500, 1.400)	$2.305\pm 0.031$ 2.200 (1.400, 3.500)	$2.370\pm 0.048$ 2.300 (1.400, 3.800)	$<0.001$	0.028
	PFNA	$0.611\pm 0.007$ 0.660 (0.480, 0.902)	$0.959\pm 0.008$ 1.000 (0.700, 1.312)	$2.216\pm 0.030$ 2.050 (1.558, 2.900)	$<0.001$	$<0.001$
	PFOA	$1.677\pm 0.021$ 1.850 (1.250, 2.570)	$3.994\pm 0.036$ 4.000 (2.900, 5.500)	$5.070\pm 0.078$ 5.100 (3.500, 7.400)	$<0.001$	$<0.001$
	PFUA	$0.113\pm 0.001$ 0.100 (0.070, 0.160)	$0.157\pm 0.002$ 0.140 (0.140, 0.200)	$0.413\pm 0.008$ 0.400 (0.230, 0.600)	$<0.001$	$<0.001$

Note: GMs and medians were weight-adjusted using NHANES-specified sampling weights. $p$-Values were calculated using Mann–Whitney U test. Samples with test values below the LOQ were substituted with the value of the LOQ divided by the square root of 2. —, not applicable; GM, geometric mean; LOQ, limit of quantification; MPAH, 2-($N$-methyl-perfluorooctane sulfonamido) acetic acid; NHANES, National Health and Nutrition Examination Survey; PFAS, per- and polyfluoroalkyl substances; PFDE, perfluorodecanoic acid; PFHS, perfluorohexane sulfonate acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctane sulfonic acid; PFUA, perfluoroundecanoic acid; SE, standard error.