Table 1.

Summary statistics for PCB measurements in dust collected during two rounds from 289 residences in the California Childhood Leukemia Study, 2001–2007 and 2010

PCB	Number of chlorine atoms	MRL, ng/g	Round 1, 2001-2007, N=288		Round 2, 2010, N=202		Maximum Concentration, ng/g	Rank correlation between rounds
			Values above MRL, N (%)	Median concentration, ng/g	Values above MRL, N (%)	Median concentration, ng/g		r s	p-value
PCB-28	3	0.15	286(99)	1.5	199(99)	1.2	270	0.54	<0.0001
PCB-52	4	0.28	286(99)	2.9	200(99)	2.4	190	0.62	<0.0001
PCB-101	5	0.45	276(96)	3.8	182(90)	3.4	480	0.67	<0.0001
PCB-105	5	0.08	277(96)	1.0	191(95)	0.8	200	0.68	<0.0001
PCB-114	5	0.24	21(7)	<MRL	15(7)	<MRL	10	0.15	0.03
PCB-118	5	0.21	281(98)	2.5	186(92)	2.0	460	0.69	<0.0001
PCB-138	6	0.73	285(99)	5.8	169(84)	3.2	480	0.60	<0.0001
PCB-153	6	0.60	261(91)	3.6	176(87)	3.4	350	0.63	<0.0001
PCB-156	6	0.04	266(92)	0.3	144(71)	0.2	60	0.54	<0.0001
PCB-157	6	0.01	212(74)	0.05	61(30)	<MRL	20	0.35	<0.0001
PCB-167	6	0.04	223(77)	0.2	120(59)	0.10	20	0.45	<0.0001
PCB-180	7	0.72	224(78)	2.4	136(67)	1.8	180	0.62	<0.0001
PCB-189	7	0.01	169(62)	0.02	14(10)	<MRL	2	0.23	0.01
PCB-194	8	0.22	200(69)	0.7	102(50)	0.4	50	0.55	<0.0001
PCB-209	10	0.04	222(77)	0.2	63(31)	<MRL	50	0.49	<0.0001

MRL = Method reporting limit = 3× σ_blanks