Table 2.

Detection frequencies and median concentrations (ng/g) of tobacco constituents in vacuum dust collected from homes participating in the California Childhood Leukemia Study during the first and second sampling rounds, by tobacco use at the index home.

Tobacco constituent	1st sampling round (2002-2007)						2nd sampling round (2010)
	Smokeless tobacco users, N=6		Active Smokers, N=6		Tobacco-free homes, N=20		Smokeless tobacco users, N=5		Active Smokers, N=6		Tobacco-free homes, N=20
	% Det	Median	% Det	Median	% Det	Median	% Det	Median	% Det	Median	% Det	Median
Nicotine	100	14,000a	100	7,000a	90	520	100	15,000a	100	7,800a	95	510
Tobacco-specific nitrosamines
NNN	67	5.7a	67	1.6a	5	<1.4b	80	4.3a	83	2.9a	10	<1.4b
NNK	100	6.3a	100	3.7a	40	<0.45b	100	3.4a	100	5.8a	65	0.51
NNA	50	1.2a	67	0.46a	0	<0.45b	40	<0.45a, b	50	0.60a	5	<0.45b
NAB	50	0.28	33	<0.15b	20	<0.15b	60	0.29a	50	0.18a	10	<0. 15b
NAT	50	3.6a	0	<4.2b	0	<4.2b	40	<4.2b	0	<4.2b	5	<4.2b
Minor tobacco alkaloids
Cotinine	100	680a	100	430a	80	54	100	450a	100	460a	70	26
Myosmine	100	310a	100	440a	85	54	100	140a	100	700a	80	45
N-formylnornicotine	100	370a	100	480a	90	43	100	200a	100	660a	75	30
Nicotelline	100	5.5	100	8.0a	95	1.0	100	2.9a	100	7.1a	100	0.62
2,3'-Bipyridine	83	76a	100	74a	60	6.2	100	52a	100	72a	75	5.9

%Det=Detection frequency; NNN=N′-nitrosonornicotine; NNK=4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone; NNA=4-(methylnitrosamino)-4-(3-pyridyl)butanal; NAB=N′-nitrosoanabasine; NAT=N′-nitrosoanatabine

^aSignificantly greater than concentrations of the tobacco constituent in dust samples collected during the same sampling round from tobacco-free homes; using the Wilcoxon two-sample Z-test, two-sided p<0.05

^bAverage lower limit of quantitation, determined as the lowest calibration standard for which back-calculated values were within ±20% of the expected concentration, with units converted from ng/sample to ng/g using average sample mass of 0.066 g.