Biomarkers of exposure to environmental tobacco smoke in infants.

Non-invasive biomonitoring of exposure to environmental tobacco smoke (ETS) by means of hair is attractive in children, although systematic evaluation is required in infants. The objective was to compare nicotine and cotinine concentrations in hair and plasma and parentally reported exposure to ETS in a birth cohort of 411 infants. Plasma was collected from 356 six-month-old infants and hair samples were collected from 368 one-year-old infants. Concentrations of nicotine and cotinine were measured by an optimized gas chromatography-mass spectrometry (GC/MS)-based method requiring 4 mg hair or 200 microl plasma. Information was obtained on the number of days with ETS exposure during the first year of life, the smoking habits of the parents, and the number of cigarettes smoked per day in the home. All three parentally reported indices of ETS exposure were significantly associated with the biomarkers, with clear dose response relationships. There was a significant association between days with ETS exposure and nicotine in hair at relatively low exposure levels (10-99 days per year), whereas the other biomarkers only showed significant increases at higher exposure levels. In conclusion, nicotine in hair appears to be the biomarker most strongly associated with parental reports on exposure to ETS in infants.