Within-person variability in urinary bisphenol A concentrations: measurements from specimens after long-term frozen storage.
BACKGROUND
Bisphenol A (BPA) is an estrogenic contaminant of food and water associated with adverse developmental effects in laboratory animals. BPA has recently been linked to morbidity in adult humans, but studies of developmental effects in humans are methodologically more difficult. The ability to measure BPA in urine samples after long-term storage could aid in such studies. Because the half-life of BPA is < 6h, a single measurement would be useful only if the environmental exposure is relatively constant over weeks or months. Our aims were to evaluate the stability of BPA in specimens after 22-24 years of storage and to measure within-person temporal variability in urinary BPA.


METHODS
We measured total BPA concentration by mass spectrometry in first-morning urine samples from 60 premenopausal women. We selected from each woman's stored daily collections three urine samples approximately 2 and 4 weeks apart. Samples were selected from both the follicular and luteal phases of the menstrual cycle to assess cycle effects. Temporal variability was assessed with mixed model regression and correlations.


RESULTS
BPA levels had an inter-quartile range from 1.1 to 3.1 ng/mg creatinine, slightly higher than levels in specimens from NHANES collected 3-11 years later. The Spearman correlation was approximately 0.5 for samples 2 weeks apart and 0.3 for samples 4 weeks apart. Menstrual cycle phase did not influence levels. BPA tended to increase during the three-year collection period, but not significantly.


CONCLUSIONS
The similar distribution to NHANES samples and correlation of BPA levels taken at 2-week intervals provide indirect evidence that BPA is relatively stable during long-term freezer storage. The correlations indicate generally stable exposures over periods of weeks. These findings suggest that developmental effects of BPA exposure could be investigated with measurements from stored urine.
Nepomnaschy
Pablo A
PA
Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, USA.
Baird
Donna Day
DD
Weinberg
Clarice R
CR
Hoppin
Jane A
JA
Longnecker
Matthew P
MP
Wilcox
Allen J
AJ
D001559:Benzhydryl Compounds; D003627:Data Interpretation, Statistical; D004785:Environmental Pollutants / Q000652:urine*; D005260:Female; D005615:Freezing; D006801:Humans; D008597:Menstrual Cycle / Q000502:physiology; D010636:Phenols / Q000652:urine*; D010829:Physiological Phenomena; D017697:Premenopause / Q000502:physiology; D013048:Specimen Handling / Q000379:methods*; D013997:Time Factors; D016482:Urinalysis / Q000379:methods*; D000098826:Bisphenol A Compounds
D001559:Benzhydryl Compounds; D004785:Environmental Pollutants; D010636:Phenols; C006780:bisphenol A; D000098826:Bisphenol A Compounds