Determination of free and total bisphenol A in urine of infants.

Infants may be particularly sensitive regarding hormonally active compounds such as Bisphenol A (BPA), which is widely distributed and exhibits weak oestrogenic activity. Since only free (unconjugated) BPA exhibits endocrine activity, both free and total (after hydrolysis of conjugates) BPA were determined in urine samples of infants to support valid risk assessments. Free BPA was observed above the LOQ in only 3 of 91 (3%) samples from 47 infants. As total BPA was observed in only 38 (42%) urine samples, with concentrations between <LOQ and 17.85 μg/l, the median concentration was below the LOQ of 0.45 μg/l. Based on 0.225 μg/l (half of the LOQ), a margin of exposure 1400-fold below the tolerable daily intake (TDI) of 50 μg/kg bw was calculated. The highest concentration observed (17.85 μg/l) was 18-fold below the TDI. Infants who were fed using baby bottles show approximately 2-fold higher median levels of total BPA. Importantly, the higher levels of total BPA compared to free BPA demonstrate that conversion of BPA to biologically inactive conjugates such as glucuronides or sulphates, which is well known to efficiently occur in adults, also occurs in infants.