A sensitive and selective GC-MS method was developed and used to analyse human milk samples for both free and total bisphenol A (BPA). Total BPA was detected in 72 of the 278 human milk samples (25.9%) at concentrations from < 0.036 to 2.5 ng g(-1) with a geometric mean (GM) of 0.13 ng g(-1) and median of 0.11 ng g(-1), while free BPA was detected in fewer samples, 46 of the 278 samples (16.5%) at concentrations ranging from < 0.036 to 2.3 ng g(-1) with a GM of 0.11 ng g(-1) and median of 0.10 ng g(-1). Ratios of [free BPA]/[total BPA] for the positive samples ranged from 7.9% to 100% with a GM of 57.2% and median of 70.3%. Concentrations of free and total BPA in most samples were low with 0.39 and 0.65 ng g(-1) at the 95th percentile for free and total BPA, respectively, and they are also lower than those reported in other countries. Based on the low frequency of detection of free BPA in human milk samples, in general, dietary exposure to BPA for Canadian breast-fed infants is expected to be somewhat lower compared with exposure among formula-fed infants.
Keywords: GC-MS; bisphenol A; free BPA; human milk; total BPA.