An article published on February 7, 2017 in the peer-reviewed journal Regulatory Toxicology and Pharmacology discussed the aggregate exposure assessment of bisphenol A (BPA, CAS 80-05-7), i.e. the assessment looking at both dietary and non-dietary sources. Natalie von Goetz from the Swiss Federal Institute of Technology (ETH) Zurich, Switzerland, together with colleagues from several European institutes dealing with food safety assessment, compared forward and backward approaches to the calculation of internal levels of total BPA. Forward calculation was based on source-to-dose modeling for different age groups, and backward calculation was based on urinary biomonitoring data.
Both calculation methods yielded aggregate exposure estimates being in the same order of magnitude, but the estimates obtained by forward modeling were generally higher and were associated with larger uncertainty. Nonetheless, both methods are seen as complementary to each other: While backward modeling provides for the most reliable exposure estimate, forward modeling is the only method allowing to decipher the relative contribution of different sources.
Dietary exposure, particularly via canned food, was found to contribute around 90% to internal levels of total (conjugated and unconjugated) BPA. Another 10% for some age groups were found to come mainly from dermal exposure via thermal paper and to a lesser extent via cosmetics, while exposure by inhalation (e.g. through the air) was found to be negligible.
The authors further pointed out that only the unconjugated form of BPA is toxicologically relevant, and concluded that this makes the “dermal sources . . . of equal or even higher toxicological relevance than dietary source.” This is because there is no first-pass metabolism resulting in BPA conjugation after the dermal absorption, while most of the BPA absorbed in the gut after oral intake is considered to get conjugated rapidly upon absorption. Of note, however, several studies have demonstrated that some BPA present in food may be absorbed directly in the mouth while chewing (FPF reported). As this uptake route also lacks first-pass metabolism, it may also contribute to the internal levels of unconjugated BPA.
Reference
Von Goetz, N., et al. (2017). «Including non-dietary sources into an exposure assessment of the European Food Safety Authority: The challenge of multisector chemicals such as Bisphenol A.» Regulatory Toxicology and Pharmacology 85: 70-78.
