A new study on “Evidence of absence: Estrogenicity assessment of a new food-contact coating and the bisphenol used in its synthesis” was published online on January 18, 2017 in the peer-reviewed journal Environmental Science & Technology. The aim of the study was the assessment of estrogenic activity of a bisphenol-based monomer, tetramethyl bisphenol F (TMBPF, CAS 5384-21-4), and a novel polymeric coating derived from TMBPF. Three of the study authors are scientists at Tufts University School of Medicine, Boston, U.S., and the other two authors work at the Valspar Corporation and as independent consultant, respectively.
For several decades, bisphenol A-based can coatings have been used in the vast majority of food and beverage cans because of their technical performance and low cost (FPF reported). However, the search for alternatives to bisphenol A (BPA, CAS 80-05-7) started several years ago, in response to toxicological evidence of its endocrine disrupting properties, public discussions, and regulatory decisions (FPF reported). In the study, the authors used a guidance principle targeting at inherently safe molecules to find suitable replacements for BPA-based can coatings. They identified estrogenic activity as the critical biological effect and based their decision on the structure-activity relationship of bisphenols and the availability of suitable testing methods. TMBPF was chosen as potential candidate because i) computer-based modelling indicated low binding affinity of TMBPF to the estrogen receptor, ii) the synthesis route allows efficient separation of unbound TMBPF from the final polymeric coating, and iii) the functionality of the coating is maintained.
In the study, TMBPF migration from polymer-coated panels into 3% acetic acid and 50% ethanol was tested according to standardized conditions and measured by liquid chromatography and tandem mass spectrometry (LC-MS/MS). TMBPF concentrations remained below the level of detection (LOD, 0.2 ppb). Further, migration of non-intentionally added substances (NIAS) into the two food simulants was measured by liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS). Approximately 650 masses were detected in each extract, but details on their chemical identity were not provided.
Estrogenic activity of TMBPF was assessed by three in vitro and two in vivo assays (see table). The two total migrates from the can coating were evaporated to dryness, redissolved in dimethyl sulfoxide and, subsequently, estrogenic activity was measured in one in vitro assay. A summary of the test results is provided in the table.
|Estrogen receptor transactivation assay||MCF7 cells, |
OECD test guideline 455
|0.0001-1 µg/ml: |
No induction of luciferase activity;
>3.9 µM: cytotoxic
|E-SCREEN bioassay||MCF7 cells||10 pM-100 µM: |
>1 µM: cytotoxic
>2 ppm: cytotoxic
|Quantitative real-time PCR||Target genes: PGRAB, BIK, APOD, WNT1||0.1, 1 and 2.5 µM:|
No activation of 4 estrogen response genes
|Uterotrophic assay||Sprague-Dawley rats; gavage 1x/d; |
females: PND19 to 21
|100, 300 and 1000 mg/kg bw/d:|
No changes in uterus weight and microscopic findings in the mammary glands; small effects on the body weight gain, few treated animals with dried yellow material in the urogenital area
|Pubertal assay||Sprague-Dawley rats; |
females: PND22 to 42;
males: PND23 to 53
|200 and 600 mg/kg bw/d: |
- Females: No changes in age at vaginal opening, vaginal cytology and histopathology, estrous cycling, structures of mammary glands
- Males: changes in preputial separation at the higher dose (not statistically significant)
- Males and females: no effects on body weight and weight of reproductive organs
PND = postnatal day, bw = body weight
The authors of the study conclude that these “findings provide strong evidence for the absence of endocrine activity by TMBPF and the polymer coating … derived from TMBPF.” In combination with the low migration of TMBPF, human exposure is judged to be exceedingly small.
Sarah Vogel (January 23, 2017). “A non-estrogenic alternative to Bisphenol A at last?” EDF Health
Soto, A.M., et al. (2017). “Evidence of absence: Estrogenicity assessment of a new food-contact coating and the bisphenol used in its synthesis.” Environmental Science & Technology (published online January 18, 2017).
Food Packaging Forum (December 15, 2016). “Dossier: Can coatings.” (pdf)