Disposition and metabolism of diphenyl ether in rats

A descriptive analysis of first trimester urinary concentrations of 14 bisphenol analogues in the MIREC Canadian pregnancy cohort

BACKGROUND

Concern over the health effects of BPA, particularly for the developing fetus, has led to an increasing use of bisphenol analogues in industrial and consumer products, which may be as hormonally active as BPA. Biomonitoring data for many bisphenol analogues, especially in pregnant populations, are limited.

METHODS

We measured concentrations of 14 bisphenol analogues in 1st trimester urine samples (n = 1851) from the Maternal-Infant Research on Environmental Chemicals (MIREC) Canadian pregnancy cohort (2008-2011). We examined patterns of exposure according to sociodemographic and sampling characteristics as well as occupation and frequency of consumption of canned fish within the previous 3 months.

RESULTS

BPA was detected in 89% of participants with a specific gravity standardized geometric mean concentration of 0.990 μg/L. Biphenol 4,4' (BP 4,4'), 4,4'-dihydroxydiphenyl ether (DHDPE), and bisphenol E (BPE) were detected in >97% of participants. Bisphenol F (BPF) and bisphenol S (BPS) were detected in >60% of participants. Specific gravity standardized geometric mean concentrations of these 5 compounds ranged from 0.024 to 0.564 μg/L. Nine bisphenol analogues were detected in <9% of participants. Concentrations of BP 4,4', DHDPE, and BPE were higher in younger women and those with higher pre-pregnancy BMI, lower household income, lower education, and among smokers. We found a similar pattern of differences in BPF for age, education, and smoking status while BPS similarly differed across categories of pre-pregnancy BMI. Participants who were unemployed or working in the service industry had higher molar sum of 7 bisphenol analogues than those working in healthcare, education, or an office setting. Canned fish consumption was not related to bisphenol analogue concentrations.

CONCLUSION

BP 4,4', DHDPE, BPE, BPF, and BPS were highly detected in 1st trimester urine samples in this large pan-Canadian pregnancy cohort. This suggests widespread exposure to these analogues around 2008-2011 and warrants further investigation into associations with health outcomes.

Safety evaluation of dibenzyl ether

Dibenzyl ether (FEMA No. 2371, CAS No. 103-50-4) was given in the diet to rats at a rate of 62, 196 or 620 mg/kg/day for 91 consecutive days. Body weights and food consumption were measured weekly; haematological, clinical chemistry and urinalysis values were obtained at wk 6 and 12. Gross and microscopic pathological changes were observed and organ weights recorded. The high-dose females had increased absolute and relative liver weights; this was considered to be related to dose. Other statistically significant events that occurred sporadically within the test groups were unrelated to dose and were considered to be normal adaptive change. No toxicological or pathological effects were noted at any of the dose levels after 91 consecutive days of feeding dibenzyl ether. A no-effect level was achieved at 196 mg/kg/day. In a 60-kg human, this would be equivalent to approximately 11.8 g/day, assuming a direct relationship between dose and body weight across species. Based on the possible average daily intake of 19.2 mg/day, this would confer a safety factor of 600. The safety factor based on the more realistic consumption per capita of 23.6 micrograms/day would be approximately 500,000.

Biotransformation of diphenyl ether by trout and guinea-pigs after intraperitoneal administration

Diphenyl ether (DPE) was administered intraperitoneally to rainbow trout (Salmo gairdneri) and guinea-pigs (Duncan Hartley). DPE metabolites in the urine and bile of trout and the urine of guinea-pigs were isolated and analysed by g.l.c.-mass spectrometry. No unchanged DPE was found in the biological fluids of guinea-pigs and trout. Only conjugated metabolites of DPE were present in the bile and urine of the trout: 4-hydroxy- and possible 3-hydroxy-DPE conjugates were found in the bile whereas 4-hydroxy- and 4,4-dihydroxy-DPE conjugates were detected in the urine. Both free and conjugated metabolites of DPE were isolated from the urine of guinea-pigs. These metabolites were 2-hydroxy-, 4-hydroxy, 4,4'-dihydroxy-, 4-methoxy-monohydroxy- and methoxy-dihydroxy-derivatives of DPE.