Disposition of the Emerging Brominated Flame Retardant, 2-Ethylhexyl 2,3,4,5-Tetrabromobenzoate, in Female SD Rats and Male B6C3F1 Mice: Effects of Dose, Route, and Repeated Administration

Abstract

2-Ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB; MW 549.92 g/mol; CAS 183658-27-7) is a brominated component of flame retardant mixtures used as substitutes for some PBDEs. EH-TBB is added to various consumer products, including polyurethane foams, and has been detected in humans. The present study characterized the fate of EH-TBB in rodents. [¹⁴C]-labeled EH-TBB was absorbed, metabolized, and eliminated via the urine and feces following single administrations of 0.1-100 µmol/kg (∼0.05-55 mg/kg) or repeated administration (0.1 µmol/kg/day × 5-10 days) by gavage to female Hsd:Sprague DawleySD (SD) rats. Cumulative excretion via feces increased (39-60%) with dose (0.1-10 µmol/kg) with corresponding decreases in urinary excretion (54 to 37%) after 72 h. Delayed excretion of [¹⁴C]-radioactivity in urine and feces of a 100 µmol/kg oral dose was noted. Recovery was complete for all doses by 72 h. IV-injected rats excreted more of the 0.1 µmol/kg dose in urine and less in feces than did gavaged rats, indicating partial biliary elimination of systemically available compound. No tissue bioaccumulation was found for rats given 5 oral daily doses of EH-TBB. Parent molecule was not detected in urine whereas 2 metabolites, tetrabromobenzoic acid (TBBA), a TBBA-sulfate conjugate, and a TBBA-glycine conjugate were identified. EH-TBB and TBBA were identified in extracts from feces. Data from gavaged male B6C3F1/Tac mice indicated minimal sex- or species differences are likely for the disposition of EH-TBB. Approximately 85% of a 0.1 µmol/kg dose was absorbed from the gut. Overall absorption of EH-TBB is expected to be even greater at lower levels.

Keywords: 2-Ethylhexyl 2,3,4,5-Tetrabromobenzoate; disposition; metabolism..

FIG. 1

Chemical structure of EH-TBB; asterisk denotes position of [¹⁴C]-radiolabel.

FIG. 2

Excretion of [¹⁴C]-radioactivity following a single administration of EH-TBB. N = 4 per dose group, mean ± SD. (A) 0.1 µmol/kg, IV, (B) 0.1 µmol/kg, oral, (C) 1 µmol/kg, oral, (D) 10 µmol/kg, oral, and (E) 100 µmol/kg, oral (▲:Recovery in urine; •:Recovery in feces; ▪: Total recovery).

FIG. 3

Time-blood concentration curve following a single oral dose of EH-TBB to female SD rats (0.1 µmol/kg). N = 4, mean ± SD.

FIG. 4

Elimination of [¹⁴C]-radioactivity following 1, 5, or 10 doses of EH-TBB (0.1 µmol/kg, PO). N = 4 per dose group, mean ± SD. (A) Recovery in urine. (B) Recovery in feces (*P < .05, **P < .01).

FIG. 5

Representative HPLC-radiochromatograms of [¹⁴C]-radioactivity in urine collected between 12 and 24 h from female SD rats administered EH-TBB. (A) [¹⁴C]-EH-TBB and TBBA standards; (B) 0.1 µmol/kg (IV); (C) 0.1 µmol/kg (oral); (D) 1 µmol/kg (oral); (E) 10 µmol/kg (oral); (F) 100 µmol/kg (oral).

FIG. 6

Representative mass spectra of extracted urine following EH-TBB (100 µmol/kg) administration by gavage to female SD rats. (A) Total ion chromatogram for extracted urine after UPLC separation. (B) Full-scale mass spectrum for peak eluting between 9.1and 9.3 min, m/z of 489.46 Da is consistent with the mass of a TBBA-glycine [M–H]⁻ ion. (C) Full-scale mass spectrum for peak eluting between 9.6 and 9.8 min, m/z of 514.56 Da is consistent with the TBBA-sulfate [M–H]⁻. (D) Full-scale mass spectrum for peak eluting between 10.7 and 11.2 min, m/z of 481.23 Da is consistent with the TBBA [M + H]⁻ ion with a formic acid adduct (m/z = 481.23 Da); a mass consistent with at TBBA dimer (m/z = 871.56) was formed as well (this was also seen in the TBBA standard, see Supplementary Fig. S3).

FIG. 7

Representative HPLC-radiochromatograms of [¹⁴C]-radioactivity extracted from feces collected between 12 and 24 h from female SD rats administered EH-TBB. (A) [¹⁴C]-EH-TBB and TBBA standards; (B) 0.1 µmol/kg (IV); (C) 0.1 µmol/kg (oral); (D) 1 µmol/kg (oral); (E) 10 µmol/kg (oral); (F) 100 µmol/kg (oral).