title: Disruption of thyroxine and sex hormones by 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (DBE-DBCH) in American kestrels (Falco sparverius) and associations with reproductive and behavioral changes.
abstract: 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (DBE-DBCH - formerly TBECH) is an emerging brominated flame retardant (BFR) pollutant with androgen potentiating ability and other endocrine disrupting effects in birds and fish. The objectives of this study were to determine the effects of exposure to environmentally-relevant levels of DBE-DBCH on circulating levels of thyroid and sex steroid hormones in American kestrels, and if hormonal concentrations were related to previously reported changes in reproductive success and courtship behaviors. Sixteen kestrel pairs were exposed to 0.239ng β-DBE-DBCH/g kestrel/day by diet, based on concentrations in wild bird eggs, from 4 weeks before pairing until the chicks hatched (mean 82 d), and were compared with vehicle-only-exposed control pairs (n=15). As previously reported, DBE-DBCH concentrations were not detected in tissue or eggs of these birds, nor were any potential metabolites, despite the low method limits of detection (≤0.4ng/g wet weight), suggesting it may be rapidly metabolized and/or eliminated by the kestrels. Nevertheless, exposed kestrels demonstrated changes in reproduction and behavior, indicating an effect from exposure. During early breeding, males were sampled at multiple time points at pairing and during courtship and incubation; females were blood sampled at pairing only; both sexes were sampled at the end of the season. All comparisons are made to control males or control females, and the relative differences in hormone concentrations between treatment and control birds, calculated separately for each sex, are presented for each time point. Males exposed to β-DBE-DBCH demonstrated significantly (p=0.05) lower concentrations of total thyroxine (TT4) overall, that were 11-28% lower than those of control males at the individual sampling points, yet significantly higher (p=0.03) concentrations of free thyroxine (FT4), that were 5-13% higher than those of control males at the individual sampling points; females had similar concentrations of TT4and FT4at the time of pairing, and T4was similar in both sexes at the end of the breeding season. Testosterone (T) concentrations in the treatment males were significantly higher during early (85%) and mid-courtship (30%) (time*treatment p=0.001), whereas females demonstrated a reduction in T at the time of pairing (17%, p=0.05). In the treatment females, concentrations of 17β-estradiol (E2) showed a non-significant decrease (20%) and were positively correlated with T concentrations (p=0.03); E2concentrations were below quantification limits in males. For males, some variation in T was also significantly associated with their sexual behavior (p<0.001) and FT4concentrations (p=0.01). For females, there was no relationship between hormones measured at pairing and subsequent sexual behaviors or reproductive measures. This study demonstrates that exposure to β-DBE-DBCH at levels that are likely below those experienced by wild birds, affects the thyroid and sex steroid axes in birds and thus may be a contaminant of concern for wildlife warranting further research.
authors.affiliation: Ecotoxicology & Wildlife Health Division, Science & Technology Branch, Environment and Climate Change Canada, Burlington, Ontario, Canada.
authors.forename: Sarah C
authors.initials: SC
authors.lastname: Marteinson
authors.affiliation: International Institute for Sustainable Development - Experimental Lakes Area (IISD-ELA), 111 Lombard, Suite 325, Winnipeg, Manitoba R3B 0T4, Canada.
authors.forename: Vince
authors.initials: V
authors.lastname: Palace
authors.affiliation: Ecotoxicology & Wildlife Health Division, Science & Technology Branch, Environment and Climate Change Canada, National Wildlife Research Centre, Ottawa, Ontario, Canada.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Letcher
authors.affiliation: Ecotoxicology & Wildlife Health Division, Science & Technology Branch, Environment and Climate Change Canada, Burlington, Ontario, Canada. Electronic address: kim.fernie@canada.ca.
authors.forename: Kim J
authors.initials: KJ
authors.lastname: Fernie
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003510:Cyclohexanes / Q000633:toxicity*; D004781:Environmental Exposure / Q000032:analysis*; D004785:Environmental Pollutants / Q000009:adverse effects*; D046093:Falconiformes / Q000502:physiology*; D005260:Female; D005411:Flame Retardants / Q000633:toxicity*; D012739:Gonadal Steroid Hormones; D008297:Male; D012726:Sexual Behavior, Animal / Q000187:drug effects*; D013974:Thyroxine / Q000187:drug effects*
chemical_list: D003510:Cyclohexanes; D004785:Environmental Pollutants; D005411:Flame Retardants; D012739:Gonadal Steroid Hormones; C517232:1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane; D013974:Thyroxine
keywords: Androgen agonist; Bird; Sex steroids; TBECH; Thyroxine