Margaret L. Eng

Developmental exposure to a brominated flame retardant: An assessment of effects on physiology, growth, and reproduction in a songbird, the zebra finch

Mixtures of polybrominated diphenyl ethers (PBDEs) have been widely used as additive flame retardants, and BDE-99 is one of the most predominant congeners found in the environment. BDE-99 has been reported in avian samples worldwide, yet knowledge of its toxicity to birds is minimal. We assessed the short- and long-term effects of nestling exposure to environmentally relevant levels of BDE-99 in a model passerine, the zebra finch. Early exposure to BDE-99 did not affect hematocrit, oxidative stress, or thyroid hormones in either the juvenile or adult stages, and there were no effects on chick growth or survival. BDE-99 exposure caused a dose-dependent delay in timing of reproduction, but there were no other effects on reproductive success. In zebra finches, endpoints related to reproductive behavior appear to be the most sensitive to BDE-99. However, passerines overall appear to be less sensitive than birds of prey or mammals to PBDE exposure.

Assessment of neuroanatomical and behavioural effects of in ovo methylmercury exposure in zebra finches (Taeniopygia guttata)

&NA; Methylmercury (MeHg) readily crosses the blood brain barrier and is a known neuro‐toxicant. MeHg accumulation in the brain causes histopathological alterations, neurobehavioral changes, and impairments to cognitive motor functions in mammalian models. However, in birds the neurotoxic effects of MeHg on the developing pre‐hatching brain and consequent behavioral alterations in adult birds have not received much attention. Moreover, passerine birds are poorly represented in MeHg neurotoxicology studies in comparison to other avian orders. Hence in this study, we used the egg injection method to investigate the long term effects of in ovo MeHg exposure on brain histopathology and courtship behavior in a model songbird species, the zebra finch (Taeniopygia guttata). Egg treatment groups included: a low MeHg dose of 0.2 &mgr;g Hg g−1 egg, a high MeHg dose of 3.2 &mgr;g Hg g−1 egg, and a vehicle control (water). No adverse effects of in ovo MeHg treatment were detected on courtship song quality or on mating behavior in experimental males at sexually maturity which would suggest that observable neurobehavioral effects of MeHg exposure may depend on the timing of exposure during offspring development. However, neuroanatomical analysis indicated an increase in telencephalon volume with increased MeHg concentrations which may suggest a prolonged inflammatory response in this region of the brain. HighlightsAssessed the long term effects of in ovo MeHg exposure on courtship behavior and associated neuroanatomy in a model songbird species.Utilized the egg injection method.No adverse long term effects of in ovo MeHg treatment on courtship behavior or singing were observed in male zebra finches.An increase in telencephalon volume, with increasing in ovo MeHg concentrations, was measured.

Acute embryotoxic effects but no long‐term reproductive effects of in ovo methylmercury exposure in zebra finches (Taeniopygia guttata)

Mercury bioaccumulates in terrestrial ecosystems as methylmercury (MeHg), yet little is known about its effects on terrestrial organisms, including songbirds. The authors used a model songbird species, the zebra finch (Taeniopygia guttata), to assess short-term embryotoxic effects of in ovo MeHg exposure on hatching success and posthatching growth and nestling survival, as well as longer-term effects on mating behavior and reproduction. Egg treatment groups included a low-MeHg dose of 0.2 μg Hg g(-1) egg (n = 36), a high-MeHg dose of 3.2 μg Hg g(-1) egg (n = 49), and a control (n = 34). Doses were dissolved in nanopure filtered water and injected into the albumen on the day eggs showed signs of viability (3 d incubation). In ovo exposure to MeHg significantly reduced hatching success (53% in the high-MeHg dose group vs 94% in vehicle controls). Among hatched chicks, however, no effects of MeHg on growth, hematological variables, or nestling survival were detected. While the in ovo injection method resulted in a dose-dependent pattern of MeHg concentrations in blood of surviving chicks at 15 d and 30 d posthatching, there was evidence of rapid excretion of MeHg with nestling age during that growth period. At reproductive maturity (90 d of age), no long-term effects of in ovo exposure to MeHg on female mating behavior, reproductive effort (egg or clutch size), or growth and survivorship of offspring were observed. Environ Toxicol Chem 2016;35:1534-1540.

In ovo tris(2-butoxyethyl) phosphate concentrations significantly decrease in late incubation after a single exposure via injection, with no evidence of effects on hatching success or latent effects on growth or reproduction in zebra finches.

Zebra finch (Taeniopygia guttata) eggs were injected with the organophosphate triester flame retardant tris(2-butoxyethyl) phosphate (TBOEP) at 0 μg/g, 0.01 μg/g, 1 μg/g, 10 μg/g, or 50 μg/g egg. Subsets of high-dose eggs were collected throughout incubation to measure TBOEP, which started declining in late incubation and then decreased rapidly to 28% of injected concentration by hatching. The authors found no effects of TBOEP on survival, growth, or reproduction even at very high doses. Environ Toxicol Chem 2017;36:83-88.

Ecologically-relevant exposure to methylmercury during early development does not affect adult phenotype in zebra finches (Taeniopygia guttata)

Methylmercury causes behavioural and reproductive effects in adult mammals via early developmental exposure. Similar studies in birds are limited and mostly focussed on aquatic systems, but recent work has reported high blood mercury concentrations in terrestrial, passerine songbirds. We used the zebra finch (Taeniopygia guttata) as a model to explore the long-term effects of early developmental exposure to methylmercury exposure. Chicks were dosed orally with either the vehicle control, 0.0315 µg Hg/g bw/day, or 0.075 µg Hg/g bw/day throughout the nestling period (days 1–21 post-hatching). We then measured (a) short-term effects on growth, development, and behaviour (time to self-feeding, neophobia) until 30 days of age (independence), and (b) long-term effects on courtship behaviour and song (males) and reproduction (females) once methylmercury-exposed birds reached sexual maturity (90 days post-hatching). High methylmercury treated birds had mean blood mercury of 0.734 ± 0.163 µg/g at 30 days post-hatching, within the range of values reported for field-sampled songbirds at mercury contaminated sites. However, there were no short-term effects of treatment on growth, development, and behaviour of chicks, and no long-term effects on courtship behaviour and song in males or reproductive performance in females. These results suggest that the nestling period is not a critical window for sensitivity to mercury exposure in zebra finches. Growing nestlings can reduce blood mercury levels through somatic growth and depuration into newly growing feathers, and as a result they might actually be less susceptible compared to adult birds receiving the same level of exposure.

Catbirds are the New Chickens: High Sensitivity to a Dioxin-like Compound in a Wildlife Species

Dioxins and dioxin-like compounds (DLCs) are highly toxic and persistent global pollutants with extremely large differences in sensitivity across taxonomic groups. The chicken has long been considered uniquely sensitive to DLCs among avian species; but DLC toxicity in nondomesticated birds is largely untested, and the relevance of the chicken as an ecological model is uncertain. New approaches that use genotyping of the AHR1 ligand binding domain to screen for DLC sensitivity among avian species predicted that the gray catbird, a relevant wildlife species, is also highly sensitive. We tested this prediction using egg injections of a dioxin-like PCB (PCB-126) and found that the catbird is at least as sensitive as the chicken to DLCs, based on both embryotoxicity and mRNA induction of phase I metabolizing enzymes (CYP1A4/5). This study is the first to confirm that there are wildlife species as sensitive as the chicken and demonstrates how using predictive genotyping methods and targeted bioassays can focus toxicity assessments on ecologically relevant species.

The Flame-Retardant Tris(1,3-dichloro-2-propyl) Phosphate Represses Androgen Signaling in Human Prostate Cancer Cell Lines

The effects of six organophosphate flame retardants (OPFRs) tris(2‐butoxyethyl) phosphate, tris(2‐chloroethyl) phosphate, tris(1‐chloro‐2‐propyl) phosphate, tris(methylphenyl) phosphate, tris(1,3‐dichloro‐2‐propyl) phosphate (TDCIPP), and triethyl phosphate on the activities of androgen receptor (AR), estrogen receptor (ER), and aryl hydrocarbon receptor (AhR) were assessed in human prostate and endometrial cancer cells. OPFRs had no effect on ER or AhR target gene activation in ECC‐1 cells. The effect of TDCIPP on mRNA and protein accumulation of AR target genes was examined further. AR‐inducible gene and protein expression were significantly altered by TDCIPP exposure and repressed PSA levels in conditioned media of prostate cancer cells. We demonstrated that TDCIPP has no affinity for the AR ligand binding domain (AR‐LBD) and exerts its antiandrogenic effects in a noncompetitive fashion. Thus, the clinical relevance of TDCIPP exposure on prostate cancer detection and progression to a therapeutically refractile state ought to be investigated further.

Embryonic exposure to environmentally relevant concentrations of a brominated flame retardant reduces the size of song-control nuclei in a songbird: BDE99 Reduces Volume of Song-Control Nuclei

Environmental contaminants have the potential to act as developmental stressors and impair development of song and the brain of songbirds, but they have been largely unstudied in this context. 2,2′,4,4′,5‐Pentabromodiphenyl ether (BDE‐99) is a brominated flame retardant congener that has demonstrated endocrine disrupting effects, and has pervaded the global environment. We assessed the effects of in ovo exposure to environmentally relevant levels of BDE‐99 on the neuroanatomy of the song‐control system in a model songbird species, the zebra finch (Taeniopygia guttata). Embryos were exposed via egg injection to a vehicle control (DMSO), 10, 100, or 1000 ng BDE‐99/g egg on the day the egg was laid. Chicks were raised to sexual maturity to investigate long‐term effects of BDE‐99 on the adult male brain. Three key song‐control nuclei (Area X, HVC, RA) all showed a dose‐dependent trend toward decreasing volume as BDE‐99 concentration increased, and birds exposed to 1000 ng/g in ovo BDE‐99 had significantly smaller song‐control nuclei volume compared to control birds. High environmental concentrations of BDE‐99 in avian tissues can be within that range and thus could affect development of the song‐control system in birds, and potentially other processes. We previously found that BDE‐99 exposure during the nestling period had no effect of on the song‐control system, although it did have significant effects on some behaviural endpoints. Taken together, these results suggest that exposure to polybrominated diphenyl ether (PBDEs) during critical developmental windows can significantly alter neurological development.