Zhihua Han

A review on the effects of PBDEs on thyroid and reproduction systems in fish.

The objective of this review was to summarize and discuss the effects of Polybrominated diphenyl ethers (PBDEs) on thyroid and reproduction systems in fish. We reviewed the evidences and mechanisms for PBDEs-induced thyroid and reproduction disruption, as well as the cross-talk between the two systems in fish. In thyroid disruption, we mainly paid attention to the effects of PBDEs on hypothalamic-pituitary-thyroid (HPT) axis, thyroid hormones (THs) transport and metabolism, thyroid receptors (TRs) and thyroid follicle histology. In reproduction disruption, we focused on the effects of PBDEs on steroid hormone production, expression of genes involved in steroidogenesis, and gonadal development. Despite that there is an interaction between thyroid and reproductive systems in fish, it is still remains unclear that PBDE-induced reproductive impairments are caused by direct effects on hypothalamic-pituitary-gonadal (HPG) functioning or by indirect action through cross-talk between the two systems. Future studies are needed to explore the relationships between reproductive toxicity and thyroid system disruption after PBDEs exposure.

Multiple bio-analytical methods to reveal possible molecular mechanisms of developmental toxicity in zebrafish embryos/larvae exposed to tris(2-butoxyethyl) phosphate

The flame retardant tris(2-butoxyethyl) phosphate (TBEP) is a frequently detected contaminant in the environment, wildlife and human milk. The potentially toxic effects of TBEP and their underlying molecular mechanisms have not been elucidated. Here, zebrafish embryos were exposed to different concentrations of TBEP from 4 hours of post-fertilization (hpf) to 120 hpf, and effects on embryonic development and global protein expression patterns examined. Our results demonstrate that treatment with TBEP (0.8-100mg/L) causes a concentration- and time-dependent decrease in embryonic survival and the hatching percentage. The median lethal concentration was 10.7 mg/L at 120 hpf. Furthermore, exposure to 150 or 800 μg/L TBEP inhibited the degradation and utilization of vitellogenins and down-regulated the expression of proteins related to cation binding, and lipid transport, uptake and metabolism, accompanied by a decrease in heart rate and body length. Exposure to TBEP (150 or 800 μg/L) also decreased the expression of proteins involved in cell proliferation and DNA repair, and led to an increased number of apoptotic cells in the tail region. Collectively, our results suggest that exposure to TBEP causes toxicity in the developing zebrafish by inhibiting the degradation and utilization of nutrients from the mother and inducing apoptosis.

Prenatal transfer of decabromodiphenyl ether (BDE-209) results in disruption of the thyroid system and developmental toxicity in zebrafish offspring

Decabromodiphenyl ether (BDE-209) was one of most widely-used polybrominated diphenyl ether (PBDE) flame retardants and is frequently detected in both abiotic and biotic samples from environment. However, knowledge of its transgenerational risks is limited. Here, 4-month-old zebrafish were exposed to various concentrations of BDE-209 (0, 3, 30 or 300μg/L) for 28days and spawned in clean water without BDE-209. Concentrations of triiodothyronine (T3) and thyroxine (T4) as well as expressions of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis were measured in offspring after exposure of adult zebrafish to BDE-209. BDE-209 was accumulated in adult fish and F1 eggs, which suggests transfer of this compound from adult fish to their offspring. Exposure of BDE-209 to parents resulted in developmental abnormalities in offspring and a significant decrease in T4 concentrations in F1 larvae 120h post-fertilization (hpf). Furthermore, expressions of several genes involved in the HPT axis were also altered. Expressions of thyroid hormone receptor α (tr-α), thyrotropin releasing hormone (trh), thyroid stimulating hormone β (tsh-β) and deiodinase 1 (dio 1) were significantly down-regulated in F1 individuals, while expressions of thyroid stimulating hormone receptor (tshr) and transthyretin (ttr) were significantly up-regulated. These results suggest that exposure of parent zebrafish to BDE-209 can cause developmental toxicity in offspring and disruption of the thyroid endocrine system of offspring.

Whole-Life-Stage Characterization in the Basic Biology of Daphnia magna and Effects of TDCIPP on Growth, Reproduction, Survival, and Transcription of Genes

Toxicity tests of chemicals have mainly focused on the partial life-cycle evaluation of model animals. Limited information is available for the evaluation of effects of chemicals from a whole-life-stage exposure perspective. The objective of this study was to perform a whole-life-stage characterization in the basic biology of Daphnia magna (D. magna) and evaluate the effects of a known organophosphate ester (OPE) contaminant, tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), on growth, reproduction, survival, and transcription of genes. The whole-life-stage characterization in growth, reproduction, and survival of D. magna was conducted, and representative sampling time points for the three developmental stages were identified (day 6, day 32, and day 62). Transcriptomic profiles for these three stages were compared, and stage-specific PCR arrays of D. magna were developed. The whole-life-stage exposure to environmentally relevant or greater concentrations of TDCIPP significantly inhibited growth and reproduction of D. magna and decreased survival at the later stage of the exposure experiment (≥32 days). Such adverse effects were not observed in the early stage of the exposure (<32 days), suggesting that short-term toxicity tests, such as the standard 21-day test, might underestimate the environmental risk of TDCIPP. Furthermore, expressions of genes selected at day 6, day 32, and day 62 were significantly changed after TDCIPP exposure, and the changes in the expressions of partial genes were correlated to the inhibitory effects on growth, reproduction, and survival.

Occurrence and partitioning behavior of organophosphate esters in surface water and sediment of a shallow Chinese freshwater lake (Taihu Lake): Implication for eco-toxicity risk

Organophosphate esters (OPEs) are ubiquitous in the aquatic environment, which have been considered or suspected as carcinogens and neurotoxicants. In this study, the occurrence, spatial distribution, potential sources, partitioning character and potential risks of OPEs in the surface water and sediment collected from Taihu Lake were investigated. The concentrations of ∑12 OPEs varied from 1.0 × 102 to 1.7 × 103 ng/L for the surface water and from 8.1 to 4.2 × 102 ng/g dw for the sediment. Trimethyl phosphate (TEP) was the predominant congener in the surface water, while Tris(2-ethylhexyl) phosphate (TEHP) in the sediment. Positive correlations between OPEs indicated that they may have the same sources and/or similar environmental behavior. The pseudo-partitioning values of OPEs ranged from 0.59 to 6.5 × 104 L/kg. TEHP has the highest pseudo-partitioning coefficient, which indicated that TEHP inclined to be enriched in the sediment in Taihu Lake. Risk assessment (RQ) showed that individual OPEs in the surface water and sediment posed no/low risk to aquatic organisms, except 2-Ethylhexyl diphenyl phosphate (EHDPP) (moderate risk) in water.