The plasticizer bisphenol A affects somatic and sexual development, but differently in pipid, hylid and bufonid anurans

Fabrication of magnetic Fe3O4 doped β-cyclodextrin microporous organic network for the efficient extraction of endocrine disrupting chemicals from food takeaway boxes

Endocrine disrupting chemicals (EDCs) are a typical class of natural or man-made endogenous hormone agonists or antagonists that can directly or potentially interfere with human endocrine system. However, it is still difficult to analyze trace EDCs directly from complex environment and food matrices. Therefore, the proper sample pretreatment is highly desired and the preparation of efficient adsorbents is of great challenge and importance. Herein, we report the facile one-pot solvothermal synthesis of Fe3O4 nanoparticle doped magnetic β-cyclodextrin microporous organic network composites (MCD-MONs) for the magnetic solid phase extraction (MSPE) of four phenolic EDCs in water and food takeaway boxes prior to the high-performance liquid chromatography analysis. The sheet-like Fe3O4 doped MCD-MONs offered good magnetic property (16.5 emu g-1) and stability, and provided numerous hydrogen bonding, hydrophobic, π-π, and host-guest interaction sites for EDCs. Under the optimal experimental conditions, the established method was successfully verified with wide linear range (2.0-1000 µg L-1), low limits of detection (0.6-1.0 µg L-1), good precisions (intra-day and inter-day RSDs < 5.2 %, n = 3), large enrichment factors (88-98) and adsorption capacity (90.3-255.8 mg g-1), short extraction time (6 min), less adsorbent consumption (3 mg), and good reusability (at least 8 times) for EDCs. The proposed method was successfully applied to detect the trace EDCs in real samples with the recovery of 84.0-99.7 %. This work demonstrated the great potential of MCD-MONs for the efficient MSPE of trace EDCs from complex food takeaway boxes and water samples and uncovered the prospect of CD-based MONs in sample pretreatment.

Structural and energetic basis of interaction between human estrogen-related receptor γ and environmental endocrine disruptors from multiple molecular dynamics simulations and free energy predictions

Environmental endocrine disruptors (EEDs), a class of molecules that are widespread in our environment, may adversely affect the endocrine system. Exploring the interactions between these compounds and their potential targets is important for assessing their role in the organism. Focused on the human estrogen-related receptor γ (hERRγ) with BPA, BPB, HPTE, BPE, BP(2,2)(Et), and BP(2,2)(MeO) complexes, respectively, we groped for the mechanisms of conformational changes and interactions of hERRγ when binding to these six EEDs by combining multiple molecular dynamics (MD) simulations with energy prediction (MM-PBSA and solvated interaction energy (SIE)). Dynamics analysis results revealed these six EEDs have different effects on the internal dynamics of hERRγ, resulting in significant changes in the interaction of key residues around Leu268, Val313, Leu345, and Phe435 with EEDs, and thus affected its binding energy with these EEDs. The energy calculations further demonstrated that van der Waals interactions are critical for these EEDs binding to hERRγ. These results present detailed molecular insight into the interaction features between EEDs and hERRγ and help guide the search for safer alternatives to BPA.

Bisphenol B disrupts testis differentiation partly via the estrogen receptor-mediated pathway and subsequently causes testicular dysgenesis in Xenopus laevis

There is growing concern about adverse effects of bisphenol A alternatives including bisphenol B (BPB) due to their estrogenic activity. However, limited data are available concerning the influences of BPB on male reproductive development in vertebrates, especially in amphibians, which are believed to be susceptible to estrogenic chemicals. The present study investigated the effects of 10, 100 and 1000 nM BPB (2.42, 24.2 and 242 μg/L) on testis development in Xenopus laevis, a model amphibian species for studying gonadal feminization. We found that exposure to BPB from stages 45/46 to 52 resulted in down-regulation of testis-biased gene expression and up-regulation of ovary-biased gene and vitellogenin (vtgb1) expression in gonad-mesonephros complexes (GMCs) of tadpoles at stage 52, coupled with suppressed cell proliferation in testes and reduced gonadal metameres, resembling the effects of 17ß-estradiol. Moreover, an estrogen receptor (ER) antagonist ICI 182780 antagonized BPB-caused up-regulation of ovary-biased gene and vtgb1 expression to some degree, indicating that the effects of BPB on X. laevis testis differentiation could be partly mediated by ER. All observations demonstrate that early exposure to BPB inhibited testis differentiation and exerted certain feminizing effects during gonadal differentiation. When exposure was extended to post-metamorphosis, testes exhibited histological and morphological abnormalities including segmented, discontinuous and fragmented shapes, besides altered sex-dimorphic gene expression. Notably, most of BPB-caused alterations were not concentration-dependent, but the lowest concentration indeed exerted significant effects. Overall, our study for the first time reveals that low concentrations of BPB can disrupt testis differentiation partly due to its estrogenic activity and subsequently cause testicular dysgenesis after metamorphosis, highlighting its reproductive risk to amphibians and other vertebrates including humans. Our finding also implies that estrogenic chemicals-caused testis differentiation inhibition at tadpole stages could predict later testicular dysgenesis after metamorphosis, meaning a possibility of early detection of abnormal testis development caused by estrogenic chemicals.

Exposure to the synthetic phenolic antioxidant 4,4'-thiobis(6-t-butyl-m-cresol) disrupts early development in the frog Silurana tropicalis

Many chemicals in commonly used household and industrial products are being released into the environment, yet their toxicity is poorly understood. The synthetic phenolic antioxidant, 4,4'-thiobis(6-t-butyl-m-cresol) (CAS 96-69-5; TBBC) is present in many common products made of rubber and plastic. Yet, this phenolic antioxidant has not been tested for potential toxicity and developmental disruption in amphibians, a sensitive and susceptible class. We investigated whether acute and chronic exposure to TBBC would interfere with thyroid hormone-dependent developmental processes in the frog Silurana tropicalis and thus affect its early life-stage development. We exposed S. tropicalis embryos at the Nieuwkoop-Faber (NF) 9-10 stage to TBBC at nominal concentrations (0, 25, 50, 75, 100, 200 and 400 μg/L) to determine the 96h lethal concentrations and sublethal effects. We conducted a chronic exposure starting at stage NF47-48 to three sublethal TBBC nominal concentrations (0, 0.002, 0.1 and 5 μg/L) for 48-52 days to evaluate effects on growth and metamorphosis. The 96h lethal and effective (malformations) TBBC concentrations (LC₅₀ and EC₅₀) were 70.5 and 76.5 μg/L, respectively. Acute exposure to all TBBC concentrations affected S. tropicalis growth and was lethal at 200 and 400 μg/L. Chronic exposure to sublethal TBBC concentrations reduced body size by 8% at 5 μg/L and body mass by 17% at 0.002 μg/L when metamorphosis was completed. This study demonstrates that TBBC is toxic, induces malformations and inhibits tadpole growth after acute and chronic exposures. These findings call for further investigations on the mode of actions of TBBC and related antioxidants for developmental disruption in amphibians.

Bisphenol AF and Bisphenol F Induce Similar Feminizing Effects in Chicken Embryo Testis as Bisphenol A

The plastic component bisphenol A (BPA) impairs reproductive organ development in various experimental animal species. In birds, effects are similar to those caused by other xenoestrogens. Because of its endocrine disrupting activity, BPA is being substituted with other bisphenols in many applications. Using the chicken embryo model, we explored whether the BPA alternatives bisphenol AF (BPAF), bisphenol F (BPF), and bisphenol S (BPS) can induce effects on reproductive organ development similar to those induced by BPA. Embryos were exposed in ovo from embryonic day 4 (E4) to vehicle, BPAF at 2.1, 21, 210, and 520 nmol/g egg, or to BPA, BPF, or BPS at 210 nmol/g egg and were dissected on embryonic day 19. Similar to BPA, BPAF and BPF induced testis feminization, manifested as eg testis-size asymmetry and ovarian-like cortex in the left testis. In the BPS-group, too few males were alive on day 19 to evaluate any effects on testis development. We found no effects by any treatment on ovaries or Müllerian ducts. BPAF and BPS increased the gallbladder-somatic index and BPAF, BPF and BPS caused increased embryo mortality. The overall lowest-observed-adverse-effect level for BPAF was 210 nmol/g egg based on increased mortality, increased gallbladder-somatic index, and various signs of testis feminization. This study demonstrates that the BPA replacements BPAF, BPF, and BPS are embryotoxic and suggests that BPAF is at least as potent as BPA in inducing estrogen-like effects in chicken embryos. Our results support the notion that these bisphenols are not safe alternatives to BPA.

Digit ratio in the common toad Bufo bufo: the effects of reduced fingers and of age dependency

INTRODUCTION

Despite the growing number of studies describing digit ratio patterns in tetrapods, knowledge concerning certain basic issues is still scarce. In lower vertebrates such as tailless amphibians (Anura), the numbering of individual fingers on the forelimbs and their homology with the fingers of other vertebrates pose an unsolved problem. Based on reviewed data on anuran limb development, we argue that the correct finger numbering scheme should be based on the assumption that the first finger, not the fifth finger, was reduced on the forelimbs. We analyzed the digit ratio in the common toad (Bufo bufo, Bufonidae), a species characterized by well-developed sexual dimorphism whereby females are larger than males, using both numbering schemes present in the literature.

RESULTS

We found that the digit ratio on hindlimbs differed significantly between the sexes only in the cases of left 2D:3D, with lower digit ratios in females, and of left 3D:4D, with lower digit ratios in males. We found that sex was the only significant variable for forelimbs, differentiating 2D:3D on the left forelimb, with lower digit ratios in females; 2D:4D on the right forelimb, with lower digit ratios in males; and 3D:4D on both forelimbs, with lower digit ratios in males. These results relate to variant II reflecting the hypothesis that the first digit was reduced during phylogenesis. There was no relationship between the body size (SVL) of individuals and any digit ratio, excluding 2D:4D on the right forelimbs in models with age variables. Additionally, for a subset of data where individual age was known, the models indicated that age was linked to significant differences in 2D:4D and 3D:4D on the left hindlimbs, while age, SVL, and sex influenced 2D:4D on the right forelimbs.

CONCLUSION

We emphasize the importance of the problem of the correct numbering of forelimb digits in Anura and, under the assumption that it was the fifth digit that was reduced, argue that earlier results on digit ratio in this group should be interpreted with caution. The detected relationship between digit ratio and age in amphibians expands our knowledge, indicating that the age of individuals should be included in future digit ratio studies. This relationship may also apply to studies using digit ratio as a noninvasive indicator of endocrine disruption in amphibians.

Xenopus in revealing developmental toxicity and modeling human diseases

The Xenopus model offers many advantages for investigation of the molecular, cellular, and behavioral mechanisms underlying embryo development. Moreover, Xenopus oocytes and embryos have been extensively used to study developmental toxicity and human diseases in response to various environmental chemicals. This review first summarizes recent advances in using Xenopus as a vertebrate model to study distinct types of tissue/organ development following exposure to environmental toxicants, chemical reagents, and pharmaceutical drugs. Then, the successful use of Xenopus as a model for diseases, including fetal alcohol spectrum disorders, autism, epilepsy, and cardiovascular disease, is reviewed. The potential application of Xenopus in genetic and chemical screening to protect against embryo deficits induced by chemical toxicants and related diseases is also discussed.

Tissues injury and pathological changes in Hyla intermedia juveniles after chronic larval exposure to tebuconazole

Tebuconazole (TBZ), an azole pesticide, is one of the most frequently detected fungicides in surface water. Despite its harmful effects, mainly related to endocrine disturbance, the consequences of TBZ exposure in amphibians remain poorly understood. Here, we investigated the adverse and delayed effects of TBZ chronic exposure on a native anuran species, often inhabiting cultivated areas, the Italian tree frog (Hyla intermedia). To disclose the multiple mechanisms of action through which TBZ exerts its toxicity we exposed tadpoles over the whole larval period to two sublethal TBZ concentrations (5 and 50 μg/L), and we evaluated histological alterations in three target organs highly susceptible to xenobiotics: liver, kidney, and gonads. We also assessed morphometric and gravimetric parameters: snout-vent length (SVL), body mass (BM), liver somatic index (LSI), and gonad-mesonephros complex index (GMCI) and determined sex ratio, gonadal development, and differentiation. Our results show that TBZ induces irreversible effects on multiple target organs in H. intermedia, exerting its harmful effects through several pathological pathways, including a massive inflammatory response. Moreover, TBZ markedly affects sexual differentiation also by inducing the appearance of sexually undetermined individuals and a general delay of germ cell maturation. Given the paucity of data on the effects of TBZ in amphibians, our results will contribute to a better understanding of the environmental risk posed by this fungicide to the most endangered group of vertebrates.

Microplastic ingestion by tadpoles of pond-breeding amphibians-first results from Central Europe (SW Poland)

Microplastics (MPs) are one of the major threats to aquatic ecosystems. Surprisingly, our knowledge of its occurrence and its impact on the organisms that dwell in small water bodies is still scarce. The aim of this study was to investigate the occurrence and chemical composition of MPs in tadpoles of pond-breeding amphibians. In total, 201 tadpoles belonging to 5 species were collected from 8 ponds located in southwestern Poland. MPs were found in all examined sites and in all studied species. Among those tested, 53 (26%) tadpoles ingested a total of 71 MPs. IR-ATR analysis revealed that particles were of anthropogenic origin and included nylon, polyurethane, polyisoprene and 1,2 polybutadiene.

Agrochemicals disrupt multiple endocrine axes in amphibians

Concern over global amphibian declines and possible links to agrochemical use has led to research on the endocrine disrupting actions of agrochemicals, such as fertilizers, fungicides, insecticides, acaricides, herbicides, metals, and mixtures. Amphibians, like other species, have to partition resources for body maintenance, growth, and reproduction. Recent studies suggest that metabolic impairments induced by endocrine disrupting chemicals, and more particularly agrichemicals, may disrupt physiological constraints associated with these limited resources and could cause deleterious effects on growth and reproduction. Metabolic disruption has hardly been considered for amphibian species following agrichemical exposure. As for metamorphosis, the key thyroid hormone-dependent developmental phase for amphibians, it can either be advanced or delayed by agrichemicals with consequences for juvenile and adult health and survival. While numerous agrichemicals affect anuran sexual development, including sex reversal and intersex in several species, little is known about the mechanisms involved in dysregulation of the sex differentiation processes. Adult anurans display stereotypical male mating calls and female phonotaxis responses leading to successful amplexus and spawning. These are hormone-dependent behaviours at the foundation of reproductive success. Therefore, male vocalizations are highly ecologically-relevant and may be a non-invasive low-cost method for the assessment of endocrine disruption at the population level. While it is clear that agrochemicals disrupt multiple endocrine systems in frogs, very little has been uncovered regarding the molecular and cellular mechanisms at the basis of these actions. This is surprising, given the importance of the frog models to our deep understanding of developmental biology and thyroid hormone action to understand human health. Several agrochemicals were found to have multiple endocrine effects at once (e.g., targeting both the thyroid and gonadal axes); therefore, the assessment of agrochemicals that alter cross-talk between hormonal systems must be further addressed. Given the diversity of life-history traits in Anura, Caudata, and the Gymnophiona, it is essential that studies on endocrine disruption expand to include the lesser known taxa. Research under ecologically-relevant conditions will also be paramount. Closer collaboration between molecular and cellular endocrinologists and ecotoxicologists and ecologists is thus recommended.

Evaluation of the effects of low concentrations of bisphenol AF on gonadal development using the Xenopus laevis model: A finding of testicular differentiation inhibition coupled with feminization

Developmental exposures to estrogenic chemicals possibly cause structural and functional abnormalities of reproductive organs in vertebrates. Bisphenol AF (BPAF), a bisphenol A (BPA) analogue, has been shown to have higher estrogenic activity than BPA, but little is known about the effects of BPAF on gonadal development, particularly gonadal differentiation. We aimed to determine whether low concentrations of BPAF could disrupt gonadal differentiation and subsequent development using Xenopus laevis, a model species for studying feminizing effects of estrogenic chemicals. X. laevis tadpoles were exposed to BPAF (1, 10, 100 nM) or 17β-estradiol (E2, positive control) from stages 45/46 to 53 and 66 in a semi-static exposure system, with a prolonged treatment with the highest concentration to the eighth week post-metamorphosis (WPM8). Gonadal morphology and histology as well as sexually dimorphic gene expression were examined to evaluate the effects of BPAF. All concentrations of BPAF caused changes in testicular morphology at different developmental stages compared with controls. Specifically, at stage 53, BPAF like E2 resulted in decreases in both the size and the number of gonadal metameres (gonomeres) in testes, looking like ovaries. Some of BPAF-treated testes remained segmented and even became discontinuous and fragmented at subsequent stages. Histological abnormalities were also observed in BPAF-treated testes, such as ovarian cavity at stages 53 and 66 and poorly developed seminiferous tubules on WPM8. At the molecular level, BPAF inhibited expression of male highly expressed genes in testes at stage 53. Correspondingly, BPAF, like E2, inhibited cell proliferation in testes at stage 50. All results show that low concentrations of BPAF inhibited testicular differentiation and subsequent development in X. laevis, along with feminizing effects to some degree. Our finding implies a risk of BPAF to the male reproductive system of vertebrates including humans.

A suggested bisphenol A metabolite (MBP) interfered with reproductive organ development in the chicken embryo while a human-relevant mixture of phthalate monoesters had no such effects

Bisphenol A (BPA) and phthalate diesters are ubiquitous environmental contaminants. While these compounds have been reported as reproductive toxicants, their effects may partially be attributed to metabolites. The aim of this study was to examine reproductive organ development in chicken embryos exposed to the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP; 100 µg/g egg) or a human-relevant mixture of 4 phthalate monoesters (85 µg/g egg). The mixture was designed within the EU project EDC-MixRisk based upon a negative association with anogenital distance in boys at 21 months of age in a Swedish pregnancy cohort. Chicken embryos were exposed in ovo from an initial stage of gonad differentiation (embryonic day 4) and dissected two days prior to anticipated hatching (embryonic day 19). No discernible effects were noted on reproductive organs in embryos exposed to the mixture. MBP-treated males exhibited retention of Müllerian ducts and feminization of the left testicle, while MBP-administered females displayed a diminished the left ovary. In the left testicle of MBP-treated males, mRNA expression of female-associated genes was upregulated while the testicular marker gene SOX9 was downregulated, corroborating a feminizing effect by MBP. Our results demonstrate that MBP, but not the phthalate monoester mixture, disrupts both male and female reproductive organ development in an avian embryo model.

Xenopus laevis as a Bioindicator of Endocrine Disruptors in the Region of Central Chile

One of the direct causes of biodiversity loss is environmental pollution resulting from the use of chemicals. Different kinds of chemicals, such as persistent organic pollutants and some heavy metals, can be endocrine disruptors, which act at low doses over a long period of time and have a negative effect on the reproductive and thyroid system in vertebrates worldwide. Research on the effects of endocrine disruptors and the use of bioindicators in neotropical ecosystems where pressure on biodiversity is high is scarce. In Chile, although endocrine disruptors have been detected at different concentrations in the environments of some ecosystems, few studies have been performed on their biological effects in the field. In this work, Xenopus laevis (African clawed frog), an introduced species, is used as a bioindicator for the presence of endocrine disruptors in aquatic systems with different degrees of contamination in a Mediterranean zone in central Chile. For the first time for Chile, alterations are described that can be linked to exposure to endocrine disruptors, such as vitellogenin induction, decreased testosterone in male frogs, and histological changes in gonads. Dioxin-like and oestrogenic activity was detected in sediments at locations where it seem to be related to alterations found in the frogs. In addition, an analysis of land use/cover use revealed that urban soil was the best model to explain the variations in frog health indicators. This study points to the usefulness of an invasive species as a bioindicator for the presence of endocrine-disruptive chemicals.

A pilot study on polycystic ovarian syndrome caused by neonatal exposure to tributyltin and bisphenol A in rats

The development of polycystic ovary syndrome (PCOS) could be caused by exposure to environmental endocrine disrupting chemicals (EDCs). In the current study, two commonly found EDCs, bisphenol A (BPA) and tributyltin (TBT), were investigated for their effects on PCOS occurrence in neonatal female rats. TBT (10 and 100 ng kg^-1 d^-1), BPA (50 μg kg^-1 d^-1), and a mixture of the two (TBT 100 ng kg^-1 d^-1 with BPA 50 μg kg^-1 d^-1) were administered to female rats from postnatal day 1-16. TBT, BPA, and TBT + BPA treatment resulted in an irregular estrus cycle and disturbed ovarian development, with less corpora lutea and antral follicles, but more atretic follicles and cysts. In addition, serum testosterone and luteinizing hormone levels were significantly elevated, whereas a reduced level of serum sex hormone-binding globulin was observed after TBT100, BPA50, and TBT + BPA treatments. Moreover, gene expression analyses identified significant differential expression of the genes involved in a variety of biological pathways, such as lipid transport and steroidogenesis. Moreover, the expression level of proteins regulating lipid and androgen biosynthesis was elevated after the treatments. In conclusion, this study demonstrated that exposure to TBT, BPA, and a mixture of the two in newborn rats could contribute to a PCOS-like syndrome. The mechanism of PCOS pathogenesis caused by exposure to TBT and BPA is likely to be mediated by the lipid metabolism and steroidogenesis pathways. Our results provide novel insight into female reproduction affected by EDCs, which may be helpful for revealing the pathogenesis of PCOS.

Impacts of the synthetic androgen Trenbolone on gonad differentiation and development - comparisons between three deeply diverged anuran families

Using a recently developed approach for testing endocrine disruptive chemicals (EDCs) in amphibians, comprising synchronized tadpole exposure plus genetic and histological sexing of metamorphs in a flow-through-system, we tested the effects of 17β-Trenbolone (Tb), a widely used growth promoter in cattle farming, in three deeply diverged anuran families: the amphibian model species Xenopus laevis (Pipidae) and the non-models Bufo(tes) viridis (Bufonidae) and Hyla arborea (Hylidae). Trenbolone was applied in three environmentally and/or physiologically relevant concentrations (0.027 µg/L (10-10 M), 0.27 µg/L (10-9 M), 2.7 µg/L (10-8 M)). In none of the species, Tb caused sex reversals or masculinization of gonads but had negative species-specific impacts on gonad morphology and differentiation after the completion of metamorphosis, independently of genetic sex. In H. arborea and B. viridis, mounting Tb-concentration correlated positively with anatomical abnormalities at 27 µg/L (10-9 M) and 2.7 µg/L (10-8 M), occurring in X. laevis only at the highest Tb concentration. Despite anatomical aberrations, histologically all gonadal tissues differentiated seemingly normally when examined at the histological level but at various rates. Tb-concentration caused various species-specific mortalities (low in Xenopus, uncertain in Bufo). Our data suggest that deep phylogenetic divergence modifies EDC-vulnerability, as previously demonstrated for Bisphenol A (BPA) and Ethinylestradiol (EE2).

Validation of an HPLC Method for Determination of Bisphenol-A Migration from Baby Feeding Bottles

A simple and economic high-performance liquid chromatography (HPLC-UV-Vis) analytical method was validated for the quantitation of specific Bisphenol-A migration from baby feeding bottles. Overall and specific migration assays were done with different food simulating matrices using the filling method. Good linearity was obtained over the concentration range of 0.01-0.6 mg/kg. The limit of detection (LOD) and limit of quantification (LOQ) were 0.004 and 0.010 mg/kg, respectively. The repeatability of the method (%RSD, n=10) was between 89.5 and 99.0%, while recovery ranged from 83.2 to 98.4%. The method was applied to specific migration assays from baby feeding bottles purchased from different plastic producers in Colombia. The results show that, in a first migration assay, Bisphenol-A was not detectable in all samples. In a second migration test, Bisphenol-A concentrations were higher than the most restricted limit (0.05 mg/kg) with ethanol 95% and isooctane as food simulants.

Molecular evidence for sex reversal in wild populations of green frogs (Rana clamitans)

In vertebrates, sex determination occurs along a continuum from strictly genotypic (GSD), where sex is entirely guided by genes, to strictly environmental (ESD), where rearing conditions, like temperature, determine phenotypic sex. Along this continuum are taxa which have combined genetic and environmental contributions to sex determination (GSD + EE), where some individuals experience environmental effects which cause them to sex reverse and develop their phenotypic sex opposite their genotypic sex. Amphibians are often assumed to be strictly GSD with sex reversal typically considered abnormal. Despite calls to understand the relative natural and anthropogenic causes of amphibian sex reversal, sex reversal has not been closely studied across populations of any wild amphibian, particularly in contrasting environmental conditions. Here, we use sex-linked molecular markers to discover sex reversal in wild populations of green frogs (Rana clamitans) inhabiting ponds in either undeveloped, forested landscapes or in suburban neighborhoods. Our work here begins to suggest that sex reversal may be common within and across green frog populations, occurring in 12 of 16 populations and with frequencies of 2–16% of individuals sampled within populations. Additionally, our results also suggest that intersex phenotypic males and sex reversal are not correlated with each other and are also not correlated with suburban land use. While sex reversal and intersex are often considered aberrant responses to human activities and associated pollution, we found no such associations here. Our data perhaps begin to suggest that, relative to what is often suggested, sex reversal may be a relatively natural process in amphibians. Future research should focus on assessing interactions between genes and the environment to understand the molecular and exogenous basis of sex determination in green frogs and in other amphibians.

New insights into the metabolism and toxicity of bisphenol A on marine fish under long-term exposure

Bisphenol A (BPA) exposure receives great ecotoxicological concern. However, gaps in knowledge, such as metabolism of BPA and inconsistent reports on reproductive toxicity, still exist. In this study, a marine fish model (Oryzias melastigma) was exposed to serial concentrations of BPA throughout its whole life cycle. The level of BPA-glucuronide (BPAG) dramatically increased throughout the embryonic stage since 4 dpf. Accordingly, the mRNA level and enzymatic activity of UDP-glucuronosyltransferases (UGTs) increased across the embryonic stage. The mRNA level of UGT2 subtype rather than UGT1 or UGT5 showed a concentration dependent response to BPA exposure. BPA exposure led to the morphological disruption of the chorion and villi as shown by scanning electron microscopy; however, the hatchability was not significantly influenced after exposure. Newly hatching larvae were continuously exposed to BPA for 120 days. Lower mRNA levels of hormone metabolism-related genes, decreased ratio of E2/T, slower ovary development and decreased egg production confirmed the inhibitory effect of BPA on reproduction. Overall, our results showed the conjugation of BPA into BPAG by UGT2 at the embryonic stage and convinced the reproductive toxicity from multiple levels after whole life exposure to BPA.

Endocrine disruptors in breeding ponds and reproductive health of toads in agricultural, urban and natural landscapes

Many chemical pollutants have endocrine disrupting effects which can cause lifelong reproductive abnormalities in animals. Amphibians are the most threatened group of vertebrates, but there is little information on the nature and quantity of pollutants occurring in typical amphibian breeding habitats and on the reproductive capacities of amphibian populations inhabiting polluted areas. In this study we investigated the occurrence and concentrations of endocrine disrupting chemicals in the water and sediment of under-studied amphibian breeding habitats in natural, agricultural and urbanized landscapes. Also, we captured reproductively active common toads (Bufo bufo) from these habitats and let them spawn in a 'common garden' to assess among-population differences in reproductive capacity. Across 12 ponds, we detected 41 out of the 133 contaminants we screened for, with unusually high concentrations of glyphosate and carbamazepine. Levels of polycyclic aromatic hydrocarbons, nonylphenol and bisphenol-A increased with urban land use, whereas levels of organochlorine and triazine pesticides and sex hormones increased with agricultural land use. Toads from all habitats had high fecundity, fertilization rate and offspring viability, but the F1 generation originating from agricultural and urban ponds had reduced development rates and lower body mass both as larvae and as juveniles. Females with small clutch mass produced thicker jelly coat around their eggs if they originated from agricultural and urban ponds compared with natural ponds. These results suggest that the observed pollution levels did not compromise reproductive potential in toads, but individual fitness and population viability may be reduced in anthropogenically influenced habitats, perhaps due to transgenerational effects and/or costs of tolerance to chemical contaminants.

Microplastics as an emerging threat to terrestrial ecosystems

Microplastics (plastics <5 mm, including nanoplastics which are <0.1 μm) originate from the fragmentation of large plastic litter or from direct environmental emission. Their potential impacts in terrestrial ecosystems remain largely unexplored despite numerous reported effects on marine organisms. Most plastics arriving in the oceans were produced, used, and often disposed on land. Hence, it is within terrestrial systems that microplastics might first interact with biota eliciting ecologically relevant impacts. This article introduces the pervasive microplastic contamination as a potential agent of global change in terrestrial systems, highlights the physical and chemical nature of the respective observed effects, and discusses the broad toxicity of nanoplastics derived from plastic breakdown. Making relevant links to the fate of microplastics in aquatic continental systems, we here present new insights into the mechanisms of impacts on terrestrial geochemistry, the biophysical environment, and ecotoxicology. Broad changes in continental environments are possible even in particle-rich habitats such as soils. Furthermore, there is a growing body of evidence indicating that microplastics interact with terrestrial organisms that mediate essential ecosystem services and functions, such as soil dwelling invertebrates, terrestrial fungi, and plant-pollinators. Therefore, research is needed to clarify the terrestrial fate and effects of microplastics. We suggest that due to the widespread presence, environmental persistence, and various interactions with continental biota, microplastic pollution might represent an emerging global change threat to terrestrial ecosystems.

Atrazine feminizes sex ratio in Blanchard's cricket frogs (Acris blanchardi) at concentrations as low as 0.1 μg/L

We exposed Blanchard's cricket frogs (Acris blanchardi) to ecologically relevant concentrations (0, 0.1, 1, and 10 μg/L) of a commercial formulation of atrazine throughout the larval period to determine effects on survival, somatic growth and development (time to metamorphosis and mass at metamorphosis), and gonadal development (sex ratio at metamorphosis and the prevalence of testicular ova in phenotypic males). We tested the following hypotheses: 1) atrazine feminizes the sex ratio, 2) atrazine increases the proportion of phenotypic males with testicular ova, and 3) atrazine differentially affects somatic growth (mass at metamorphosis) and development (time to metamorphosis) for males and females. Although the control sex ratio was male-biased, exposure to 0.1 and 10 μg/L atrazine feminized sex ratios, because these treatments produced 51 and 55% fewer males than the control, respectively. We did not observe testicular ova. Atrazine did not impact survival or metamorphosis, and we did not detect sexually dimorphic impacts on time to metamorphosis or mass at metamorphosis. However, males metamorphosed 2.3 d later than females, regardless of treatment. Sex biases in timing of metamorphosis are underexplored in anurans, but if prevalent, could have important implications for theory surrounding the impact of environmental factors on metamorphosis. Our data suggest that cricket frog sex ratios are sensitive to environmentally relevant concentrations of atrazine and that feminization in the field is likely. Environ Toxicol Chem 2018;37:427-435. © 2017 SETAC.