Male-biased sex ratios and vitellogenin induction in zebrafish exposed to effluent water from a Swedish pulp mill

Biotransformation strategies for steroid estrogen and androgen pollution

The common steroid hormones are estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2), and testosterone (T). These steroids are reported to contaminate the environment through wastewater treatment plants. Steroid estrogens are widespread in the aquatic environment and therefore pose a potential risk, as exposure to these compounds has adverse impacts on vertebrates. Excessive exposure to steroid estrogens causes endocrine disruption in aquatic vertebrates, which affects the normal sexual life of these animals. Steroid pollutants also cause several health problems in humans and other animals. Microbial degradation is an efficient method for removing hormone pollutants from the environment by remediation. Over the last two decades, microbial metabolism of steroids has gained considerable attention due to its higher efficiency to reduce pollutants from the environment. The present review is focused on the major causes of steroid pollution, concentrations of these pollutants in surface water, groundwater, drinking water, and wastewater, their effect on humans and aquatic animals, as well as recent efforts by various research groups that seek better ways to degrade steroids by aerobic and anaerobic microbial systems. Detailed overview of aerobic and anaerobic microbial biotransformation of steroid estrogens and testosterone present in the environment along with the active enzyme systems involved in these biotransformation reactions is described in the review article, which helps readers to understand the biotransformation mechanism of steroids in depth. Other measures such as co-metabolic degradation, consortia degradation, algal, and fungal steroid biotransformation are also discussed in detail.

Endocrine Disruption and Reproductive Pathology

During the past 20 years, investigations involving endocrine active substances (EAS) and reproductive toxicity have dominated the landscape of ecotoxicological research. This has occurred in concert with heightened awareness in the scientific community, general public, and governmental entities of the potential consequences of chemical perturbation in humans and wildlife. The exponential growth of experimentation in this field is fueled by our expanding knowledge into the complex nature of endocrine systems and the intricacy of their interactions with xenobiotic agents. Complicating factors include the ever-increasing number of novel receptors and alternate mechanistic pathways that have come to light, effects of chemical mixtures in the environment versus those of single EAS laboratory exposures, the challenge of differentiating endocrine disruption from direct cytotoxicity, and the potential for transgenerational effects. Although initially concerned with EAS effects chiefly in the thyroid glands and reproductive organs, it is now recognized that anthropomorphic substances may also adversely affect the nervous and immune systems via hormonal mechanisms and play substantial roles in metabolic diseases, such as type 2 diabetes and obesity.

Changes in fish sex ratio as a basis for regulating endocrine disruptors

Fish sex ratio (SR) is an endpoint potentially indicating both endocrine activity and adversity, essential elements for identifying Endocrine Disrupting Chemicals (EDCs) as required by the EU regulations. Due to different protocols and methods in the literature studies, SR data vary greatly. This study analyses literature SR data and discusses important considerations for using SR data in the regulatory context for the hazard identification, classification, PBT (persistent, bioaccumulative and toxic) assessment, testing, and risk assessment. A total number of 106 studies were compiled for SR of zebrafish, medaka and fathead minnow exposed to 84 chemicals or mixtures. About 53% of literature studies determined SR by methods different from the standard histology method, leading to uncertainty of quantifying SR and differential sensitivity. SR was determined after depuration in 40 papers, which may lead to chemical-induced SR changes reversible to the control. SR was responsive to chemicals with EAS (estrogen, androgen, steoroidogenesis) activity and also to those with thyroid and progesterone activity. Besides, SR was influenced by non-chemical factors, e.g., inbreeding and temperature, leading to difficulty in data interpretation. The ECHA/EFSA/JRC Guidance suggests that SR and gonad histology data can be used for identifying EDCs. Due to reversibility, influence of confounding factors, and responsiveness to chemicals with endocrine activity other than EAS, this study suggests that SR/gonad histology should be combined with certain mode of action evidence for identifying EDCs. Important considerations for using SR data in the identification, classification, PBT assessment, testing, and risk assessment are discussed.

The Bioaccumulation and Biodegradation of Testosterone by Chlorella vulgaris

: In the present study, the accumulation and degradation of testosterone by Chlorella vulgaris were studied. The results showed that C. vulgaris has a significant ability to eliminate testosterone by bioaccumulation and biodegradation, and during the 96 h experimental period, the data demonstrated that the accumulation of testosterone followed a sigmoidal accumulation pattern. At the end of the experiment, the bioconcentration percentages of testosterone by C. vulgaris in the high-concentration group and the low-concentration group were 11.49 ± 2.78% and 40.10 ± 1.98%, respectively, and the biodegradation percentages of testosterone were 69.64 ± 4.33% and 42.48 ± 1.92%, respectively. The rate of biodegradation of testosterone by C. vulgaris mainly depended on the relative initial concentration of testosterone. When the relative initial concentration of testosterone increases, the degradation may gradually change from zero-order kinetics to second-order kinetics.

Exposure to a Brazilian pulp mill effluent impacts the testis and liver in the zebrafish

While many studies have shown that pulp mill effluents can affect ovarian physiology in fish, far fewer studies have considered the effects in males. We conducted a lab study to examine the effects of effluent from a Brazilian pulp and paper mill on hepatic and testicular morphology and various aspects of testicular physiology in the zebrafish Danio rerio. Males were exposed to lab water (control) or 4% effluent for 14 days. Effluent exposure did not affect testis size as measured by the gonadosomatic index, but contributed to morphological changes in the seminiferous tubules. The number of cysts with histopathological changes was elevated in effluent-exposed fish and the number of cysts containing spermatids was significantly reduced. The testis of effluent exposed fish had reduced levels of lactate, elevated lactate dehydrogenase activity, increased levels of reactive oxygen species and reduced levels of phosphorylated P38 mitogen-activated protein kinase (pP38 MAPK). Separate studies showed that the addition of lactate to testicular tissue incubated in vitro increased the activation of P38 MAPK. Effluent exposure also increased vacuolization, necrosis, apoptosis, hyperemia, and fat infiltration of the hepatocytes. Collectively, we provide evidence of short term effects of pulp mill effluent on testicular and hepatic physiology and biochemistry in the zebrafish.

Two common mild analgesics have no effect on general endocrine mediated endpoints in zebrafish (Danio rerio)

Mild analgesics such as acetylsalicylic acid (ASA) and acetaminophen (APAP) exert their pain-relieving effect in humans by inhibition of prostaglandin synthesis. Prostaglandins play key roles in developmental and reproductive processes in vertebrates, and in recent years, it has been suggested that weak analgesics might also act as endocrine disrupters. In a set of experiments we investigated if ASA and APAP affect well-established endocrine endpoints in zebrafish (Danio rerio), which is a commonly used model organism in the investigation of endocrine disrupting chemicals. Zebrafish were exposed to APAP (0.22, 2.3, and 30mgL^-1) or ASA (0.2, 0.5, 1.7, and 8.2mgL^-1) from hatch to sexual maturity in a test design resembling the OECD Fish Sexual Development Test. No effects on sex ratio and vitellogenin levels were observed. Adult zebrafish were exposed to high concentrations (mgL^-1) of ASA or APAP for eight or 14days. ASA reduced the levels of prostaglandin E₂, but had no effect on the concentration of 11-ketotestosterone and vitellogenin. Overall, ASA decrease prostaglandin E₂ concentrations, but well-established endpoints for endocrine disruption in zebrafish are generally not affected by aquatic exposure neither during development nor adulthood. According to the WHO/IPCS definition of an endocrine disrupter, the present results do not define APAP and ASA as endocrine disrupters.

Concentration and timing of application reveal strong fungistatic effect of tebuconazole in a Daphnia-microparasitic yeast model

Given the importance of pollutant effects on host-parasite relationships and disease spread, the main goal of this study was to assess the influence of different exposure scenarios for the fungicide tebuconazole (concentration×timing of application) on a Daphnia-microparasitic yeast experimental system. Previous results had demonstrated that tebuconazole is able to suppress Metschnikowia bicuspidata infection at ecologically-relevant concentrations; here, we aimed to obtain an understanding of the mechanism underlying the anti-parasitic (fungicidal or fungistatic) action of tebuconazole. We exposed the Daphnia-yeast system to four nominal tebuconazole concentrations at four timings of application (according to the predicted stage of parasite development), replicated on two Daphnia genotypes, in a fully crossed experiment. An "all-or-nothing" effect was observed, with tebuconazole completely suppressing infection from 13.5μgl^-1 upwards, independent of the timing of tebuconazole application. A follow-up experiment confirmed that the suppression of infection occurred within a narrow range of tebuconazole concentrations (3.65-13.5μgl^-1), although a later application of the fungicide had to be compensated for by a slight increase in concentration to elicit the same anti-parasitic effect. The mechanism behind this anti-parasitic effect seems to be the inhibition of M. bicuspidata sporulation, since tebuconazole was effective in preventing ascospore production even when applied at a later time. However, this fungicide also seemed to affect the vegetative growth of the yeast, as demonstrated by the enhanced negative effect of the parasite (increasing mortality in one of the host genotypes) at a later time of application of tebuconazole, when no signs of infection were observed. Fungicide contamination can thus affect the severity and spread of disease in natural populations, as well as the inherent co-evolutionary dynamics in host-parasite systems.

Zebrafish as a possible bioindicator of organic pollutants with effects on reproduction in drinking waters

Organic contaminants can be detected at low concentrations in drinking water, raising concerns for human health, particularly in reproduction. In this respect, we attempted to use the zebrafish as a bioindicator to detect the possible presence of these substances in drinking water, aiming to define the most relevant parameters to detect these substances, which particularly affect the development and reproduction of zebrafish. To this end, batches of 30 embryos with the chorion intact were cultured in drinking waters from different sources, throughout their full life-cycle up to 5 months, in 20 L tanks. Six replicates were performed in all water groups, with a total of 24 aquariums. Two generations (F0 and F1) were studied and the following parameters were tested: in the F0 generation, survival and abnormality rates evaluated at 5 dpf (days post-fertilization) and at 5 mpf (months post-fertilization), the onset of spawning and the fertility rate from 3 mpf to 5 mpf, and the sex ratio and underdeveloped specimens at 5 mpf. Furthermore, in the F0 offspring (F1), survival and abnormality rates were evaluated at 5 dpf and the hatching rate at 72 hpf. These results revealed that the hatching rate is the most sensitive parameter to distinguish different levels of effects between waters during the early life stages, whereas the rate of underdeveloped specimens is more suitable at later life stages. Regarding adult reproduction, fertility rate was the most sensitive parameter. The possible reversibility or accumulative nature of such effects will be studied in future work.

Exposure to the pesticide linuron affects androgen-dependent gene expression in the three-spined stickleback (Gasterosteus aculeatus)

Previous research demonstrated that exposure to exogenous androgens and effluents with androgenic activity can induce spiggin mRNA production in the kidney of the three-spined stickleback (Gasterosteus aculeatus). In the present study, we determine whether a short-term exposure to a known antiandrogenic pesticide, linuron (LN), suppresses spiggin mRNA in male stickleback and in androgenized female stickleback. Primers were designed from previously characterized sequences for each androgen receptor (AR) isoform in stickleback, arα and arβ, to assess whether these receptors are differentially regulated by androgen or antiandrogen exposure. Fish were exposed for 72 h to one of four treatments: control, LN (250 µg/L), 17α-methyltestosterone (MT, 500 ng/L), and an LN-MT mixture at those same concentrations. There was no effect of LN on spiggin and arβ mRNA levels in male kidney, while levels of arα were significantly increased twofold. Exposure to LN significantly inhibited MT-induced spiggin RNA production in female kidney with no effect on expression of arα and arβ. The present study is the first to demonstrate the antiandrogenic effect of LN at the transcript level and to examine androgenic/antiandrogenic responsiveness of the two ARs in the stickleback. From the present study, it was determined that measurement of spiggin RNA is a reliable and sensitive screening tool for the detection of both androgenic and antiandrogenic compounds.

Reproductive consequences of exposure to waterborne phytoestrogens in male fighting fish Betta splendens

Phytoestrogens are plant compounds that can act as endocrine disruptors in vertebrates. Biologically active levels of phytoestrogens have been found in aquatic habitats near wood pulp and paper mills, biofuel manufacturing plants, sewage-treatment plants, and agricultural fields. Phytoestrogens are known to cause hormonal and gonadal changes in male fish, but few studies have connected these effects to outcomes relevant to reproductive success. In one experiment, we exposed sexually mature male fighting fish Betta splendens to environmentally relevant (1 μg L(-1)) and pharmacological concentrations (1000 μg L(-1)) of the phytoestrogen genistein as well as to a positive control of waterborne 17β-estradiol (E2; 1 μg L(-1)), and a negative control of untreated water. In a second experiment, we exposed male B. splendens to environmentally relevant concentrations (1 μg L(-1)) of genistein and β-sitosterol singly and in combination as well as to the positive and negative controls. All exposures were 21 days in duration. We measured sex-steroid hormone levels, gonadosomatic index (GSI), sperm concentration and motility, and fertilization success in these fish. We found that exposure to genistein did not affect circulating levels of the androgen 11-ketotestosterone or the estrogen E2 relative to negative-control fish. We also found that neither of the compounds nor their mixture affected GSI, sperm concentration or motility, or fertilization success in exposed fish relative to negative-control fish. However, fish exposed to phytoestrogens showed some evidence of fewer but more motile sperm than fish exposed to the positive control E2. We conclude that sexually mature male B. splendens are relatively immune to reproductive impairments from short-term exposure to waterborne phytoestrogens.

Chronic exposure of 2,2',4,4'-tetrabromodiphenyl ether (PBDE-47) alters locomotion behavior in juvenile zebrafish (Danio rerio)

In the present study, we used zebrafish (Danio rerio) as a model to address possible effects of chronic exposure of polybrominated diphenyl ether (PBDE) flame retardants on locomotion behavior, body size, and gonad development in fish. Zebrafish were fed food dosed with PBDE-47 (control, solvent control, low, medium, and high dose groups) from 21 days post hatch (dph) to 90 dph. Fish locomotion parameters, including maximum swimming speed, total distance moved, and percent time active, were assessed using a video-based animal movement analysis system. At the end of the exposure, all fish were euthanized for length and weight measurement, and then subjected to either whole fish histological analysis or tissue PBDE-47 measurement. Survival, body size, and gonad histology were similar between the five groups. However, both total swimming distance and percent time active were negatively correlated with tissue PBDE-47 concentration and were significantly lower in the high dose group. Tissue levels of PBDE-47 in the exposed fish were comparable to that reported in previous field studies. In summary, this study showed that developmental exposure of PBDE-47 at an ecologically relevant level altered locomotion behavior without affecting body size or gonad development of zebrafish.

Investigating the link between pulp mill effluent and endocrine disruption: attempts to explain the presence of intersex fish in the Wabigoon River, Ontario, Canada

The ability of some pulp mill effluents (PME) to act as reproductive and endocrine disrupters in fish is well documented in the literature. However, changes are not always consistent with regard to species, gender, hormones, or reproductive effects. In the present study, the presence of the first intersexed fish that, to our knowledge, has been found in a Canadian river exposed to PME, is reported. A field survey of the Wabigoon River near Dryden, Ontario, in the fall of 2000 found intersexed walleye (Sander vitreus vitreus) with significantly altered hormone levels and reduced gonad size. The Wabigoon River receives discharge from a bleached kraft pulp and paper mill and a municipal wastewater (MWW) plant. It also has historical sediment contamination (wood fiber mats) contributing to extended periods of low dissolved oxygen under low flow, drought conditions. A mesocosm-based partial life cycle test exposing fathead minnows (Pimephales promelas) to reference water, 20% effluent volume to river volume (v/v), 40% (v/v), or 60% (v/v) PME as well as a field survey of the walleye in the Wabigoon River were conducted. The only change in our mesocosm exposure was a decrease in testosterone in males with increasing effluent concentration and vitellogenin induction in males exposed to 60% (v/v) effluent. These results did not reflect the magnitude of endocrine disruption seen in the wild fish survey. Several hypotheses that may explain these discrepancies are proposed. Specifically, evidence is offered from published studies indicating that either hypoxia or MWW, alone or in combination with PME, may explain the discrepancy between our field experiment and the wild fish survey. The present study illustrates the complexities of multistressor receiving environments and the need for the development of cumulative effects assessment approaches.

Growth and transcriptional effect of dietary 2,2',4,4'-tetrabromodiphenyl ether (PBDE-47) exposure in developing zebrafish (Danio rerio)

In this study, zebrafish (Danio rerio) were fed food dosed with pure PBDE-47 (2,2',4,4'-tetrabromodiphenyl ether) congener or a blank from 20 to 60 day post-hatch (dph). At 38 dph, half of the fish were sampled for body size measurements and gene expression analyzes (CYP1A1, VTG, TTR, D1, and TSH-beta). At 60 dph, body size was measured again for all fish remaining. Whole-fish histology was performed and the PBDE levels in fish were determined. PBDE treated fish was significantly smaller at 38 dph but not at 60 dph. No apparent histopathological effect was observed. In the PBDE treated fish, there was a weak induction of CYP1A1 mRNA transcription, but not of the other genes. The tissue levels of PBDE-47 were comparable to that found in other wild fish reported in the literature, indicating that our exposure level was ecologically relevant.

Simultaneous determination of androgenic and estrogenic endpoints in the threespine stickleback (Gasterosteus aculeatus) using quantitative RT-PCR

A method to evaluate the expression of three hormone responsive genes, vitellogenin (estrogens), spiggin (androgens), and an androgen receptor (ARbeta) using real-time PCR in threespine stickleback is presented. Primers were designed from previously characterised spiggin and ARbeta sequences, while a homology cloning strategy was used to isolate a partial gene sequence for stickleback vitellogenin (Vtg). Spiggin mRNA was significantly higher in kidneys of field-caught males compared to females by greater than five orders of magnitude while ARbeta levels were only 1.4-fold higher in males. Female fish had four order of magnitude higher liver Vtg expression than wild-captured males. To determine the sensitivity of these genes to induction by hormones, male and female sticklebacks were exposed to 1, 10 and 100 ng/L of methyltestosterone (MT) or estradiol (E2) in a flow-through exposure system for 7 days. Spiggin induction in females, and Vtg induction in males were both detectable at 10 ng/L of MT and E2, respectively. MT exposure did not induce ARbeta expression in the kidneys of female stickleback. In vitro gonadal steroid hormones production was measured in testes and ovaries of exposed stickleback to compare gene expression endpoints to an endpoint of hormonal reproductive alteration. Reduction in testosterone production in ovaries at all three MT exposure concentrations, and ovarian estradiol synthesis at the 100 ng/L exposure were the only effects observed in the in vitro steroidogenesis for either hormone exposure. Application of these methods to assess both androgenic, estrogenic, and anti-steroidogenic properties of environmental contaminants in a single fish species will be a valuable tool for identifying compounds causing reproductive dysfunction in fishes.

Endocrine modulating actions of a phytosterol mixture and its oxidation products in zebrafish (Danio rerio)

In this study, a phytosterol preparation ("ultrasitosterol"; 80% beta-sitosterol) and an oxidized ultrasitosterol preparation were evaluated for reproductive effects in zebrafish. Adults were exposed in a continuous flow to 10 microg/L and 100 microg/L ultrasitosterol and oxidized ultrasitosterol, and to 0.27 microg/L 17beta-estradiol and 0.28 microg/L testosterone for 3 weeks. Biomarkers analysed included plasma vitellogenin, testosterone, 11-ketotestosterone, 17beta-estradiol, and gonadal histopathology. Ovarian steroid production of testosterone and 17beta-estradiol was examined in isolated zebrafish follicles exposed in vitro to the compounds at the same concentrations as in vivo. Vtg was induced in males exposed to ultrasitosterol, and in males and females exposed to 17beta-estradiol. Males exposed to oxidized phytosterols showed increased levels of testosterone and 11-ketotestosterone, and accelerated spermatogenesis. Increased follicular atresia was observed in females exposed to oxidized phytosterols and 17beta-estradiol. Correlation analyses between biomarkers revealed more intercorrelated values for females than for males, and the strongest associations were found in females exposed to oxidized phytosterols. Testosterone production was significantly increased in follicles exposed to the oxidized phytosterol preparations. These findings indicate that the phytosterol mixture is weakly estrogenic in male fish, and that the oxidized phytosterol mixture contains substances that may interfere with spermatogenesis, oogenesis and gonadal steroidogenesis in zebrafish.