Effects of atrazine on sex steroid dynamics, plasma vitellogenin concentration and gonad development in adult goldfish (Carassius auratus)

Effects of crosstalk between steroid hormones mediated thyroid hormone in zebrafish exposed to 4-tert-octylphenol: Estrogenic and anti-androgenic effects

Alkylphenols, such as nonylphenol and 4-tert-octylphenol (OP), are byproducts of the biodegradation of alkylphenol ethoxylates and present substantial ecological and health risks in aquatic environments and higher life forms. In this context, our study aimed to explore the effect of OP on reproductive endocrine function in both female and male zebrafish. Over a period of 21 days, the zebrafish were subjected to varying concentrations of OP (0, 0.02, 0.1, and 0.5 μg/L), based on the lowest effective concentration (EC10 = 0.48 μg/L) identified for zebrafish embryos. OP exposure led to a pronounced increase in hepatic vitellogenin (vtg) mRNA expression and 17β-estradiol biosynthesis in both sexes. Conversely, OP exhibits anti-androgenic properties, significantly diminishes gonadal androgen receptor (ar) mRNA expression, and reduces endogenous androgen (testosterone and 11-ketotestosterone) levels in male zebrafish. Notably, cortisol and thyroid hormone (TH) levels demonstrated concentration-dependent elevations in zebrafish, influencing the regulation of gonadal steroid hormones (GSHs). These findings suggest that prolonged OP exposure may result in sustained reproductive dysfunction in adult zebrafish, which is largely attributable to the intricate reciprocal relationship between hormone levels and the associated gene expression. Our comprehensive biological response analysis of adult zebrafish offers vital insights into the reproductive toxicological effects of OP, thereby enriching future ecological studies on aquatic systems.

Behavioral and biochemical consequences after chronic exposition to the herbicide atrazine in tadpoles

Atrazine (ATZ) is the third most sold herbicide in Brazil, occupying the seventh position between most widely used pesticides. Due to its easy outflow, low reactivity and solubility, moderate adsorption to organic matter and clay, and long soil persistence, residual herbicide can be identified after long periods following application, and its usage has been prohibited in diverse countries. Amphibians are important bioindicators to assess impact of pesticide like atrazine, due to having a partial aquatic life cycle. This study had as objective to assess the response of bullfrog (Lithobates catesbeianus) tadpoles when exposed to this herbicide. Animals were exposed for a total of 168h to following concentrations: negative control, 40 μg/L, 200 μg/L, 2000 μg/L, 20000 μg/L of ATZ. Analysis of swimming activity was performed, and biochemical profile was assessed by analysis of blood and plasma glucose levels, urea, creatinine, cholesterol, HDL, triglycerides, glutamic pyruvic transaminase (GPT), alkaline phosphatase (AP), calcium, total proteins, phenol, peroxidase and polyphenol oxidase activity. Results exhibited malnutrition, anemia, likely muscle mass loss, and hepatic damage, indicating that ATZ can lead to an increase in energy to maintain homeostasis for animal survival.

Pesticides in the Great Barrier Reef catchment area: Plausible risks to fish populations

Waterways that drain the Great Barrier Reef catchment area (GBRCA) transport pollutants to marine habitats, provide a critical corridor between freshwater and marine habitats for migratory fish species, and are of high socioecological value. Some of these waterways contain concentrations of pesticide active ingredients (PAIs) that exceed Australian ecotoxicity threshold values (ETVs) for ecosystem protection. In this article, we use a "pathway to harm" model with five key criteria to assess whether the available information supports the hypothesis that PAIs are or could have harmful effects on fish and arthropod populations. Strong evidence of the first three criteria and circumstantial weaker evidence of the fourth and fifth criteria are presented. Specifically, we demonstrate that exceedances of Australian and New Zealand ETVs for ecosystem protection are widespread in the GBRCA, that the PAI contaminated water occurs (spatially and temporally) in important habitats for fisheries, and that there are clear direct and indirect mechanisms by which PAIs could cause harmful effects. The evidence of individuals and populations of fish and arthropods being adversely affected species is more circumstantial but consistent with PAIs causing harmful effects in the freshwater ecosystems of Great Barrier Reef waterways. We advocate strengthening the links between PAI concentrations and fish health because of the cultural values placed on the freshwater ecosystems by relevant stakeholders and Traditional Owners, with the aim that stronger links between elevated PAI concentrations and changes in recreationally and culturally important fish species will inspire improvements in water quality. Integr Environ Assess Manag 2024;00:1-24. © 2023 Commonwealth of Australia and The Commonwealth Scientific and Industrial Research Organisation. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Experimental and Theoretical Estimations of Atrazine's Adsorption in Mangosteen-Peel-Derived Nanoporous Carbons

Nanoporous carbons were prepared via chemical and physical activation from mangosteen-peel-derived chars. The removal of atrazine was studied due to the bifunctionality of the N groups. Pseudo-first-order, pseudo-second-order, and intraparticle pore diffusion kinetic models were analyzed. Adsorption isotherms were also analyzed according to the Langmuir and Freundlich models. The obtained results were compared against two commercially activated carbons with comparable surface chemistry and porosimetry. The highest uptake was found for carbons with higher content of basic surface groups. The role of the oxygen-containing groups in the removal of atrazine was estimated experimentally using the surface density. The results were compared with the adsorption energy of atrazine theoretically estimated on pristine and functionalized graphene with different oxygen groups using periodic DFT methods. The energy of adsorption followed the same trend observed experimentally, namely the more basic the pH, the more favored the adsorption of atrazine. Micropores played an important role in the uptake of atrazine at low concentrations, but the presence of mesoporous was also required to inhibit the pore mass diffusion limitations. The present work contributes to the understanding of the interactions between triazine-based pollutants and the surface functional groups on nanoporous carbons in the liquid-solid interface.

High doses of GrassOut Max poses reproductive hazard by affecting male reproductive function and early embryogenesis in Swiss albino mice

Clethodim is a widely used and approved class II herbicide, with little information about its impact on the reproductive system. Herein, we investigated the male reproductive toxicity of clethodim using a mouse model. GrassOut Max (26% clethodim-equivalent) or 50 mg kg^-1 body weight analytical grade clethodim (≥90%) were given orally to male mice for 10 d in varying doses. All parameters were assessed at 35 d from the first day of treatment. Significant decrease in testicular weight, decreased germ cell population, elevated DNA damage in testicular cells and lower serum testosterone level was observed post clethodim-equivalent exposure. Epididymal spermatozoa were characterized with significant decrease in motility, elevated DNA damage, abnormal morphology, chromatin immaturity and, decreased acetylated-lysine of sperm proteins. In the testicular cells of clethodim-equivalent treated mice, the expression of Erβ and Gper was significantly higher. Proteomic analysis revealed lower metabolic activity, poor sperm-oocyte binding potential and defective mitochondrial electron transport in spermatozoa of clethodim-equivalent treated mice. Further, fertilizing ability of spermatozoa was compromised and resulted in defective preimplantation embryo development. Together, our data suggest that clethodim exposure risks male reproductive function and early embryogenesis in Swiss albino mice via endocrine disrupting function.

The protective effect of resveratrol on largemouth bass (Micropterus salmoides) during out-of-season spawning

In aquaculture production, out-of-season spawning is beneficial to solve the seasonal shortage of fry that are normally produced once annually by species such as largemouth bass (Micropterus salmoides), thereby implementing year-round fry production. Maintaining low temperature over a period of several months can delay largemouth bass ovarian development, but it can cause severe stress to their reproductive function, leading to decreased fertility during out-of-season spawning. Feeding with antioxidants is one of the most effective methods to alleviate the negative effects of low temperature stress. Therefore, the purpose of this study is to: (a) evaluate the changes in oocyte morphology, antioxidant capacity, reproductive hormone-related index, cell apoptosis and autophagy during the out-of-season spawning of largemouth bass, and (b) to investigate the protective effect of the antioxidant resveratrol on this fish during out-of-season spawning from May through August. The study was divided into two groups (three replicates per group, 2000 fish per replicate): control group (Control) (exposure to water temperature of 12-17 °C) and resveratrol supplementation group (Res) (exposure to water temperature of 12-17 °C and fed with 200 mg/kg resveratrol). The results show that: (1) The serum hormones LH and E2 increased first and then remained unchanged, and the ovarian section showed that the ovary remained in stage IV. (2) In the process of off-season reproduction, a large number of follicles experienced follicular atresia, accompanied by endoplasmic reticulum expansion, nuclear chromatin condensation and mitochondrial swelling, which was relieved after feeding resveratrol. (3) Resveratrol decreased the ovarian ROS content and improved the activities of CAT and other antioxidant enzymes in the ovary and liver to some extent. (4) Resveratrol reduced the level of pro-apoptotic (Bax, Caspase3, Caspase8, Caspase9) and autophagy-related components (LC3-B, Beclin-1) while increasing the transcription level of anti-apoptotic (Bcl-2) factors. These findings suggest that resveratrol alleviates some adverse effects of largemouth bass during out-of-season spawning to some extent and provide a model for efficient and high-quality out-of-season spawning.

Atrazine alters early sexual development of the South American silverside, Odontesthes bonariensis

Atrazine (ATZ) is a frequent contaminant in freshwater ecosystems within agricultural regions. The capacity of this herbicide to interfere with the vertebrate endocrine system is broadly recognized, but the mechanisms and responses usually differ among species. In this study, ATZ effects on hypothalamus-pituitary-gonadal (HPG) axis key genes expression and early gonadal development were evaluated in Odontesthes bonariensis larvae waterborne exposed during the gonadal differentiation period. Fish were treated to 0, 0.7, 7.0, and 70 µg ATZ/L at 25 °C from the 2nd to 6th week after hatching (wah), and a group was kept in clean water until the 12th wah. Parallelly, a group was submitted to 0.05 µg/L of ethinylestradiol (EE₂) as a positive estrogenic control. From each treatment, eight larvae were sampled at 6 wah for gene expression analysis and twelve larvae at 12 wah for phenotypic sex histological determination. The expression of gnrh1, lhb, fshb, and cyp19a1b was assessed in the head, and the ones of amha, 11βhsd2, and cyp19a1a in the trunk. Fish growth was significantly higher in fish exposed to 7 and 70 µg ATZ/L in the 6 wah, but the effect vanished at the 12 wah. The expression of lhb was upregulated in both sex larvae exposed from 7 µg ATZ/L. However, a dimorphic effect was induced on cyp19a1a expression at 70 µg ATZ/L, up or downregulating mRNA transcription in males and females, respectively. Delayed ovarian development and increased number of testicular germ cells were histologically observed from 7 to 70 µg ATZ/L, respectively, and a sex inversion (genotypic male to phenotypic female) was found in one larva at 70 µg ATZ/L. The lhb expression was also upregulated by EE₂, but the cyp19a1a expression was not affected, and a complete male-to-female reversal was induced. Further, EE₂ upregulated gnrh1 in females and cyp19a1b in both sexes, but it did not alter any assessed gene in the trunk. In conclusion, ATZ disrupted HPG axis physiology and normal gonadal development in O. bonariensis larvae at environmentally relevant concentrations. The responses to ATZ only partially overlapped and were less active when compared to the model estrogenic compound EE₂.

CdO-supported ZrO2heterojunctions: facile synthesis and rapid visible-light oxidation of atrazine herbicide with superb recyclability

The advancement in ceramic oxide-based photocatalysis has got much attention recently for environmental issues. Atrazine (AZ) is one of the major used herbicides in agricultural and related industries. This work familiarizes a polymeric-assisted sol-gel preparation of high surface area zirconium oxide (ZrO₂) supported with cadmium oxide nanoparticles at minor content (0.5-2.0 wt%). Exploration of the synthesized heterostructures revealed the enhancement of visible-light absorbance and reduction of bandgap energy to 2.76 eV keeping the same crystalline form and high surface area of 170 m²g^‒1. The prepared photocatalysts were used to degrade AZ in water at a concentration of 231.8μM (50 ppm). The 1.5%-introduced CdO to ZrO₂revealed the best-performed photocatalyst for complete oxidation of AZ within 40 at an optimized dose of 1.6 g l^-1. This novel ceramic photocatalyst showed a chemical and structural ability to keep 98.5% of its initial efficiency after five regenerated cycles. The construction of p-n heterojunction between the p-type ZrO₂and the n-type CdO contributed to the comprehensive photocatalytic competence toward the efficient charge separation and photooxidation process.

Histopathological, immunohistochemical, and molecular investigation of atrazine toxic effect on some organs of adult male albino rats with a screening of Acacia nilotica as a protective trial

Atrazine (ATZ) is a widely used herbicide; however, it has deleterious effects. The current study aimed to investigate the potential toxic effect of ATZ as a neuroendocrine disruptor on the cerebellum and thyroid gland and on the liver as a detoxifying organ. We examined the ability of ATZ to induce oxidative stress and subsequent apoptosis in these organs. Moreover, we investigated the potential protective effect of Acacia nilotica, because of its potent antioxidant activity. Thus, our study was carried out on 40 adult male albino rats that were divided equally into 4 groups (10 rats/each group). The first group received distilled water, while the second group received ATZ dissolved in corn oil at 200 mg/kg body weight/day by stomach gavage. The third group was treated orally by ATZ (200 mg/kg body weight/day) plus Acacia nilotica (400 mg/kg/day). Group IV received Acacia nilotica only at a dose (400 mg/kg/day). After successive 30 days of the experiment, blood and tissue samples were collected from all groups. Our findings revealed the ability of ATZ to induce toxic effects was observed microscopically in the form of degenerated neurons and vacuolated neuropil of the cerebellum, degenerated hepatocytes, and vacuolation of the follicular cells of the thyroid gland. Furthermore, ATZ significantly elevated AST, ALT, and ALP serum levels and TB concentration, while decreased GSH. DNA fragmentation% and activated caspase-3 expression significantly increased after ATZ exposure. Interestingly, Acacia nilotica administration was able to partially protect the examined organs against the toxic effect of ATZ exposure.

First report on atrazine monitoring in drinking water from Ijebu-North, South-West Nigeria: Human health risk evaluation and reproductive toxicity studies

There are no available data on the level of atrazine in drinking water from rural agricultural areas in Nigeria and its potential health implications. Here, we measured atrazine residue in 69 hand-dug wells (HDW), 40 boreholes (BH), and four major streams from the six communities (Ago-Iwoye, Ijebu-Igbo, Oru, Awa, Ilaporu, and Mamu) in Ijebu North Local Government Area, Southwest Nigeria. Values of atrazine obtained were further used for the evaluation of non-carcinogenic risk associated with ingestion and dermal contact in adults and children as well as reproductive toxicity evaluation. A total of 41 HDW, 22 BH, and the four streams showed varying concentrations of atrazine, which was higher in HDW than BH and stream. Ago-Iwoye recorded the highest concentration of 0.08 mg/L in its HDW while the lowest concentration of 0.01 mg/L was recorded in HDW from Oru. Although the Hazard Index (HI) values associated with ingestion and dermal contact for children were higher than in adults, the values were below the acceptable limit for all the communities. Significant (p < 0.05) alterations in the oxidative stress parameters, reproductive hormones, sperm parameters, and mild testicular lesions were only observed in rats exposed to atrazine at 0.08 mg/L compared to control. But atrazine at 0.01, 0.03, and 0.04 mg/L triggered a defence mechanism capable of protecting the structural integrity of the testes and preventing reproductive dysfunction.

Pesticide Pollution: Detrimental Outcomes and Possible Mechanisms of Fish Exposure to Common Organophosphates and Triazines

Pesticides are well known for their high levels of persistence and ubiquity in the environment, and because of their capacity to bioaccumulate and disrupt the food chain, they pose a risk to animals and humans. With a focus on organophosphate and triazine pesticides, the present review aims to describe the current state of knowledge regarding spatial distribution, bioaccumulation, and mode of action of frequently used pesticides. We discuss the processes by which pesticides and their active residues are accumulated and bioconcentrated in fish, as well as the toxic mechanisms involved, including biological redox activity, immunotoxicity, neuroendocrine disorders, and cytotoxicity, which is manifested in oxidative stress, lysosomal and mitochondrial damage, inflammation, and apoptosis/autophagy. We also explore potential research strategies to close the gaps in our understanding of the toxicity and environmental risk assessment of organophosphate and triazine pesticides.

Effects of Anthropic Pollutants Identified in Pampas Lakes on the Development and Reproduction of Pejerrey Fish Odontesthes bonariensis

Anthropic activities can seriously affect the health of the organisms inhabiting them, and the observation of any alteration in the reproduction of fish could be associated with the presence of endocrine disruptors. In this manuscript we have collected information on the adverse effects of pollutants (heavy metals, environmental steroids, and agrochemicals), present in Chascomús lake, Argentina, either at environmentally relevant and pharmacological concentrations on reproduction, embryonic development, and larval survival of pejerrey fish Odontesthes bonariensis. During development, it has been reported that 17β-estradiol (E₂) feminized and reduced larval survival, while 17α-ethinyl-estradiol (EE₂) not only feminized but also affected both embryo and larval survival. In adult male fish, treatments with EE₂ and E₂ + EE₂ were able to increase mRNA abundance of gnrh3 and cyp19a1b and decreased those of gonadotropin receptors (fshr and lhcgr). Heavy metals such as cadmium, chromium, and copper negatively affected sperm quality, diminishing the motility. Also, a decrease in the percentage of hatching rate and larval survival was also observed with the same metals, highlighting zinc as the most detrimental metal. Furthermore, all these metals altered the expression of hypothalamic and pituitary genes related to reproduction in male pejerrey (gnrh1,2,3; cyp19a1b; fshb; lhb; fshr and, lhcgr). Moreover, in all cases pyknotic cells, corresponding to the degeneration of the germ cells, were observed in the testes of exposed fish. For agrochemicals, exposure of male pejerrey to environmental concentrations of glyphosate did not cause alterations on the endocrine reproductive axis. However, male pejerrey with gonadal abnormalities such as the presence of intersex (testis-ova) gonads were found in other Pampa´s lakes with high concentrations of atrazine and glyphosate associated with soybean and corn crops near their coasts. These types of studies demonstrate that pejerrey, an endemic species with economic importance inhabiting the Pampas shallow lakes, can be used as a sentinel species. It should be noted that increased pollution of aquatic ecosystems and the effects on the reproduction of organisms can lead to a decline in fish populations worldwide. Which, added to overfishing and other external factors such as global warming, could cause an eventual extinction of an emblematic species.

Curcumin improves the protective effects of quercetin against atrazine-induced testicular injury in adult Wistar rats

This study evaluated the beneficial protective effect of cotreatment of curcumin (CUR) and quercetin (QUE) on atrazine (ATZ)-induced testicular toxicity in rats. ATZ challenge diminished luteinizing hormone, follicular stimulating hormone, testosterone and myeloperoxidase enzyme activity, but these effects were attenuated on co-treatment with CUR and QUE. Also, co-treatment of CUR + QUE was better than separate administration of QUE at diminishing malondialdehyde and glutathione and improving tumour necrosis factor-α concentration, germ cell numbers (spermatogonia, spermatocytes and round spermatids) and epididymal sperm quality. Histologically, smaller sized tubules with degenerated epithelia and few germ cells were seen in the seminiferous tubules of the ATZ group whereas CUR + QUE pretreatment improved the histo-morphologic features of the tubules compared to the ATZ group and was also better than separate administration of QUE. We conclude that CUR can improve the protective effects of QUE against ATZ-induced testicular injury by enhancing the levels of reproductive hormones, recovering testicular biochemical parameters and improving the histological features of the testes.

Concentration of current-use pesticides in frogs from the Pampa region and correlation of a mixture toxicity index with biological effects

Contamination with current-use pesticides is frequently mentioned as a key factor in global amphibian declines although a limited number of studies have examined the mixture of pesticides accumulated by free-living frogs. This study examined the presence of 46 different pesticide residues in the muscle and kidney tissues of two frog species living in close association with row crops in the Pampa region of Argentina: The terrestrial Leptodactylus latinasus and the semi-aquatic Leptodactylus latrans. A total of 20 different pesticides were identified in frog tissues; chlorpyrifos-methyl, pirimiphos-methyl and acetochlor being the most frequently detected molecules. Overall, one or more pesticide residues (up to 12 in a single frog) were detected in 40-57 % of L. latrans. L. latinasus was found to present more pesticide detections than L. latrans. Interestingly, frog sampled in a natural reserve where no pesticides are applied presented an equivalent frequency of detections as frogs living near a crop. In L. latrans, the calculation of a pesticide toxicity index (PTI) permitted to highlight the existence of a strong positive correlation between PTI and liver GSH contents of females whereas, in males, PTI was negatively correlated with the perimeter of testicular seminiferous tubules. Males also presented near significant negative correlations between PTI and both body condition and the scaled fat index. These results indicate that frogs inhabiting agricultural regions are exposed to a complex and diffuse contamination by pesticide mixtures which is likely responsible for a number of biological effects that may be relevant at the population level.

Reproductive toxicity due to herbicide exposure in freshwater organisms

Excessively used pesticides in agricultural areas are spilled into aquatic environments, wherein they are suspended or sedimented. Owing to climate change, herbicides are the fastest growing sector of the pesticide industry and are detected in surface water, groundwater, and sediments near agricultural areas. In freshwater, organisms, including mussels, snails, frogs, and fish, are exposed to various types and concentrations of herbicides. Invertebrates are sensitive to herbicide exposure because their defense systems are incomplete. At the top of the food chain in freshwater ecosystems, fish show high bioaccumulation of herbicides. Herbicide exposure causes reproductive toxicity and population declines in freshwater organisms and further contamination of fish used for consumption poses a risk to human health. In addition, it is important to understand how environmental factors are physiologically processed and assess their impacts on reproductive parameters, such as gonadosomatic index and steroid hormone levels. Zebrafish is a good model for examining the effects of herbicides such as atrazine and glyphosate on embryonic development in freshwater fish. This review describes the occurrence and role of herbicides in freshwater environments and their potential implications for the reproduction and embryonic development of freshwater organisms.

Chronic effects of a binary insecticide Acer 35 EC on Nile tilapia Oreochromis niloticus through a multi-biomarker approach

Acer 35 EC is a widely used insecticide (a binary mixture of lambda-cyhalothrin and acetamiprid) in pest control in many West African countries, particularly in the cotton culture in north Benin. The aim of this study was to investigate the chronic effects of Acer 35 EC on Nile tilapia Oreochromis niloticus juveniles using a multi-biomarker approach under laboratory conditions. For this purpose, fish were exposed to sublethal concentrations of Acer 35 EC (0, 1 and 10% of LC₅₀- 96 h value). After 28 and 56 days of exposure, several biomarkers were measured in males and females including enzymatic activities related to detoxification and oxidative stress, neurotoxicity and immune responses, sex steroid hormones (testosterone, 17β-estradiol and 11-keto-testosterone) and histological alterations of liver, kidney and gonads. An Integrated Biomarker Response (IBR) was then calculated. The results showed a reduction of cholinesterase activity in muscles, and intercellular superoxide anion production in both sexes. Female steroidogenesis and gametogenesis were affected, especially testosterone levels and oocyte growth. More alterations were observed in liver after exposure to Acer 35 EC. In both sexes, IBR values were higher after 56 days than after 28 days of exposure. In conclusion, based on a large set of biomarkers and IBR values, the chronic exposure to low doses of insecticide Acer 35 EC seems to impair different physiological functions in Nile tilapia juveniles on a time-dependent manner, with a stronger impact on females than on males.

Atrazine impairs testicular function in BalB/c mice by affecting Leydig cells

Several studies have reported the effects of atrazine on the gonads of many experimental models. However, the short-term effects of in vivo exposure to atrazine on the testes of mice are not well clarified. Here we reported that adult BalB/c mice exposed to atrazine (50 mg kg^-1 body weight) by gavage for three consecutive days have reduced numbers of 3β-hydroxysteroid dehydrogenase positive Leydig cells (LCs), associated with increased in situ cell death fluorescence and caspase-3 immuno-expression in the testes. Consequently, immunostaining for cell cycle gene regulators showed increased expressions of p45, accompanied with increased expressions of cyclin D2 and E2. Histological observations of the gonads showed reduced number of germ cells in particular areas, sloughed seminiferous epithelium, presence of giant apoptotic cells close to the seminiferous tubule lumen and in the epididymal lumen along with low numbers of Leydig cells in the testicular interstitial areas. Similarly, LCs isolated from the testes of BalB/c mice that were exposed to atrazine (0.5, 25, 50 mg kg^-1 body weight) in the same manner as in the first experiment presented dose-dependent increased caspase-3 activity, decreased cell viability, intratesticular and serum testosterone concentrations and LCs testosterone secretion. In summary, atrazine appears to directly decrease the number of testosterone secreting LCs in mice through apoptosis.

Optimal combination of temperature and photoperiod for sex steroid hormone secretion and egg development of Oreochromis niloticus as determined by response surface methodology

For successful reproduction of farmed fish, it is important to understand the relationship between gonadal development and environmental factors such as temperature and photoperiod. In this study, we determined the effects of temperature (T) and photoperiod (Pp) on serum estradiol-17β (E₂) and progesterone (P) contents, gonadosomatic index (GSI), and oocyte development in female tilapia. We used a central composite experimental design and response surface methodology. The experimental ranges were 18-36 °C for T and 0-24 h for Pp. The results show that the quadratic effects of T and Pp were highly significant for serum E₂ and P contents, GSI, and the ratio of stage III to stage II oocytes (P < 0.01), and that the linear effects of T and Pp were also significant for these indicators (P < 0.05). The T × Pp interaction significantly affected serum E₂ content (P < 0.05). Serum E₂ and P content, GSI, and the ratio of stage III to stage II oocytes increased and then decreased with increasing T or Pp. The best combination of T and Pp for egg development was 28.6 °C/14.29 h. We observed the part of ovarian tissue containing stage V oocytes that are about to be discharged. Shortening the photoperiod or lowering the water temperature delayed the development of ovarian tissue so that most oocytes remained at stage II, and there were many atretic follicles. There were significant positive correlations between female GSI and serum E₂, P, and the ratio of stage III to stage II oocytes. The results of this study provide a reference for the regulation of temperature and photoperiod to control broodstock gonadal maturation and hormone-induced broodstock spawning.

Chronic toxicity of technical atrazine to the fathead minnow (Pimephales promelas) during a full life-cycle exposure and an evaluation of the consistency of responses

Fathead minnows (Pimephales promelas) were continuously exposed to the herbicide atrazine (0.15, 0.25, 0.46, 0.99, and 2.0 mg a.i./L, plus dilution water and solvent controls) for a complete life cycle (274 days). Concentrations of atrazine up to 2.0 mg a.i./L did not significantly reduce hatching success, larval survival at 30 or 60 days post-hatch, or reproduction (eggs/spawn, total eggs, spawns/female, or eggs/female) in the F0 generation. However, at 60 days of exposure, total length and total survival to study completion were significantly reduced in ≥0.46 mg a.i./L and ≥ 0.99 mg a.i./L treatments, respectively. In the F1 generation, hatchability of embryos at ≥0.25 mg a.i./L (range 74-82%) was significantly less than that of pooled control organisms (86%). Following 30 days' post-hatch exposure, F1 survival was not significantly different from pooled control for any treatment. Finally, tissues representing major life stages had bioconcentration factors ranging from 3.7× (F1 embryos, <24 h) to 8.5× (F0 adults), indicating little to no evidence of bioconcentration. We developed a series of questions to assess the consistency of observed responses in order to place the data in context with the wider available and relevant literature (e.g., Observed between studies? Observed between species? Observed at lower levels of biological organization?). The analysis for consistency supports the conclusion that atrazine does not pose a significant chronic risk to freshwater fish in terms of growth, reproduction, or survivorship at concentrations of up to at least 100 μg/L.

Effects of subchronic exposure to environmentally relevant concentrations of the herbicide atrazine in the Neotropical fish Astyanax altiparanae

Atrazine (ATZ) is among the most widely used herbicides in the world, and yet it has a potential to contaminate aquatic environments due to pesticide leaching from agricultural areas. In the Neotropical region, studies about the effects of this herbicide in native aquatic wildlife is scarce.Our study aimed at investigating the effects of a 30-day exposure to a commercial atrazine formulation on oxidative stress parameters, histopathology in testis and liver, and hormone levels in males and female of yellow-tailed tetra fish (Astyanax altiparanae). Adults were exposed to low but environmentally relevant concentrations of atrazine as follows: 0 (CTL-control), 0.5 (ATZ0.5), 1 (ATZ1), 2 (ATZ2) and 10 (ATZ10) μg/L. Our results showed decreased GST activity in gills in all groups of exposed animals and increased CAT activity in gills from the ATZ10 group. In the liver, there was an increase in lipid peroxidation in fish from ATZ1 and ATZ2 groups. Histological analysis of the liver showed increased percentage of sinusoid capillaries in ATZ2 fish, increased vascular congestion in ATZ1 and increased leukocyte infiltration in the ATZ10 group. Hepatocyte diameter analysis revealed a decrease in cell size in all groups exposed to ATZ, and a decrease in hepatocyte nucleus diameter in ATZ1, ATZ2 and ATZ10 groups. Endocrine parameters did not show significant changes following ATZ exposure, although an increase of triiodothyronine/thyroxine (T₃/T₄) ratio was observed in ATZ2 fish. Our results provide evidence that even low, environmentally relevant concentrations of ATZ produced oxidative damage and histological alterations in adult yellow-tailed tetra.

Impact of herbicide pretilachlor on reproductive physiology of walking catfish, Clarias batrachus (Linnaeus)

Herbicide pretilachlor is widely used in paddy fields to control annual weeds. The present study has been carried out in walking catfish, Clarias batrachus, to evaluate the impact of herbicide pretilachlor on reproductive physiology after chronic exposure. Based on the median lethal concentration value (96 h), fish were exposed to three nominal test concentrations of pretilachlor ((SL-I (1/20th LC₅₀), SLII (1/15th LC₅₀), and SL-III (1/10th LC₅₀)) for 30, 45, and 60 days after which plasma sex steroid profile, plasma vitellogenin concentration, and gonadal aromatase activity were analyzed in both sexes. Plasma concentration of testosterone decreases in herbicide-exposed male fish. Significant increase in plasma 17β-estradiol, plasma vitellogenin concentration, and gonadal aromatase activity were observed in herbicide-exposed male fish. All these alterations in reproductive parameters in male fish are dependent on concentration and exposure duration of herbicide. On the other hand, significant decrease in plasma concentration of testosterone was observed in female fish which was also dependent on concentration and exposure duration of herbicide. No significant changes in plasma 17β-estradiol concentrations, plasma vitellogenin concentration, and gonadal aromatase activity were observed in female fish. Above findings clearly suggested that herbicide pretilachlor acts as endocrine disruptor in fish and affects overall reproductive physiology of fish, but its ability to induce reproductive toxicity in male and female differs considerably.

Hypoxia-mediated inhibition of cholesterol synthesis leads to disruption of nocturnal sex steroidogenesis in the gonad of koi carp, Cyprinus carpio

Reproductively mature koi carps (Cyprinus carpio) showed a prominent diurnal variation of sex steroids with sustained nocturnal rise. Exposure to chronic hypoxia (DO < 0.8 mg/l) disrupted nocturnal sex steroid production in koi carp gonads. Inhibition of sex steroidogenesis is linked to the down-regulation of HMG-Co A reductase (p < 0.05), which acts as a rate-limiting enzyme in the mevalonate pathway for cholesterol production. HMG-CoA reductase inhibition was obvious in the gonads and liver of both sexes during 18.00 h and 21.00 h resulting in hypocholesterolemia (p < 0.05). The levels of sex steroids, such as estradiol, testosterone, and 11-keto-testosterone in gonads were depleted below the optimum levels owing to disruption of de novo cholesterol synthesis along with attenuation of HDL-cholesterol level in serum. Inhibition of melatonin under hypoxic conditions indicates disruption of melatonin effects on the hypothalamus-pituitary-gonadal (HPG) axis of koi carp. Under severe hypoxic stress, koi carp promoted energy conservation by switching over to the triglyceride (TGA) pathway instead of the mevalonate pathway to suppress cholesterol production. Chronic hypoxia inhibited cholesterol synthesis, a prerequisite for gonadal maturation. It promoted TGA production, as an alternative energy source, suggesting a probable mitigation strategy adopted by hypoxia-tolerant fish to deal with low dissolved oxygen frequently occurring in aquatic bodies.

Comparing the effect of triadimefon and its metabolite on male and female Xenopus laevis: Obstructed growth and gonad morphology

Amphibians are the most endangered class of vertebrates. In this study, Xenopus laevis frogs were exposed to 0, 1 and 10 mg/L of triadimefon or triadimenol. After 14 or 28 days of exposure, high levels of triadimefon or triadimenol obstructed the growth of frogs. However, low levels of triadimefon induced the growth of females after the longer period of exposure. We also found that the antioxidant enzyme activity and LDH levels in males were higher than those in females after 28-days exposure. In histopathology tests, triadimenol exerted more effect on the ovary while triadimefon exerted more effect on the testes. Additionally, the levels of Estradiol in all 14-day treatments, except 1 mg/L triadimenol, were significantly decreased, however, there was no difference in testosterone levels. Furthermore, triadimefon and triadimenol disrupted the expression of genes controlling hormone homeostasis and reproduction, and this effect depended on the exposure time and the gender of the organism. Our experiments explored the effect of triadimefon and its metabolite on the gonads of frogs and highlighted the role that pesticides are likely to play in the global decline of amphibians.

Changes induced by atrazine in Clarias gariepinus provide insight into alterations in ovarian histoarchitecture and direct effects on oogenesis

Clarias gariepinus juveniles were exposed to environmentally relevant concentrations of 0 (control), 2.5, 25, 250 and 500 μg L^-1 atrazine in a quality-controlled 28-day laboratory procedure. Findings revealed a significant decrease in the levels of follicle-stimulating hormone, luteinizing hormone and prolactin relative to control (p < 0.05). Atrazine reduced the levels of testosterone while increasing the concentration of progesterone. Histologically, the control and treatments presented three stages of oocyte maturation: the chromatin nucleolar oocyte stage, early perinucleolar oocyte stage and the vitellogenic oocyte stage. However, in the ovaries of the treatment group with the lowest treatment concentration (2.5 μg L^-1), atretic oocytes with broken membranes invaded many of the dead ova and empty spaces. In other treatments (25, 250 and 500 μg L^-1), interfollicular spaces, vacuolation in oocyte formation, and dissolution of oocyte walls were observed. Disruption of the yolk vesicle and clumping of the cytoplasm in maturing oocytes was observed only at the highest atrazine concentration (500 μg L^-1). Gross alterations in ovarian histoarchitecture and reproductive hormone levels observed in this study showed interference with oogenesis which may result in reduced egg viability and fecundity in fish with ecological implications in water bodies exposed to atrazine even at reduced concentrations.

Study on the efficacy and mechanism of Fe-TiO2 visible heterogeneous Fenton catalytic degradation of atrazine

In order to improve the catalytic activity and recycling performance of heterogeneous Fenton catalyst, a heterogeneous Fenton catalyst Fe/TiO₂ based on TiO₂ supported visible light response was prepared by a simple method using TiO₂ synthesized by sol-gel method as carrier and ferric nitrate as Fe source. It was characterized by SEM, EDX, XRD, UV-vis instruments. The influencing factors of catalytic degradation of atrazine by visible light heterogeneous Fenton of Fe/TiO₂ were studied and the reaction kinetics were fitted. The mineralization degree of atrazine was reflected by the removal rate of TOC. The intermediate products by the degradation of the catalytic system was analyzed and the reaction mechanism of Fe/TiO₂-H₂O₂ visible light system was discussed. The XRD results showed that Fe was highly dispersed on the surface of TiO₂ in the form of α-Fe₂O₃. The Fe/TiO₂ catalyst with heterogeneous Fenton and visible light photocatalytic activity was successfully optimized, forbidden bandwidth of Fe/TiO₂ after Fe supported was narrower, the scope of light absorption red-shifted, the electron-hole pairs were more generated, and there was a significant synergistic effect between the carrier TiO₂ and the supported Fe, which exhibited good oxidation capacity for degradation of 10 mg L^-1 atrazine in pH of 3, the concentration of H₂O₂ was 1.6 mM, and the catalyst was added at 1 g L^-1, achieving over 95% removal efficiency within 30 min, and, in the range of pH 3-7, the degradation rate of the reaction for 30 min can be maintained above 75%, which greatly broadened the range of pH application and had good recycling performance. The degradation process conformed to the quasi-first-order kinetic model. Through LC-MS analyzed, 12 intermediate products were formed during the degradation of atrazine, the final products were all cyanuric acid, and then the triazine ring was mineralized into inorganic substances such as CO₂, H₂O and NO₃^- by oxidation of ·OH, and the possible degradation pathways were inferred.

Impacts of herbicide pendimethalin on sex steroid level, plasma vitellogenin concentration and aromatase activity in teleost Clarias batrachus (Linnaeus)

Pendimethalin (PM) is a selective herbicide, widely present in aquatic environment. It causes detrimental effects in fishes, but little is known regarding its reproductive toxicity. The present study was carried out in Clarias batrachus exposed to sub lethal concentrations of PM for 30, 45 and 60 days. Male fish showed a significant increase in plasma 17β-estradiol (E2) however plasma E2 in females was not affected. Plasma testosterone levels were significantly decreased in both sexes. In male plasma vitellogenin (VTG) and gonadal aromatase activity was increased irrespective of herbicide concentration and exposure duration. In females concentration and time dependent reduction in plasma VTG but no significant change in the gonadal aromatase activity were observed. Results indicated that PM act as endocrine disruptor but act differentially in male and female fishes and plasma E2, T and VTG levels and aromatase activity can be considered as reliable biomarkers for PM toxicity in fishes.

Exposure to atrazine during puberty reduces sperm viability, increases weight gain and alters the expression of key metabolic genes in the liver of male mice

Atrazine (ATZ) is one of the most widely used herbicides worldwide and is a common contaminant in human drinking water. It disrupts metabolic pathways in plants, and has metabolic and reproductive effects in vertebrates, including humans. Few studies have investigated the effects of exposure to low doses of ATZ, especially during sexual development in males. In this study, we exposed C57BL/6J male mice from weaning for 8 weeks to drinking water containing 0.5mgkg-1 bodyweight (BW) day-1 ATZ, the 'no observed effect' level used by the Australian government, or a 10-fold higher dose (5mgkg-1 BW day-1). Mice treated with the low dose of ATZ showed increased total and cumulative weight gain. At 12 weeks of age, there was a significant increase in the percentage of dead spermatozoa in both ATZ-exposed groups, as well as decreased epididymal sperm motility in the low-dose ATZ group. Significant changes in testis and liver gene expression were also observed following ATZ exposure. These data demonstrate that a low dose of ATZ can perturb metabolic and reproductive characteristics in male mice. A chronic reduction in sperm quality and increased weight gain could have negative consequences on the reproductive capacity of males, and further studies should consider the effects of long-term ATZ exposure on male reproductive health.

Effects of short-time exposure to atrazine on miRNA expression profiles in the gonad of common carp (Cyprinus carpio)

BACKGROUND

Atrazine is widely used in agriculture and is a known endocrine disrupting chemical. Atrazine can seep into the water body through surface, posing a potential threat to the aquatic ecological environment and human drinking water source. In vertebrate, studies have shown that it can affect reproduction and development seriously, but its molecular mechanism for aquatic animals is unknown. Aquaculture is very common in China, especially common carp, whose females grow faster than males. However, the effects of atrazine on the reproduction of carp, especially miRNA, have not been investigated.

RESULTS

In this study, common carp (Cyprinus carpio) at two key developmental stages were exposed to atrazine in vitro. Sex ratio was observed to analyze the effect of atrazine on the sex. MiRNA expression profiles were analysed to identify miRNAs related to gonad development and to reveal the atrazine mechanisms interfering with gonad differentiation. The results showed that the sex ratio was biased towards females. Atrazine exposure caused significant alteration of multiple miRNAs. Predicted targets of differently-expressed miRNAs were involved in many reproductive biology signalling pathways.

CONCLUSIONS

Our results indicate that atrazine promoted the expression of female-biased genes by decreasing miRNAs in primordial gonad. In addition, our results indicate that atrazine can up-regulate aromatase expression through miRNAs, which supports the hypothesis that atrazine has endocrine-disrupting activity by altering the gene expression profile of the Hypothalamus-Pituitary-Gonad axis through its corresponding miRNAs.

Estrogenic potency of MC-LR is induced via stimulating steroidogenesis: In vitro and in vivo evidence

Waterborne microcystin-LR (MC-LR) has been reported to disrupt sex hormones, while its estrogenic potency remains controversial. We hypothesized that MC-LR could induce estrogenic effects via disrupting sex hormone synthesis, and verified this hypothesis by in vitro and in vivo assays. Effects of MC-LR (1, 10, 100, 500, 1000 and 5000 μg/L) on steroidogenesis were assessed in the H295R cells after 48 h. The contents of 17β-estradiol (E2) and testosterone (T) increased in a non-dose-dependent manner, which showed positive correlations with the expression of steroidogenic genes. In the in vivo assay, adult male zebrafish were exposed to 0.3, 1, 3, 10 and 30 μg/L MC-LR for 30 d. Similarly, E2 and T contents in the testis were increased, accompanied by extensive up-regulation of steroidogenic genes, especially cyp19a. Meanwhile, the percentage of spermatid in the testis declined. In the liver, the vtg1 gene was significantly up-regulated while both the transcriptional and protein levels of the estrogenic receptor (ER) declined. These results indicate that MC-LR induced non-dose-dependent estrogenic effects at environmental concentrations, which may result from steroidogenesis stimulation via a non-ER-mediated pathway. Our findings support a paradigm shift in the risk assessment of MC-LR from traditional toxicity to estrogenic risk, particularly at low concentrations, and emphasize the potential threat to the male reproductive capacity of wildlife in bloom areas.

Atrazine promotes immunomodulation by melanomacrophage centre alterations in spleen and vascular disorders in gills from Oreochromis niloticus

Atrazine is a herbicide that is banned in Europe but remains widely used on different types of crops in several countries in the American continent. Atrazine is known to be an endocrine disruptor and its effects on gonads have been extensively reported, but the toxic action on other organs is poorly documented. In this paper, we investigated the toxicity of atrazine on the gills and spleens of Nile tilapia (Oreochromis niloticus). The median lethal concentration (LC₅₀), capable of killing one-half of the test animals was calculated, and sublethal concentrations of atrazine were used in a semistatic and subchronic assay. The following four experimental groups were formed: control not exposed to atrazine, a group exposed to 1 ppm atrazine for 15 days, a group exposed to 2 ppm for 7 days, and a group exposed to 2 ppm for 15 days. The concentrations were verified during the study by high performance liquid chromatography. The gills and spleens were stained with hematoxylin and eosin and histopathological findings were made. The Perls technique was used on the spleens to identify hemosiderin, lipofuscin, and melanin pigments in the cells from melanomacrophage centres (MMCs). The spleens were submitted to proliferating cell nuclear antigen (PCNA) and inducible nitric oxide synthase (iNOS) immunohistochemistry, and morphometry was used to assess splenocyte proliferation and melanomacrophage iNOS expression. Finally, a colorimetric assay for caspase-3 was performed on the spleens to identify apoptosis. Vascular and structural alterations, such as venous sinus congestion, aneurysm, hemorrhage, pillar cell hypertrophy, disarrangement of secondary lamellae, and epithelial lifting were observed in the gills. The frequency of individuals with aneurysms was higher in the groups treated with 2 ppm than in other groups. Atrazine had an immunomodulatory effect on the spleen, observed by the alteration in the percentage of red and white pulp, alteration of the MMC area, changes in the melanomacrophage pigment content, slight iNOS suppression, decrease in splenocyte proliferation under 1 ppm atrazine, and increased caspase 3 activity under 2 ppm atrazine after 7 and 15 d. Such effects could compromise oxygenation and the immune response and, ultimately, the survival and fitness of the fish.

Extended fish short term reproduction assays with the fathead minnow and Japanese medaka: No evidence of impaired fecundity from exposure to atrazine

Short-term reproduction assays were conducted with fathead minnow (Pimephales promelas) and Japanese medaka (Oryzias latipes) to evaluate responses from atrazine exposure at environmentally relevant concentrations and above. Breeding groups of fish with multiple males and females were exposed to atrazine under flow-through conditions. Fathead minnows were exposed to mean measured concentrations of 1.0, 10, 26, 52, and 105 μg atrazine/L for 28 days. Medaka were exposed to mean measured concentrations of 9.4, 48, 74, 97, and 244 μg atrazine/L for 28 or 29 days. Fish were evaluated for survival, fecundity, fertility, total length, wet weight, secondary sex characteristics, gonadosomatic index (GSI) (P. promelas only), plasma or hepatic vitellogenin (VTG), and histopathology of gonads. General observations of health and behaviour were also conducted. There were no statistically significant effects (i.e., p < 0.05) of atrazine on survival, size, reproduction, behaviour, GSI, VTG, or secondary sex characteristics in either species at any exposure level. In fathead minnows, there were no histopathological findings associated with atrazine exposure in male fish, but there was an increased proportion of Stage 4.0 ovaries accompanied by an increase in proportion of Grade 3 post-ovulatory follicles in females of the 105 μg/L treatment group. Without a concomitant increase in oocyte atresia, neither of these findings are considered adverse for the health of the fish. In medaka, there were no significant effects of atrazine exposure on histopathology in either sex. These data support current weight-of-evidence assessments that atrazine does not cause direct adverse effects on fish reproduction at environmentally realistic concentrations.

Why goldfish? Merits and challenges in employing goldfish as a model organism in comparative endocrinology research

Goldfish has been used as an unconventional model organism to study a number of biological processes. For example, goldfish is a well-characterized and widely used model in comparative endocrinology, especially in neuroendocrinology. Several decades of research has established and validated an array of tools to study hormones in goldfish. The detailed brain atlas of goldfish, together with the stereotaxic apparatus, are invaluable tools for the neuroanatomic localization and central administration of endocrine factors. In vitro techniques, such as organ and primary cell cultures, have been developed using goldfish. In vivo approaches using goldfish were used to measure endogenous hormonal milieu, feeding, behaviour and stress. While there are many benefits in using goldfish as a model organism in research, there are also challenges associated with it. One example is its tetraploid genome that results in the existence of multiple isoforms of endocrine factors. The presence of extra endogenous forms of peptides and its receptors adds further complexity to the already redundant multifactorial endocrine milieu. This review will attempt to discuss the importance of goldfish as a model organism in comparative endocrinology. It will highlight some of the merits and challenges in employing goldfish as an animal model for hormone research in the post-genomic era.

Low atrazine dosages reduce sperm quality of Calomys laucha mice

Reproductive effects caused by the exposure to environmentally relevant dosages of atrazine on wild animals are poorly understood. This study evaluated the effects of three dosages of atrazine on sperm parameters of adult Calomys laucha males. Adult mice were orally exposed to dosages of 0 (water and vehicle control), 0.1, 1, and 10 mg/kg of animal weight for a 21-day period. Following exposure, analyses were performed to determine sperm motility parameters, plasma membrane integrity and fluidity, mitochondrial functionality, acrosome integrity, DNA damage, lipid peroxidation, and production of reactive oxygen species (ROS) in the sperm samples. Total and progressive motility were reduced in all dosages in comparison to control groups. Membrane integrity and mitochondrial functionality of sperm were reduced in all dosages, and the sperm membrane fluidity increased in the higher dosages of atrazine (1 and 10 mg/kg), in comparison with the vehicle control. A decrease in the acrosome integrity was noted at 10 mg/kg of atrazine, compared to the control groups. The integrity of DNA, ROS generation, and lipid peroxidation of sperm showed no significant differences when compared with the control groups. These results suggest that exposure to low dosages of atrazine can affect sperm parameters of Calomys laucha and therefore reduce the reproductive capacity of wild rodent species.

Fish as a model to assess chemical toxicity in bone

Environmental toxicology has been expanding as growing concerns on the impact of produced and released chemical compounds over the environment and human health are being demonstrated. Among the toxic effects observed in organisms exposed to pollutants, those affecting skeletal tissues (osteotoxicity) have been somehow overlooked in comparison to hepato-, immune-, neuro- and/or reproductive toxicities. Nevertheless, sub-lethal effects of toxicants on skeletal development and/or bone maintenance may result in impaired growth, reduced survival rate, increased disease susceptibility and diminished welfare. Osteotoxicity may occur by acute or chronic exposure to different environmental insults. Because of biologically and technically advantagous features - easy to breed and inexpensive to maintain, external and rapid rate of development, translucent larvae and the availability of molecular and genetic tools - the zebrafish (Danio rerio) has emerged in the last decade as a vertebrate model system of choice to evaluate osteotoxicity. Different experimental approaches in fish species and analytical tools have been applied, from in vitro to in vivo systems, from specific to high throughput methodologies. Current knowledge on osteotoxicity and underlying mechanisms gained using fish, with a special emphasis on zebrafish systems, is reviewed here. Osteotoxicants have been classified into four categories according to the pathway involved in the transduction of the osteotoxic effects: activation/inhibition of membrane and/or nuclear receptors, alteration of redox condition, mimicking of bone constituents and unknown pathways. Knowledge on these pathways is also reported here as it may provide critical insights into the development, production and release of future chemical compounds with none or low osteotoxicity, thus promoting the green/environmental friendly chemistry.

Evaluation of toxicological endpoints in female zebrafish after bisphenol A exposure

Given the importance of bisphenol A (BPA) as a xenoestrogen and its potential effects on human and animal health, we evaluated BPA exposure's short-term effects on follicular development, yolk protein vitellogenin (VTG) production and aromatase expression in female zebrafish. Histological modifications were observed along with increased presence of atretic follicles. Whole-body VTG concentration increased with the dose of BPA exposure. In contrast, expression of Cyp19a mRNA in the ovaries of BPA-exposed fish exhibited an apparent non-monotonic response curve, marked by downregulation at 1 μg/L BPA, upregulation at 10 μg/L BPA, and a return to downregulation at 100 μg/L BPA and higher doses. Ovaries only exhibited significant increases in follicular atresia and VTG concentration after exposure to 100 μg/L BPA and higher doses. Ovarian histopathology, aromatase Cyp19a transcript levels and whole-body VTG protein abundance may be good biomarkers for early detection of environmental BPA exposure.

Diel cyclic hypoxia alters plasma lipid dynamics and impairs reproduction in goldfish (Carassius auratus)

Diel cyclic hypoxia occurs with varying frequency and duration in freshwater habitats, yet little is known about its effects on reproduction of freshwater fishes. The present study shows that long-term exposure of goldfish (Carassius auratus) to cyclic hypoxia (0.8 ± 0.2 mg/l dissolved oxygen) for 9 h or more, per day, altered plasma lipid and sex steroid profiles, which in turn directly or indirectly suppressed ovarian growth and viable spermatozoa production. Hypoxia decreased total cholesterol and high density lipoprotein (HDL p < 0.05) and elevated triglycerides (TG; p < 0.05) in both sexes. Plasma steroid concentrations particularly of 17α-hydroxyprogesterone (17-HP), estradiol (E2), testosterone (T) in females, and T and 11-ketotestosterone (11-KT) in males were attenuated under diel hypoxic conditions. Intriguingly, both diel and continuous hypoxia elevated plasma E2 and vitellogenin levels in males. However, neither lipid nor steroid profiles recorded any variation in a dose-dependent manner in response to diel hypoxia. The reduced GSI, decreased number of tertiary oocytes, and motile spermatozoa in hypoxic fish clearly indicate suppression of gametogenesis. Thereby, prolonged diel cyclic hypoxia may affect valuable fishery resources and fish population structure by impairing reproductive performances and inducing estrogenic effects in males.

Fish short-term reproduction assay with atrazine and the Japanese medaka (Oryzias latipes)

Breeding groups of Japanese medaka (Oryzias latipes) were exposed to atrazine at measured concentrations of 0.6, 5.5, and 53 μg/L for 35 d. Evaluated endpoints included survival, fecundity, fertility, growth (weight and length), behavior, secondary sex characteristics (anal fin papillae), gonad histopathology, and hepatic vitellogenin. No statistically significant effects of atrazine exposure on survival and growth of medaka were noted during the test, and mean survival was ≥97.5% in all treatment groups on day 35. No significant effects of atrazine exposure on reproduction were observed. The number of mean cumulative eggs produced in the negative control and the 0.6, 5.5, and 53 μg/L treatment groups was 7158, 6691, 6883, and 6856, respectively. The mean number of eggs per female reproductive day was 40.9, 38.2, 40.2, and 39.2, respectively. There were also no dose-dependent effects on mean anal fin papillae counts among male fish or expression of vtg-II in males or females. In addition, atrazine exposure was not related to the developmental stage of test fish, with testes stages ranging from 2 to 3 in all groups and ovaries ranging from stage 2 to 2.5. Overall, exposure to atrazine up to 53 µg/L for 35 d did not result in significant, treatment-related effects on measured endpoints related to survival, growth, or reproduction in Japanese medaka. Environ Toxicol Chem 2017;36:2327-2334. © 2017 SETAC.

Persistent testicular structural and functional alterations after exposure of adult rats to atrazine

Atrazine is an endocrine disruptor affecting testicular steroidogenesis, and promoting testicular atrophy and 3β-HSD reduction. However, it remains unknown whether these effects are reversible or permanent. To address this issue was the aim of this study. Exposition of rats to 200mg/kg of atrazine resulted in transient increase in testicular weight, seminiferous tubules dilation and atrophy, and reduction in Leydig cell 3β-HSD. Testicular atrophy and 3β-HSD reduction were more pronounced after the recovery period of 75days. There was increase in aromatase expression after long-term exposure but it returned to control level after recovery. Moreover, there was increase in ED1^-/ED2⁺, ED1⁺/ED2⁺ and ED1⁺/ED2^- macrophages, in the recovery group. These macrophages were positive for 3β-HSD, thereby raising possibility of their involvement in steroidogenesis. These findings further emphasize the adverse effects of atrazine on male reproduction, highlighting that testicular damages may be irreversible even after a recovery period longer than the spermatogenic cycle.

Derivation of predicted no-effect concentration and ecological risk for atrazine better based on reproductive fitness

Atrazine (ATZ) is an herbicide most commonly used in China and other regions of the world. It is reported toxic to aquatic organisms, and frequently occurs at relatively high concentrations. Currently, ATZ has been proved to affect reproduction of aquatic species at much lower levels. So it is controversial to perform ecological risk assessment using predicted no-effect concentrations (PENCs) derived from traditional endpoints, which fail to provide adequate protection to aquatic organisms. In this study, PNECs of ATZ were derived based on six endpoints of survival, growth, behavior, biochemistry, genetics and reproduction. The PNEC derived from reproductive lesion was 0.044μg ATZ L^-1, which was obviously lower than that derived from other endpoints. In addition, a tiered ecological risk assessment was conducted in the Taizi River based on six PNECs derived from six categories of toxicity endpoints. Results of these two methods of ecological risk assessment were consistent with each other, and the risk level of ATZ to aquatic organisms reached highest as taking reproductive fitness into account. The joint probability indicated that severe ecological risk rooting in reproduction might exist 93.9% and 99.9% of surface water in the Taizi River, while 5% threshold (HC₅) and 1% threshold (HC₁) were set up to protect aquatic organisms, respectively. We hope the present work could provide valuable information to manage and control ATZ pollution.

Effect of methomyl on sex steroid hormone and vitellogenin levels in serum of male tilapia (Oreochromis niloticus) and recovery pattern

Tilapia were exposed to sub-lethal concentrations of 0, 0.2, 2, 20 or 200 μg/L for 30 days, then transferred to methomyl-free water for 18 days. E₂ , T, 11-KTand VTG in serum were examined. There were no significant changes in all the parameters in serum of tilapia exposed to 0.2 μg/L and 2 μg/L methomyl compared to the control. However, 20 μg/L and 200 μg/L have the potential to disrupt the endocrine system of male tilapia, as shown by its ability to increase VTG and E₂ and decrease T and 11-KT in serum. Thus it would appear the no observed adverse effect level for sexual steroid hormones of methomyl is lower than 2 μg/L. Recovery data showed that the effects produced by 20μg/L were reversible but not at 200μg/L. Furthermore, the sensitivity of above parameters to methomyl followed the order of VTG>E₂ >11-KT>T>GSI, suggesting VTG being the better biomarkers.

Effects of atrazine and chlorothalonil on the reproductive success, development, and growth of early life stage sockeye salmon (Oncorhynchus nerka)

The effects of 2 currently used commercial pesticide formulations on Pacific sockeye salmon (Oncorhynchus nerka), from fertilization to emergence, were evaluated in a gravel-bed flume incubator that simulated a natural streambed. Embryos were exposed to atrazine at 25 µg/L (low atrazine) or atrazine at 250 µg/L (high atrazine) active ingredient (a.i.), and chlorothalonil at 0.5 µg/L (low chlorothalonil) or chlorothalonil at 5 µg/L a.i. (high chlorothalonil) and examined for effects on developmental success and timing, as well as physical and biochemical growth parameters. Survival to hatch was reduced in the high chlorothalonil group (55% compared with 83% in controls), accompanied by a 24% increase in finfold deformity incidence. Reduced alevin condition factor (2.9-5.4%) at emergence and elevated triglyceride levels were seen in chlorothalonil-exposed fish. Atrazine exposure caused premature hatch (average high atrazine time to 50% hatch [H50] = 100 d postfertilization [dpf]), and chlorothalonil exposure caused delayed hatch (high chlorothalonil H50 = 108 dpf; controls H50 = 102 dpf). All treatments caused premature emergence (average time to 50% emergence [E50]: control E50 = 181 dpf, low chlorothalonil E50 = 175 dpf, high chlorothalonil E50 = 174 dpf, high atrazine E50 = 175 dpf, low atrazine E50 = 174 dpf), highlighting the importance of using a gravel-bed incubator to examine this subtle, but critical endpoint. These alterations indicate that atrazine and chlorothalonil could affect survival of early life stages of sockeye salmon in the wild. Environ Toxicol Chem 2017;36:1354-1364. © 2017 SETAC.

Assessing the potential for trace organic contaminants commonly found in Australian rivers to induce vitellogenin in the native rainbowfish (Melanotaenia fluviatilis) and the introduced mosquitofish (Gambusia holbrooki)

In Australia, trace organic contaminants (TrOCs) and endocrine active compounds (EACs) have been detected in rivers impacted by sewage effluent, urban stormwater, agricultural and industrial inputs. It is unclear whether these chemicals are at concentrations that can elicit endocrine disruption in Australian fish species. In this study, native rainbowfish (Melanotaenia fluviatilis) and introduced invasive (but prevalent) mosquitofish (Gambusia holbrooki) were exposed to the individual compounds atrazine, estrone, bisphenol A, propylparaben and pyrimethanil, and mixtures of compounds including hormones and personal care products, industrial compounds, and pesticides at environmentally relevant concentrations. Vitellogenin (Vtg) protein and liver Vtg mRNA induction were used to assess the estrogenic potential of these compounds. Vtg expression was significantly affected in both species exposed to estrone at concentrations that leave little margin for safety (p<0.001). Propylparaben caused a small but statistically significant 3× increase in Vtg protein levels (p=0.035) in rainbowfish but at a concentration 40× higher than that measured in the environment, therefore propylparaben poses a low risk of inducing endocrine disruption in fish. Mixtures of pesticides and a mixture of hormones, pharmaceuticals, industrial compounds and pesticides induced a small but statistically significant increase in plasma Vtg in rainbowfish, but did not affect mosquitofish Vtg protein or mRNA expression. These results suggest that estrogenic activity represents a low risk to fish in most Australian rivers monitored to-date except for some species of fish at the most polluted sites.

Immunotoxic effects of atrazine and its main metabolites at environmental relevant concentrations on larval zebrafish (Danio rerio)

Atrazine (ATZ) and its main metabolites, i.e., diaminochlorotriazine (DACT), deisopropylatrazine (DIP), and deethylatrazine (DE), have been widely detected in surface water around the world. In the present study, to determine their immunotoxic effects, zebrafish during the early developmental stage were exposed to ATZ and its main metabolites at environmental concentrations (30, 100, 300 μg L^-1). It was observed that ATZ, DACT, DIP and DE selectively induced the transcription of immunotoxic related genes including Tnfα, Il-1β, Il-6, Il-8, Cxcl-clc and Cc-chem in larval zebrafish. Pretreatment with ATZ and its metabolites also changed the immune response of larval zebrafish to LPS and E. coli challenge, which was indicated by the alternation in the mRNA levels of some cytokines. In addition, 300 μg L^-1 ATZ and DACT exposure could also increase the release of tryptase into water, indicating that they increased the anaphylactoid reaction in the larval zebrafish. According to these results, both of ATZ and its metabolites exposure could cause the immunotoxicity in larval zebrafish. Thus, we thought that the ecological risks of the metabolites of ATZ on aquatic organisms could not be ignored.

Responses and recovery pattern of sex steroid hormones in testis of Nile tilapia (Oreochromis niloticus) exposed to sublethal concentration of methomyl

Tilapia were exposed to sublethal methomyl concentrations of 0, 0.2, 2, 20 or 200 μg/L for 30 days, and then transferred to methomyl-free water for 18 days. The sexual steroid hormones 17β-estradiol (E2), testosterone (T), and 11-ketotestosterone (11-KT) in tilapia testes were examined at 0, 6, 12, 18, 24 and 30 days after methomyl exposure, and at 18 days after fish were transferred to methomyl-free water. There were no significant changes in the hormone parameters in testes of tilapia exposed to low concentration 0.2 and 2 μg/L methomyl compared with the controls. However, high concentration 20 and 200 μg/L methomyl had the potential to disrupt the endocrine system of male tilapia, as shown by an increase in E₂ and a decrease in T and 11-KT in the testes. Thus, it would appear that the 2 μg/L methomyl might be considered the no-observed-adverse-effect level. Recovery data showed that the effects produced by the lower concentration of 20 μg/L were reversible but the effects were not reversible at the higher concentration of 200 μg/L.

Mechanistic study of chlordecone-induced endocrine disruption: Based on an adverse outcome pathway network

The adverse outcome pathway (AOP) framework could be helpful for chemical risk assessment and mechanistic research. The aim of the present study was to unravel the mechanism of chlordecone-induced endocrine disruption by illustrating the main molecular initiating event (MIE)/perturbations responsible for the observed effects. In silico simulations were performed to predict the MIE(s), and the results pointed to agonistic interaction with estrogen receptors (ERα, ERβ), androgen receptor (AR), cytochrome P450 (CYP19A) by chlordecone. In vivo endocrine disruptions were evaluated in rare minnow (Gobiocypris rarus) exposed to 0.01, 0.1, 1 and 10 μg L(-1) chlordecone from 2 h post-fertilization until sexually mature. In the females, increases of vitellogenin (vtg) mRNA levels in liver and gonad, plasma estradiol (E2), testosterone (T) and E2/T, and renalsomatic index confirmed the role of agonism of ER and CYP19A as MIEs, but the decreased gonadosomatic index, degenerated ovaries as well as the feed-forward response pointed to other potential but important MIEs and corresponding AOPs. In the males, increased E2/T ratio, increased testis vtg mRNA levels and occurrence of intersex confirmed the roles of agonism of ERα and CYP19A as main MIEs in chlordecone-induced endocrine disruptions. Our results also fetches out the limit of AOPs in predicting the adverse outcomes and explaining the mechanism of chemicals at present, thus reflected a critical need for expanding AOPs and AOP network before using it in chemical risk assessment.

Gene expression profiles in testis of developing male Xenopus laevis damaged by chronic exposure of atrazine

As a widely used herbicide, atrazine (AZ) has been extensively studied for its adverse effects on the reproductive system, especially feminization in male animals. However, the relationship of gene expression changes and associated toxicological endpoints remains unclear. In this study, developing Xenopus laevis tadpoles were exposed to concentration of AZ at 0.1, 1, 10 or 100 μg/L continuously. Compared with froglets in the control group, there were no significant differences in body length, body weight, liver weight and hepatosomatic index (HSI) of males in groups treated with AZ for 90 d. At 100 μg/L AZ treatment caused a significant reduction of gonad weight and gonadosomatic index (GSI) of males (p < 0.01). In addition, AZ at all dose levels caused testicular degeneration, especially in froglets from the groups with 0.1 and 100 μg/L which exhibited U-shaped dose-response trend. We further investigated the gene expression changes associated with the testicular degeneration induced by AZ. We found that the expression of 1165 genes was significantly altered with 616 upregulated and 549 downregulated compared to the expression profile of the control animals. KEGG analysis showed that genes which were significantly affected by AZ are mainly involved in arginine and proline metabolism, cell cycle, riboflavin metabolism, spliceosome, base excision repair and progesterone-mediated oocyte maturation pathway. Our results show that AZ may affect reproductive and immune systems by interference with the related gene expression changes during the male X. laevis development. The findings may help to clarify the feminization mechanisms of AZ in male X. laevis.

Evaluation of potential mechanisms of atrazine-induced reproductive impairment in fathead minnow (Pimephales promelas) and Japanese medaka (Oryzias latipes)

Atrazine has been implicated in reproductive dysfunction of exposed organisms, and previous studies documented decreased egg production in Japanese medaka (Oryzias latipes) and fathead minnows (Pimephales promelas) during 30-d to 38-d exposures to 0.5 µg/L, 5 µg/L, and 50 µg/L atrazine. The authors evaluated possible mechanisms underlying the reduction in egg production. Gene expression in steroidogenesis pathways and the hypothalamus-pituitary-gonad axis of male and female fish was measured. Atrazine did not significantly induce gonad aromatase (cyp19a1a) expression. An atrazine-induced shift in the number of females in an active reproductive state was observed. Expression of the egg maturation genes vitellogenin 1 (vtg1) and zona pellucida glycoprotein 3.1 (zp3.1) in medaka females was correlated and had a bimodal distribution. In both species, females with low vtg1 or zp3.1 expression also had low expression of steroidogenesis genes in the gonad, estrogen receptor in the liver, and gonadotropins in the brain. In the medaka, the number of females per tank that had high expression of zp3.1 was significantly correlated with egg production per tank. The number of medaka females with low expression of zp3.1 increased significantly with atrazine exposure. Thus, the decline in egg production observed in response to atrazine exposure may be the result of a coordinated downregulation of genes required for reproduction in a subset of females. Environ Toxicol Chem 2016;35:2230-2238. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and, as such, is in the public domain in the United States of America.