Maternal transfer of xenobiotics and effects on larval striped bass in the San Francisco Estuary

Ecotoxicological impact of the fungicide tebuconazole on fish: a historical review, global trends and challenges

Tebuconazole (TBZ) is a triazole fungicide broadly used to control fungal diseases in agricultural crops, fruit-bearing plants and forestry plantations. However, its increasing use and release into aquatic environments has raised concerns about its hazardous effects on the health of fish. Thus, the aim of the present study was to review the scientific literature on the ecotoxicological effects of TBZ and TBZ-based commercial formulations on fish. Historical review data (publication year and geographical distribution), TBZ type, experimental design, fish species, habitat, life stage, tissue/organ, lethal concentration (LC50), concentration and exposure time, biomarkers and effects were compiled and critically analyzed. Studies were mainly conducted with freshwater species at adult and larval stages, whereas no data were find for marine fish species. Zebrafish, (Danio rerio) was the most assessed species. Both TBZ and TBZ-based commercial formulations induced oxidative stress, endocrine disruption, neurotoxicity, genotoxicity, histopathologies, behavior impairments and mortality on fish. TBZ can induce synergistic and antagonistic effects on fish when it is combined to other pesticides. Overall, the current study has shown the potential hazardous effects of TBZ and TBZ-based commercial formulations on the health of fish.

Exposure of Parental Zebrafish to Difenoconazole throughout Their Life Cycle May Lead to Developmental Toxicity in the F1 Generation through Epigenetic Changes in Gametes, Impaired Nutrient Supply from the Ovum, and Maternal Transfer of Difenoconazole

Difenoconazole is a widely used agricultural fungicide that has been frequently detected in aquatic environments. Given its stable presence in aquatic environments, long-term exposure of wild fish may pose a risk to offspring embryonic development. This study demonstrated that exposure of zebrafish to environmental concentrations of difenoconazole throughout their life cycle resulted in abnormal development of offspring embryos/larvae, including decreased heart rate, delayed hatching, increased malformation rate, shortened body length, and increased mortality. These changes were significantly correlated with the affected apoptosis, autophagy, energy metabolism and MAPK signaling pathways in F1 generation. This transgenerational toxic effect results from epigenetic alterations in gametes, impaired nutrient supply from the ovum, and maternal transfer of difenoconazole. After exposure to difenoconazole, the development of female fish offspring was affected more than that of male fish offspring, which was mainly caused by the impaired nutrient supply from the ovum and the maternal transfer of difenoconazole. Because this transgenerational developmental toxicity was observed at environmental levels, difenoconazole may pose a threat to the survival of wild larvae and therefore a risk to wild fish populations.

Maternal Exposure to Environmentally Relevant Concentrations of Tris(2,4-di-tert-butylphenyl) Phosphate-Induced Developmental Toxicity in Zebrafish Offspring via Disrupting foxO1/ripor2 Signaling

Abnormal development and mortality in early life stages pose significant threats to the growth and continuation of fish populations. Tris(2,4-di-tert-butylphenyl) phosphate (TDtBPP) is a novel organophosphate ester contaminant detected in natural waters. However, the potential effects of maternal exposure to TDtBPP on the early development of offspring embryos in fish remain unknown. Here, 30-day-old zebrafish were exposed to TDtBPP at 0, 50, 500, or 5000 ng/L for 180 days, and the exposed females were spawned with unexposed males. TDtBPP accumulation was detected in offspring embryos, accompanied by an increased malformation rate and mortality. The developmental abnormality of offspring embryos was identified to originate from the gastrula stage. Furthermore, based on transcriptome analysis, the down-regulation of RHO family interacting cell polarization regulator 2 gene (ripor2) was considered as a key toxic event, and this was confirmed in the subsequent knockdown experiment. Moreover, molecular docking studies and forkhead box O1 (foxO1) transcription factor inhibitor (AS1842856) exposure experiments demonstrated that the blockade of foxO1 transcriptional regulation was responsible for the decreased expression of ripor2. The results of this study demonstrated that the occurrence of developmental malformation and mortality in zebrafish offspring embryos following maternal TDtBPP exposure were triggered by the blockade of foxO1 transcriptional regulation and the consequent down-regulation of ripor2.

6PPD-quinone affects the photosynthetic carbon fixation in cyanobacteria by extracting photosynthetic electrons

Photosynthetic carbon fixation by cyanobacteria plays a pivotal role in the global carbon cycle but is threatened by environmental pollutants. To date, the impact of quinones, with electron shuttling properties, on cyanobacterial photosynthesis is unknown. Here, we present the first study investigating the effects of an emerging quinone pollutant, i.e., 6PPD-Q (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone), on the cyanobacterium Synechocystis sp. over a 400-generation exposure period. Synechocystis sp. exhibited distinct sequential phases, including hormesis, toxicity, and eventual recovery, throughout this exposure. Extensive evidence, including results of thylakoid membrane morphological and photosynthetic responses, carbon fixation rate, and key gene/protein analyses, strongly indicates that 6PPD-Q is a potent disruptor of photosynthesis. 6PPD-Q accepts photosynthetic electrons at the plastoquinone QB site in photosystem II (PSII) and the phylloquinone A1 site in PSI, leading to a sustained decrease in the carbon fixation of cyanobacteria after an ephemeral increase. This work revealed the specific mechanism by which 6PPD-Q interferes with photosynthetic carbon fixation in cyanobacteria, which is highly important for the global carbon cycle.

Reduced Freshwater Mussel Juvenile Production as a Result of Agricultural and Urban Contaminant Mixture Exposures

Freshwater mussels provide invaluable ecological services but are threatened by habitat alteration, poor water quality, invasive species, climate change, and contaminants, including contaminants of emerging concern (CECs). Contaminants of emerging concerns are well documented in aquatic environments, including the Great Lakes Basin, but limited information is available on how environmentally relevant mixtures affect freshwater mussel biology throughout their varied life stages. Our main goal was to assess mussels' reproductive output in response to exposure to agricultural and urban CEC mixtures during glochidial development through juvenile transformation and excystment focusing on how exposure duration and treatment affect: (1) the number of glochidia prematurely released by brooding females, (2) glochidial transformation through host-fish excystment, and (3) the number of fully metamorphosed juveniles able to continue the lifecycle. Mussels and host fish were exposed to either a control water (CW), control ethanol (CE), agriculture CEC mixture (AM), or urban CEC mixture (UM) for 40 and 100 days. We found no effect from treatment or exposure duration on the number of glochidia prematurely released. Fewer partially and fully metamorphosed AM juveniles were observed during the 100-day exposure, compared with the 40-day. During the 40-day exposure, CW produced more fully metamorphosed individuals compared with CE and UM, but during the 100-day exposure AM produced more fully metamorphosed individuals compared with the CW. There was reduction in fully metamorphosed juveniles compared with partially metamorphosed for CE and UM during the 40-day exposure, as well as in the CW during the 100-day exposure. These results will be important for understanding how mussel populations are affected by CEC exposure. The experiments also yielded many insights for laboratory toxicology exposure studies. Environ Toxicol Chem 2024;00:1-14. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Embryonic exposure to environmentally relevant levels of tributyltin affects embryonic tributyltin bioaccumulation and the physiological responses of juveniles in cuttlefish (Sepia pharaonis)

Tributyltin (TBT) is a typical organic pollutant that persists in aquatic sediments due to its wide usage as an antifouling fungicide during the past few decades. Despite increased awareness of the serious negative consequences of TBT on aquatic species, studies on the effects of TBT exposure on cephalopod embryonic development and juvenile physiological performance are scarce. To investigate the lasting effects of TBT toxicity on Sepia pharaonis from embryo to hatchling, embryos (gastrula stage, 3-5 h post fertilization) were exposed to four levels of TBT until hatching: 0 (control), 30 (environmental level), 60, and 120 ng/L. Subsequently, juvenile growth performance endpoints and behavioral alterations were assessed over 15 days post-hatching. Egg hatchability was significantly reduced and embryonic development (i.e., premature hatching) was accelerated in response to 30 ng/L TBT exposure. Meanwhile, TBT-induced alterations in embryonic morphology primarily included yolk-sac lysis, embryonic malformations, and uneven pigment distributions. During the pre-middle stage of embryonic development, the eggshell serves as an effective barrier to safeguard the embryo from exposure to 30-60 ng/L TBT, according to patterns of TBT accumulation and distribution in the egg compartment. However, even environmental relevant levels of TBT (30 ng/L) exposure during embryonic development had a negative impact on juvenile behavior and growth, including slowing growth, shortening eating times, causing more irregular movements, and increasing inking times. These findings indicate that after TBT exposure, negative long-lasting effects on S. pharaonis development from embryo to hatchling persist, suggesting that long-lasting toxic effects endure from S. pharaonis embryos to hatchlings.

Growth inhibition of offspring larvae caused by the maternal transfer effects of tetrabromobisphenol A in zebrafish

Tetrabromobisphenol A (TBBPA) is an industrial chemical and the most widely used brominated flame retardant, and has raised environmental health concerns. However, the maternal transfer toxicity of TBBPA is less studied in fish despite its frequency in the water environment, and limited evidence exists to confirm the major contributing factors. In this study, we performed a 28-d experiment on female and male zebrafish exposed to TBBPA (0, 5, 50, and 500 μg/L), and shortened body length of offspring larvae was observed at the maximum exposure concentration. By cross-mating control and exposed zebrafish (male or female), our results showed that the observed growth inhibition in the progeny was attributed to the maternal transfer effect. Although 28-d exposure resulted in the existence of TBBPA in ovaries and ova, the maternal transfer of TBBPA was not responsible for the shortened body length of offspring larvae, as evidenced through TBBPA embryo microinjection. Moreover, proteomic analyses in ova indicated that the abundance of apolipoproteins (apoa1, apoa1b, apoa2, apoa4b, and apoc1) was significantly downregulated in the ova, which may be partially responsible for the shortened body length of offspring larvae. Interestingly, these proteins did not differentially express in the ovaries. Therefore, our results demonstrate that TBBPA exposure disturbed maternal protein transfer from the ovaries to the ova, providing novel insights into the underlying maternal transfer effects.

Impacts of chemical stress, season, and climate change on the flounder population of the highly anthropised Seine estuary (France)

The main objective of this study was to improve our knowledge on the responses of fish populations to multistress (diffuse pollution and warming waters) in estuaries. Adult flounders were caught in two estuaries in the Eastern English Channel: the heavily polluted Seine estuary vs the moderately contaminated Canche estuary. Fish samplings were conducted in January just before the reproduction period, and in July when gonads were at rest. The overall rise in coastal winter water temperatures detected over the Channel impairs the flounder's phenology of reproduction in the two estuaries, inducing a delay of maturation process and probably also spawning. The higher liver histopathology index in Seine vs Canche could be the consequence of the fish exposition to a complex cocktail of contaminants in a strongly industrialized estuary. Higher levels of neurotoxicity, gill lipid peroxidation, and liver EROD activity were observed in Seine vs Canche. Furthermore, a possible impairment in mitochondrial metabolism was suggested in the Seine flounder population. We confirmed in this study the potential role of two membrane lipids (sphingomyelin and phosphatidylserine) in the resistance towards oxidative stress in Seine and Canche. Finally, we suggest that the Seine flounder population (and possibly the connected Eastern English Channel flounder populations over the French Coast) could be seriously impacted in the future by multistress: higher winter temperatures and chemical contamination.

Feminizing effects of ethinylestradiol in roach (Rutilus rutilus) populations with different estrogenic pollution exposure histories

Experimental exposures aimed at assessing the risks posed by estrogens in waste-water treatment work (WwTW) effluents to fish populations have rarely considered whether populations differ in their sensitivity to estrogenic compounds. This is despite evidence that selection at genes involved in the estrogen response has occurred in wild populations, and evidence that genotype can influence estrogen-response. In this study we compare the effects of a two-year exposure to a low measured concentration (1.3 ng/L) of ethinylestradiol (EE2) on the sexual development of roach (Rutilus rutilus) whose parental generation was sampled from two river stretches heavily contaminated with WwTW effluent and from two without any known WwTW effluent contamination. Exposure to EE2 significantly reduced the proportion of genetic males and induced a range of feminized phenotypes in males. Significantly, exposure also increased the proportion of genetic females with vitellogenic oocytes from 51 to 96%, raising the possibility that estrogen pollution could impact populations of annually spawning fish species through advancing female reproduction by at least a year. However, there was no evidence that river origin affected sensitivity to estrogens in either sex. Thus, we conclude that chronic exposure to low level EE2 has reproductive health outcomes for both male and female roach, but we find no evidence that the nature or magnitude of the response is affected by the population origin.

Effects of dietary 2-(2H-benzotriazol-2-yl)-4-methylphenol (UV-P) exposure on Japanese medaka (Oryzias latipes) in a short-term reproduction assay

Benzotriazole ultraviolet stabilizers (BZT-UVs) are added to various products to prevent damage caused by UV light and have emerged as contaminants of concern. Although BZT-UVs are detected in aquatic biota globally, few studies have assessed their potential toxic effects. The objective of the present study was to assess effects of 2-(2H-Benzotriazol-2-yl)-4-methylphenol (UV-P) on reproductive success of Japanese medaka (Oryzias latipes) in a standard 21-day reproduction assay. Japanese medaka were exposed to dietary UV-P at concentrations of 0, 36, 158, and 634 ng UV-P/g food, for a total of 28 days which included 7 days of exposure prior to the start of the 21-day reproduction assay. No significant effect on egg production or fertilization success was observed. Abundances of transcripts of erα, vtgI, cyp1a, or cyp3a4 were not significantly different in livers from male or female fish exposed to UV-P. However, abundances of transcripts of cyp11a and cyp19a were significantly lower in gonads from female fish. There was a trend of increasing concentrations of E2 and a non-significant increase of T in the 634 ng/g treatment in plasma from female fish exposed to UV-P. Concentrations of 11-KT were unchanged in plasma from males exposed to UV-P. These responses suggest weak perturbation of steroidogenesis, consistent with an antiandrogenic mode of action. However, this perturbation was insufficient to impair reproductive performance. Metabolomics analysis of female livers suggests altered concentrations of various metabolites and biological pathways, including glutathione metabolism, suggesting that UV-P might cause responses related to oxidative stress or phase II metabolism. However, metabolomics revealed no obvious mechanism of toxicity. Overall, results of this study indicate that dietary exposure to UV-P up to 634 ng/g food does not significantly impact reproductive performance of Japanese medaka but impacts on steroidogenesis could indicate a potential mechanism of toxicity which might lead to reproductive impairment in more sensitive species.

Emerging Midges Transport Pesticides from Aquatic to Terrestrial Ecosystems: Importance of Compound- and Organism-Specific Parameters

Emerging aquatic insects have the potential to retain aquatic contaminants after metamorphosis, potentially transporting them into adjacent terrestrial food webs. It is unknown whether this transfer is also relevant for current-use pesticides. We exposed larvae of the nonbiting midge, Chironomus riparius, to a sublethal pulse of a mixture of nine moderately polar fungicides and herbicides (logK_ow 2.5-4.7) at three field relevant treatment levels (1.2-2.5, 17.5-35.0, or 50.0-100.0 μg/L). We then assessed the pesticide bioaccumulation and bioamplification over the full aquatic-terrestrial life cycle of both sexes including the egg laying of adult females. By applying sensitive LC-MS/MS analysis to small sample volumes (∼5 mg, dry weight), we detected all pesticides in larvae from all treatment levels (2.8-1019 ng/g), five of the pesticides in the adults from the lowest treatment level and eight in the higher treatment levels (1.5-3615 ng/g). Retention of the pesticides through metamorphosis was not predictable based solely on pesticide lipophilicity. Sex-specific differences in adult insect pesticide concentrations were significant for five of the pesticides, with greater concentrations in females for four of them. Over the duration of the adults' lifespan, pesticide concentrations generally decreased in females while persisting in males. Our results suggest that a low to moderate daily dietary exposure to these pesticides may be possible for tree swallow nestlings and insectivorous bats.

Bioaccumulation and maternal transfer of two understudied DDT metabolites in wild fish species

While the secondary metabolites of DDT such as 2,2-bis(chlorophenyl)-1-chloroethylene (DDMU) and 2,2-bis(chlorophenyl)methane (DDM) have been detected in the environment for several decades, knowledge is extremely limited on their bioaccumulation characteristics. Here, we reported the bioaccumulation and maternal transfer of p,p'-DDMU and p,p'-DDM in two wild fishes, i.e., the northern snakehead (Channa argus) and crucian carp (Carassius auratus), from a DDT contaminated site in South China. The hepatic concentrations of p,p'-DDMU and p,p'-DDM in the fish were up to 549 and 893 ng/g lipid weight, contributing 5.3% and 3.2% in average to ΣDDXs (the sum concentrations of DDT and its 6 metabolites), respectively. The residues of p,p'-DDMU and p,p'-DDM in the fish exhibited interspecific and intraspecific variations, resulting from the differences in lipid content, sex, and body sizes (length and mass) between or within species. Both p,p'-DDMU and p,p'-DDM were consistently detected in the fish eggs, demonstrating their maternal transfer in female fish. The mean eggs to liver lipid-normalized concentration (E/L) ratios of p,p'-DDMU and p,p'-DDM were 0.98 and 1.77 in the northern snakehead, 0.35 and 0.01 in crucian carp, respectively; which were comparable to or even exceeded those of DDT and its major metabolites calculated in the same individual. Statistical analyses of the data showed that the E/L ratios were positively correlated with body sizes of the fish, but negatively correlated with the hepatic concentrations of p,p'-DDMU and p,p'-DDM in females; suggesting the influences of fish sizes and the mother body residues on their maternal transfer efficiencies.

Venlafaxine deposition in the zygote disrupts the endocrine control of growth in juvenile zebrafish

The antidepressant venlafaxine can be found at levels nearing μg/L in waterways receiving municipal wastewater effluent, exposing non-target organisms, such as fish, to this chemical. We showed previously that zygotic exposure to venlafaxine alters neurodevelopment and behaviour in zebrafish (Danio rerio) larvae. Here, we tested the hypothesis that the zygotic deposition of venlafaxine disrupts endocrine pathways related to growth in zebrafish. This was carried out by microinjecting embryos (1-4 cell stage) with either 0, 1, or 10 ng venlafaxine. Zygotic venlafaxine deposition reduced the growth of fish after 30 days post-fertilization. Specific growth rate was particularly impacted by 1 ng venlafaxine. This growth retardation corresponded with the disruption of endocrine pathways involved in growth and metabolism. Venlafaxine exposed embryos displayed reduced transcript abundance of key genes involved in anabolic hormone action. Early-life venlafaxine exposure also reduced whole-body insulin and glucose content in juveniles. Target-tissue glucose uptake measurements indicated that high venlafaxine deposition preferentially increased glucose uptake to the brain. Zygotic venlafaxine did not affect feed intake nor altered the transcript abundance of key feeding-related peptides. Taken together, zygotic venlafaxine deposition compromises zebrafish growth by disrupting multiple endocrine pathways, and this study has identified key markers for potential use in risk assessment.

Exposure of adult zebrafish (Danio rerio) to Tetrabromobisphenol A causes neurotoxicity in larval offspring, an adverse transgenerational effect

Tetrabromobisphenol A (TBBPA) is one of the most extensively used brominated flame retardants and is universally detected in the environment. However, information related to its transgenerational toxicity is sparse. Using zebrafish as a study model, adult fish were exposed to TBBPA at different concentrations (0, 3, 30, or 300 μg/L) for 42 d and then, the exposed adults were spawned in TBBPA-free water. The neurobehavior of adults and larval offspring was evaluated, and the levels of thyroxine (T4), triiodothyronine (T3) and neurotransmitters (acetylcholine, dopamine and gamma-aminobutyric acid) were quantified in larvae and embryos. Our results showed that TBBPA was detected in embryo and the locomotor activity of larval offspring was significantly reduced, suggesting that TBBPA can transfer to offspring and result in neurotoxicity in larval offspring. Furthermore, a reduction in T3 levels was observed in both the larvae and embryos. We also found a significantly decreased content of dopamine in larval offspring, accompanied by downregulated mRNA expression of rdr2b and drd3. Our results demonstrated that TBBPA can be transferred to offspring embryos, and subsequently induce neurotoxicity in larval offspring by affecting the amount of T3 transferred from the parents to embryos and the production of dopamine in larvae.

Maternal Transfer of 2-Ethylhexyl Diphenyl Phosphate Leads to Developmental Toxicity Possibly by Blocking the Retinoic Acid Receptor and Retinoic X Receptor in Japanese Medaka (Oryzias latipes)

2-Ethylhexyl diphenyl phosphate (EHDPP) has been detected in wild fish with high concentrations, which may pose a risk in the embryo development considering its potential maternal transfer. In this study, EHDPP was demonstrated to elicit antagonistic activity to medaka retinoic acid receptor (mRAR) and retinoic X receptor (mRXR) with 50% inhibitory concentration of 18 and 36 μM, respectively. After adult female medaka were exposed to EHDPP at 156, 405, and 1161 ng/L for 35 days, the embryonic EHDPP concentrations (364-4824 ng/g lipid weight (lw)) were higher than those in the maternal tissues (15.0-4166 ng/g lw), showing notable maternal transfer. The embryonic concentration of EHDPP decreased limitedly during 1-2 day post-fertilization (dpf, the main developmental window of eye) but then decreased sharply after 2 dpf. The transcript abundance of cyp26a1 was inhibited and subsequent increasing embryonic all-trans RA level was observed in embryos, showing RAR/RXR antagonistic activity. These results may specifically contribute to the increased eye deformity incidences in all exposure groups (up to 8.0%; 51/637) relative to the control (1.0%, 7/733). The response behavior of the larvae to light stimulation was impaired in a dose-dependent manner, demonstrating a vision disorder. Because such developmental toxicities were observed at the environmental level, EHDPP may pose a threat to the survival of wild larvae and therefore a population risk for wild fish.

Maternal transfer of polychlorinated biphenyls in Pacific sand lance (Ammodytes personatus), Puget Sound, Washington

We measured polychlorinated biphenyls (PCBs) in multiple age and size classes of Pacific sand lance (Ammodytes personatus), including eggs, young-of-the year, and adults to evaluate maternal transfer as a pathway for contaminant uptake and to add to the limited information on the occurrence of PCBs in sand lance in Puget Sound. Sampling was replicated at an urban embayment (Eagle Harbor) and a state park along an open shoreline (Clayton Beach), during spring and fall. Lipid-normalized concentrations of PCBs in sand lance at Eagle Harbor were 5-11 times higher than PCB concentrations in comparable samples at Clayton Beach. This was true for every life stage and size class of sand lance, including eggs removed from females. The same trend was observed in environmental samples. In Eagle Harbor, PCB concentrations in unfiltered water (0.19 ng/L), sieved (<63 μm) nearshore bed sediments (0.78 ng/g dw) and suspended particulate matter (1.69 ng/g dw) were 2-3 times higher than equivalent samples from near Clayton Beach. Sand lance collected in the fall (buried in sediment during presumed winter dormancy) had lower lipid content and up to four times higher PCB concentrations than comparably sized fish collected in the spring (by beach seine). Lipid content was 5-8% in spring fish and was reduced in fall fish (1-3%). Male sand lance had higher PCB concentrations than comparable females. All egg samples contained PCBs, and the lipid normalized egg/female concentration ratios were close to 1 (0.87-0.96), confirming that maternal transfer of PCBs occurred, resulting in sand lance eggs and early life stages being contaminated with PCBs even before they are exposed to exogenous sources. These life stages are prey for an even wider range of species than consume adult sand lance, creating additional exposure pathways for biota and increasing the challenges for mitigation of PCBs in the food web.

Zygotic exposure to venlafaxine disrupts cortisol stress axis activity in multiple generations of zebrafish

Ubiquitous use of antidepressants has resulted in increased concentrations of these pharmaceuticals in waterways receiving municipal wastewater effluent. Amongst these, venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is commonly found at concentrations surpassing 1 ppb in surface waters. We recently showed that the deposition of venlafaxine in zebrafish (Danio rerio) embryos impacts neural development in the hypothalamus, suggesting the possibility of neuroendocrine disruptions due to this antidepressant. Here, we tested the hypothesis that early developmental exposure to venlafaxine disrupts the long-term functioning of the hypothalamus-pituitary-interrenal (HPI) axis in zebrafish. Embryos (1-4 cell stage) were injected with either 0, 1, or 10 ng venlafaxine, and the ontogeny of cortisol content, as well as changes in cortisol levels following a stressor in larvae and adults were assessed across 3 generations. Zygotic venlafaxine exposure did not affect the ontogeny of cortisol production, but there was a disruption in the cortisol response to stressor exposure, which was also evident in multiple generations. In the F₀ generation, venlafaxine exposure did not affect cortisol levels in response to stressor exposure in larvae, but adult females, and not males, showed an attenuated cortisol response compared to control fish. This reduction in cortisol levels in the females was rescued by stimulation with adrenocorticotropic hormone, suggesting that the disruption was at the level of the hypothalamus-pituitary axis. Venlafaxine-mediated disruption in HPI axis functioning was also evident in the F₁ and F₂ generations, including impaired cortisol responses to a stressor in adult female and larval fish, respectively. Taken together, our results suggest that venlafaxine is an endocrine disruptor, and early developmental exposure to this antidepressant may have long-term and generational consequences on cortisol stress axis activity in zebrafish.

Zygotic Venlafaxine Exposure Impacts Behavioral Programming by Disrupting Brain Serotonin in Zebrafish

The antidepressant venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is present in surface waters downstream of wastewater treatment plants. We previously showed that zygotic venlafaxine deposition alters larval behavior in zebrafish (Danio rerio), but the mechanisms were unknown. Here we tested the hypothesis that venlafaxine disrupts central serotonergic development, leading to impaired behavioral responses in zebrafish larvae. This was tested by microinjecting embryos with venlafaxine immediately after fertilization and performing spatial distribution of serotonin immunoreactivity, as well as characterizing target genes involved in serotonin turnover in the zebrafish brain. We provide evidence that venlafaxine exposure reduces serotonin immunoreactivity and tyrosine hydroxylase-positive cell populations in specific larval brain regions, and this corresponded with reduced larval activity observed in the drug-exposed group. Lowered serotonin was not due to either reduced synthesis or increased breakdown capacity. However, co-injection of serotonin alongside venlafaxine in embryos recovered brain serotonin immunoreactivity, tyrosine hydroxylase-positive cell populations, and rescued venlafaxine-mediated behavioral changes. Overall, our results demonstrate for the first time that early life exposure to venlafaxine perturbs brain development, which may be due to reduced serotonin, leading to altered larval behavior in zebrafish.

Parental exposure to tebuconazole causes thyroid endocrine disruption in zebrafish and developmental toxicity in offspring

Azole fungicides are one class of the most extensively applied current-use pesticides. Tebuconazole is a common azole fungicide that has been frequently detected in aquatic ecosystems, thus raising concerns about its ecological safety. However, adverse effects of tebuconazole remain largely unknown, especially with regard to endocrine function in aquatic organisms. In the present study, sexually immature zebrafish were exposed to different concentrations of tebuconazole (0.05, 0.20 and 0.50 mg/L) for 60 days in order to test for transgenerational toxicity on the thyroid endocrine system. Thyroid hormone homeostasis, neuronal, and cardiovascular development were investigated in the F1 generation, which were reared in tebuconazole-free water. In the F0 generation, exposure to 0.20 and 0.50 mg/L tebuconazole reduced both thyroxine (T₄) and 3,5,3'-triiodothyronine (T₃) levels in females, while the T₃ levels were unchanged in males. Decreased heart rate was found in F1 larvae, as well as diminished T₄ levels in F1 eggs/larvae. We also observed significantly increased expression of ugt1ab mRNA in two generations of zebrafish. Moreover, expression of mRNA associated with neuronal development (e.g. α1-tubulin, mbp, gap43) and cardiovascular development (e.g. cacna1ab, tnncal) were significantly downregulated in F1 larvae at 5 and 10 dpf. In addition, tebuconazole was detected in F1 eggs following parental exposure, indicating maternal transfer. This study demonstrated that tebuconazole can be transferred to offspring from exposed parents, causing thyroid endocrine disruption and developmental toxicity.

Venlafaxine in Embryos Stimulates Neurogenesis and Disrupts Larval Behavior in Zebrafish

Venlafaxine, a widely prescribed antidepressant, is a selective serotonin and norepinephrine reuptake inhibitor in humans, and this drug is prevalent in municipal wastewater effluents. While studies have shown that this drug affects juvenile fish behavior, little is known about the developmental impact on nontarget aquatic animals. We tested the hypothesis that venlafaxine deposition in the egg, mimicking maternal transfer of this antidepressant, disrupts developmental programming using zebrafish (Danio rerio) as a model. Embryos (1-4 cell stage) were microinjected with either 1 or 10 ng venlafaxine, which led to a rapid reduction (90%) of this drug in the embryo at hatch. There was a concomitant increase in the concentration of the major metabolite o-desmethylvenlafaxine during the same period. Embryonic exposure to venlafaxine accelerated early development, increased hatching rate and produced larger larvae at 5 days post fertilization. Also, there was an increase in neuronal birth in the hypothalamus, dorsal thalamus, posterior tuberculum, and the preoptic region, and this corresponded with a higher spatial expression of nrd4, a key marker of neurogenesis. The venlafaxine-exposed larvae were less active and covered shorter distance in a light and dark behavioral test compared to the controls. Overall, zygotic exposure to venlafaxine disrupts early development, including brain function, and compromises larval behavior, suggesting impact of this drug on developmental programming in zebrafish.

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

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

Tissue Contaminant Burdens in San Francisco Estuary White Sturgeon (Acipenser transmontanus): Implications for Population Recovery

The San Francisco Estuary (SFE) is heavily influenced by anthropogenic activities, including historic and chronic contaminant inputs. These contaminants can adversely affect SFE fish populations, particularly white sturgeon, because they are a benthic dwelling, long-lived species. We measured a suite of metals and organic contaminants in liver and gonad tissues of 25 male and 32 female white sturgeon as well as several physiological indicators of sturgeon health. Most sturgeon (68% of males and 83% of females) were estimated to be between 13 and 17 years of age. Sturgeon tissues had elevated concentrations of several metals, including As, Ba, Cd, Cu, Cr, Pb, Hg, Ni, Se, and Zn. The most frequently detected organic contaminants in sturgeon livers and gonads were DDE, PCBs, PBDEs, and galaxolide. Selenium was detected at levels similar to those shown to cause impaired liver physiology and reproductive success in white sturgeon. Observed Hg levels were higher than those shown to result in lower condition factor and gonadosomatic indices in white sturgeon. Liver galaxolide levels correlated with decreased plasma estradiol levels in female sturgeon. The Cd, As, and Cu warrant further investigation, because they were detected at levels known to impair fish health. Our results suggest contaminants are negatively affecting SFE white sturgeon health and fitness. Future SFE white sturgeon contaminant research is suggested.

In vivo EROD assays with the zebrafish (Danio rerio) as rapid screening tools for the detection of dioxin-like activity

The present study compares two alternative in vivo approaches for the measurement of ethoxyresorufin-O-deethylase (EROD) activity in zebrafish (Danio rerio) following exposure to acetonic model sediment extracts: (1) the live-imaging EROD assay for the direct detection of EROD induction in individual livers via epifluorescence, and (2) the fish embryo EROD assay in subcellular fractions derived from entire zebrafish embryos after in vivo exposure. For toxicity assessment, each sediment extract was tested with the standard fish embryo test (FET). Upon completion of a functioning liver after 72h, the embryos gave a distinct fluorescent signal in the liver, and a corresponding EROD activity could be detected in the fish embryo EROD assay. The exposure time in the live-imaging EROD assay was reduced to 3h, which resulted in a stronger, less variable and more sensitive EROD response. Overall, the live-imaging and the fish embryo EROD assays showed the same tendencies and gave comparable results, e.g. a concentration-dependent increase in EROD activity at concentrations one order of magnitude below concentrations producing macroscopically visible abnormalities. At higher concentrations, however, a decrease of EROD activity was observed in either test. Both tests ranked the three model sediment extracts in the same order. Results indicate that both test systems complement each other and together provide a rapid and reliable in vivo tool to investigate the presence of dioxin-like substances in environmental samples.

Dynamics of maternally transferred trace elements in oyster larvae and latent growth effects

Understanding the maternal transfer of contaminants and their potential effects has great implications for a valid ecological assessment of environmental pollution. However, relevant studies on marine bivalves are very limited. Here, we examined the maternal transfer of trace metals in populations of oyster Crassostrea hongkongensis with contrasting metal exposure histories. Elevated accumulation of trace metals was observed in eggs and larvae from contaminated sites, suggesting maternal transfer of multi-metals in natural oyster populations. The dynamics of maternally transferred metals was for the first time documented in this study. We demonstrated that excessively transferred metals in contaminated larvae were rapidly eliminated during the early developmental stage, and the efflux rate of metals in larvae was greatly dependent on environmental contamination level. These results provided the first field evidence of modified metal biokinetics in offsprings due to exposure history of adults in marine bivalves. Moreover, egg production was negatively correlated with the contamination level of metals in eggs. There was a further lagged growth in the contaminated larvae, indicating the potential adverse and latent effects of maternally transferred metals on the viability of oyster offspring. Our findings highlighted the importance of transgenerational studies on long-term metal exposure in marine bivalves.

Maternal transfer and reproductive effects of Cr(VI) in Japanese medaka (Oryzias latipes) under acute and chronic exposures

Maternal transfer of metals can be an important exposure route for animals. The maternal transfer of Cr and its effects on reproduction in fish are still largely unknown. In this study, Japanese medaka were exposed to a sublethal Cr(VI) concentration for 6 days (acute) and for 3 months (chronic). Chromium accumulation in the gonads, maternal transfer of Cr, and effects of Cr on the reproduction, histopathology and expressions of antioxidants in the gonads were evaluated. Both acute and chronic exposures resulted in significant Cr accumulation in gonads, eggs and larvae. In chronic Cr-exposed fish, approximately 61% of the Cr accumulated in the ovary was depurated by spawning during the first 3 days after exposure, suggesting that maternal transfer is a very important pathway for accumulation in offspring. The chronic exposure caused decreases in body weight, standard length, gonad weight, gonad-somatic index (GSI) and fecundity. The last of these was most severely affected: the total number of broods and eggs per female decreased by 57.1% and 75.9%, respectively. Moreover, egg weight and fertilization rate were also reduced (by approximately 20%) following chronic Cr(VI) exposure. Histopathological analyses showed that the Cr exposure resulted in the onset of follicular atresia and a reduction in the number of mature oocytes, along with a reduction in abundance of mature spermatozoa in testes. The GSH/GSSG ratio was greatly elevated after chronic Cr(VI) exposure, implying that GSH played a role in scavenging the reactive oxygen species generated by the reduction of Cr(VI) inside cells. This study provides evidence for the maternal transfer of Cr, highlights the importance of spawning in Cr depuration from the ovary, and demonstrates that chronic Cr(VI) exposure has serious impacts on reproduction in the Japanese medaka. Our results suggest that the issue of chronic Cr pollution deserves more attention than it has received to date.

Cryopreservation in fish: current status and pathways to quality assurance and quality control in repository development

Cryopreservation in aquatic species in general has been constrained to research activities for more than 60 years. Although the need for application and commercialisation pathways has become clear, the lack of comprehensive quality assurance and quality control programs has impeded the progress of the field, delaying the establishment of germplasm repositories and commercial-scale applications. In this review we focus on the opportunities for standardisation in the practices involved in the four main stages of the cryopreservation process: (1) source, housing and conditioning of fish; (2) sample collection and preparation; (3) freezing and cryogenic storage of samples; and (4) egg collection and use of thawed sperm samples. In addition, we introduce some key factors that would assist the transition to commercial-scale, high-throughput application.

Relationship between metal and polybrominated diphenyl ether (PBDE) body burden and health risks in the barnacle Balanus amphitrite

In the present study, we employed the widespread and gregarious barnacle species Balanus amphitrite in a biomonitoring program to evaluate coastal pollution around three piers (i.e., Tso Wo Hang, Sai Kung and Hebe Haven) in Hong Kong. An integrated approach was used herein, combining both the chemical determination of contaminant concentrations, including metals and polybrominated diphenyl ethers (PBDEs), and a suite of biological responses across the entire barnacle lifecycle (i.e., adult, nauplius, cyprid and juvenile). The analytical results revealed a distinct geographical distribution of metals and PBDEs. Adult physiological processes and larval behaviors varied significantly among the three piers. Furthermore, a correlation analysis demonstrated a specific suite of biological responses towards metal and PBDE exposure, likely resulting from their distinct modes of action. Overall, the results of this study indicated that the combination of chemical and biological tests provided an integrated measure for the comprehensive assessment of marine pollution.

Maternal transfer of bisphenol A impacts the ontogeny of cortisol stress response in rainbow trout

Bisphenol A (BPA) is widespread in the aquatic environment, and early life-stage exposure to this chemical affects growth and development in fish. We tested the hypothesis that BPA accumulation in eggs, mimicking maternal transfer, impacts the development and function of the hypothalamus-pituitary-interrenal (HPI) axis in rainbow trout (Oncorhynchus mykiss). To mimic maternal transfer, oocytes were loaded with 0 (control), 1, 4 and 40ng BPA embryo(-1). We measured the temporal changes in whole body cortisol content, transcript levels of corticosteroidogenesis-related genes and glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) protein expressions during early development. In addition, trout larvae were subjected to an acute stressor at key developmental stages (at hatch, just prior to first feed and post hatch) and whole body cortisol levels measured to assess the functional integrity of the HPI axis. The developmental profile of whole body cortisol content was altered in the 1 and 40ng BPA groups compared to the control group. Also, the two key rate-limiting steps in steroidogenesis, the steroidogenic acute regulatory protein (StAR) and cytochrome P450 side chain cleavage (P450scc) enzyme transcript levels were disrupted in the larvae originating from BPA accumulated eggs prior to first feed. Whole body GR and MR protein expressions were higher in the 40ng BPA group compared to other groups prior to first feed. Stressor-induced elevation in whole body cortisol levels were evident at 65 days post-fertilization (dpf) and later, but not at 42 dpf in trout larvae. This cortisol response to a stressor exposure was attenuated in the 4 and 40ng BPA groups at 65 dpf, but not at 140 dpf. Together, accumulation of BPA in eggs, mimicking maternal transfer of this chemical, disrupts the ontogeny of cortisol stress response in trout larvae and may compromise the target tissue responsiveness to cortisol stimulation during early development.

Parental effects of endocrine disrupting compounds in aquatic wildlife: Is there evidence of transgenerational inheritance?

The effects of endocrine disrupting compounds (EDCs) on aquatic wildlife are increasingly being recognized for their complexity. Investigators have detected alterations at multiple levels of biological organization in offspring exposed to EDCs through the blood or germ line of the parents, suggesting that generational consequences of EDCs are evident. Exposure to EDCs through the parents is concerning because if the resulting phenotype of the offspring is heritable and affects fitness, then evolutionary consequences may be evident. This review summarizes the evidence for transgenerational effects of EDCs in aquatic wildlife and illustrates cases where alterations appear to be transmitted maternally, paternally, or parentally. The literature indicates that EDC exposure to the parents induces developmental, physiological, endocrinological, and behavioral changes as well as increased mortality of offspring raised in clean environments. What is lacking, however, is a clear demonstration of heritable transgenerational effects in aquatic wildlife. Therefore, it is not known if the parental effects are the result of developmental or phenotypic plasticity or if the altered phenotypes are durably passed to subsequent generations. Epigenetic changes to gene regulation are discussed as a possible mechanism responsible for EDC induced parental effects. Additional research is needed to evaluate if heritable effects of EDCs are evident in aquatic wildlife, as has been demonstrated for terrestrial mammals.

Variations of sediment toxicity in a tidal estuary: a case study of the South Passage, Changjiang (Yangtze) Estuary

Sediments in estuaries, especially those containing a large reservoir of contaminants released from urban and industrial activities, have had great impacts on benthic fauna and associated species. A better understanding of the toxicity of contaminants in estuarine sediments is of great significance to ecological assessments. Here, based on the collected sediments from neap to spring tides in the South Passage, Changjiang Estuary, the toxicity of the sediments was first studied using the frog embryo teratogenesis assay-Xenopus (FETAX). The results showed that the extracts of estuarine sediments induced multiple malformations in the embryos and that the phenotypes of malformation had two distinct patterns of variations corresponding to the tidal cycles. The phenotypes in the first pattern were dominated by hypopigmentation and edema of the heart, and the pattern was mainly controlled by fine-grained fractions. The phenotypes in the second pattern were dominated by edema of the heart and enlarged proctodeum, and it was mostly controlled by coarse-grain fractions. The sediment toxicity was higher during the spring and flood tides, which may be influenced by the grain size and sediment resuspension. Furthermore, obvious periodicities existed in the changes of the percentages of hatching (14-16 h and 6 h), enlarged proctodeum (15-18 h), and bent tail (5-7 h) due to the influence of tidal cycles. Moreover, our results also suggested that FETAX is an appropriate cost-effective biological monitoring tool to assess estuarine ecological health in contaminated sediments.

Physiological effects and reduced tolerance following maternal metal exposure in the live-bearing fish Gambusia affinis

The present study assessed the effects of maternal copper or cadmium exposure in a live-bearing fish. After a 10-d exposure to background levels (control) or 0.15 μM copper or cadmium, gravid females were transferred to clean water. Once a female gave birth, the authors analyzed her newborn offspring for lipid peroxidation, elemental composition (copper, cadmium, and calcium), and metal tolerance. The authors raised other offspring until sexual maturity and analyzed their growth rate, incidence of abnormalities, and sex ratio. Their earlier research, using the same species and exposure design, demonstrated that cadmium and copper were transferred from gravid females to their offspring. The present study showed that offspring of copper-exposed females had a reduced size at birth, developmental abnormalities, elevated tissue cadmium levels, and reduced tissue calcium levels. Offspring of cadmium-exposed females had elevated levels of lipid peroxidation, developmental abnormalities, and lower tissue levels of both copper and calcium. No effects were detected with respect to offsprings' growth rate or sex ratio. Offspring of metal-exposed fish had a reduced tolerance to the metal that their female parent had been exposed to, and the tolerance showed an inverse relationship to the tissue metal level in the offspring. The latter indicates that the reduced tolerance was the result of an increased body burden prior to the tolerance quantification. The present study constitutes the first report in live-bearing fishes showing that maternal metal exposure has a wide range of negative impacts on the offspring.

Bioconcentration and transfer of the organophorous flame retardant 1,3-dichloro-2-propyl phosphate causes thyroid endocrine disruption and developmental neurotoxicity in zebrafish larvae

Organophosphate flame retardants are emerging environmental contaminants, although knowledge of their health risks is limited. Here, thyroid hormone homeostasis and neuronal development was studied in the progeny of adult zebrafish exposed to tris(1,3-dichloro-2-propyl) phosphate (TDCPP). Adult zebrafish were exposed to TDCPP (0, 4, 20, and 100 μg/L) for 3 months. Increased generation of reactive oxygen species and reduced survival rates was observed in exposed F1 larvae. We also observed a significant decrease in plasma thyroxine and 3,5,3'-triiodothyronine levels in F0 females and F1 eggs/larvae. The mRNA and protein expression of factors associated with neuronal development (e.g., α1-tubulin, myelin basic protein, and synapsin IIa) were significantly downregulated in exposed F1 larvae, as was the level of the neurotransmitters dopamine, serotonin, gamma amino butyric acid, and histamine. Larval locomotion was significantly decreased in exposed fish, but there was no effect on acetylcholinesterase activity. Bioconcentration of TDCPP was observed in F0 fish. TDCPP was also detected in F1 eggs following parental exposure, indicating maternal transfer of this compound. This study uniquely shows that TDCPP can be transferred to the offspring of exposed adults, causing thyroid endocrine disruption and developmental neurotoxicity.

Effects on life history variables and population dynamics following maternal metal exposure in the live-bearing fish Gambusia affinis

This study investigated the effect of maternal copper and maternal cadmium exposure on life history variables and population dynamics in a live-bearing fish species. Gravid females were exposed to copper, cadmium, or background metal levels (control); maternal transfer of the metals was previously demonstrated using the exact same design. Each female's first brood, born after the exposure, was subdivided into two groups. One group was raised in the laboratory, to assess time-to and size-at sexual maturity, reproductive output and other life history variables. Offspring from the other group were used to start four mesocosm populations for each treatment. These populations were sampled monthly, for about 18 months, to assess population dynamics. For the laboratory-reared fish, offspring of copper-exposed females reached sexual maturity at a smaller size than did offspring from the other treatments. Maternal copper exposure and maternal cadmium exposure both resulted in fewer broods and an increase in gestation time. No impacts were detected for brood size, inter-brood interval, time-to-sexual-maturity, or life span. In the greenhouse population study, no effect of maternal copper or cadmium exposure was evident for population parameters, other than that the relative abundance of juveniles and/or newborns was reduced in populations established with offspring of the exposed females. This study provided evidence that a short-term metal exposure of gravid females can negatively affect their offspring's life history variables and potentially influence population dynamics in a life-bearing fish species.

Bisphenol A accumulation in eggs disrupts the endocrine regulation of growth in rainbow trout larvae

Bisphenol A (BPA), a monomer used in the production of plastics and epoxy resins, is ubiquitously present in the aquatic environment. BPA is considered a weak estrogen in fish, but the effects of this chemical on early developmental events are far from clear. We tested the hypothesis that BPA accumulation in eggs, mimicking maternal transfer, disrupts growth hormone/insulin-like growth factor (GH/IGF) axis function, leading to defects in larval growth in rainbow trout. Trout oocytes were exposed to 0 (control), 0.3, 3, and 30 μg ml(-1) BPA for 3h, which led to an accumulation of around 0, 1, 4 and 40 ng BPA per egg, respectively. All treatment groups were fertilized with clean milt and reared in clean water for the rest of the experiment. The embryo BPA content declined over time in all groups and was completely eliminated by 42 days post-fertilization (dpf). Hatchlings from BPA accumulated eggs had higher water content and reduced total energy levels prior to first feed. There was an overall reduction in the specific growth rate and food conversion ratio in larvae reared from BPA-laden eggs. BPA accumulation disrupted the mRNA abundance of genes involved in GH/IGF axis function, including GH isoforms and their receptors, IGF-1 and -2 and IGF receptors, in a life stage-dependent manner. Also, there was a temporal disruption in the mRNA levels of thyroid hormone receptors in the larvae raised from BPA-laden eggs. Altogether, BPA accumulation in eggs, mimicking maternal transfer, affects larval growth and the mode of action involves disruption of genes involved in the GH/IGF and thyroid axes function in trout.

Evidence of maternal copper and cadmium transfer in two live-bearing fish species

We studied maternal transfer of an essential metal (copper) and a non-essential one (cadmium) in the live-bearing fishes Heterandria formosa and Gambusia affinis. The goals of this study were: (1) to determine whether metals are transferred from exposed females to their developing offspring; (2) to determine if this transfer differs between two fish species that differ in their degree of maternal provisioning during development; (3) to determine the duration of maternal metal transfer once females are no longer exposed; and (4) to determine whether copper and cadmium are transferred equivalently. We exposed gravid females to background levels (control) or 0.15 µM of metal for 10 days, and then transferred them to clean water. We allowed females to give birth to up to three broods, and then quantified metal levels in offspring born at least 3 days after the transfer. We detected maternal metal transfer for both metals and in both species. Offspring metal levels decreased as females spent more time in clean water. Similarly, metal levels were lower in later broods than in earlier ones. Maternal metal transfer was higher in H. formosa than in G. affinis. Our results constitute the first report of maternal metal transfer in live-bearing fishes, and show that developing embryos acquire both essential and non-essential metals from their mothers in both species. This shows that metal toxicity may be an issue for live-bearing fish in clean environments when the previous generation has encountered metal pollution.

Developmental toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in artificially fertilized crucian carp (Carassius auratus) embryo

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent bioaccumulative environmental contaminant that is an endocrine disruptor. Embryos of various fish species are responsive to TCDD and have been used as an alternative method to the acute toxicity test with juvenile and adult fish. The TCDD test has similar endpoints of developmental toxicity. However, their sensitivity and signs of TCDD-induced toxicity are different depending on fish species and its habit. Crucian carp (Carassius auratus) - the sentinel species for persistent organic pollutants and a common foodfish in China, Japan, and Korea - was used to identify the developmental toxicity of TCDD. We obtained the fertilized eggs from the artificial fertilization of crucian carp (97.45% success rate). Embryos at 3h post fertilization (hpf) were exposed to no vehicle, vehicle (dimethylsulfoxide, 0.1% v/v) or TCDD (0.128, 0.32, 0.8, 2 and 5 μg/L) for 1h and then fresh water was changed and aerated. Embryonic development and toxicity were monitored until 150 hpf. TCDD-exposed group showed no effects on embryo mortality and hatching rate from 6 to 126 hpf. On the other hand, the post-hatching mortality rate in TCDD-exposed group was increased in a dose-dependent manner, especially at high doses (0.8, 2 and 5 μg/L). The LD50 for larval mortality was calculated to 0.24 ng TCDD/g embryo. Pericardial edema was continuously observed in larvae of TCDD-exposed groups from hatching complete time (78 hpf), followed by the onset of yolk sac edema. Hemorrhage and edema showed a significant increase depending on exposure concentration and time. Expression of TCDD-related CYP1A genes was evaluated quantitatively. Embryo and larvae in TCDD-exposed groups displayed a significant increase of CYP1A gene expression. Overall, we defined TCDD-induced toxicity in artificially fertilized crucian carp embryo and these results suggest that crucian carp can be applied as an early life stage model of TCDD-induced toxicity.

Sex-dependent accumulation and maternal transfer of Dechlorane Plus flame retardant in fish from an electronic waste recycling site in South China

Knowledge is limited on sex-related accumulation and maternal transfer of Dechlorane Plus (DP) flame retardant in wildlife. In the present study, DP isomers were examined in liver and eggs of two fish species, northern snakehead and crucian carp, from an electronic waste recycling site in China. Hepatic ∑DP (sum of syn- and anti-DP) concentrations ranged 260-1920 ng/g lipid in northern snakehead and 340-1670 ng/g in crucian carp, with significantly higher levels in males relative to females. ∑DP concentrations ranged 4.6-310 ng/g lipid in the eggs, demonstrating their maternal transfer in the female fish. The mean eggs to liver concentration ratios (E/L ratios) were 0.03 and 0.03 in northern snakehead, and 0.26 and 0.25 in crucian carp, for syn- and anti-DP, respectively. A significantly negative correlation between the E/L ratios and the hepatic DP concentrations was observed, indicating a dose-dependent maternal transfer of DP isomers in the fish.

Effects of acute exposure to polybrominated diphenyl ethers on retinoid signaling in zebrafish larvae

The objectives of the present study were to investigate the effects of acute exposure to PBDEs on retinoid signaling in fish. Zebrafish embryos (2h post-fertilization, hpf) were exposed to DE-71 (0, 31.0, 68.7, and 227.6μg/L) until 120hpf. Retinoid profiles showed the content of retinal and retinoic acid was reduced significantly. While a significant up-regulation was observed in the transcription of retinal dehydrogenase (raldh2), the transcription of retinol binding protein (rbp1a), retinol dehydrogenase (rdh1), cellular retinoic acid binding protein (crabp1a and crabp2a) and retinoic acid receptor subunit (raraa) were down-regulated significantly, indicating disruption of retinoid signaling. However, the transcriptions of five opsin genes (zfrho, zfuv, zfred, zfblue, and zfgr1) were up-regulated. Furthermore, whole mount immunostaining and western blotting demonstrated increased rhodopsin protein expression in the exposure groups. Overall, the results indicated that acute exposure to PBDEs could disturb retinoid signaling and may impact on eye development of zebrafish larvae.

Acute exposure to DE-71: effects on locomotor behavior and developmental neurotoxicity in zebrafish larvae

The aim of the present study was to investigate the acute developmental neurotoxicity of polybrominated diphenyl ethers (PBDEs) in zebrafish larvae. From 2 to 120 h postfertilization zebrafish embryos were exposed to DE-71 (0, 31.0, 68.7, and 227.6 µg/L). The authors studied the locomotor behavior of larvae, involvement of the cholinergic system, and selected gene and protein expressions in the central nervous system. The results showed that low DE-71 concentration caused hyperactivity, whereas higher concentrations decreased activity during the dark period. During the light period, larval activity was significantly reduced in a concentration-dependent manner. In the cholinergic system, acetylcholinesterase activity significantly increased (10.7 and 12.4%) in the 68.7 and 227.6 µg/L exposure groups, respectively, and acetylcholine concentration accordingly decreased (60.5%) in the 227.6 µg/L exposure group. The mRNA expressions of genes encoding myelin basic protein, neuron microtubule protein (α1-tubulin), and sonic hedgehog a were significantly downregulated. Western blotting assay demonstrated that the protein concentration of α1-tubulin was also decreased. Overall, the present study demonstrated that acute exposure to PBDEs can disrupt the neurobehavior of zebrafish larvae and affect cholinergic neurotransmission and neuron development.

Prenatal transfer of polybrominated diphenyl ethers (PBDEs) results in developmental neurotoxicity in zebrafish larvae

Parental exposure to polybrominated diphenyl ethers (PBDEs) in animals has been found to be transferred to the offspring. The environmental health risk and toxicity to the offspring are still unclear. The objective of the present study was to identify environmentally relevant concentrations of PBDEs for parental exposure that would cause developmental neurotoxicity in the offspring. Adult zebrafish were exposed to environmentally relevant concentrations of DE-71 (0.16, 0.8, 4.0 μg/L) via water. The results showed that PBDE exposure did not affect larvae hatching, malformation, or survival. The residue of PBDEs was detected in F1 eggs upon parental exposure. Acetylcholinesterase (AChE) activity was significantly inhibited in F1 larvae. Genes of central nervous system development (e.g., myelin basic protein, synapsin IIa, α1-tubulin) were significantly downregulated in larvae. Protein levels of α1-tubulin and synapsin IIa were also reduced. Decreased locomotion activity was observed in the larvae. This study provides the first evidence that parental exposure to environmentally relevant concentrations of PBDEs could cause adverse effects on neurodevelopment in zebrafish offspring.

Cytochrome P4501A mRNA and protein induction in striped bass (Morone saxatilis)

The striped bass (Morone saxatilis) supports a valuable recreational fishery and is among the most important piscivorous fish of the San Francisco Estuary. This species has suffered a significant decline in numbers over the past decades, and there is indication that contaminants are important contributors. Polycyclic aromatic hydrocarbons (PAHs) and polyhalogenated aromatic hydrocarbons (PHAHs) including PCBs and dioxins are widespread in the estuary, they typically bioaccumulate through trophic levels, reaching highest levels in top predators and are known to affect the fish health and development. The aim of this study was to investigate the dynamics of cytochrome P4501A (Cyp1a) induction simultaneously at different levels of biological organization (RNA transcription and protein synthesis) as a biomarker of exposure to PAHs and PHAHs. We utilized β-naphthoflavone (BNF) as a model PAH to induce Cyp1a responses in juvenile striped bass in both dose-response and time-response assessments and determined Cyp1a mRNA and protein levels. Significant responses were measured in both systems at 10 mg ΒΝF kg⁻¹, a concentration used for time-response studies. Messenger RNA levels peaked at 6 h post-injection, while protein levels increased progressively with time, significantly peaking at 96 h post-injection; both remaining elevated throughout the duration of the test (8 days). Our data suggest that rapid induction of gene transcription following exposure and subsequent cumulative protein synthesis could provide a useful means of identifying temporal variants in exposure to Cyp1a inducers in Morone saxatilis. The potential application of this combined Cyp1a gene and protein biomarker in this species for field studies is discussed.

Adsorption and desorption of chlorpyrifos to soils and sediments

Chlorpyrifos, one of the most widely used insecticides, has been detected in air, rain, marine sediments, surface waters, drinking water wells, and solid and liquid dietary samples collected from urban and rural areas. Its metabolite, TCP, has also been widely detected in urinary samples collected from people of various age groups. With a goal of elucidating the factors that control the environmental contamination, impact, persistence, and ecotoxicity of chlorpyrifos, we examine, in this review, the peer-reviewed literature relating to chlorpyrifos adsorption and desorption behavior in various solid-phase matrices. Adsorption tends to reduce chlorpyrifos mobility, but adsorption to erodible particulates, dissolved organic matter, or mobile inorganic colloids enhances its mobility. Adsorption to suspended sediments and particulates constitutes a major off-site migration route for chlorpyrifos to surface waters, wherein it poses a potential danger to aquatic organisms. Adsorption increases the persistence of chlorpyrifos in the environment by reducing its avail- ability to a wide range of dissipative and degradative forces, whereas the effect of adsorption on its ecotoxicity is dependent upon the route of exposure. Chlorpyrifos adsorbs to soils, aquatic sediments, organic matter, and clay minerals to differing degrees. Its adsorption strongly correlates with organic carbon con- tent of the soils and sediments. A comprehensive review of studies that relied on the batch equilibrium technique yields mean and median Kd values for chlorpyrifos of 271 and 116 L/kg for soils, and 385 and 403 L/kg for aquatic sediments. Chlorpyrifos adsorption coefficients spanned two orders of magnitude in soils. Normalizing the partition coefficient to organic content failed to substantially reduce variability to commonly acceptable level of variation. Mean and median values for chlorpyrifos partition coefficients normalized to organic carbon, K, were 8,163 and 7,227 L/kg for soils and 13,439 and 15,500 L/kg for sediipents. This variation may result from several factors, including various experimental artifacts, variation in quality of soil organic matter, and inconsistencies in experimental methodologies. Based on this review, there appears to be no definitive quantification of chlorpyrifos adsorption or desorption characteristics. Thus, it is difficult to predict its adsorptive behavior with certainty, without resorting to experimental methods specific to the soil or sediment of interest. This limitation should be recognized in the context of current efforts to predict the risk, fate, and transport of chlorpyrifos based upon published partition coefficients. Based on a comprehensive review of the peer-reviewed literature related to adsorption and desorption of chlorpyrifos, we propose the following key areas for future research. From this review, it becomes increasingly evident that pesticide partitioning cannot be fully accounted for by the fraction of soil or solid-matrix organic matter or carbon content. Therefore, research that probes the variation in the nature and quality of soil organic matter on pesticide adsorption is highly desirable. Pesticide persistence and bioavailability depend on insights into desorption capacity. Therefore, understanding the fate and environmental impact of hydrophobic pesticides is incomplete without new research being performed to improve insights into pesticide desorption from soils and sediments. There is also a need for greater attention and consistency in developing experimental methods aimed at estimating partition coefficients. Moreover, in such testing, choosing initial concentrations and liquid-solid ratios that are more representative of environmental conditions could improve usefulness and interpretation of data that are obtained. Future monitoring efforts should include the sampling and analysis of suspended particulates to account for suspended solid-phase CPF, a commonly underestimated fraction in surface water quality monitoring programs. Finally, management practices related to the reduction of off-site migration of CPF should be further evaluated, including alternative agricultural practices leading to reduction in soil erosion and structural best management practices, such as sedimentation ponds, treatment wetlands, and vegetated edge-of-field strips.

Parental transfer of polybrominated diphenyl ethers (PBDEs) and thyroid endocrine disruption in zebrafish

Polybrominated diphenyl ethers (PBDEs) have the potential to disrupt the thyroid endocrine system. The objective of the present study was to characterize the disrupting effects of long-term exposure on the thyroid endocrine system in adult fish and their progeny following parental exposure to PBDEs. Zebrafish (Danio rerio) embryos were exposed to environmentally relevant concentrations (1, 3, and 10 μg/L) of the PBDE mixture DE-71 for 5 months until sexual maturation. In the F0 generation, exposure to DE-71 significantly increased plasma thyroxine (T4) but not 3,5,3'-triiodothyronine (T3) in females. This increased T4 was accompanied by decreased mRNA levels of corticotropin-releasing hormone (CRH) and thyrotropin β-subunit (TSHβ) in the brain. The F1 generation was further examined with or without continued DE-71 treatment conditions. Exposure to DE-71 in the F0 fish caused significant increases in T4 and T3 levels in the F1 larvae and modified gene expressions in the hypothalamic-pituitary-thyroid axis (HPT axis) under both conditions. Decreased hatching and inhibition of growth in the F1 offspring were observed in the condition without DE-71 treatment. Continued DE-71 treatment in the F1 embryos/larvae resulted in further decreased hatching, and increased malformation rates compared with those without DE-71 exposure. Analysis of F1 eggs indicated that parental exposure to DE-71 could result in a transfer of PBDEs and thyroid hormones (THs) to their offspring. For the first time, we demonstrated that parental exposure to low concentrations of PBDEs could affect THs in the offspring and the transgenerational PBDE-induced toxicity in subsequent nonexposed generations.

Influences of DMP on the fertilization process and subsequent embryogenesis of abalone (Haliotis diversicolor supertexta) by gametes exposure

Di-methyl phthalate (DMP), a typical endocrine disrupting chemical (EDC), is ubiquitously distributed in aquatic environments; yet studies regarding its impact on gametes and the resulting effects on embryogenesis in marine gastropods are relatively scarce. In this study, the influences of DMP on the gametes and subsequent developmental process of abalone (Haliotis diversicolor supertexta, a representative marine benthic gastropod) were assessed. Newborn abalone eggs and sperm were exposed separately to different DMP concentrations (1, 10 or 100 ppb) for 60 min. At the end-point of exposure, the DMP-treated eggs and sperm were collected for analysis of their ultra-structures, ATPase activities and total lipid levels, and the fertilized gametes (embryos) were collected to monitor related reproductive parameters (fertilization rate, abnormal development rate and hatching success rate). Treatment with DMP did not significantly alter the structure or total lipid content of eggs at any of the doses tested. Hatching failures and morphological abnormalities were only observed with the highest dose of DMP (100 ppb). However, DMP exposure did suppress sperm ATPase activities and affect the morphological character of their mitochondria. DMP-treated sperm exhibited dose-dependent decreases in fertilization efficiency, morphogenesis and hatchability. Relatively obvious toxicological effects were observed when both sperm and eggs were exposed to DMP. Furthermore, RT-PCR results indicate that treatment of gametes with DMP changed the expression patterns of physiologically-regulated genes (cyp3a, 17β-HSD-11 and 17β-HSD-12) in subsequent embryogenesis. Taken together, this study proofed that pre-fertilization exposure of abalone eggs, sperm or both to DMP adversely affects the fertilization process and subsequent embryogenesis.

Does maternal exposure to an environmental stressor affect offspring response to predators?

There is growing recognition of the ways in which maternal effects can influence offspring size, physiological performance, and survival. Additionally, environmental contaminants increasingly act as stressors in maternal environments, possibly leading to maternal effects on subsequent offspring. Thus, it is important to determine whether contaminants and other stressors can contribute to maternal effects, particularly under varied ecological conditions that encompass the range under which offspring develop. We used aquatic mesocosms to determine whether maternal effects of mercury (Hg) exposure shape offspring phenotype in the American toad (Bufo americanus) in the presence or absence of larval predators (dragonfly naiads). We found significant maternal effects of Hg exposure and significant effects of predators on several offspring traits, but there was little evidence that maternal effects altered offspring interactions with predators. Offspring from Hg-exposed mothers were 18% smaller than those of reference mothers. Offspring reared with predators were 23% smaller at metamorphosis than those reared without predators. There was also evidence of reduced larval survival when larvae were reared with predators, but this was independent of maternal effects. Additionally, 5 times more larvae had spinal malformations when reared without predators, suggesting selective predation of malformed larvae by predators. Lastly, we found a significant negative correlation between offspring survival and algal density in mesocosms, indicating a role for top-down effects of predators on periphyton communities. Our results demonstrate that maternal exposure to an environmental stressor can induce phenotypic responses in offspring in a direction similar to that produced by direct exposure of offspring to predators.

Natural factors to consider when using acetylcholinesterase activity as neurotoxicity biomarker in Young-Of-Year striped bass (Morone saxatilis)

Acetylcholinesterase (AChE) activity is one of the most common biomarkers of neurotoxicity used in aquatic organisms. However, compared to its extensive use as biomarker, the effects of natural factors on AChE activity remain unclear especially in estuarine fishes. The aim of this study was to evaluate the effects of natural factors on AChE activity of striped bass (Morone saxatilis) juveniles. Brain AChE activity was measured in YOY (Young-Of-Year) individuals collected monthly from August 2007 to January 2008 at 12 different sites in the San Francisco Estuary system. The spatio-temporal variability of AChE was analyzed relative to water temperature and salinity as well as fish size. AChE activity was highly positively correlated with water temperature and to a lesser extent negatively with fish size while no relationship was detected with salinity. Taking into account these natural factors when using AChE as a biomarker will help to determine and understand the effects of neurotoxic contaminants on fish in estuarine systems.

Environmental contaminant effects on juvenile striped bass in the San Francisco Estuary, California, USA

The decline of pelagic organisms in the San Francisco Estuary (SFE) (California, USA) is attributed to several factors, including water diversions, invasive species, and exposure to environmental toxicants. The present study evaluated the effects of environmental contaminants on liver vitellogenin, metallothionein, 7-ethoxyresorufin-O-deethylase (EROD), and benzyloxyresorufin O-deethylase (BROD) activity in juvenile striped bass (Morone saxitilis) in the SFE. Analysis of juvenile striped bass liver extracts revealed site-specific elevations of vitellogenin, metallothionein, and EROD biomarkers across the estuary. Although some striped bass in the estuary showed EROD activity similar to unhandled hatchery controls, several sites in the estuary showed significantly higher EROD activity that was in the range of beta-naphthoflavone (BNF)-injected, positive controls. Overall, EROD activity averaged 283% higher in estuary fish than in hatchery controls. Chemical analyses of extracts from semipermeable membrane devices (SPMDs) deployed in the estuary for one month showed elevated polyaromatic hydrocarbon (PAH) levels. Semipermeable membrane devices extract injections-induced metallothionein and BROD in striped bass livers. These data show that environmental exposures are impacting EROD and other biomarkers in the SFE striped bass population. Previous studies in our laboratory have associated poor larval development with maternal transfer of environmental contaminants. Further studies are needed to monitor contaminant exposures by the use of biomarkers and to integrate them into a more effective pelagic species recovery plan in the SFE.