The last frontier: Coupling technological developments with scientific challenges to improve hazard assessment of deep-sea mining

The growing economic interest in the exploitation of mineral resources on deep-ocean beds, including those in the vicinity of sensitive-rich habitats such as hydrothermal vents, raise a mounting concern about the damage that such actions might originate to these poorly-know ecosystems, which represent millions of years of evolution and adaptations to extreme environmental conditions. It has been suggested that mining may cause a major impact on vent ecosystems and other deep-sea areas. Yet, the scale and the nature of such impacts are unknown at present. Hence, building upon currently available scientific information it is crucial to develop new cost-effective technologies embedded into rigorous operating frameworks. The forward-thinking provided here will assist in the development of new technologies and tools to address the major challenges associated with deep sea-mining; technologies for in situ and ex situ observation and data acquisition, biogeochemical processes, hazard assessment of deep-sea mining to marine organisms and development of modeling tools in support of risk assessment scenarios. These technological developments are vital to validate a responsible and sustainable exploitation of the deep-sea mineral resources, based on the precautionary principle.

The use of biomarkers as integrative tools for transitional water bodies monitoring in the Water Framework Directive context - A holistic approach in Minho river transitional waters

The Water Framework Directive (WFD) provides an important legislative opportunity to promote and implement an integrated approach for the protection of inland surface waters, transitional waters, coastal waters and groundwaters. The transitional waters constitute a central piece as they are usually under high environmental pressure and by their inherent characteristics present monitoring challenges. Integrating water quality monitoring with biological monitoring can increase the cost-effectiveness of monitoring efforts. One way of doing this is with biomarkers, which effectively integrate physical-chemical status and biological quality elements, dealing holistically with adverse consequences on the health of water bodies. The new Marine Strategy Framework Directive (MSFD) already incorporates the biomarker approach. Given the recent activities of OSPAR and HELCOM to harmonize existing monitoring guidelines between MSFD and WFD the use of similar methodologies should be fostered. To illustrate the potential of the biomarker approach, juveniles of flounder (Platichthys flesus) were used to evaluate the quality of the Minho river-estuary water bodies. The use of juveniles instead of adults eliminates several confounding factors such changes on the biological responses associated with reproduction. Here, a panel of well-established biomarkers, EROD, AChE, SOD, CAT, GST, LPO, ENA and FACs (1-Hydroxyrene) were selected and measured along with a gradient of different physical conditions, and integrated with trace elements characterization on both biota and sediments. In general, a clear profile along the water bodies was found, with low seasonal and spatial variation, consistent with a low impacted area. Overall, the results support the use of both the battery of biomarkers and the use of juvenile flounders in the monitoring of the water quality status within the WFD.

Toxicity effects of hazardous and noxious substances (HNS) to marine organisms: acute and chronic toxicity of p-xylene to the amphipod Gammarus locusta

Despite the recent focus on hazardous and noxious substances (HNS) spills preparedness and responses, much remains to be done regarding the threat posed by HNS spills on marine biota. Among the identified priority HNS, p-xylene was selected to conduct ecotoxicological assays. The aim of this study was to assess the performance of the amphipod Gammarus locusta under acute and chronic exposure to p-xylene simulating conditions of a spill incident. In the acute exposure (96 h) the p-xylene LC50 was estimated. In the chronic bioassay (36 d), an integration of organism-level endpoints (survival, growth rate, and sex ratio) with biochemical markers indicative of oxidative stress including catalase (CAT), glutathione S-transferase (GST), and superoxide dismutase (SOD) activities and lipid peroxidation (LPO) levels was determined. The aim was to increase the xylene ecotoxicological database and better predict its impact in aquatic environments. p-Xylene induced several chronic toxicity effects in G. locusta. Significant alterations in antioxidant enzymes and lipid peroxidation levels as well as growth rate and biased sex-ratio were observed. p-Xylene significantly affected the activities of CAT, SOD, and GST in G. locusta and produced oxidative damage by increasing levels of LPO in males. Further, impacts in key ecological endpoints, that is, growth and sex ratio, were noted that might be indicative of potential effects at the population level in a spill scenario. The present data may be useful to assist relevant bodies in preparedness and response to HNS spills.

A real-time PCR assay for differential expression of vitellogenin I and II genes in the liver of the sentinel fish species Lipophrys pholis

Abstract The recent advances in molecular biology techniques have prompted the use of vitellogenin (VTG) gene expression as a sensitive and reliable indicator of estrogenic chemicals (EC) exposure. However, data on the dynamic response of the different VTGs genes upon EC exposure is still poorly understood, particularly in sentinel fish species used in field monitoring studies. Hence, the present study aimed at developing a sensitive real-time PCR assay for determining the response of VTG I and II in the recently proposed marine sentinel species Lipophrys pholis upon exposure to the model EC 17α-ethinylestradiol (EE2). The findings of the laboratory study indicate that L. pholis VTG I proved to be not only more inducible but also more sensitive to EE2 exposure than VTG II, for the same range of concentrations. In fact, VTG I gene induction was 475-fold higher than VTG II at 15 ng/L EE2, and 13-fold at 5 ng/L EE2. Overall, the findings of the present study indicate that in the field, expression of VTG I in L. pholis should be preferentially used in the screening of EC exposure because of its higher sensitivity. Furthermore, the present study favors L. pholis integration in monitoring programs associated with EC's pollution within the European water policy legislation.

Simulation of a Hazardous and Noxious Substances (HNS) spill in the marine environment: lethal and sublethal effects of acrylonitrile to the European seabass

Despite the extensive maritime transportation of Hazardous and Noxious Substances (HNS), there is a current lack of knowledge on the effects posed by HNS spills on the marine biota. Among the HNS identified as priority, acrylonitrile was selected to conduct ecotoxicological assays. We assessed the acute and subletal effects of acrylonitrile in seabass, followed by a recovery phase to simulate the conditions of a spill incident. The work aimed at testing a broad range of biological responses induced by acrylonitrile. Sublethal exposure to the highest two doses increased the fish mortality rate (8.3% and 25% mortality in 0.75 and 2 mg L(-1) acrylonitrile concentrations), whereas no mortality were observed in control and 0.15 mg L(-1) treatments. Additionally, important alterations at sub-individual level were observed. Acrylonitrile significantly induced the activities of Catalase- CAT and Glutathione S-Transferase - GST; and the levels of DNA damage were significantly increased. Conversely, Superoxide Dismutase- SOD - activity was found to be significantly inhibited and no effects were found on Lipid Peroxidation- LPO and ethoxyresorufin O-deethylase - EROD - activity. Following a 7d recovery period, the levels of CAT, GST and EROD fell to levels at or below those in the control. In the 2 mg L(-1) group, SOD remained at the levels found during exposure phase. This study has gathered essential information on the acute and subletal toxicity of acrylonitrile to seabass. It also demonstrated that 7d recovery allowed a return of most endpoints to background levels. These data will be useful to assist relevant bodies in preparedness and response to HNS spills.

Zebrafish (Danio rerio) life-cycle exposure to chronic low doses of ethinylestradiol modulates p53 gene transcription within the gonads, but not NER pathways

Parental full life-cycle exposure to ethinylestradiol (EE₂) significantly affects embryo development and survival. One of the possible mechanisms of action of EE₂ may involve the impairment of an organism's ability to repair DNA damage. DNA repair mechanisms have sophistically evolved to overcome DNA damaging hazards that threaten the integrity of the genome. In the present study, changes in the transcription levels of key genes involved in two of the most thoroughly studied DNA repair systems in mammals were evaluated in adult zebrafish (Danio rerio) gonad upon full life-cycle exposure to chronic environmentally low levels of EE₂ (i.e., 0.5, 1 and 2 ng/L EE₂). Real time PCR was used to analyse the expression levels of nucleotide excision repair genes (NER) as well as the tumor suppressor p53 and downstream selected effectors, i.e., p21 (cyclin-dependent kinase inhibitor), GADD45α (growth arrest and DNA damage induced 45, alpha), bax (bcl2-associated X protein) and p53 key regulator MDM2 (murine double minute 2 protein). NER genes transcription levels in gonads did not differ significantly among treatments. In contrast, the number of transcripts of p53 gene was significantly increased in male gonads at all EE₂ exposure concentrations and in females at 1 ng/L EE₂. Despite the increase in p53 transcripts, transcription levels of p21, GADD45α and bax genes were not affected upon EE₂ treatment, whereas MDM2 gene expression significantly increased in females at the intermediate EE₂ dose (1 ng/L). Overall, the present study indicate that chronic low levels of EE₂ significantly modulates the transcription of p53, a key gene involved in DNA repair, particularly in male zebrafish gonads, which supports the hypothesis of an impact of EE2 in male gonad DNA repair pathways.

Review of oil and HNS accidental spills in Europe: identifying major environmental monitoring gaps and drawing priorities

The European Atlantic area has been the scene of a number of extensive shipping incidents with immediate and potential long-term impacts to marine ecosystems. The occurrence of accidental spills at sea requires an effective response that must include a well executed monitoring programme to assess the environmental contamination and damage of the affected marine habitats. Despite a number of conventions and protocols developed by international and national authorities that focused on the preparedness and response to oil and HNS spills, much remains to be done, particularly in relation to the effectiveness of the environmental monitoring programmes implemented after oil and HNS spills. Hence, the present study reviews the status of the environmental monitoring programmes established following the major spill incidents over the last years in European waters, aiming at identifying the key monitoring gaps and drawing priorities for an effective environmental monitoring of accidental spills.

Drifting towards the surface: a shift in newborn pipefish's vertical distribution when exposed to the synthetic steroid ethinylestradiol

Endocrine disrupting chemical (EDC) effects during early life have the potential to modulate population structure, either directly through increased mortality or by causing inappropriate aggregation events, thus affecting the number of young that will reach adulthood. An alteration in the dispersal and recruitment patterns can also impair the connectivity among geographically distant populations. However, the detection of EDC-induced effects occurring after egg hatch, when newborns increase their chances of contacting with environmentally dispersed contaminants, is not a simple process as effects might be masked by the large natural mortality rates that usually occur during fish early life. Since there is a lack of information regarding the impact of EDCs on fish early life dispersal patterns, particularly on vertical migrations patterns, the effects of environmentally relevant concentrations of EE(2) on the vertical distribution of newborn fish was assessed through an ex situ exposure experiment. Syngnathus abaster newborns were exposed to EE(2) (nominal concentrations of 8, 12 and 36 ng L(-1)) and the dynamics of their vertical distribution was monitored for up to 40 d. No significant differences in overall mortality were observed between treatments or in the dynamics of the registered death curves. Nevertheless, an alteration in the distribution patterns was observed. The commonly benthic newborn tended to shift their vertical distribution towards the surface, in a dose-dependent manner. Curiously, a follow up of the exposed pipefish confirmed that EE(2) effects were also noticeable upon sexual maturity, namely by the alteration of several primary and secondary sexual characters. The observation that vertical distributional patterns, at least in pipefish, are clearly altered at environmentally relevant EE(2) concentrations indicates that EDC's impact in fish larvae behaviour should be considered when addressing the effects of contaminants, given the obvious implications on population connectivity, stability and persistence.

The unpredictable effects of mixtures of androgenic and estrogenic chemicals on fish early life

Estuarine shallow areas and coastal lagoons are known to receive and concentrate multiple inputs, either from land, rivers or coastal areas, being intensively impacted by chemical contamination, namely endocrine disrupting chemicals (EDCs). Despite the ubiquitous coexistence of several classes of EDCs in most of these aquatic ecosystems, there is still limited information regarding their combined effects. Furthermore, given the immediate implications for population dynamics, the available laboratory studies almost invariably focus on very specific life history stages, such as embryonic development or reproduction, thus creating a gap on our knowledge of what happens in between. During this 'intermediate phase', the newborn larvae and juveniles face numerous challenges whose outcome may impair reproduction or even survival. The black-striped pipefish, Syngnathus abaster, member of the Syngnathidae family (comprising pipefish, seahorses and seadragons), usually breeds in coastal areas such as estuaries, where its newborns are immediately exposed to EDCs. Given the ongoing decline of pipefish populations, together with the observed shrinkage and fragmentation of seagrass meadows, known to be impacted by EDCs, a first reasonable question to address is if pipefish newborns respond to environmentally relevant concentrations of ubiquitous EDCs, either single or in combination. Hence, a seven days exposure experiment to the estrogenic chemical ethinylestradiol (EE(2)) and the androgenic chemical tributyltin (TBT), single and in binary mixtures, was conducted. Selected behavioural (e.g. predator avoidance) and developmental variables (e.g. growth) were monitored in pipefish juveniles after EDCs insult. The obtained results indicate that EE(2), TBT, or their combined exposure, do impact pipefish early life. However, the pattern of results emerging from the measured variables clearly indicates that mixtures significantly modulate newborn responses in distinct ways when compared to individual chemical's exposure. These findings further demonstrate the importance of addressing the issue of chemical mixtures of pollutants acting through dissimilar mode of action. Independently of all the observed response variations, an ultimate conclusion seems certain: EE(2) and TBT, single or in combination, induce disruption patterns able to imbalance pipefish survival. Since these (as well as other) contaminants are present in estuarine areas, profound implications in population structure could be expected, ranging from a decrease in recruitment to a disruption of sexual selection. Inexorably, these stressors simultaneously operate in already declining populations.

Tributyltin-induced imposex in marine gastropods involves tissue-specific modulation of the retinoid X receptor

Despite the large number of studies on the phenomenon of imposex, the mechanism underlying the abnormal growth of male sexual characters onto females in numerous gastropod species is yet to be fully elucidated. Although several hypotheses have been raised over the years, a convincing body of evidence indicates that tributyltin-induced imposex involves the abnormal modulation of the retinoid X receptor (RXR). Here, we investigate the RXR gene transcription at different timings and tissues upon exposure to environmentally relevant concentrations of tributyltin (TBT) (100 ng Sn/L TBT) in both genders of the imposex susceptible gastropod Nucella lapillus. RXR gene transcription was determined at two time-points (i.e., before and after imposex initiation) by quantitative Real Time PCR in potential target tissues: the central nervous system (CNS), penis/penis forming area (PFA), gonads and digestive gland. TBT-exposure altered transcription of RXR gene in a tissue and sex specific manner. In the CNS, a significant down-regulation was observed in females both before and after imposex initiation (P≤0.01 and P≤0.05, respectively). A similar trend was observed in male CNS at the first time-point, although differences between control and the TBT-exposed group were just above significance (P=0.059). The penis/PFA showed no differences in transcription of RXR gene between control and TBT exposed female snails before imposex induction, or before and after imposex initiation for males. However, male penis showed higher transcription of RXR gene in comparison to the PFA of females. After imposex has been induced, a significant (P≤0.001) increase in transcription of RXR gene was observed in penis of females with vas deference sequence index (VDS) levels of 3-4 in comparison with the PFA of both control and imposex females with VDS 1-2. At advanced stages of imposex, females displayed RXR transcription patterns in penis identical to those of males, which points to a functional role of RXR in the penis of both genders. In the other tissues, gonads and digestive gland, RXR gene transcription was not affected by TBT, at any of the analysed time-points. These patterns of RXR gene transcription upon TBT exposure highlight the pivotal involvement of the CNS in the mechanism of imposex induction. We integrate the results in a conceptual model, and discuss the central role of RXR and the retinoic acid signalling pathways in imposex and male genitalia formation in gastropods.

Hazardous and Noxious Substances (HNS) in the marine environment: prioritizing HNS that pose major risk in a European context

Increases in the maritime transportation of Hazardous and Noxious Substances (HNS), alongside the need for an effective response to HNS spills have led environmental managers and the scientific community to focus attention on HNS spill preparedness and responsiveness. In the context of the ARCOPOL project, a weight-of-evidence approach was developed aimed at prioritizing HNS that pose major environmental risks to European waters. This approach takes into consideration the occurrence probability of HNS spills in European Atlantic waters and the severity of exposure associated with their physico-chemical properties and toxicity to marine organisms. Additionally, a screening analysis of the toxicological information available for the prioritization of HNS was performed. Here we discuss the need for a prioritization methodology to select HNS that are likely to cause severe marine environmental effects as an essential step towards the establishment of a more effective preparedness and response to HNS incidents.

Validating a multi-biomarker approach with the shanny Lipophrys pholis to monitor oil spills in European marine ecosystems

Oil spills are an importance source of polycyclic aromatic hydrocarbons (PAHs) in the aquatic environment. Intertidal communities are particularly sensitive since most organisms from these ecosystems are sessile or present reduced mobility. Hence, it is important to validate the use of resident species as sentinels to characterize the impact of oil spills on the rocky shores and the improvement during the restoration process. Recently the advantages of using the shanny Lipophrys pholis in pollution monitoring within the northwestern Atlantic coast has been pointed out. Therefore, with the aim of further validating the use of L. pholis in pollution monitoring associated with petrogenic hydrocarbon contamination, a multi-biomarker approach study was carried out 1 week after a moderate oil spill from the waste treatment plant (WTP) of the major Portuguese refinery in the north of Portugal (Petrogal). Fish collected at 2 km from the accident displayed a significant induction of ethoxyresorufin-O-deethylase activity (EROD) and fluorescent aromatic compounds (FACs) in bile (up to a 5-fold induction) in comparison with the pre-spill scenario, and a 15% induction in erythrocytic nuclear abnormalities (ENA), a biomarker of genotoxicity. In contrast, no significant differences were recorded in the reference site. In order to better characterize the time-course accumulation of FACs in bile after a PAH insult, laboratory exposure of L. pholis to benzo[a]pyrene (B[a]P) was performed. A clear dose-response accumulation of B[a]P metabolites was observed that closely reflected nominal exposure concentrations already after 3d. Overall, the findings of the present study highlight the potential of L. pholis in pollution monitoring dealing not only with chronic contamination, but also with oil spill accidents of a moderate scale. Taking into consideration that EROD and FACs determinations in L. pholis are cost effective, rapid and easy to use, they offer a great potential to be incorporated into risk assessment of PAHs in the scope of national monitoring programs and the European Water Policy legislation.

Sexing blennies using genital papilla morphology or ano-genital distance

Information on the genital morphology of male and female Lipophrys pholis is provided, as well as for two other sympatric blenniid species, Coryphoblennius galerita and Lipophrys trigloides. The use of non-invasive sex determination procedures described may be extremely useful not only for ecological studies but also as a proxy for the detection of environmental exposure to endocrine disruptive chemicals, given that blennies have been proposed as potential sentinel species for chemical contamination.

Disruption of zebrafish (Danio rerio) embryonic development after full life-cycle parental exposure to low levels of ethinylestradiol

Exposure of fish to the synthetic estrogen ethinylestradiol (EE2) has been shown to induce a large set of deleterious effects. In addition to the negative impact of EE2 in reproductive endpoints, concern has recently increased on the potential effects of EE2 in fish embryonic development. Therefore, the present study aimed at examining the effects of EE2 on the full embryonic development of zebrafish in order to identify the actual phases where EE2 disrupts this process. Hence, zebrafish were exposed to environmentally relevant low levels of EE2, 0.5, 1 and 2ng/L (actual concentrations of 0.19, 0.24 and 1ng/L, respectively) from egg up to eight months of age (F(1)), and the survival as well as the occurrence of abnormalities in their offsprings (F(2)), per stage of embryonic development, was investigated. A thorough evaluation of reproductive endpoints and transcription of vtg1 gene in the parental generation (F(1)) at adulthood, was performed. No significant differences could be observed for the two lowest EE2 treatments, in comparison with controls, whereas vtg1 transcripts were significantly elevated (40-fold) in the 2ng/L EE2 treatment. In contrast to the findings in the F(1) generation,a significant concentration-dependent increase in egg mortality between 8 and 24hours post-fertilization (hpf) was observed for all EE2 treatments, when compared with controls. The screening of egg and embryo development showed a significant increase in the percentage of abnormalities at 8 hpf for the highest EE2 concentration, a fact that might explain the increased embryo mortality at the 24 hpf time-point observation. Taken together, these findings indicate that the two lowest tested EE2 concentations impact late gastrulation and/or early organogenesis, whereas exposure to 2ng/L EE2 also disrupts development in the blastula phase. After early organogenesis has been completed (24 hpf), no further mortality was observed. These results show that increased embryo mortality occurs at EE2 levels below those inducing reproductive impairment and vtg1 gene induction in the male parental generation, thus suggesting that EE2 may impact some fish populations at levels below those inducing an increase in vtg1 transcripts. Hence, these findings have important implications for environmental risk assessment, strongly supporting the inclusion of embryonic development studies in the screening of endocrine disruption in wild fish populations.

Organotin levels in seafood from Portuguese markets and the risk for consumers

Because of their ubiquity in the aquatic environment, the antifouling agent tributyltin (TBT) and other organotins (OTs) accumulate through the food chain, resulting in the occurrence of OTs in seafood products. Despite a high number of studies on the negative impact of TBT in female prosobranch gastropods, few works exist in Europe reporting the levels of these compounds in edible parts of marine organisms used in Human diet. Therefore, within the scope of an EU project OT-SAFE the levels of several OTs were evaluated in the most relevant seafood products for Portuguese consumers. Butyltins (BTs) have been detected in all analysed groups (fish, crustaceans, bivalves, cephalopods), whereas triphenyltin, tricyclohexyltin, monooctyltin and dioctyltin could not be detected and tetrabutyltin was present above detection limits in a single sample. In general, levels of BTs in edible parts of fish, crustaceans and cephalopods collected in Portuguese markets during this study are in the lower range of that reported for these animal groups from other locations (i.e. below 30ngg(-1) wet weight). In contrast, moderate to high concentrations have been observed in bivalves (up to 275ng TBTg(-1) wet weight). While most samples showed TBT plus DBT levels below the tolerable average residue levels (TARL), which may indicate low risk for consumer, four bivalve samples displayed BT levels above TARL, thus indicating that higher bivalve consumer groups may be at risk. The results found are discussed in relation to the potential risk for consumers and integrated with recent finds on the molecular targets of OTs in mammals.

Vitellogenin gene expression in the intertidal blenny Lipophrys pholis: a new sentinel species for estrogenic chemical pollution monitoring in the European Atlantic coast?

The presence of estrogenic chemicals (ECs) in the aquatic environment is a growing problem. While most attention was initially given to fresh water and estuarine ecosystems, it is now evident that coastal marine areas are also vulnerable to these pollutants. The use of vitellogenin induction in male fish, a specific biomarker of EC exposure, has been the most widely applied methodology. However, in some occasions, the high mobility and migratory behaviour of common sentinel fish species makes data interpretation difficult. Hence, there is the need to validate new sentinel marine fish species which should display, among other features, a strong homing behaviour. The shanny, Lipophrys pholis, is an intertidal fish that combines many of the required characteristics for a sentinel species: abundance and easy of catch, wide geographical distribution and restricted home range. Thus, in order to evaluate, in the field, the species sensitivity to ECs, L. pholis males were collected at two sites reflecting different degrees of anthropogenic contamination. The vitellogenin II gene (VTGII) was isolated and its liver expression evaluated by RT-PCR in the field samples. A significant induction of gene expression was observed in the specimens collected in the urban area, if compared to the reference site, which suggests exposure to ECs. Moreover, a 21-days laboratory exposure to environmental relevant concentrations of ethinylestradiol (EE2) was also performed. A significant induction of L. pholis VTGII gene in EE2 exposed males was observed suggesting similar sensitivity to that of other marine/estuarine fishes. Even though further validation is currently in progress, the available data indicates that L. pholis is responsive to ECs, thus favouring its future integration in monitoring programmes designed to evaluate the presence of ECs in European marine ecosystems.

Organ-specific accumulation and elimination patterns of PCBs in adult seabass (Dicentrarchus labrax)

The present study quantifies and explains the differences between measured organ-specific polychlorinated biphenyls (PCBs) accumulation and elimination kinetics in seabass (Dicentrarchus labrax), comparing these results with calculations using the generic model OMEGA. Specimens of approximately 250 g were selected and fed with contaminated food with PCBs 18, 44, 49, 52, 101, 105, 118, 138, 180 and 187. The OMEGA model was applied using a measured biomass (re)production coefficient and the food ingestion coefficient. It produced estimations of total body concentrations within a factor between 1.5 and 7.0 times of the measured and it also reproduced the general trend of the PCB concentrations during the experiment. This study allows us to confirm that internal distribution of PCBs is slow, producing significant differences in the tissues elimination rate constants and consequently in tissues bioaccumulation factors (BAF). The distribution of PCBs within the organism was slower than reported before, due to the bigger body size and the high lipid content of these fish.

Anti-androgenic effects of sewage treatment plant effluents in the prosobranch gastropod Nucella lapillus

Recent studies performed under laboratory conditions have shown that single exposure to high levels of several xenoestrogens is able to induce imposex in at least two neogastropod species. In an attempt to evaluate if xenoestrogens, at environmentally relevant conditions, do contribute to imposex induction, we have tested the effects of a mixture containing xenoestrogens (municipal sewage effluents) on imposex development in the dogwhelk Nucella lapillus. Exposure for 3 months to the raw (0.25% and 1%) and the final sewage effluent (12.5% and 50%) rendered no increase in the severity of imposex. Conversely, as exposure to high concentrations of natural steroids, estradiol and estrone, had previously been shown to partially rescue imposex development under laboratory conditions, we have also tested if exposure to the final sewage effluent could ameliorated the severity of imposex induction by tributyltin (TBT). The results demonstrated that co-exposure to the final sewage effluent leads to a decrease trend in the severity of imposex in the presence of TBT. Within the studied imposex parameters, the Relative Penis Size index (RPSI) was the most affected with a 50% decrease in the effluent 12.5% plus TBT exposed group and 25% decrease in the effluent 50% plus TBT, if compared with the TBT alone. Overall, our results give further support to the use of imposex in N. lapillus as a specific biomarker of TBT contamination. However, in areas of high inputs of sewage effluents, the assessment of TBT contamination by the use of the imposex phenomenon should ideally also include data on the tissue levels of butyltins.

The use of the shanny Lipophrys pholis for pollution monitoring: a new sentinel species for the northwestern European marine ecosystems

The contamination of aquatic ecosystems by organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) is a matter of great concern. Mussels have been extensively used as sentinel species in a large number of monitoring programs. However, the use of bivalves as the sole species has some limitations, because they are not as responsive as fish to Aryl Hydrocarbon Receptor agonists. Hence, for many marine areas, there is the need to validate new sentinel fish species that can be used in the assessment of pollution by organic contaminants. The shanny Lipophrys pholis is an intertidal fish that combines many characteristics required in a sentinel species: is abundant and easy to catch, has a wide geographical distribution and restrict home range. After larvae recruitment to the intertidal rocky shores, they remain in the same area for the rest of the life-cycle, thus reflecting local pollutants exposure. In order to evaluate the species sensitivity to organic contaminants under field conditions, L. pholis were collected at six sites reflecting different degrees of anthropogenic contamination. The induction of two biomarkers extensively validated in the assessment of PAHs contamination ethoxyresorufin-O-deethylase activity (EROD) and Fluorescent Aromatic Compounds (FACs) was evaluated. In parallel, mussels were collected at the same locations and levels of 16 PAHs and selected heavy metals determined. Overall, the specimens collected in the urban areas showed a significant induction of EROD and FACs (up to a six-fold induction) if compared with the reference sites. Additionally, a positive correlation was observed between the biomarkers and PAHs levels in mussel tissues. Even though further validation is currently in progress, the available data indicate that L. pholis is responsive to organic contaminants such as PAHs, suggesting its future integration in monitoring programmes designed to evaluate the presence of these contaminants in European marine ecosystems.

Imposex induction is mediated through the Retinoid X Receptor signalling pathway in the neogastropod Nucella lapillus

The imposex phenomenon in female prosobranch gastropods provides one of the best documented examples of endocrine disruption in wildlife. While many field studies have demonstrated the negative impact of tributyltin (TBT) upon female gastropods, the mechanism(s) underlying imposex development has not yet been fully clarified. Over the years several hypotheses have been raised to determine the biochemical and molecular determinants of this process. Nevertheless, the interplay between the different suggested pathways (neuroendocrine, steroid and retinoid) is still unknown. Hence, through a combination of exposure experiments, we show that the 9-cis-retinoic acid (9cisRA), the proposed natural ligand of the retinoic X receptor (RXR), induces imposex in females of Nucella lapillus to the same degree as tributyltin, when administered at similar concentrations (1 microg/g body weight). Methoprene acid, a selective ligand for RXR, also induces imposex, albeit to a lower degree than that of the positive control. In contrast, testosterone significantly induced imposex, but had no effect on female penis induction, while the neuropeptide APGWamide had no effect on imposex development. These results clearly demonstrate that imposex induction in N. lapillus is mediated through the modulation of the RXR signalling pathways. In addition to the effects reported in female dogwhelks, both TBT and RA significantly increased male penis length, thus suggesting that TBT may also impact male secondary sex organs through the RXR signalling pathways. As a step for future studies, we have cloned the orthologue of N. lapillus RXR and provide experimental evidence that it binds 9cisRA. Finally, the basal expression level of RXR in several tissues of N. lapillus was determined through real-time PCR, thus showing that RXR is ubiquitously expressed in mollusc tissues, with the highest expression levels being recorded in female and male gonads. The mechanistic impacts of the overall findings to the imposex process are discussed.

Genotoxic effects of binary mixtures of xenoandrogens (tributyltin, triphenyltin) and a xenoestrogen (ethinylestradiol) in a partial life-cycle test with Zebrafish (Danio rerio)

A partial life-cycle test with the model fish Danio rerio was performed in order to evaluate the genotoxic potential of binary mixtures of xenoandrogenic (tributyltin--TBT; triphenyltin--TPT) and an estrogenic compound (ethinylestradiol--EE2). Five days post-fertilisation larvae were diet-exposed to environmental relevant concentrations of TBT and TPT (25 ng/g-100 ng/g), and water-exposed to ethinylestradiol (3.5 ng/L) for a four-month period; binary mixtures of TBT plus EE2 and TPT plus EE2 were run in parallel. The erythrocytic nuclear abnormalities (ENA) assay in circulating erythrocytes was used to evaluate genotoxicity in the end of the four-month exposure period. A significant increase (p<0.05, Kruskall-Wallis non-parametric ANOVA) in ENA frequency, in comparison with control animals, was observed in those animals exposed to TBT and TPT (the highest doses only), and to EE2 and the binary mixtures, although neither synergistic nor additive effects of the tested compounds were evident. Overall, the results clearly indicate that chronic exposure to low levels of TBT, TPT, EE2 and binary mixtures of TBT plus EE2 and TPT plus EE2 are genotoxic to zebrafish, which may suggest that wild fish populations may be under increased DNA damage in areas contaminated by these endocrine disrupting chemicals.

Tilapia larvae Aroclor 1254 exposure: effects on gonads and circulating thyroid hormones during adulthood

Aroclor 1254 a polychlorinated biphenyls (PCBs) mixture, when administrated through the diet, was previously found to inhibit adult tilapia (Oreochromis niloticus) reproduction. Since fish larvae can be more sensitive to contaminants, the objectives of this study were to evaluate in adults the impact in gonad development and in thyroid function of Aroclor 1254 administrated at larvae stages. Aroclor 1254 exposed tilapia presented both ovary and testicular alterations and a decline in T4 plasma concentration while T3 remained unaltered. This work shows exposure to Aroclor 1254 during tilapia early life stages causes a disruption of the reproductive axis that enables reproduction.

The estrogen receptor of the gastropod Nucella lapillus: modulation following exposure to an estrogenic effluent?

The molecular targets of estrogenic endocrine disrupting chemicals have been studied in detail in vertebrates. The lack of basic endocrine knowledge impairs similar approaches for invertebrates. Evidence indicates that the signalling pathways of invertebrates may also be a target of estrogenic chemicals (ECs). In fact, the exposure to effluents containing ECs has been reported to impact mollusc reproduction. Despite the reported estrogen independence of the mollusc nuclear estrogen receptor (ER), its role in EC-induced toxicity has not been investigated in vivo. Therefore, we have cloned the ER of the gastropod Nucella lapillus and evaluated the effects of a mixture of estrogenic chemicals (sewage effluent) on its expression in the ovary. Here, we show that the exposure to a raw domestic/industrial effluent, impact ER expression with a simultaneous reproductive maturation. These results highlight the need to further investigate the role of ER on the reproductive process in prosobranch gastropods and whether this signalling pathway is prone to disruption by ECs.

The effect of long-term depuration on levels of oxidative stress biomarkers in mullets (Mugil cephalus) chronically exposed to contaminants

The present study aimed to obtain additional data on the effect of long-term depuration on the levels of oxidative stress biomarkers, and to clarify the role of mullets for monitoring pollution in River Douro estuary. Mullets chronically exposed to a mixture of contaminants in Douro estuary were captured in Spring of 2001, 2002 and 2003. The activities of antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPX); and oxidative damages in lipids (lipid peroxidation) and in proteins (protein carbonyl content) were assessed at capture day and after transfer to unpolluted seawater for 1, 4 and 8 months. An overall decrease in the activities of the antioxidant enzymes was detected, except for the GPX after 4 months depuration. CAT activity exhibited the more significant decrease at the end of the long-term depuration. The decrease in SOD activity after 1 month of depuration was then maintained during the remaining depuration period. Regarding oxidative damages, a decrease in lipid peroxidation as well as the content of oxidised proteins was observed during depuration. Indeed, at capture the activities of antioxidant defences were higher as a result of the formation of reactive oxygen species (ROS) from the metabolism of pollutants. The oxidative damaged molecules were repaired or degraded during the depuration period, supporting the use of such damages as indicators of exposure to pro-oxidant pollutants.

Depuration of PCBs and DDTs in mullet under captivity clean conditions

Contaminated mullet (Mugil cephalus) from Douro estuary was allowed to depurate in clean water and fed with uncontaminated food. Levels of PCBs and DDTs in muscle and liver, and ethoxyresorufin O-deethylase (EROD) activity were measured at day 0, 21, 120 and 270. In specimens captured in the estuary total PCB and total DDT concentrations were 311 and 65 ng g(-1) in muscle and 686 and 115 ng g(-1) in liver, respectively. At day 21, after an initial 10-15 days period of starvation, organochlorines levels increased in both analyzed tissues. Thereafter levels of all PCB congeners and DDT compounds decreased in muscle, and at the end of the 270 days were 49 ng g(-1) and 13 ng g(-1), respectively. These decreases were correlated to the lipids consumption. In liver no relationship between those variables was observed, suggesting different elimination processes and eventual exchange of contaminants between muscle and liver. EROD activities decreased in the first days of depuration experiment, but showed no relations with analysed organochlorines.

The effect of paraquat on hepatic EROD activity, liver, and gonadal histology in males and females of Nile tilapia, Oreochromis niloticus, exposed at different temperatures

The activity of fish monooxygenases has been used as a monitoring tool to evaluate contamination by cytochrome P450 inducing agents. In this study ethoxyresorufin O-deethylase (EROD) activity was analyzed in males and females of Nile tilapia exposed to a low concentration of paraquat (PQ) at 17 degrees C and 27 degrees C. PQ-treated fish showed a high hepato-somatic index, except females acclimated at 17 degrees C. No differences were found for the gonado-somatic index (GSI) between males. However, PQ-treated females showed high GSI values (6.46+/-1.75) when compared with the control group (2.30+/-0.26) maintained at 27 degrees C. Males and females exposed to PQ showed higher microsomal protein values than the control group (9.46+/-0.22 vs. 6.20+/-0.18 at 17 degrees C; 9.51+/-0.35 vs. 4.70+/-0.19 mg of protein at 27 degrees C, in PQ-treated and control groups, respectively). The EROD activity was high in females exposed to PQ when compared with the control group at 17 degrees and 27 degrees C. The liver histology showed that PQ also caused some hepatic alterations of parenchyma, like vacuolization, necrosis, and an increase of macrophages aggregates and eosinophilic granular cells. Females exposed to PQ showed a greater increase of late-vitellogenic (22.2+/-3.2) and mature (12.1+/-2.0) percentage of oocytes than the control group (9.9+/-3.0 and 8.0+/-4.3, respectively), and a lower percentage of primary oocytes (8.0+/-3.3) at 27 degrees C. In short, this work has advanced new knowledge on the influence of gender in biotransformation activity and the reproductive activity of Nile tilapia exposed to a low concentration of paraquat, and demonstrated that their effects could be observed at different temperatures.

Urogenital papilla feminization in male Pomatoschistus minutus from two estuaries in northwestern Iberian Peninsula

Recently, male urogenital papilla feminization (UGPF) in the sand goby Pomatoschistus minutus was reported in several UK estuaries with high levels of estrogenic compounds. The fact that this species is also common in southern European estuaries, together with its life-cycle characteristics, prompted us to investigate P. minutus UGPF in the northwestern of Iberian Peninsula. Specimens of P. minutus were periodically sampled during 2004 at several locations in two estuaries (Minho and Lima). Evidence for UGPF was recorded in both estuaries, the highest incidence being observed in the Lima estuary (50%). Estrogen levels (17beta-estradiol and estrone) above 100 pg/l were observed in both estuaries, the higher concentrations being found in the Lima estuary. Overall, the results suggest a relationship between the feminization of male P. minutus urogenital papilla and the presence of estrogenic compounds. In the future, more in-depth studies are required in order to use P. minutus as a sentinel species for estrogenic compound monitoring in estuaries.

The effect of long-term depuration on phase I and phase II biotransformation in mullets (Mugil cephalus) chronically exposed to pollutants in River Douro Estuary, Portugal

Pollutants such polycyclic aromatic hydrocarbons (PAHs) are released into the environment by urban communities and industries and the enzymes that catalyse the biotransformation of pollutants play a key role regarding the accumulation of these compounds in fish species inhabiting these areas. In this study the relationship between phase I (EROD activity) and phase II (GST activity) and PAH metabolites was measured in grey mullet (Mugil cephalus) after capture in the Douro estuary, and after long-term depuration in an unpolluted laboratory environment. The results showed a significant decrease in EROD activity after 1 month and in bile metabolites after 4 months in captivity, with both maintaining reduced levels at 4 and 8 months depuration. Liver GST activity did not showed significant changes. This study provides evidence that Douro estuary waters contain bioavailable PAHs that can be associated with the induction of cytochrome P450, and that mullets have the ability to metabolise and eliminate PAHs.

Estrogens counteract the masculinizing effect of tributyltin in zebrafish

Recently, it has been demonstrated that the biocide tributyltin (TBT) can interfere with fish sex differentiation, leading to a bias of sex toward males. On the contrary, it is well known that estrogenic compounds can induce fish feminization. Yet, the combined effects of mixtures of androgenic and estrogenic compounds on fish sex differentiation have never been investigated before, even though in the environment animals are frequently exposed to both groups of xenobiotics. Therefore, in order to investigate whether exposure to estrogenic compounds can block the masculinizing effect of TBT, 5 days post-fertilization zebrafish (Danio rerio) larvae were exposed for a four month period to TBT and to the synthetic estrogen-ethinylestradiol (EE2). The fish were fed a diet containing TBT at nominal concentrations of 25 and 100 ng TBT/g, and two groups of animals were also dosed with TBT plus EE2 at nominal water concentration of 3.5 ng/L, using a flow-through design. As expected, fish exposed to TBT showed a bias of sex toward males (62.5% males in control tanks and 86% and 82% in TBT 25 and TBT 100 ng TBT/g, respectively). Co-exposure to EE2 completely blocked the masculinizing effect of TBT, with 7% males in the TBT 25 ng/g + EE2 treatment and 0% in the EE2 alone and in the TBT 100 ng/ + EE2 exposed groups. These results clearly indicate that EE2, at environmentally relevant concentrations, can block the TBT masculinizing effects in zebrafish, which suggests that in the aquatic environment the presence of estrogens may neutralize the fish masculinizing effect of TBT. Our findings highlight the need of testing the combined effects of contaminants, as single exposure studies may not be sufficient to predict the effects of mixtures of xenobiotics with antagonistic properties.

New insights into the mechanism of imposex induction in the dogwhelk Nucella lapillus

In an attempt to clarify the mechanism(s) of tributyltin-mediated imposex induction in females of the neogastropod Nucella lapillus, dogwhelks collected in an almost imposex free population were exposed to several treatments for a 3 month-period, and the effects on imposex induction and testosterone/estradiol levels were evaluated. As a positive control, tributyltin (50 ng TBT Sn/L) clearly induced imposex and led to a significant increase in the severity of the phenomenon. In contrast, although a selective P450 aromatase inhibitor (formestane at 0.3 mg/L) was capable of imposex induction, it failed to increase its severity. A vertebrate androgen receptor (AR) antagonist (cyproterone acetate at 1.25 mg/L) in combination with TBT completely blocked the imposex induction capacity of TBT. On the other hand, an estrogen receptor antagonist (tamoxifen at 0.3 mg/L) rendered no effect. The determination of steroid levels in female specimens revealed that TBT induces an elevation of free testosterone (but not the total amount, free+esterified), while the co-administration of the anti-androgen and TBT was able to rescue the increase of free testosterone levels. Despite a minor decrease in the amount of testosterone-fatty acid esters in the TBT group, significant differences in esterified testosterone were not found among treatments. On the contrary, free estradiol levels were elevated in the TBT, anti-androgens and TBT plus anti-androgens groups. These results indicate that free estradiol biosynthesis in TBT-exposed females does not seem to be affected. Overall, our results demonstrate that a selective aromatase inhibitor can induce imposex in N. lapillus but not to a similar extent of TBT, which may suggest the involvement of other mechanism in imposex induction, besides aromatase inhibition. Additionally, the study points to the involvement of AR receptors in imposex induction.

Oxidative stress biomarkers in two resident species, mullet (Mugil cephalus) and flounder (Platichthys flesus), from a polluted site in River Douro Estuary, Portugal

Exposure of marine animals to certain pollutants can enhance reactive oxygen species (ROS) production with subsequent damage to macromolecules and alterations in oxidant defences levels. Aimed at correlating the tissue concentration of certain contaminants (PCBs, DDT) with antioxidant defence levels and oxidative damages, two fish species with different life strategies (mullet, Mugil cephalus, and flounder, Platichthys flesus) were collected in the Douro Estuary (NW Portugal). After capture, the fish were left to depurate for 1 month in clean seawater. The levels of the two antioxidant enzyme activities revealed that they are species-dependent with mullet's livers showing higher superoxide dismutase (SOD) (13.2+/-0.5 U/mg protein) and catalase (CAT) (15.5+/-1.0 mmol/min/mg protein) activities than flounder (SOD: 7.9+/-0.9 U/mg protein; CAT: 11.1+/-0.8 mmol/min/mg protein). After 1 month in captivity the antioxidant enzymes activities in liver decreased in mullets, while for flounders the responses were not consistent because during the experimental period flounders did not ate and responses of antioxidant enzymes and oxidative damages were dependent on the fasting condition. The liver oxidative damages were evaluated by estimating oxidised lipids and proteins. Both species showed similar levels for these two parameters. The hepatic lipid peroxidation in flounder increased after 1 month in captivity, while in mullet an increase was observed only in summer and autumn. The oxidised protein content increased for both species after the depuration period. This study reveals differences between species under oxidative stress when exposed to pollutants. In a clean environment, the mullet's primary antioxidant defences decreased indicating that the animals living in Douro estuary were facing an oxidative stress. The data indicate that, namely in mullet, the presence of pollutants induce oxidative stress responses.

Organochlorine contaminants in flounder (Platichthys flesus) and mullet (Mugil cephalus) from Douro estuary, and their use as sentinel species for environmental monitoring

In order to monitor the presence of organic pollutants in Douro estuary (NW Portugal), two sentinel fish species, grey mullet (Mugil cephalus) and flounder (Platichthys flesus), were periodically sampled from May 2001 to April 2002. At all sampling periods, several specimens of both species were allowed to depurate in clean sea water. Levels of PCBs and DDTs were quantified in liver and muscle of both species. The accumulation of PCBs was higher in muscle of mullet, with a maximum of 345 ng/g dw, than in flounder, with a maximum 52ng/g dw. In the liver, flounder showed the highest levels (811 ng/g dw). Of the 18 congeners analysed, CBs 180 (hepta), 153 and 138 (hexachlorobiphenyls) were predominant in the tissue of both species. The maximum concentration of tDDT was measured in flounder liver (301ng/g dw). In contrast, a 10-fold higher tDDT was recorded in mullet muscle (63-69 ng/g dw and 8-16 ng/g dw for mullet and flounder, respectively). The hepatic ethoxyresorufin O-deethylase (EROD) activity was periodically determined. Consistently, a 10-fold higher enzymatic activity was present in mullet in comparison with flounder (1536 pmol/min/mg protein in mullet and 156 pmol/min/mg protein in flounder). In mullet, no correlation could be found between EROD activity and gonado-somatic index (GSI) or hepato-somatic index (HSI). On the contrary, during the reproductive season, female flounder showed a negative correlation between EROD activity and GSI. Despite being in clean sea water for 1 month period, no significant decrease in the tissue content of PCBs and tDDT was found. However, mullet's EROD activity followed a clear pattern, with a decrease enzymatic activity after being in captivity. Female flounder displayed a similar trend during the resting season. Yet, during the reproductive season, an increased EROD activity was recorded after being in captivity for 1 month, which may be associated with a modulation effect of steroids on CYP 1A1. Histological analyses of gonad revealed that 21% of male mullet displayed testis-ova, while no male flounder was found to show gonadal abnormalities. Overall, the study reports the accumulation of significant levels of PCBs and DDTs in the tissues of the studied species. It also provides important evidences supporting the use of grey mullet as a sentinel species for monitoring the presence of organic contaminants and xeno-estrogenic pollution in southern European estuaries.

Imposex and butyltin contamination off the Oporto Coast (NW Portugal): a possible effect of the discharge of dredged material

Imposex in the gastropod Hinia reticulata, a bioindicator for tributyltin (TBT) contamination, was investigated in locations at different distances from the Oporto harbour-dredged material discharge site. The degree of imposex found was inversely related to the distance to the discharge site, the highest imposex frequency being found closest to the discharge area. However, the levels of imposex found were low when compared with those reported for H. reticulata populations from moderately TBT-contaminated areas. Despite detectable levels of dibutyltin (DBT) and monobutyltin (MBT) in snail tissues (total butyltins ranging from 84 to 410 ng/g Sn dry wt.), TBT was below detection limit in all snail samples collected in open sea.

Plasma steroid levels in female flounder (Platichthys flesus) after chronic dietary exposure to single polycyclic aromatic hydrocarbons

The chronic effects of polycyclic aromatic hydrocarbons (PAHs) on ovary development, total hepatic lipids and plasma sex- and corticosteroid levels in female flounder (Platichthys flesus) were examined. Sexually mature feral female flounder were exposed via the diet to phenanthrene (0.5, 2.5 or 12.5 nmol/g food) or chrysene (0.4 nmol/g food) for 12 weeks, during the previtellogenic phase of the annual reproductive cycle. PAH exposure did not directly affect germ cell development since no structural and/or developmental differences were observed between control and exposed fish. On the contrary, all treatments resulted in altered plasma steroid levels. The most pronounced effect was the significant decrease in plasma 17 beta-estradiol to 19 +/- 11%, 27 +/- 7%, 63 +/- 20% and 61 +/- 12% in relation to control fish, respectively, in flounders exposed to 12.5, 2.5 or 0.5 nmol phenanthrene/g food and 0.4 nmol chrysene/g food. Impaired ovarian growth was not observed, most likely because experiments were ended before the period of vitellogenesis, even though a non-significant general decline in total hepatic lipids could be observed. Moreover, all exposed flounders, except fish fed with the highest amount of phenanthrene, showed a negative correlation between plasma 17 beta-estradiol and 17 alpha-hydroxyprogesterone levels (r = -0.46). One possible explanation is that PAH action may be mediated by a specific inhibition of steroidogenic enzymes. These findings provide evidence that selected PAHs are antiestrogenic xenobiotics with the capability to impair female teleost reproductive function.

Polycyclic aromatic hydrocarbons inhibit in vitro ovarian steroidogenesis in the flounder (Platichthys flesus L.)

The in vitro effect of polycyclic aromatic hydrocarbons (PAHs) on ovarian steroidogenesis of the flounder (Platichthys flesus L.) was determined. Fully vitellogenic ovary tissue was in vitro incubated in the presence of phenanthrene, benzo[a]pyrene or chrysene, using 17alpha-hydroxyprogesterone or androstenedione as precursors. Androstenedione (A), testosterone (T) and 17beta-estradiol (E(2)) synthesised in the presence of PAHs were assayed by radioimmunoassay and results compared with control incubations. In order to establish the effect of PAHs on the steroidogenic enzyme systems cytochrome P450 17,20-lyase (P450-17,20l), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and cytochrome P450 aromatase (P450-arom), results were also compared with the action of ketoconazole (KCZ) and aminoglutethimide (AMG), wich are, respectively, inhibitors of cytochrome P450 steroidogenic enzymes and of P450-arom. KCZ inhibited secretion of A and E(2) in 65% and T in 40%, as a consequence of inhibited P450-17,20l and P450-arom. AMG inhibited P450-arom, which resulted in decreased E(2) synthesis to approximately 50% of control incubations. All the three PAHs inhibited A secretion by approximately 50% and E(2) from 10 to 40%. Because steroid conjugation was also inhibited by phenanthrene, it could be concluded that PAH action was mediated by an inhibitory effect over P450-17,20l, 17beta-HSD and P450-arom. Except for 17beta-HSD, PAHs resembled KCZ, and P450-17,20l was the most sensitive to their inhibitory effect. In conclusion, PAHs strongly blocked the activity of P450-17,20l, a rate-limiting enzyme for conversion of C21 to C19 steroids, and showed, therefore, the potential to disrupt the reproductive cycle of fish living in polluted environments, due to impairment of steroid biosynthesis.

Evidence for an involvement of vitellogenin in the steroidogenic activity of rainbow trout (Oncorhynchus mykiss) vitellogenic oocytes

In vivo and in vitro the concentration of vitellogenin (VTG) inside the oocyte can alter VTG production by the liver, modulating the synthesis of 17beta-estradiol (E(2)) by the ovary. To gain a greater insight into this mechanism, the in vitro production of free and conjugated testosterone (T), E(2), and androstenedione (A) by rainbow trout oocytes from the early and middle vitellogenic stage was measured by radioimmunoassay. There was a decreased E(2) production that was greater in September (40%) than October (30%), by the oocytes incubated with the vitellogenic fraction. The production of E(2) conjugated as glucuronide was lower than sulfate (P < 0.05), but similar in control and VTG-incubated oocytes. Levels of free T increased from September to October, and conjugates were both produced at low levels, and no differences were detected between control and incubated VTG oocytes. The decreased synthesis of E(2) by oocytes incubated with VTG was not followed by an increase in the amount of T or conjugated E(2), because there were no differences under the two circumstances. However, there was a reduced synthesis of A with oocytes producing low levels of E(2). These results suggest that the presence of high levels of VTG in the oocyte suppresses the synthesis of A and E(2), affecting the activities of the enzymes C17,20 lyase and aromatase and probably interfering with the heme protein cytochrome P450 which in the ovary catalyses C 17,20 lyase (P450 c17) and aromatase (P450 arom).

Steroid metabolism by ovarian follicles of the sea bass Dicentrarchus labrax

Ovarian samples from fear sea bass, Dicentrarchus labrax, were collected for the in vitro incubations during the spawning period. Follicles with fully developed vitellogenic oocytes showing central germinal vesicle (stage I follicles) and follicles with oocytes showing initial germinal vesicle migration (stage II follicles) were treated with either (1) 20 microg sea bass hypophysis plus 50 ng 17-hydroxyprogesterone (17-P), (2) 20 microg hypophysis alone, (3) 50 ng 17-P alone and (4) media alone. Structure-activity experiments used stage II follicles treated with several dosages (0.1, 1.0 and 10.0 ng/ml) of either 17-P, 17,20beta-P, or 17,20beta,21-P. Free and conjugated (sulfates and glucuronides) levels of the established teleost oocyte maturation inducing steroids (MIS), i.e. 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) and 17,20beta,21-trihydroxy-4-pregnen-3-one (17,20beta,21-P) were measured in the incubation media by high performance liquid chromatography. Our results show that the synthesis of free and conjugated 17,20beta-P is constant (0.1-0.2 ng/ml) in all incubates. In contrast, the synthesis of free and conjugated 17,20beta,21-P is higher in incubates containing stage II follicles (up to 5 ng/ml) than in those having stage I follicles (up to 3 ng/ml; P<0.01). Structure-activity data reveal that 17-P is not effective at inducing in vitro germinal vesicle breakdown whereas both 17,20beta-P and 17,20beta,21-P are equally potent and highly effective. These results demonstrate that 17,20beta-P and 17,20beta,21-P are synthesized in vitro by follicles of sea bass and that sulfation is the main route for the metabolism of the C(21)-steroids in riper follicles. The highest levels of 17,20beta,21-P, found in incubates containing stage II follicles, points at 17,20beta,21-P, rather than 17,20beta-P, as the most probable MIS in sea bass, nonetheless, this hypothesis requires further confirmation.

Plasma and urine levels of C18, C19 and C21 steroids in an asynchronous fish, the tilapia Oreochromis mossambicus (Teleostei, Cichlidae)

Female and male tilapia, Oreochromis mossambicus, were treated with luteinizing hormone-releasing hormone analogue (LH-RHa) and pimozide (PIM) or with human chorionic gonadotropin (hCG) to stimulate gonadal development and sexual maturation. Plasma (both sexes) and urine (males) samples were collected periodically for steroid analysis by radioimmunoassay. Plasma levels of estradiol-17 beta (3-6 ng/ml) and testosterone, higher in female (up to 25 ng/ml) than in male (6-13 ng/ml; P < 0.05), were in the range of those established in other tilapia species. Plasma levels of the established teleost oocyte maturation-inducing steroids (MIS), that is 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P) and 17 alpha,20 beta, 21-trihydroxy-4-pregnen-3-one (17,20 beta,21-P) were low (1-9 ng/ml) and were not different between treated and control fishes at 8, 12, 16, 24, 48, 72 and 96 hr after injection. Furthermore, in male O. mossambicus, 17,20 beta,21-P was undetectable. Plasma levels of 3 alpha,17 alpha,21-trihydroxy-5 beta-pregnan-20-one (3,17,21-P-5 beta) were very high in both sexes (up to 700 ng/ ml), mostly in hormone-treated groups, whose levels were higher than controls (P < 0.05). Urine levels of conjugated 17,20 beta,21-P (glucuronides and sulphates) were not detectable, but those of 17, 20 beta-P (up to 25 ng/ ml) and 3,17,21-P-5 beta (up to 1 microgram/ml) were higher than free 17,20 beta-P and 3,17,21-P-5 beta measured in the plasma of the same animals (P < 0.05). Both LH-RHa + PIM and hCG induced sexual maturation of O. mossambicus (histological data); nevertheless, during that period all measured steroids, either in plasma or urine, almost did not fluctuate. Thus, this study does not make any comment about the MIS of tilapia. Nevertheless, the high levels of conjugated 3,17,21-P-5 beta and 17,20 beta-P in urine suggest a probable pheromone role for these steroids in this species.