Chronic nitrate exposure alters reproductive physiology in fathead minnows

Realistic nitrate concentrations diminish reproductive indicators in Skiffia lermae, an endemic species in critical endangered status

Goodeinae is a subfamily of critically endangered fish native to central Mexico. Populations of Skiffia lermae, a species belonging to this subfamily, have significantly decreased in the past two decades. A previous study showed that S. lermae is sensitive to acute nitrate-nitrogen (NO3-N) exposure, leading to noticeable changes in both behavioral and histopathological bioindicators. The aim herein was to determine the vulnerability of S. lermae to NO3-N exposure at realistic concentrations registered in freshwater ecosystems in central Mexico where the species was historically reported. Offspring of S. lermae were chronically exposed during 60 days to concentrations of 5, 10 and 20 mg NO3-N/L, with 2 mg NO3-N/L used as the reference value (control). Survival rate, feeding behavior, aquatic surface respiration, body growth, scaled mass index, immature red blood cells, as well as histopathological changes in branchial, hepatic and gonadal tissues were evaluated. Additionally, this study analyzed water quality in freshwater ecosystems where S. lermae presently persists. The results showed decreased survival as NO3-N concentration increased, as well as increased feeding latency, aquatic surface respiration and histological damage in the gills and liver. These organs showed differential sex-dependent responses to NO3-N exposure; females were more sensitive than males. In the ovaries, a decreased density of stage III oocytes was associated with increased NO3-N concentrations. No changes were observed in body growth and number of immature red blood cells. Concentrations recorded in the three freshwater ecosystems that S. lermae inhabit were below 2 mg NO3-N/L. Together, the results could explain why the species has disappeared from more contaminated freshwater ecosystems where NO3-N levels exceed 5 mg/L. Moreover, the study warns about the risks of increasing NO3-N concentrations in the current sites where the species lives.

Toxicity threshold and ecological risk of nitrate in rivers based on endocrine-disrupting effects: A case study in the Luan River basin, China

Nitrate, as a crucial nutrient, is consistently targeted for controlling water eutrophication globally. However, there is considerable evidence suggesting that nitrate has endocrine-disrupting potential on aquatic organisms. In this study, the sensitivity of various adverse effects to nitrate nitrogen (nitrate-N) was compared, and a toxicity threshold based on endocrine-disrupting effects was derived. The spatiotemporal variations of nitrate-N concentrations in the Luan River basin were investigated, and the associated aquatic ecological risks were evaluated using a comprehensive approach. The results showed that reproduction and development were the most sensitive endpoints to nitrate, and their distribution exhibited significant differences compared to behavior. The derived threshold based on endocrine-disrupting effects was 0.65 mgL-1, providing adequate protection for the aquatic ecosystem. In the Luan River basin, the mean nitrate-N concentrations during winter (4.4 mgL-1) were significantly higher than those observed in spring (0.7 mgL-1) and summer (1.2 mgL-1). Tributary inputs had an important influence on the spatial characteristics of nitrate-N in the mainstream, primarily due to agricultural and population-related contamination. The risk quotients (RQ) during winter, summer, and spring were evaluated as 6.7, 1.8, and 1.1, respectively, and the frequency of exposure concentrations exceeding the threshold was 100 %, 64.3 %, and 42.5 %, respectively. At the ecosystem level, nitrate posed intermediate risks to aquatic organisms during winter and summer in the Luan River basin and at the national scale in China. We suggest that nitrate pollution control should not solely focus on water eutrophication but also consider the endocrine disruptive effect on aquatic animals.

Changes in chemical occurrence, concentration, and bioactivity in the Colorado River before and after replacement of the Moab, Utah wastewater treatment plant

Long-term (2010-19) water-quality monitoring on the Colorado River downstream from Moab Utah indicated the persistent presence of Bioactive Chemicals (BC), such as pesticides and pharmaceuticals. This stream reach near Canyonlands National Park provides critical habitat for federally endangered species. The Moab wastewater treatment plant (WWTP) outfall discharges to the Colorado River and is the nearest potential point-source to this reach. The original WWTP was replaced in 2018. In 2016-19, a study was completed to determine if the new plant reduced BC input to the Colorado River at, and downstream from, the outfall. Water samples were collected before and after the plant replacement at sites upstream and downstream from the outfall. Samples were analyzed for as many as 243 pesticides, 109 pharmaceuticals, 20 hormones, 51 wastewater indicator chemicals, 20 metals, and 8 nutrients. BC concentrations, hazard quotients (HQs), and exposure activity ratios (EARs) were used to identify and prioritize contaminants for their potential to have adverse biological effects on the health of native and endangered wildlife. There were 22 BC with HQs >1, mostly metals and hormones; and 23 BC with EARs >0.1, mostly hormones and pharmaceuticals. Most high HQs or EARs were associated with samples collected at the WWTP outfall site prior to its replacement. Discharge from the new plant had reduced concentrations of nutrients, hormones, pharmaceuticals, and other BC. For example, all 16 of the hormones detected at the WWTP outfall site had maximum concentrations in samples collected prior to the WWTP replacement. The WWTP replacement had less effect on instream concentrations of metals and pesticides, BC whose sources are less directly tied to domestic wastewater. Study results indicate that improved WWTP technology can create substantial reductions in concentrations of non-regulated BC such as pharmaceuticals, in addition to regulated contaminants such as nutrients.

Theoretical Evaluation of Highly Efficient Nitrate Reduction to Ammonia on InBi

Electrocatalytic reduction of nitrate to ammonia has become a popular approach for wastewater treatment and ammonia production. However, the development of highly efficient electrocatalysts remains a great challenge. Herein, we systematically studied the potential of InBi for nitrate reduction to ammonia (NRA) based on density functional theory (DFT) calculations. Our results reveal that InBi exhibits high activity for NRA via an O-end pathway, where the free energy evolution of all intermediates is downhill in the most favorable elementary steps. The activation of nitrate originates from the strong orbital hybridization between oxygen and indium atoms, leading to an enhanced charge transfer as well as NO₃^- adsorption. In particular, the competing hydrogen evolution reaction (HER) is effectively suppressed due to the weak adsorption of proton. Our study not only proves the great electrocatalytic potential of InBi as a novel catalyst for NRA but also points out a new way to design NRA electrocatalysts for practical applications.

Multi-omics provide mechanistic insight into the Pb-induced changes in tadpole fitness-related traits and environmental water quality

Water pollution from lead/Pb²⁺ poses a significant threat to aquatic ecosystems, and its repercussions on aquatic animals have received considerable attention. Although Pb²⁺ has been found to affect numerous aspects of animals, including individual fitness, metabolic status, and symbiotic microbiota, few studies have focused on the associations between Pb²⁺-induced variations in fitness, metabolome, symbiotic microbiome, and environmental parameters in the same system, limiting a comprehensive understanding of ecotoxicological mechanisms from a holistic perspective. Moreover, most ecotoxicological studies neglected the potential contributions of anions to the consequences generated by inorganic lead compounds. We investigated the effects of Pb(NO₃)₂ at environmentally relevant concentrations on the Rana omeimontis tadpoles and the water quality around them, using blank and NaNO₃-treated groups as control. Results showed that Pb(NO₃)₂ not only induced a rise in water nitrite level, but exposure to this chemical also impaired tadpole fitness-related traits (e.g., growth and development). The impacts on tadpoles were most likely a combination of Pb²⁺ and NO₃^-. Tissue metabolomics revealed that Pb(NO₃)₂ exposure influenced animal substrate (i.e., carbohydrate, lipid, and amino acid) and prostaglandin metabolism. Pb(NO₃)₂ produced profound shifts in gut microbiota, with increased Proteobacteria impairing Firmicutes, resulting in higher aerobic and possibly pathogenic bacteria. NaNO₃ also influenced tadpole metabolome and gut microbiome, in a manner different to that of Pb(NO₃)₂. The presence of NO₃^- seemed to counteract some changes caused by Pb²⁺, particularly on the microbiota. Piecewise structural equation model and correlation analyses demonstrated connections between tissue metabolome and gut microbiome, and the variations in tadpole phenotypic traits and water quality were linked to changes in tissue metabolome and gut microbiome. These findings emphasized the important roles of gut microbiome in mediating the effects of toxin on aquatic ecosystem. Moreover, it is suggested to consider the influences of anions in the risk assessment of heavy metal pollutions.

Exposure to nitrate induces alterations in blood parameter responses, liver immunity, and lipid metabolism in juvenile turbot (Scophthalmus maximus)

Nitrate (NO₃^-) pollution of waterbodies has attracted significant global attention as it poses a serious threat to aquatic organisms and human beings. This study aimed to evaluate the role of NO₃^-, an end product of biological nitrification processes, in immune status and lipid metabolism to have a comprehensive understanding of its toxic effects on fishes. Therefore, in this work, juvenile turbot (Scophthalmus maximus) were subjected to four nominal concentrations of NO₃^- (i.e., 0, 50, 200, 400 mg/L of NO₃^--N) for a 60-day period. The results indicated that increased exposure to NO₃^- (200 and/or 400 mg/L) enhanced the concentrations of plasma heat shock protein concentrations (HSP70), complement component 3 (C3), complement component 4 (C4), immunoglobulin M (IgM) and lysozyme (LYS), which meant that NO₃^-caused fluctuations in the plasma immune system. Higher exposure to NO₃^- (200 and/or 400 mg/L) also caused significant enhancements in plasma glutamic pyruvic transaminase (GPT), as well as glutamic oxaloacetic transaminase (GOT) activity. Furthermore, NO₃^- exposure resulted in upregulation of liver TNF-α, IL-1β, HSP70, HSP90, and LYS. Additionally, the results suggested that NO₃^-exposure caused a certain degree of histological damage and inflammation in the liver and activated the immune defense processes of juvenile turbot. Furthermore, the mRNA expression levels of certain genes associated with lipid metabolism (peroxisome proliferator-activated receptor-alpha [PPAR-α], carnitine palmitoyltransferase 1[CPT1], liver X receptor [LXR] together with sterol regulatory element binding protein-1 [SREBP-1]) increased significantly within fish liver exposed to 200/400 mg/L NO₃^--N treatments. Finally, the results obtained from the analysis of the integrated biological responses version 2 (IBRv2) also confirmed the toxic effects of NO₃^- on juvenile turbot. According to these findings, it can be found that NO₃^- emission in the aquatic environment needs to be strictly controlled, as it may cause immune and lipid metabolism disorders in fish.

Conjoint applications of meta-analysis and bioinformatic data toward understanding the effect of nitrate on fish

The extensively accumulation of nitrate in different water resources is currently regarded as one of the most predominant threats facing aquatic organisms on worldwide scale. In recent years, a growing body of evidences have been attempting to uncover the influences of nitrate on fish growth and health, thereby evaluating its environment security. However, the systematic assessment and intrinsic mechanism of such influences are apparently devoid. Hence, this investigation employed systematic analysis, meta-analysis and bioinformatic analysis to evaluate the nitrate biotoxicity. We first speculated two levels of nitrate concentration according to forty-four published bibliographies. Systematic analysis indicated that the broad variations of fish sensitivity to chronic and acute nitrate exposures were found in juvenile and larval stage, respectively, comparing to egg. Meta-analysis further revealed that survival rate, CF and SGR were significantly improved in low nitrate concentration during chronic exposure. Such improvements were reflected by Total mean differences (TMD) and 95% CIs (Confidence Intervals): Survival rate (-4.06 [-7.67, -0.45]), Fulton's condition factor (CF) (-0.03 [-0.03, -0.02]) and Specific growth rate (SGR) (-0.10 [-0.16, -0.04]). To trace the impact, the alternations of molecular expression and histology in brain, gill, liver, intestine, and blood suggested that the chronic and acute nitrate exposures could result in abnormal tissue structures and molecular dynamics. Moreover, omics analysis via integrating intestinal microbiome (microbial composition; %) and liver transcriptome (Gene Ontology: biological processes) revealed that the low concentration exposure induced a weakly immune response in fish liver and it matched to the intestinal immune response. Overall, current study has filled the gaps in the field of nitrate toxicity. It could also provide a novel insight for the evaluation of pollutant toxicity on aquatic species.

Chronic nitrate exposure cause alteration of blood physiological parameters, redox status and apoptosis of juvenile turbot (Scophthalmus maximus)

Nitrate (NO₃^-) is one of the common inorganic nitrogen compound pollutants in natural ecosystems, which may have serious risks for aquatic organisms. However, its toxicological mechanism remains unclear. In the current study, juvenile turbot (Scophthalmus maximus) were exposed to different concentrations of NO₃^- (CK- 3.57 ± 0.16, LN - 60.80 ± 1.21, MN - 203.13 ± 10.97 and HN - 414.16 ± 15.22 mg/L NO₃-N) for 60 d. The blood biochemical assays results revealed that elevated NO₃^- exposure significantly increased the concentrations of plasma NO₃^-, NO₂^-, MetHb, K⁺, cortisol, glucose, triglyceride, lactate, while significantly decreased the concentrations of plasma Hb, Na⁺ and Cl^-, which meant that NO₃^- caused hypoxic stress and further affected the osmoregulation and metabolism in fish. Besides, exposure to MN and HN induced a significant decrease in the level of antioxidants, including SOD (Point: 60th day, MN, HN v.s. CK: 258.36, 203.73 v.s. 326.95 U/mL), CAT (1.97, 1.17 v.s. 2.37 U/mL), GSH (25.38, 20.74 v.s. 37.00 μmol/L), and GPx (85.32, 71.46 v.s. 129.36 U/mL), and a significant increase of MDA (7.54, 9.73 v.s. 5.27 nmol/L), suggesting that NO₃^- exposure leading to a disruption of the redox status in fish. Also, further research revealed that NO₃^- exposure altered the mRNA levels of p53 (HN: up to 4.28 folds) and p53-regulated downstream genes such as Bcl-2 (inferior to 0.44 folds), caspase-3 (up to 2.90 folds) and caspase-7 (up to 3.49 folds), indicating that NO₃^- exposure induced abnormal apoptosis in the fish gills. Moreover, IBRv2 analysis showed that the toxicity of NO₃^- exposure to turbot was dose-dependent, and the toxicity peaked on the 15th day. In short, NO₃^- is an environmental toxicological factor that cannot be ignored, because its toxic effects are long-term and could cause irreversible damage to fish. These results would be beneficial to improve our understanding of the toxicity mechanism of NO₃^- to fish, which provides baseline evidence for the risk assessment of environmental NO₃^- in aquatic ecosystems.

Synergistic Effect of Co(III) and Co(II) in a 3D Structured Co3O4/Carbon Felt Electrode for Enhanced Electrochemical Nitrate Reduction Reaction

As nitrate contamination causes serious environmental problems, it is necessary to develop stable and efficient electrocatalysts for efficient electrochemical nitrate reduction reaction (ENRR). Here, a nonprecious Co₃O₄/carbon felt (CF) electrode with a 3D structure was prepared by integrating electrodeposition with calcination methods. This 3D structured Co₃O₄/CF electrode exhibits a high-rate constant of 1.18 × 10^-4 s^-1 cm^-2 for the ENRR, surpassing other Co₃O₄ electrodes in previous literature. Moreover, it also has an excellent stability with a decrease of 6.4% after 10 cycles. Density functional theory calculations, electron spin resonance analysis, and cyclic voltammetry were performed to study the mechanism of the ENRR on the Co₃O₄/CF electrode, proving that atomic H* (indirect pathway) plays a prominent role in NO₃^- reduction and clarifying the synergistic effect of Co(III) and Co(II) in the Co(II)-Co(III)-Co(II) redox cycle for the ENRR: Co(III) prefers the adsorption of NO₃^- and Co(II) favors the production of H*. Based on this synergy, a relatively large amounts of Co(II) on the surface of the Co₃O₄/CF electrode (1.3 Co(II)/Co(III) ratio) was maintained by controlling the temperature of calcination to 200 °C with a lower energy barrier of H* formation of 0.46 eV than other ratios, which is beneficial for forming H* and enhancing the performance of the ENRR. Thus, this study suggests that building 3D structure and optimizing Co(II)/Co(III) ratio are important for designing efficient Co₃O₄ electrocatalyst for ENRR.

Reproductive Toxicity of 3,4-dichloroaniline (3,4-DCA) on Javanese Medaka (Oryziasjavanicus, Bleeker 1854)

Compound 3,4-dichloroaniline (3,4-DCA) is a metabolite of several urea herbicides and intermediate chemical of several industrial products. Moreover, 3,4-DCA has been frequently detected in aquatic ecosystems around the world. This aniline is more toxic than the parent chemicals, and it affects non-target organisms. This study evaluated a 21-day reproductive response of an emerging aquatic vertebrate model, Javanese medaka (Oryzias javanicus), exposed to 3,4-DCA. Fecundity and gonads histopathology were observed. The spawning rate and fertilisation reduced significantly in the highest exposed-group (250 µg/L). Gonadosomatic index (GSI) was significantly low in females exposed to 250 µg/L. No substantial structural alteration of male gonads. However, oocyte development and ovarian cell structure were disrupted in 250 µg/L exposed females. The gonadal developmental was not affected in the males; however, a significant reduction in the developmental of female gonads was observed at 250 µg/L. These results show that 3,4-DCA interfere with the reproduction of Javanese medaka through fecundity and alteration of gonadal tissues.

Performance of a recirculating aquaculture system using biofloc biofilters with convertible water-treatment efficiencies

To achieve high water-treatment efficiencies and simplify the setup of recirculating aquaculture systems (RAS), this study examined the use of suspended growth reactors (R1 and R2) based on biofloc technology (BFT) as water-treatment biofilters. Moreover, the conversion of the heterotrophic R1 biofilter to a nitrifying role was investigated. During RAS operation using heterotrophic BFT biofilters, R1 and R2 simultaneously controlled total ammonium nitrogen, nitrite (NO₂^--N), nitrate (NO₃^--N), soluble reactive phosphate (SRP), and alkalinity, with relevant functional microbes including denitrifying bacteria (DNB), phosphorus accumulating organisms (PAOs), denitrifying PAOs (DNPAOs), glycogen accumulating organisms, ammonia oxidizing bacteria, and nitrite oxidizing bacteria. To achieve low concentrations of nitrogen, phosphorus, and save carbon sources, we were able to quickly convert R1 into a nitrifying BFT biofilter by stopping carbohydrate addition. Although there were dominant relative abundances of DNB, PAOs, and DNPAOs in the converted R1, the lack of carbon sources resulted in continuous rise of NO₃^--N in the effluent, stable NO₂^--N removal efficiency, and absence of SRP removal after 40 h. However, R2 retained the previous NO₃^--N and SRP removal efficiencies with carbohydrate addition. This indicated that this novel RAS using BFT biofilters achieved simultaneous nitrogen and phosphate removal, and that the convertible water-treatment efficiencies of BFT biofilters could be controlled by carbohydrate addition. This approach could simplify the RAS setup and meet real-time water quality demands.

Toxicity characterization of surface sediments from a Mediterranean coastal lagoon

The occurrence of bioactive compounds and contaminant-associated effects was assessed by means of in vivo and in vitro assays using different extractable fractions of surface sediments from a contaminated coastal lagoon (Mar Menor, SE Spain). Sediment elutriates and clean seawater, previously exposed to whole sediment, were used for assessing the in vivo toxicity on embryo development of the sea urchin Paracentrotus lividus. Agonist and antagonist activities relating to estrogen and androgen receptors and agonist activities on aryl hydrocarbon receptor (expressed as ethoxyresorufin-O-deethylase (EROD) activities) were investigated in sediment extracts by using HER-Luc, AR-EcoScreenTM and fibroblast-like RTG-2 cell lines. Embryotoxicity effects were greater for sediment elutriates than those incubated in sediment-water interphase, implying that diffusion of bioactive chemicals can occur from sediments to sea water column, favoured by sediment disturbance events. In vitro results show the occurrence in extracts of compounds with estrogen antagonism, androgen antagonism and dioxin-like activities. Multidimensional scaling analysis classified the sampling sites into four sub-clusters according to their chemical-physical and biological similarities, relating in vitro bioactivity with the total organic carbon and known organic chemical load, with particular reference to total sum of PAHs, PCB 180, p,p-DDE and terbuthylazine. Overall, results pointed to the presence of unknown or unanalyzed biologically-active compounds in the sediments, mostly associated with the extracted polar fraction of the Mar Menor lagoon sediments. Our findings provide relevant information to be considered for the environmental management of contaminated coastal lagoons.

Living in polluted waters: A meta-analysis of the effects of nitrate and interactions with other environmental stressors on freshwater taxa

Nutrient effluents from urban and agricultural inputs have resulted in high concentrations of nitrate in freshwater ecosystems. Exposure to nitrate can be particularly threatening to aquatic organisms, but a quantitative synthesis of the overall effects on amphibians, amphipods and fish is currently unavailable. Moreover, in disturbed ecosystems, organisms are unlikely to face a single stressor in isolation, and interactions among environmental stressors can enhance the negative effects of nitrate on organisms. Here, the effects of elevated nitrate on activity level, deformity rates, hatching success, growth and survival of three taxonomic groups of aquatically respiring organisms are documented. Effect sizes were extracted from 68 studies and analysed using meta-analytical techniques. The influence of nitrate on life-stages was also assessed. A factorial meta-analysis was conducted to examine the effect of nitrate and its interaction with other ecological stressors on organismal survival. Overall, the impacts of nitrate are biased towards amphibians (46 studies) and fish (13 studies), and less is known about amphipods (five studies). We found that exposure to nitrate translates to a 79% decrease in activity, a 29% decrease in growth, and reduces survival by 62%. Nitrate exposure also increases developmental deformities but does not affect hatching success. Nitrate exposure was found to influence all life-stages except embryos. Differences in the sensitivity of nitrate among taxonomic groups tended to be negligible. The factorial meta-analysis (14 amphibians and two amphipod studies) showed that nitrate in combination with other stressors affects survival in a non-additive manner. Our results indicate that nitrate can have strong effects on aquatic organisms and can interact with other environmental stressors which compound the negative effects on survival. Overall, the impacts of nitrate and additional stressors are complex requiring a holistic approach to better conserve freshwater biodiversity in the face of ongoing global change.

Reconnaissance of Surface Water Estrogenicity and the Prevalence of Intersex in Smallmouth Bass (Micropterus Dolomieu) Inhabiting New Jersey

The observation of testicular oocytes in male fishes has been utilized as a biomarker of estrogenic endocrine disruption. A reconnaissance project led in the Northeastern United States (US) during the period of 2008–2010 identified a high prevalence of intersex smallmouth bass on or near US Fish & Wildlife Service National Wildlife Refuges that included the observation of 100% prevalence in smallmouth bass males collected from the Wallkill River, NJ, USA. To better assess the prevalence of intersex smallmouth bass across the state of New Jersey, a tiered reconnaissance approach was initiated during the fall of 2016. Surface water samples were collected from 101 (85 river, 16 lake/reservoir) sites across the state at base-flow conditions for estrogenicity bioassay screening. Detectable estrogenicity was observed at 90% of the sites and 64% were above the US Environmental Protection Agency trigger level of 1 ng/L. Median surface water estrogenicity was 1.8 ng/L and a maximum of 6.9 ng/L E2Eq_BLYES was observed. Adult smallmouth bass were collected from nine sites, pre-spawn during the spring of 2017. Intersex was identified in fish at all sites, and the composite intersex prevalence was 93.8%. Prevalence across sites ranged from 70.6% to 100%. In addition to intersex, there was detectable plasma vitellogenin in males at all sites. Total estrogenicity in surface water was determined at these fish collection sites, and notable change over time was observed. Correlation analysis indicated significant positive correlations between land use (altered land; urban + agriculture) and surface water estrogenicity. There were no clear associations between land use and organismal metrics of estrogenic endocrine disruption (intersex or vitellogenin). This work establishes a baseline prevalence of intersex in male smallmouth bass in the state of New Jersey at a limited number of locations and identifies a number of waterbodies with estrogenic activity above an effects-based threshold.

Effects of industrial pollution on the reproductive biology of Squalius laietanus (Actinopterygii, Cyprinidae) in a Mediterranean stream (NE Iberian Peninsula)

Mediterranean rivers are severely affected by pollutants from industry, agriculture and urban activities. In this study, we examined how industrial pollutants, many of them known to act as endocrine disruptors (EDCs), could disturb the reproduction of the Catalan chub (Squalius laietanus). The survey was conducted throughout the reproductive period of S. laietanus (from March to July 2014) downstream an industrial WWTP located in the River Ripoll (NE Iberian Peninsula). Eighty fish (28 females and 52 males) were caught by electrofishing upstream and 77 fish (33 females and 44 males) downstream a WWTP. For both sexes, the gonadosomatic index (GSI) and gonadal histology were examined and related to water chemical analysis and fish biomarkers. Female fecundity was assessed using the gravimetric method. Fish from the polluted site showed enhanced biomarker responses involved in detoxification. Also, in the polluted site, lower GSI values were attained in both sexes and females displayed lower numbers of vitellogenic oocytes. Gonadal histology showed that all maturation stages of testicles and ovaries were present at the two study sites but fish males from the polluted site had smaller diameter seminiferous tubules. Water chemical analysis confirmed greater presence of EDCs in the river downstream the industrial WWTP. The chemicals benzotriazole and benzothiazole could be partially responsible for the observed alterations in the reproductive biology of S. laietanus.

Simultaneous exposure to nitrate and low pH reduces the blood oxygen-carrying capacity and functional performance of a freshwater fish

Human activities present aquatic species with numerous of environmental challenges, including excessive nutrient pollution (nitrate) and altered pH regimes (freshwater acidification). In isolation, elevated nitrate and acidic pH can lower the blood oxygen-carrying capacity of aquatic species and cause corresponding declines in key functional performance traits such as growth and locomotor capacity. These factors may pose considerable physiological challenges to organisms but little is known about their combined effects. To characterise the energetic and physiological consequences of simultaneous exposure to nitrate and low pH, we exposed spangled perch (Leiopotherapon unicolor) to a combination of nitrate (0, 50 or 100 mg L-1) and pH (pH 7.0 or 4.0) treatments in a factorial experimental design. Blood oxygen-carrying capacity (haemoglobin concentration, methaemoglobin concentrations and oxygen equilibrium curves), aerobic scope and functional performance traits (growth, swimming performance and post-exercise recovery) were assessed after 28 days of exposure. The oxygen-carrying capacity of fish exposed to elevated nitrate (50 and 100 mg L-1) was compromised due to reductions in haematocrit, functional haemoglobin levels and a 3-fold increase in methaemoglobin concentrations. Oxygen uptake was also impeded due to a right shift in oxygen-haemoglobin binding curves of fish exposed to nitrate and pH 4.0 simultaneously. A reduced blood oxygen-carrying capacity translated to a lowered aerobic scope, and the functional performance of fish (growth and swimming performance and increased post-exercise recovery times) was compromised by the combined effects of nitrate and low pH. These results highlight the impacts on aquatic organisms living in environments threatened by excessive nitrate and acidic pH conditions.

Nitrification-denitrification of municipal wastewater without recirculation, using encapsulated microorganisms

In most municipal wastewater treatment plants, there is need for the removal of nitrogen, which usually takes place using the combined nitrification - denitrification process. Vigorous recirculation between the aeration and the anoxic tanks is enforced, to ensure complete denitrification. The scope of the present work was to investigate the possibility for nitrification-denitrification process in once-through systems (i.e.: without recirculation), without the need for the addition of extra carbon source (i.e. using the BOD in wastewater as carbon source), using encapsulated microorganisms. The primary aim was to increase the concentration of nitrifiers in the aerated reactor with parallel operation at hydraulic retention times (HRTs) below the doubling time of heterotrophic microorganisms, thus ensuring high ammonia oxidation rate and minimal reduction of organic carbon. The preserved organic carbon may be then used as carbon source at the downstream anoxic reactor. Coagulated and clarified wastewater from the effluent of the primary clarifier of a municipal wastewater treatment plant was used as feed to the system. The system comprised of two reactors (with 2 L working volume each) configured in series. The first one (aerated tank) contained encapsulated nitrifiers, while the second one (anoxic tank) contained encapsulated denitrifiers. The system operated at HRTs 8, 4 and 3 h (calculated individually for each reactor). The experiments indicated that at HRT equal to 8 h, almost all N-NH4+ was converted to N-NO3- in the aerated reactor, while the total nitrogen (TN) concentration was below 2 mg L-1 at the exit of the system. At HRT of 4 h a slight decrease in N-NH4+ removal was observed at the exit of the aerated tank (N-NH4+ concentration was measured 3.7 ± 0.1 mg L-1). At HRT equal to 4 h, N-NH4+ concentration did not change significantly during the downstream treatment in the anoxic tank, while N-NO3- concentration at the exit of the system was 1.4 ± 0.1 mg L-1. At the lowest HRT (3 h), N-NH4+ concentration was measured between 10 and 11 mg L-1, both, at the exit of the aeration tank and at the exit of the system; while, N-NO3- was measured 2.6 ± 0.2 mg L-1 at the exit of the system. On the other hand, BOD and TOC removal in the aeration tank decreased with the decrease of the HRT. BOD concentration at the exit of the anoxic tank measured 30.3 ± 2.2 and 19.4 ± 1.7 mg L-1 for HRTs 8 h or 4 h, respectively, while it was measured 51.6 ± 7.6 mg L-1 at HRT 3 h. On the other hand, TOC concentration at the outlet was measured 17.5 ± 1.2 and 13.2 ± 0.6 for HRTs 8 or 4 h, respectively, while it was measured 31.1 ± 5.6 mg L-1 at HRT equal to 3 h. Analysis of variance (ANOVA) showed significant variations of all measured parameters with the applied HRT, apart from N-NO3- concentration at the exit of the aerated tank. The latter was attributed to the complete oxidation oft N-NH4+ in the aerated tank at all HRTs. Based on the efficiency of the system, the volume of the aeration and denitrification tanks of a wastewater treatment plant using encapsulated microorganisms may be designed 16 times smaller, compared to conventional activated sludge plants, while the need for recirculation between the aerated and anoxic tanks may be completely eliminated.

Physiological and behavioural responses to acid and osmotic stress and effects of Mucuna extract in Guppies

Variation in pH (acidification) and salinity conditions have severe impact at different levels of biological organization in fish. Present study focused to assess the effects of acidification and salinity changes on physiological stress responses at three different levels of function: i) hormonal and oxidative response, ii) osmoregulation and iii) reproduction, in order to identify relevant biomarkers. Second objective of the study was to evaluate the efficacy of plant (Mucuna pruriens) extract for alleviating pH and salinity related stress. Guppies (Poecilia reticulata) were exposed to different pH (6.0, 5.5, 5.0) and salinity (1.5, 3.0, 4.5 ppt) for 7, 14 and 21 days. Following exposure to stress for respective duration, fish were fed diet containing methanol extract of Mucuna seeds (dose 0.80 gm/kg feed) for 7, 14 and 21 days to measure their possible recovery response. Stress hormone (cortisol), hepatic oxidative stress parameters [superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GRd), glutathione peroxidise (GPx), glutathione S-transferase (GST), malondialdehyde (MDA), glutathione (GSH)], gill osmoregulatory response (Na⁺-K⁺ATPase activity), sex steroid profiles and mating behaviours (gonopodial thrust and gestation period) were estimated. Cortisol and MDA levels increased with dose and duration of acid and salinity stress, and cortisol levels were higher in males than in females. Effect on Na⁺-K⁺ATPase activity was more intense by salinity stress rather than pH induced stress. Both acid and salinity stress reduced sex steroid levels, and mating response was highly affected by both stresses in a dose- and duration-dependent manner. Mucuna treatment reduced stress-induced alteration of cortisol, MDA, Na⁺-K⁺ATPase activity and reproductive parameters. Dietary administration of Mucuna seed extract decreased the intensity of environmental stressors at all three functional levels. Mucuna treatment was more effective against salinity stress than acid stress. Thus, cortisol, oxidative stress marker MDA and Na⁺-K⁺ATPase could be effective indicators for acid and salinity stress in wild and domestic fish populations. Dietary administration of Mucuna extract may limit the detrimental effects of acidification and salinity variations that are the inevitable outcomes expected under global climate change conditions.

Effects of nitrate on freshwater mussel glochidia attachment and metamorphosis success to the juvenile stage

Water quality and contaminants have been frequently identified as critical stressors for freshwater mussels, many species of which are highly imperiled throughout North America and the world. Nutrient pollution, specifically nitrate, has become one of the most prevalent causes of water quality degradation globally, with increasing anthropogenic input from suburban and agricultural runoff, municipal wastewater, and industrial waste. Nitrate acute toxicity is generally low for aquatic species, but the potential effects of nitrate exposure are largely unknown for freshwater mussels, particularly during the parasitic stage of their complex lifecycle. Therefore, this study was designed to determine the effects of short-term nitrate exposure at environmentally relevant concentrations on juvenile production in two freshwater mussel species. Lampsilis siliquoidea and L. fasciola glochidia were exposed to nitrate (0, 11, or 56 mg NO₃-N/L) for 24 h before inoculation on a primary host, Largemouth Bass (Micropterus salmoides). Glochidia attachment, metamorphosis success, and total number of juveniles produced were monitored on individual fish. Exposure of L. siliquoidea glochidia to 56 mg NO₃-N/L nitrate resulted in a significant (p = 0.02) 35% reduction of total juveniles produced, a combined result of moderate decreases in both glochidia attachment and metamorphosis success. A similar trend (28% reduction; p = 0.06) was evident with 11 mg NO₃-N/L. No effects were apparent for L. fasciola, suggesting species-specific differences in responses even among closely related species. These results are the first to suggest that glochidia exposure to nitrate may adversely affect juvenile recruitment in some species. Findings from these studies are important for improving characterization of the hazards of nitrate pollution to aquatic life and this work will help better define the role of water quality in assessing habitat suitability for mussel conservation efforts.

Investigation of the potential endocrine effect of nitrate in zebrafish Danio rerio and brown trout Salmo trutta

Nitrate has the potential to affect steroid production. Nitrate concentrations in streams in agricultural areas may exceed concentrations showing effects in laboratory studies. The effects of nitrate and/or nitrite on endocrine relevant endpoints were tested in zebrafish and brown trout. Zebrafish were exposed in two experiments to nitrate (8.8 to 89 mg NO₃^-/L) and nitrite (3.6 to 19 mg NO₂^-/L) during the period of sexual differentiation and sex ratios were determined. Vitellogenin concentrations were determined in the second experiment. The sex ratio was unaffected by the exposure to nitrate and nitrite. Vitellogenin concentrations were slightly elevated in males (but not females) in all of the groups exposed to nitrate. Juvenile brown trout were exposed to 5.7, 14, and 31 mg NO₃^-/L for 8 days and vitellogenin levels in liver were determined. Vitellogenin concentrations in the females were not affected by exposure, but in the males, there was an overall statistically significant effect of exposure to nitrate with the group exposed to 5.7 mg NO₃^-/L showing a trend of higher vitellogenin concentrations than the control group; levels in the males of the groups exposed to 14 and 31 mg NO₃^-/L were not statistically different from those of the control group. In conclusion, some marginal effect of nitrate in male fish on endocrine activity was observed but the present results for zebrafish, using environmentally relevant concentrations, do not define nitrate and nitrite as endocrine disrupting chemicals according to the generally accepted WHO/IPCS definition because no adverse effects (altered sex ratios) were demonstrated.

Reproductive endocrinology of environmental nitrate

Nitrate is a widespread contaminant of aquatic ecosystems and drinking water. It is also broadly active in organismal physiology, and as such, has the potential to both enhance and disrupt normal physiological function. In animals, nitrate is a proposed endocrine disrupter that is converted in vivo to nitrite and nitric oxide. Nitric oxide, in particular, is a potent cell signaling molecule that participates in diverse biological pathways and events. Here, we review in vivo nitrate cycling and downstream mechanistic physiology, with an emphasis on reproductive outcomes. However, in many cases, the research produces contradictory results, in part because there is good evidence that nitrate follows a non-monotonic dose-response curve. This conundrum highlights an array of opportunities for scientists from different fields to collaborate for a full understanding of nitrate physiology. Opposing conclusions are especially likely when in vivo/in vitro, long term/short term, high dose/low dose, or hypoxia/normoxia studies are compared. We conclude that in vivo studies are most appropriate for testing an organism's integrated endocrine response to nitrate. Based on the limited available studies, there is a generalized trend that shorter term studies (less than 1 month) or studies involving low doses (≤5 mg/L NO₃-N) cause steroid hormone levels to decline. Studies that last more than a month and/or involve higher, but still environmentally relevant, exposures (>50-100 mg/L NO₃-N) cause steroid hormone levels to increase. Very high nitrate doses (>500 mg/L NO₃-N) are cytotoxic in many species. Hypoxia and acidity are likely to intensify the effects of nitrate. For study design, degree of study animal reproductive maturity or activity is important, with immature/reproductively quiescent animals responding to nitrate differently, compared with reproductively active animals. A detailed table of studies is presented.

Nitrate: An Environmental Endocrine Disruptor? A Review of Evidence and Research Needs

Nitrate is heavily used as an agricultural fertilizer and is today a ubiquitous environmental pollutant. Environmental endocrine effects caused by nitrate have received increasing attention over the last 15 years. Nitrate is hypothesized to interfere with thyroid and steroid hormone homeostasis and developmental and reproductive end points. The current review focuses on aquatic ecotoxicology with emphasis on field and laboratory controlled in vitro and in vivo studies. Furthermore, nitrate is just one of several forms of nitrogen that is present in the environment and many of these are quickly interconvertible. Therefore, the focus is additionally confined to the oxidized nitrogen species (nitrate, nitrite and nitric oxide). We reviewed 26 environmental toxicology studies and our main findings are (1) nitrate has endocrine disrupting properties and hypotheses for mechanisms exist, which warrants for further investigations; (2) there are issues determining actual nitrate-speciation and abundance is not quantified in a number of studies, making links to speciation-specific effects difficult; and (3) more advanced analytical chemistry methodologies are needed both for exposure assessment and in the determination of endocrine biomarkers.