Subchronic exposure to diflubenzuron causes health disorders in neotropical freshwater fish,Prochilodus lineatus

The action of diflubenzuron (DFB) was evaluated in a freshwater fish, Prochilodus lineatus, after exposure to 0.06, 0.12, 0.25, or 0.50 mg L^?1 DFB for 14 days. Erythrocyte nuclear abnormalities (ENA), the gill activity of Na⁺/K⁺‐ATPase, H⁺‐ATPase and carbonic anhydrase (CA), and lipid peroxidation (LPO) and histopathological changes in the gills and liver were determined. The number of micronuclei increased in fish exposed to 0.25 and 0.50 mg L^?1 DFB. Plasma Cl^? and the CA activity decreased, while the activity of Na⁺/K⁺‐ATPase and of H⁺‐ATPase increased in fish exposed to 0.25 and 0.50 mg L^?1 DFB. LPO did not change in the gills but increased in the liver of fish exposed to 0.25 and 0.50 mg L^?1 DFB. In the gills, histopathological changes indicated disperse lesions and slight to moderate damage in fish exposed to 0.50 mg L^?1 DFB, whereas in the liver, these changes were significantly greater in fish exposed to 0.25 and 0.50 mg L^?1 DFB, indicating moderate to severe damage. Continuous exposure to DFB is potentially toxic to P. lineatus, causing heath disorders when the fish is exposed to the two highest DFB concentrations, which are applied to control parasites in aquaculture and to control mosquito populations in the environment. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 533–542, 2016.     

Expression of metallothionein of freshwater crab (Sinopotamon henanense) in Escherichia coli enhances tolerance and accumulation of zinc, copper and cadmium

Metallothioneins (MTs) are ubiquitous metal-binding, cysteine-rich, small proteins and play a major role in metal homeostasis and/or detoxification in all organisms. In a previous study, a novel full length MT gene was isolated from the freshwater crab (Sinopotamon henanense), a species widely distributed in Shanxi and Henan Provinces, China. In this report, the gene for the crab MT was inserted into a PET-28a-6His-SUMO vector and recombinant soluble MT was over-expressed as fusions with SUMO in Escherichia coli. The recombinant fusion protein was purified by affinity chromatography and its biochemical properties were analyzed. In addition, on the basis of constructing SUMO-MT, two mutants, namely SUMO-MTt1 and SUMO-MTt2, were constructed to change the primary structure of SUMO-MT using site-directed mutagenesis techniques with the amino acid substitutions D3C and S37C in order to increase metal-binding capacity of MT. E. coli cells expressing SUMO-MT and these single-mutant proteins exhibited enhanced metal tolerance and higher accumulation of metal ions than control cells. The results showed that the bioaccumulation and tolerance of Zn²⁺, Cu²⁺ and Cd²⁺ in these strains followed the decreasing order of SUMO-MTt1 > SUMO-MTt2 > SUMO-MT. E. coli cells have low tolerance and high accumulation towards cadmium compared to zinc and copper. These results show that the MT of S. henanense could enhance tolerance and accumulation of metal ions. Moreover, we were able to create a novel protein based on the crab MT to bind metal ions at high density and with high affinity. Therefore, SUMO-MT and its mutants can provide potential candidates for heavy metal bioremediation. This study could help further elucidate the mechanism of how the crab detoxifies heavy metals and provide a scientific basis for environment bioremediation of heavy metal pollution using the over-expression of the crab MT and mutant proteins.     

Toxicity of copper on marine diatoms,Chaetoceros calcitrans and Nitzchia closterium from Cochin estuary,India

The effects of copper (Cu) toxicity on the growth, pigments, protein, carbohydrate, lipid and antioxidant enzyme activities of two endemic microalgae, Chaetoceros calcitrans and Nitzchia closterium from Cochin estuary were studied and compared. The 96?h median inhibition concentration (IC₅₀) of Cu for C. calcitrans was 143.8?µg?L^?1 and that for N. closterium was 204.5?µg?L^?1. No observable effect concentration (NOEC), lowest observable effect concentration (LOEC) and chronic value of Cu on C. calcitrans were 17.93?µg?L^?1, 31.91?µg?L^?1and 24.92?µg?L^?1 respectively, whereas that for N. closterium were 18.35?µg?L^?1, 36.04?µg?L^?1 and 27.2?µg?L^?1 respectively. Chlorophyll a and c showed significant variation from the control at NOEC in both species. Carotenoid content showed significant increase at LOEC. The chlorophyll a/c ratio significantly decreased at NOEC and LOEC of N. closterium. In N. closterium catalase (CAT) activity showed significant increase at NOEC and LOEC, but in C. calcitrans it varied significantly above LOEC. Protein content showed a significant decrease at NOEC of C. calcitrans. No significant variation was observed for N. closterium. Carbohydrate showed significant variation between the species at NOEC. Lipid content varied significantly at NOEC of C. calcitrans. Chaetoceros calcitrans was observed to be more sensitive to copper toxicity than N. closterium. The metal stress tolerance mechanism of N. closterium and its bioremediation capacity can be established in further studies. This study also provides an insight on the biochemical changes that happened at NOEC.

     

Inducibility of metallothionein biosynthesis in the whole soft tissue of zebra mussels Dreissena polymorpha exposed to cadmium,copper, and pentachlorophenol

Freshwater mussels Dreissena polymorpha (Pallas, 1771) were exposed to the elevated concentrations of Cd (10, 50, 100, and 500 μg/L), Cu (10, 30, 50, and 80 μg/L), and an organochlorinated pesticide, pentachlorophenol (PCP) (1, 10, and 100 μg/L). Induced synthesis of biomarker metallothionein (MT) and changes in concentrations of cytosolic Cd, Cu, and Zn in the whole soft tissue of mussels were monitored after a 7‐day laboratory exposure to the contaminants. A clear dose‐dependent elevation in the MT concentration was observed after exposure to Cd at doses of 10–100 μg/L, and this increase of MT content was accompanied with a linear increase of cytosolic Cd. Cd concentration of 500 μg/L caused no additional increase of MT and Cd in mussel cytosol, suggesting possible toxic effects due to exceeding cellular inducible/defense capacity. Cu exposure resulted with variable changes in MT concentrations, with no clear linear relationship between MT and Cu concentrations in water, although a progressive dose‐dependent accumulation of Cu in the soluble fraction of mussel tissues was recorded. A decrease of cytosolic Zn was evident at higher exposure concentrations of both metals used. PCP in concentrations applied was unable to induce MT synthesis, but the higher concentrations of PCP influenced the cytosolic metal concentrations. In conclusion, the results obtained confirm the specificity of MT induction in D. polymorpha as an biological response on metal stimulation, especially by cadmium, being more closely correlated to MT than copper within the ecologically relevant concentration range. The strong induction potential of cadmium as well as an absence of MT induction following exposure to PCP as an organic chemical contaminant are supporting evidences for usage of zebra mussel MT as a specific biomarker of Cd exposure in biomonitoring programs. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2010.     

Tissue-specific cadmium and metallothionein levels in freshwater crab Sinopotamon henanense during acute exposure to waterborne cadmium

The freshwater crabs Sinopotamon henanense were exposed to different concentrations of waterborne cadmium (Cd). The relationship between tissue-specific Cd accumulation and metallothionein (MT) induction was investigated using the Cd saturation assay and atomic absorption spectrophotometry method. The results showed that Cd accumulation rose significantly in all tissues studied after Cd exposure, and the Cd accumulation level in various tissues followed the following order: gill > hepatopancreas > muscle > ovary. MT levels were clearly tissue-specific after Cd exposure. Hepatopancreas was found to have the highest MT level, followed by the gill, muscle, and ovary. In conclusion, the results indicated although Cd exposure clearly resulted in MT induction, its synthesis does not correlate with Cd accumulation in the later stage of Cd exposure. The calculated ratios of actual Cd to theoretical maximum Cd-MT in the hepatopancreas were <1.0 under acute waterborne Cd at all sampling points, indicating that the hepatopancreas had much greater Cd-binding potential of MT than the gill, muscle, or ovary. It is clear from our results that a positive correlation was shown between MT induction and Cd accumulation both in hepatopancreas and gill. Therefore, MT induction can be considered as a biomarker for acute waterborne Cd pollution.     

Individual and combined effects of cadmium and copper on the growth response of Chlorella vulgaris

The individual and combined effects of cadmium and copper on the growth response of the green alga, Chlorella vulgaris, were examined. The effects of pH alone, and in combination with copper were also evaluated. An increase in cadmium and copper concentrations caused a significant reduction in the growth of C. vulgaris cells, and the corresponding EC₅₀ values were 1.02 and 4.01 mg L⁻¹, respectively. For a pH range of 2–7, the inhibitory effect due to increased copper concentrations (coupled with the resulting drop in pH) was significantly higher than the impact due to increased acidity (by addition of HCl) alone. At lower metal concentrations (5 mg L⁻¹ Cu + < 2 mg L⁻¹ Cd or 2.5 mg L⁻¹ Cd + < 4 mg L⁻¹ Cu), a combination of copper and cadmium appeared to have a stronger inhibitory effect on cell growth than that of a single metal. In contrast, at higher metal concentrations (5 mg L⁻¹ Cu + > 2 mg L⁻¹ Cd or 2.5 mg L⁻¹ Cd + > 4 mg L⁻¹ Cu), the effect of a single metal exhibited a significantly stronger effect compared to a combination of the two metals. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 347–353, 1999     

Acute toxicity, accumulation and tissue distribution of copper in the blue crab Callinectes sapidus acclimated to different salinities: in vivo and in vitro studies

In vivo and in vitro studies were performed to evaluate acute toxicity, organ-specific distribution, and tissue accumulation of copper in Callinectes sapidus acclimated to two different experimental salinities (2 and 30 ppt). Blue crabs were quite tolerant to copper. Acute dissolved copper toxicity (96-h LC₅₀ and its corresponding 95% confident interval) was higher at salinity 2 ppt (5.3 (3.50-8.05) μM Cu) than at 30 ppt (53.0 (27.39-102.52) μM Cu). The difference between salinities can be completely explained based on the water chemistry because it disappeared when 96-h LC₅₀ values were expressed as the free Cu²⁺ ion (3.1 (1.93-4.95) μM free Cu at 2 ppt versus 5.6 (2.33-13.37) μM free Cu at 30 ppt) or the Cu²⁺ activity (1.4 (0.88-2.26) μM Cu activity at 2 ppt versus 1.7 (0.71-4.07) μM Cu activity at 30 ppt). The relationships between gill Cu burden and % mortality were very similar at 2 and 30 ppt, in accord with the Biotic Ligand Model. In vivo experiments showed that copper concentration in the hemolymph is not dependent on metal concentration in the surrounding medium at either experimental salinity. They also showed that copper flux into the gills is higher than into other tissues analyzed, and that anterior and posterior gills are similarly important sites of copper accumulation at both experimental salinities. In vitro experiments with isolated-perfused gills showed that there is a positive relationship between copper accumulation in this tissue and the metal concentration in the incubation media for both anterior and posterior gills. A similar result was observed at both low and high salinities. Furthermore, in vitro experiments showed that copper accumulation in posterior gills is also positively and strongly dependent on the incubation time with copper. Gill copper accumulation occurred at a lower rate in the first 2 h of metal exposure, increasing markedly after this “steady-state” period. This finding was corroborated by a significant increase in copper influx to the gill perfusate (corresponding to crab hemolymph) after this time, measured using ⁶⁴Cu. In vivo, after uptake from solution, ⁶⁴Cu was primarily accumulated in the gills and the rest of the body rather than in the hemolymph, hepatopancreas, or other internal tissues. Overall, the present findings indicate that gills are a key target organ for copper accumulation, as well as an important biological barrier against the excessive uptake of copper into the hemolymph and the subsequent distribution of this metal to internal organs of the blue crab.     

Toxicity thresholds for juvenile freshwater mussels Echyridella menziesii and crayfish Paranephrops planifrons,after acute or chronic exposure to Microcystis sp

Survival of juvenile freshwater mussels (Echyridella menziesii (Gray, 1843) formerly known as Hyridella menziesi) and crayfish (Paranephrops planifrons, White, 1842) decreased after four days exposure to microcystin‐containing cell‐free extracts (MCFE) of Microcystis sp. at concentrations typical of severe cyanobacterial blooms. Crayfish survival was 100, 80, and 50% in microcystin concentrations of 1339, 2426, and 11146 μg L^?1 respectively, and shade‐ and shelter‐seeking behavior was negatively affected when concentrations were ≥2426 μg L^?1. Mussel survival decreased to 92% and reburial rates decreased to 16% after exposure for 96 h to MCFE containing microcystins at concentrations of 5300 μg L^?1. Crayfish survival was 100% when fed freeze‐dried Microcystis sp. incorporated into an artificial diet (6–100 μg microcystin kg^?1 ww) at dietary doses from 0.03 to 0.55 μg g^?1 body weight d^?1 for 27 days. Specific growth rate was significantly lower in crayfish fed ≥0.15 μg g^?1 body weight day^?1 compared with controls, but not compared with a diet incorporating nontoxic cyanobacteria. Microcystins accumulated preferentially in crayfish hepatopancreas and mussel digesta as MCFE or dietary concentrations increased. These laboratory data indicate that, assuming dissolved oxygen concentrations remain adequate, and no simultaneous exposure to live Microcystis sp. cells, cell‐free microcystins will only be a significant stressor to juvenile crayfish and mussels in severe Microcystis sp. blooms. In contrast, crayfish were negatively affected by relatively low concentrations of microcystins in artificial diets compared with those measured locally in benthic cyanobacterial mats. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 487–502, 2014.     

Accumulation and toxicity of CuO and ZnO nanoparticles through waterborne and dietary exposure of goldfish (Carassius auratus)

Dietary and waterborne exposure to copper oxide (CuO) and zinc oxide (ZnO) nanoparticles (NPs) was conducted using a simplified model of an aquatic food chain consisting of zooplankton (Artemia salina) and goldfish (Carassius auratus) to determine bioaccumulation, toxic effects, and particle transport through trophic levels. Artemia contaminated with NPs were used as food in dietary exposure. Fish were exposed to suspensions of the NPs in waterborne exposure. ICP‐MS analysis showed that accumulation primarily occurred in the intestine, followed by the gills and liver. Dietary uptake was lower, but was found to be a potential pathway for transport of NPs to higher organisms. Waterborne exposure resulted in about a 10‐fold higher accumulation in the intestine. The heart, brain, and muscle tissue had no significant Cu or Zn. However, concentrations in muscle increased with NP concentration, which was ascribed to bioaccumulation of Cu and Zn released from NPs. Free Cu concentration in the medium was always higher than that of Zn, indicating CuO NPs dissolved more readily. ZnO NPs were relatively benign, even in waterborne exposure (p ≥ 0.05). In contrast, CuO NPs were toxic. Malondialdehyde levels in the liver and gills increased substantially (p < 0.05). Despite lower Cu accumulation, the liver exhibited significant oxidative stress, which could be from chronic exposure to Cu ions. © 2014 Wiley Periodicals, Inc. Environ Toxicol 30: 119–128, 2015.     

Effects of cadmium alone and in combination with low molecular weight chitosan on metallothionein,glutathione‐S‐transferase,acid phosphatase,and ATPase of freshwater crab Sinopotamon yangtsekiense

Cadmium (Cd) is an environmental contaminant showing a variety of deleterious effects, including the potential threat for the ecological environment and human health via food chains. Low molecular weight chitosan (LMWC) has been demonstrated to be an effective antioxidant. Metallothionein (MT) mRNA levels and activities of glutathione‐S‐transferase (GST), superoxide dismutase (SOD), acid phosphatase (ACP), Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase as well as malondialdehyde (MDA) contents in the gills of the freshwater crab Sinopotamon yangtsekiense were analyzed in vivo in order to determine the injury of Cd exposure on the gill tissues as well as the protective effect of LMWC against this injury. The results showed that there was an apparent accumulation of Cd in the gills, which was lessened by the presence of LMWC. Moreover, Cd²⁺ significantly increased the gill MT mRNA levels, ACP activity and MDA content while decreasing the activities of SOD, GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase in the crabs relative to the control. Cotreatment with LMWC reduced the levels of MT mRNA and ACP but raised the activities of GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase in gill tissues compared with the crabs exposed to Cd²⁺ alone. These results suggest that LMWC may exert its protective effect through chelating Cd²⁺ to form LMWC‐Cd²⁺ complex, elevating the antioxidative activities of GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase as well as alleviating the stress pressure on MT and ACP, consequently protecting the cell from the adverse effects of Cd. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 298–309, 2014.     

Effect of excess iron and copper on physiology of aquatic plant Spirodela polyrrhiza (L.) Schleid

To elucidate effect of chemical reagents addition on growth of aquatic plants in restoration of aquatic ecosystem, Spirodela polyrrhiza (L.) Schleid was used to evaluate its physiological responses to excess iron (Fe³⁺) and copper (Cu²⁺) in the study. Results showed that accumulation of iron and copper both reached maximum at 100 mg L^?1 iron or copper after 24 h short‐term stress, but excess iron and copper caused plants necrosis or death and colonies disintegration as well as roots abscission at excess metal concentrations except for 1 mg L^?1 iron. Significant differences in chlorophyll fluorescence (Fv/Fm) were observed at 1–100 mg L^?1 iron or copper. The synthesis of chlorophyll and protein as well as carbohydrate and the uptake of phosphate and nitrogen were inhibited seriously by excess iron and copper. Proline content decreased with increasing iron or copper concentration, however, MDA content increased with increasing iron or copper concentration. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2010.     

Coupled dynamics of energy budget and population growth of tilapia in response to pulsed waterborne copper

The impact of environmentally pulsed metal exposure on population dynamics of aquatic organisms remains poorly understood and highly unpredictable. The purpose of our study was to link a dynamic energy budget model to a toxicokinetic/toxicodynamic (TK/TD). We used the model to investigate tilapia population dynamics in response to pulsed waterborne copper (Cu) assessed with available empirical data. We mechanistically linked the acute and chronic bioassays of pulsed waterborne Cu at the scale of individuals to tilapia populations to capture the interaction between environment and population growth and reproduction. A three-stage matrix population model of larva-juvenile-adult was used to project offspring production through two generations. The estimated median population growth rate (λ) decreased from 1.0419 to 0.9991 under pulsed Cu activities ranging from 1.6 to 2.0?μg?L^?1. Our results revealed that the influence on λ was predominately due to changes in the adult survival and larval survival and growth functions. We found that pulsed timing has potential impacts on physiological responses and population abundance. Our study indicated that increasing time intervals between first and second pulses decreased mortality and growth inhibition of tilapia populations, indicating that during long pulsed intervals tilapia may have enough time to recover. Our study concluded that the bioenergetics-based matrix population methodology could be employed in a life-cycle toxicity assessment framework to explore the effect of stage-specific mode-of-actions in population response to pulsed contaminants.     

Developmental toxicity,EROD, and CYP1A mRNA expression in zebrafish embryos exposed to dioxin‐like PCB126

Dioxin‐like PCB126 is a persistent organic pollutant that causes a range of syndromes including developmental toxicity. Dioxins have a high affinity for aryl hydrocarbon receptor (AhR) and induce cytochrome P4501A (CYP1A). However, the role of CYP1A activity in developmental toxicity is less clear. To better understand dioxin induced developmental toxicity, we exposed zebrafish (Danio rerio) embryos to PCB126 at concentrations of 0, 16, 32, 64, and 128 μg L^?1 from 3‐h post‐fertilization (hpf) to 168 hpf. The embryonic survival rate decreased at 144 and 168 hpf. The fry at 96 hpf displayed gross developmental malformations, including pericardial and yolk sac edema, spinal curvature, abnormal lower jaw growth, and non‐inflated swim bladder. The pericardial and yolk sac edema rate significantly increased and the heart rate declined from 96 hpf compared with the controls. PCB126 did not alter the hatching rate. To elucidate the mechanism of PCB126‐induced developmental toxicity, we conducted ethoxyresorufin‐O‐deethylase (EROD) in vivo assay to determine CYP1A enzyme activity, and real‐time PCR to study the induction of CYP1A mRNA gene expression in embryo/larval zebrafish at 24, 72, 96, and 132 hpf. In vivo EROD activity was induced by PCB126 at 16 μg L^?1 concentration as early as 72 hpf but significant increases were observed only in zebrafish exposed to 64 and 128 μg L^?1 doses (p < 0.005) at 72, 96, and 132 hpf. Induction of CYP1A mRNA expression was significantly upregulated in zebrafish exposed to 32 and 64 μg L^?1 at 24, 72, 96, and 132 hpf. Overall, the severe pericardial and yolk sac edema and reduced heart rate suggest that heart defects are a sensitive endpoint, and the general trend of dose‐dependent increase in EROD activity and induction of CYP1A mRNA gene expression provide evidence that the developmental toxicity of PCB126 to zebrafish embryos is mediated by activation of AhR. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 201–210, 2016.     

Effects of malachite green on the mRNA expression of detoxification‐related genes in Nile tilapia (Oreochromis niloticus) and other major Chinese freshwater fishes

The use of malachite green (MG) in fish farming is prohibited in China due to its potentially toxicological and carcinogenic nature, but it is still illegally used in some places. The aim of this study was to investigate the time and concentration‐dependent responses of xenobiotic metabolizing and detoxification‐related genes in diverse fishes exposed to MG both in vivo and in vitro. Experimental fish were administered to two exposure groups of malachite green (MG) (0.10 and 0.50 mg L^?1) for 8 h. The hepatocytes isolated from Nile tilapia were incubated with MG (0.5, 1.0, and 2.0 mg L^?1) for 8 and 24 h, respectively. In vivo, exposure to 0.10 and 0.50 mg L^?1 MG for 8 h caused significant changes of the detoxification‐related genes on the mRNA expression levels. Low‐concentration (0.10 mg L^?1) level of MG induced significant increase on the mRNA expression level of GSTR gene in Nile tilapia and other fishes. The mRNA expression of grass carp UCP2 was significantly induced when exposed to 0.5 mg L^?1 MG. However, the mRNA expression levels of GSTA, CYP1A, and GPX were inhibited significantly by 0.5 mg L^?1 MG in Nile tilapia, grass carp, and Taiwan snakehead. In vitro, the significant increase of mRNA expression of these genes was detected after exposure to 0.5 mg L^?1 MG (UCP2), and 1.0 mg L^?1 MG (CYP1A1, GSTA, GSTR, and UCP2). The induction of hepatic CYP1A1, GSTA, GSTR, and UCP2 in response to MG suggested a potential role of fish CYP1A1, GSTA, GSTR, and UCP2 in MG metabolism. © 2011 Wiley Periodicals, Inc. Environ Toxicol, 2013.     

Metal accumulation and metallothionein in two populations of brown trout, Salmo trutta, exposed to different natural water environments during a run-off episode

Cd, Cu and Zn concentrations were measured in ambient water as well as in gills, liver and kidney tissues of two natural populations of brown trout (Salmo trutta) during a run-off episode in two rivers with different metal compositions due to mining pollution. Metallothionein (MT) was also measured in these tissues. The two rivers, Rugla (Cu contaminated) and Naustebekken (Cd and Zn contaminated), are located in two neighboring drainage basins separated by the topographic divide near the city of Røros in the County of Sør-Trøndelag, Norway. In Rugla, the Cu concentration increased from 15 μg/l at the low water level to 41 μg/l during the run-off episode. In Naustebekken, corresponding values for Cd were 90–170 ng/l and those for Zn were 49–91 μg/l. Gill concentrations of Cu and Cd/Zn MT in both populations of native trout clearly reflect the presence of these metals in the rivers during the run-off, in accordance with the hypothesis of protection caused by MT induction. When Rugla trout were transferred to Naustebekken and vice versa, both the amounts of MT itself and the Cu contents reflected the concentration of this metal in the new environment, indicating that MT induction also protects against acutely increased metal levels. The measured levels of MT in both native and transferred trout can account for all the Cd present in the tissues, but not for all of the Cu and Zn. The capacity of MT to regulate Cd and Cu in the trout populations in their natural habitat therefore seems clearly present. Our data also indicate that the MT I and II isoforms may bind metals selectively.     

Differential metallothionein induction patterns in three freshwater fish during sublethal copper exposure

We assessed whether fish that tolerate higher levels of Cu exposure have a higher capacity to induce metallothionein (MT) synthesis than other, more sensitive, fish species. Furthermore, we examined if a correlation could be found between tissue Cu accumulation and MT levels. Cu accumulation and MT concentrations in gill, liver, kidney and muscle of rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio) were measured during a 1 week exposure to a sublethal Cu (1 microM). Different patterns were observed for the three species regarding Cu accumulation as well as MT induction. Virtually no Cu accumulation was seen in rainbow trout gill, while in both cyprinid species gill Cu levels increased three- to four-fold. Cu accumulated fast in common carp (within the first day), but slow in gibel carp (1 week). Gill MT induction was obvious in gibel carp only, with an increase of 156% after 1 week of exposure. Liver accumulated most Cu in rainbow trout (235% increase) and common carp (144% increase), with Cu levels in liver being significantly higher in rainbow trout compared to the carp species from the start. MT induction was pronounced in common carp liver only (138% increase). In gibel carp liver, there was no clear Cu accumulation or MT induction. In contrast, gibel carp was the only species to show Cu accumulation in kidney after 3 days of exposure (83% increase), after which levels returned to normal. Concomitantly, gibel carp kidney was also the only kidney tissue to show MT induction (192-195% increase after 3 and 7 days). In common carp, a significant decrease of kidney MT levels was observed from day 1 onwards. In muscle, Cu accumulation was clear for the two cyprinid species (three- to four-fold increase) but not for rainbow trout. Of the species studied, gibel carp is the most resistant to copper polluted environments, and showed a positive significant relationship between tissue copper concentrations and MT levels in gill, liver and muscle tissues. Common carp showed an intermediate response, with significant correlations in liver and muscle tissue. In contrast, we found low MT induction in rainbow trout, the most sensitive species, and no correlation at all between MT concentrations and tissue copper contents. Possibly, the regulatory capacity for copper homeostasis was exceeded in rainbow trout, and MT synthesis inhibited.     

Exposure to 17α‐ethinylestradiol decreases motility and ATP in sperm of male fighting fish Betta splendens

The synthetic estrogen 17α‐ethinylestradiol (EE2) is an endocrine‐disrupting chemical released into aquatic environments from sewage treatment facilities. We tested the effects of two environmentally relevant concentrations of waterborne EE2, 10 and 100 ng L^?1, on reproductive endpoints in the teleost fish Betta splendens. In the first experiment, testes were removed from males and sperm were exposed to EE2 directly through the activation water. Direct exposure to EE2 had no effect on any measure of sperm swimming performance. In the second experiment, we exposed sexually mature male B. splendens to EE2 using a semi‐static exposure protocol for 4 weeks. There were no significant treatment effects in the 10 ng L^?1 treatment group, but at the 100 ng L^?1 dose we found that fish had smaller gonads and reduced sperm swimming velocity. When allowed to interact freely with female conspecifics, males exposed to 100 ng L^?1 EE2 built smaller nests and showed a nonsignificant decrease in fertilization success. To investigate further the potential mechanism underlying the decrease in sperm quality, we repeated the chronic exposure experiment and analyzed the ATP content of sperm from fish in each treatment group. We found that males exposed to 100 ng L^?1 of EE2 had fewer moles of ATP per sperm than did fish in the other two treatment groups, suggesting that a decrease in intracellular ATP caused a reduction in sperm swimming velocity. The current study adds to the growing body of literature that indicates the risks to aquatic organisms of exposure to environmentally relevant concentrations of EE2. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 243–252, 2014.     

Effect of acute hexavalent chromium exposure on pituitary–thyroid axis of a freshwater fish,Channa punctatus (Bloch)

Acute exposure to hexavalent chromium (10 mg L^?1, 20 mg L^?1, and 40 mg L^?1 potassium dichromate for 96 h) dose‐dependently affected the pituitary–thyroid axis of teleost, Channa punctatus. Significant hypertrophy of the thyroid follicle was observed in 20 mg L^?1 and 40 mg L^?1 groups; the follicular epithelium was however hypertrophied only in 40 mg L^?1 group. The colloid depletion in the lumen of thyroid follicle was evident in 20 mg L^?1 and 40 mg L^?1 groups. Serum thyroid hormones (thyroxine/T4 and triiodothyronine/T3) level increased significantly at both the higher doses. Increased immunointensity and significant hypertrophy of the pituitary thyrotrophs (anti TSHβ‐immunoreactive cells) was observed in both 20 mg L^?1 and 40 mg L^?1 chromium‐exposed fish. The increased thyroid hormones secretion observed in this study might be an adaptive response of the pituitary–thyroid axis under acute chromium‐induced stress condition to maintain homeostasis. The long‐term Cr(VI) exposures, however, may lead to attenuation/exhaustion of the pituitary–thyroid axis and pose serious threat to fish health and affect their population. © 2013 Wiley Periodicals, Inc. Environ Toxicol 30: 621–627, 2015.