Complexation reduces nickel toxicity to purple sea urchin embryos (Strongylocentrotus purpuratus), a test of biotic ligand principles in seawater

The potential for Ni toxicity in seawater is of concern because of mining and processing activities in coastal regions. Determining Ni speciation is vital to understanding and predicting Ni toxicity and for bioavailability-based nickel risk assessment. The goal of this study was to characterize the complexation of Ni in relation to toxicity using embryological development of purple sea urchin (S. purpuratus). It was predicted that free ion [Ni2+] would be a better predictor of toxicity than total dissolved Ni concentrations (NiD). Synthetic ligands with known logKf values (Ethylenediaminetetraacetic acid (EDTA), Nitrilotriacetic acid (NTA), tryptophan (TRP), glutamic acid (GA), histidine (HD), and citric acid (CA)) were used to test the assumptions of the biotic ligand model (BLM) for Ni in seawater. [NiD] was measured by graphite furnace atomic absorption spectroscopy (GFAAS) and Ni2+ was first quantified using the ion-exchange technique (IET) and then concentrations were measured by GFAAS; [Ni2+] was also estimated using aquatic geochemistry modelling software (Visual Minteq). The mean EC50 values for [NiD] in unmodified artificial seawater control was 3.6 µM (95% CI 3.0-4.5) [211 µg/L 95% CI 176-264] and the addition of ligands provided protection, up to 6.5-fold higher [NiD] EC50 for EDTA. Compared to the control, measured EC50 values based on total dissolved nickel were higher in the presence of ligands. As predicted by BLM theory, [Ni2+] was a better predictor of Ni toxicity with 17% variability in EDTA and CA media while there was 72% variability in the prediction of Ni toxicity with total dissolved Ni. The results of this research provide support for the application of BLM- based prediction models for estimating Ni impacts in seawater.

Influence of natural organic matter (NOM) quality on Cu-gill binding in the rainbow trout (Oncorhynchus mykiss)

Natural organic matter (NOM) in aquatic environments reduces metal toxicity to fish by forming metal-NOM complexes, which reduce metal bioavailability, metal-gill binding and toxicity. However, differences in the chemical composition of different types of NOM (quality) could also affect metal-NOM binding and toxicity. We predicted that Cu-gill binding would vary in trout exposed to Cu in the presence of NOM of different qualities. NOM was collected from three sources: Luther Marsh (terrigenous approximately allochthonous), Bannister Lake (nominally autochthonous), and from a local sewage treatment plant (designated Preston effluent). Excitation-emission matrix spectroscopy (EEMS) revealed that terrigenous Luther Marsh NOM was primarily humic acid-like material (74%), whereas Bannister Lake and Preston sewage effluent NOM had lower humic acid-like material but greater fulvic acid-like material (30% and 50%, respectively). The specific absorption coefficient (SAC) of Luther Marsh NOM was also much higher (SAC=37.8), consistent with its darker color, compared to more autochthonous, lightly coloured Bannister Lake (SAC=12.4) NOM, and Preston effluent NOM (SAC=9.2). At low-moderate waterborne Cu (0-2,000 nmol L(-1)), all NOM isolates reduced Cu-gill accumulation by 70-90%. Surprisingly, there were no measurable differences in Cu-gill binding amongst the three NOM treatments when fish were exposed to Cu in the low-moderate range. Only at higher Cu (>2,000 nmol L(-1)) were differences observed, where terrigenous Luther Marsh and Preston effluent NOM reduced Cu-gill binding by 40-50% more than the more autochthonous Bannister Lake NOM. Although Cu-gill binding estimates using the HydroQual BLM showed similar trends, the BLM consistently underestimated Cu-gill binding. We conclude that differences in Cu toxicity at lower-moderate Cu concentrations in the presence of different types of NOM are not necessarily related to measurable differences in Cu-gill accumulation. Rather, we suggest that differences in Cu toxicity reported in the presence of different types of NOM might be explained by direct actions of NOM on the gills, which are quality dependent.

The physiological effects of a biologically incorporated silver diet on rainbow trout (Oncorhynchus mykiss)

Silver was biologically incorporated into a diet by exposing rainbow trout for 7 days to 100 mg/l of waterborne silver as silver thiosulphate. These fish were processed into a fine powder (trout meal) and pelleted to form a nutritionally balanced feed which was then fed to juvenile rainbow trout (Oncorhynchus mykiss). Fish were fed either a diet containing 3.1 microg/g biologically incorporated silver (an environmentally relevant concentration), or one of three control diets containing approximately 0.05 microg/g Ag for 128 days. All dietary treatments were fed to satiation once daily. Dietary silver did not significantly affect mortality, growth, food consumption, or food conversion efficiency. Furthermore, ion regulation (plasma Na(+) levels and Na(+) influx rates), hematological parameters (hematocrit, plasma protein, hemoglobin levels), plasma glucose, metabolism (oxygen consumption, ammonia and urea excretion rates) and intestinal Na/K-ATPase and amylase activities were all unaffected. Based on the physiological parameters investigated here, this dietary silver exposure appeared to be physiologically benign to rainbow trout. However, silver concentrations in the livers of the silver-fed fish were significantly elevated at day 16, and reached a steady-state level of approximately 20 microg/g Ag by day 36. The concentration specific accumulation rate in the livers of fish fed biologically incorporated silver was about 4.6 orders of magnitude greater than when fed dietary silver sulfide, indicating much greater bioavailability. Despite this increase, hepatic metallothionein concentrations remained unchanged, in contrast to waterborne exposures, indicating that bioaccumulated silver behaves differently depending on whether it is taken up from the diet or from the water. Apart from a significant reduction in hepatic Cu at day 16, liver concentrations of Cu and Zn were not affected by dietary silver. Silver concentrations were also significantly elevated (relative to control fish) in the kidneys of the silver-treated fish on days 88 and 126, and in the gills and plasma at day 126.

Effects of chronic Cd exposure via the diet or water on internal organ-specific distribution and subsequent gill Cd uptake kinetics in juvenile rainbow trout (Oncorhynchus mykiss)

New regulatory approaches to metal toxicity (e.g., biotic ligand model [BLM]) focus on gill metal binding and tissue-specific accumulation of waterborne metals; the dietary route of exposure and dietary/waterborne interactions are not considered, nor are the consequences of chronic exposure by either route. Therefore, we studied the effect of the same gill Cd load (approximately 2.5 microg/g), achieved by a chronic, 30-d exposure to Cd either via the diet (1,500 mg/kg) or the water (2 microg/L), on tissue-specific Cd distribution and subsequent uptake of waterborne Cd in juvenile rainbow trout (Oncorhynchus mykiss). These two exposure regimes resulted in a branchial Cd load that had been taken up across either apical gill membranes (waterborne Cd) or basolateral gill membranes (through the bloodstream for dietary Cd). The BLM characteristics of the gills (i.e., short-term Cd uptake kinetics) were altered: affinity (log K(Cd Gill) [95% confidence level]) decreased from 7.05 (6.75-8.76) for control to 6.54 (6.32-7.03) for waterborne Cd and 5.92 (5.83-6.51) for dietary Cd, whereas binding capacity (Bmax) increased from 3.12 (2.14-4.09) to 4.80 (3.16-6.43) and 5.50 (2.86-8.17) nmol x g(-1) for control, waterborne, and dietary Cd, respectively. Fish exposed to dietary Cd accumulated a much greater overall chronic Cd body burden relative to fish exposed to waterborne Cd or control fish. The carcass accumulated the greatest percentage of total body Cd in control and waterborne-exposed fish, whereas the intestinal tissue accumulated the greatest percentage in dietary-exposed fish. Tissue-specific Cd burdens were highest in the kidney in both dietary and waterborne treatments. We conclude that chronic Cd exposure alters Cd uptake dynamics, and that the route of Cd exposure, whether waterborne or dietary, results in differences of internal Cd accumulation and branchial Cd uptake characteristics. These factors should be considered in future BLM development.

Plasma copper clearance and biliary copper excretion are stimulated in copper-acclimated trout

Nonacclimated and Cu-acclimated rainbow trout (Oncorhynchus mykiss) exhibited equally rapid clearance of a single bolus of injected (64)Cu (3,780 nmol/kg) from the plasma (32-40 min to half- concentration). Eight hours after Cu injection, approximately 80% of the injected Cu was found in the liver. However, when Cu labeled with (64)Cu was presented intravascularly via continuous infusion at a rate of 158 nmol x kg(-1) x h(-1) for 72 h, Cu-acclimated fish cleared plasma Cu more effectively than nonacclimated fish. The use of chronically implanted cystic bile duct cannulas revealed a fourfold increase in hepatobiliary Cu excretion in Cu-acclimated fish during infusion, demonstrating the important homeostatic role of the liver in Cu metabolism. Extrahepatobiliary Cu excretion, likely through the gills and apparently exceeding biliary Cu excretion, was evident from appearance of (64)Cu in the ambient water but was not altered by Cu acclimation. Cu accumulation in white muscle also played an important a role in copper homeostasis.

Effects of long term sublethal Cd exposure in rainbow trout during soft water exposure: implications for biotic ligand modelling

The objectives of the study were to determine the physiological and toxicological effects of chronic cadmium exposure on juvenile rainbow trout in soft water. Particular attention focused on acclimation, on comparison to an earlier hard water study, and on whether a gill surface binding model, originally developed in dilute soft water, could be applied in this water quality to fish chronically exposed to Cd. Juvenile rainbow trout, on 3% of body weight daily ration, were exposed to 0 (control), 0.07, and 0.11 microg l(-1) Cd [as Cd(NO(3))(2).4H(2)O] in synthetic soft water (hardness=20 mg l(-1) as CaCO(3), alkalinity=15 mg l(-1) as CaCO(3), pH 7.2) for 30 days. Mortality was minimal for all treatments (up to 14% for 0.11 microg l(-1) Cd). No significant effects of chronic Cd exposure were seen in growth rate, swimming performance (stamina), routine O(2) consumption, or whole body/plasma ion levels. In contrast to the hard water study, no acclimation occurred in either exposure group in soft water, with no significant increases in 96-h LC(50) values. Cadmium accumulated in a time-dependent fashion to twice the control levels in the gills and only marginally in the liver by 30 days. No significant Cd accumulation occurred in the gall bladder or whole body. Cadmium uptake/turnover tests were run using radioactive 109Cd for acute (3 h) exposures. Saturation of the gills occurred for control fish but not for Cd-exposed fish when exposed to up to 36 microg l(-1) Cd for 3 h. Cd-exposed trout accumulated less 'new' Cd in their gills compared to controls and they internalized less 109Cd than control fish. This effect of lowered Cd uptake by the gills of acclimated trout was earlier seen for the fish acclimated to 10 microg l(-1) Cd in hard water. The affinity of the gill for Cd was greater in hard water (logK(Cd-gill)=7.6) than in soft water (logK(Cd-gill)=7.3) but the number of binding sites (B(max)=0.20 microg g(-1) gill) was similar in both media. In addition, there was a shift in affinity of the gill for Cd (i.e. lowered logK(Cd-gill)) and increased B(max) with chronic Cd exposure in both soft water and hard water. We conclude that the present gill modelling approach (i.e. acute gill surface binding model or Biotic Ligand Model) does work for soft and hard water exposures but there are complications when applying the model to fish chronically exposed to cadmium.

Effects of chronic sublethal exposure to waterborne Cu, Cd or Zn in rainbow trout. 1: Iono-regulatory disturbance and metabolic costs

The relationships among growth, feeding behaviour, ion regulation, swimming performance and oxygen consumption in rainbow trout (Oncorhynchus mykiss) were compared during chronic exposure (up to 100 days) to sublethal levels of waterborne Cd (3 µg.l(-1)), Cu (75 µg.l(-1)) or Zn (250 µg.l(-1)) in moderately hard water (hardness of 140 mg.l(-1), pH 8). A pattern of disturbance, recovery and stabilization was evident for all three metal exposures, although the degree of disturbance, specific response and time course of events varied. Growth was unaffected by any of the metals under a regime of satiation feeding but appetite was increased and decreased in Cu- and Cd-exposed trout respectively. Critical swimming speed was significantly lowered in fish chronically exposed to Cu, an effect associated with elevated O(2) consumption rate at higher swimming speeds. Branchial Na(+)/K(+) ATPase activity was elevated in Cu-exposed fish but not in Cd-exposed trout. Disruption of carcass Na(+) and Ca(2+) balance was evident within 2 days of exposure to either Cd, Cu or Zn, with subsequent recovery to control levels. The loss of Ca(2+) in trout exposed to waterborne Cd persisted longest, and recovery took approximately a month. The physiological response of trout to chronic Cu exposure involves mechanisms that result in an associated metabolic cost. In comparison, Cd is neither a loading nor a limiting stress and acclimation to chronic Cd-exposure does not appear to involve a long term metabolic cost.

Effects of chronic sublethal exposure to waterborne Cu, Cd or Zn in rainbow trout 2: tissue specific metal accumulation

Tissue specific metal accumulations (gills, liver, kidney and whole body) in rainbow trout (Oncorhynchus mykiss) were compared during chronic exposure (up to 100 days) to sublethal levels of waterborne Cd (3 µg.l(-1)), Cu (75 µg.l(-1)) or Zn (250 µg.l(-1)) in moderately hard water (hardness of 140 mg.l(-1), pH 8.0). A general pattern of tissue metal increase and stabilization was evident for all three metals, although the degree and time course of accumulation varied. The exception to this general pattern was a lack of Zn accumulation in the liver and kidney although small amounts did accumulate in the gills and whole body. Accumulation of Cu occurred primarily in the liver while for Cd the kidney was the major organ of accumulation. Exponential modeling was employed to compare and contrast the saturation concentration and time to half saturation of various tissues. Accumulation of essential metals (Cu and Zn), if it occurred, was rapid and increases were relatively low. For example the time to half saturation during Cu exposures was always less than 2 weeks and the maximum level of accumulation was less than four times background levels. For non-essential Cd, time to half saturation for the liver and kidney was always longer than 5 weeks and modeled saturation concentrations were up to 80-fold higher than background. The response to Cu and Zn suggested an active regulation of tissue burdens while that of Cd appears to be more passive, resulting in continuous metal accumulation over an extended time course. While the initial patterns of accumulation for each metal were generally consistent with the damage, repair and acclimation pattern from concurrent physiological measurements it was clear that tissue metal accumulation was not a good indicator of either exposure of physiological impact.

Ionic regulation and nitrogenous excretion in rainbow trout exposed to buffered and unbuffered freshwater of pH 10.5

Rainbow trout exposed to unbuffered water of pH 10.5 initially showed significant increases in blood pH, plasma cortisol and glucose, partial pressure of NH3 (PNH3), NH4+, and HCO3- values as well as loss of plasma Cl-, reduced partial pressure of CO2 (PCO2), and inhibition of total ammonia excretion rate. After the first day, fish resisted further change, and new levels were established (for blood pH and plasma PCO2 and PNH3 levels) or imbalances corrected, either partially (for total ammonia excretion) or completely (for plasma Cl-, HCO3-, cortisol, and glucose values). During the 7-d exposure, 80% of fish in unbuffered water survived, but in buffered water (0.75 mmol L(-1) glycine-buffered KOH at pH 10.5), survival was only 50% after 3 d, and ion regulatory failure was evident. Fish in buffered and unbuffered alkaline waters had similar total ammonia excretion rates, which suggests that glycine-buffered KOH was not sufficient to significantly reduce gill boundary layer acidification. After 7 d in unbuffered alkaline water, 30% of total ammonia excretion was linked with an amiloride-sensitive (0.1 mmol L(-1)) Na+ uptake mechanism. Treatment of alkaline-exposed trout with waterborne acetazolamide (1.5 mmol L(-1)) indicated that gill boundary layer H+ production, through hydration of CO2, had a role in excretion of total ammonia. Exposure to 4-acetamino-4'-isothiocyantostilbene-2,2'-disulphonic acid (SITS; 0.1 mmol L(-1)) following 24-h exposure to unbuffered alkaline water resulted in increased plasma HCO3- and lowered plasma Cl- concentrations, indicating the role of branchial Cl-/HCO3- exchange in regaining Cl- lost and eliminating the HCO3- accumulated during exposure to alkaline water.

Effects of sodium nitroprusside on blood circulation and acid–base and ionic balance in rainbow trout: indications for nitric oxide induced vasodilation

The effects of the nitric oxide (NO) releasing antihypertensive agent sodium nitroprusside (SNP) on rainbow trout (Oncorhynchus mykiss) were investigated using either waterborne exposures of up to 1.3 mM SNP over 60 and 90 min or injections via the dorsal aorta, and cardiovascular responses were compared. Doses of up to 40 μg∙kg−1into the blood stream resulted within 5 min in significantly reduced blood pressure and pulse pressure with tachycardia. Waterborne SNP below 0.53 mM had no effect, but concentrations above this level (to 1.3 mM) after 30–60 min produced significant tachycardia and vasodilation, resulting in dose- and time-dependent reductions in dorsal aorta pulse pressure, with maximum decreases of 50–57%. At and above 0.4 mM SNP waterborne exposure, blood [Formula: see text] was significantly increased, plasma Na+, K+, and Cl−values were unchanged, and there was a mild alkalosis. The cardiovascular effects of waterborne isosorbide dinitrate at 40 μM were similar to those of SNP. Exposure of fish to waterborne potassium ferricyanide (0.67 mM), which is structurally similar to SNP but does not release NO, produced only minor cardiovascular effects compared with those of SNP. Pretreatment of fish with propranolol (1.9 mg∙kg−1via the dorsal aorta) followed by exposure to 1 mM waterborne SNP showed that adrenergic responses were unlikely to be involved in the vasodilation. The results of pretreatment with methylene blue (1.5 mg∙kg−1via the dorsal aorta) followed by 1 mM waterborne SNP suggested that the vasodilation was induced by NO activation of soluble guanylyl cyclase. This study demonstrates that NO-releasing compounds cause vasodilation in rainbow trout in vivo and provides a novel way of studying the effects of altered vascular resistance in fish.

Drinking rate in juvenile Atlantic salmon,Salmo salar L fry in response to a nitric oxide donor, sodium nitroprusside and an inhibitor of angiotensin converting enzyme, enalapril

Drinking in freshwater juvenile salmon was investigated in response to vasodilation by sodium nitroprusside (SNP), a nitric oxide donor, which significantly increased blood vessel diameter in Atlantic salmon alevins. Atlantic salmon fry (1-3 g), as previously shown, drank at a significant rate in fresh water which doubled to about 1.2 ml kg(-1) h(-1) following injection of SNP (100 μmol kg(-1)), through dilation of body vasculature and activation of a vasoconstrictive mechanism, the endogenous renin angiotensin system (RAS). This response was 50% inhibited by injection of about 100 mg kg(-1) enalapril. Fry increased drinking in response to SNP administered in the water, though the concentration required for maximal response, 1.6 mmol l(-1), was much greater than for injected SNP; this response was also inhibited by enalapril injection. Possible involvement of the gill vasculature and branchial osmoreceptors or baroreceptors in control of the drinking response is discussed.