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Microscopic epilithic algae in the River Itchen at Otterbourne near Southampton and in the Ober Water in the New Forest were studied during 1984 and 1985. The River Itchen rises from chalk springs and has a steady pH near 8.2 and a mean alkalinity of 236 mg HCO3 1−1; at the study site the river is about 16 m wide and 20 cm deep, with a mean flow rate of 0.33 m s−1 and a discharge ranging through the year between 0.34 and 2.46 m3 s−1. The Ober Water, which drains sands and gravels, has a pH between 6.9 and 7.2 and a mean alkalinity of about 50 mg HCO3 1−1; at the study site it is about 6 m wide, with a mean flow rate of 0.27 m s−1 and a discharge ranging through the year between 0.08 and 1.0 m3 s−1.

A study of water quality parameters in Cempaka Lake was conducted in January, April, July, and October 2010. The water quality parameters such as temperature, conductivity, total dissolved solid, dissolved oxygen, pH, and water hardness were determined. Six metals i.e. cadmium, chromium, lead, nickel, zinc, and copper were also determined. The water samples were collected randomly from different sampling points around the lake. The water quality parameters were compared with National Water Quality Standard (NWQS Malaysia) whereas metal concentrations were compared with international standards. Study showed that the water temperature and conductivity values increased during the months of the study with the averages of 27.6oC and 1709µS/cm respectively. The dissolved oxygen and pH values were within the normal ranges with the averages of 1.00 mg/l and 7.37 respectively while the total dissolved solid values increased during the study period with the average of 896 mg/ l. Furthermore, hardness values indicated that the water of the lake classified as soft water with the average of 34.3CaCo3 mg/l. For water quality parameters, study showed that all parameters were in natural concentration range (class I) according to National Water Quality Standard (NWQS Malaysia) except for conductivity, total dissolved solid and dissolved oxygen values. Results showed that the mean metal concentrations (in micrograms per liter) in Cempaka Lake water based on monthly sampling (in descending order) for Zn, Cu, Ni, Cr, Pb, and Cd were 11.08, 3.41, 2.80, 2.43, 0.49 and 0.24 µg/L respectively. Results showed that metals concentrations were lower than maximum concentrations allowed by Malaysian and international standards in protecting aquatic life.

Chronic exposure to water of low pH during the freshwater life stage of Pacific salmonids is presently the cause for concern due to its potential to reduce subsequent performance in the marine environment. Sockeye fry (0+) were raised under sublethal long-term, low pH conditions (pH 4.8-6.8) in soft water and assessed for effects on freshwater growth, stress physiology, and seawater tolerance following smoltification. Fish gained significantly lower mass (average 46% of control [pH 6.8] values) and had lower condition factor and liver somatic index values than control fish following a 126-days exposure to water at pH 5.0. Liver glycogen concentrations (49% of control values) and whole-body lipid content (65% of control values) were also significantly lower. Low pH exposure also resulted in a sustained organismal stress response that included significant and substantial increases in plasma cortisol concentrations. Fish exposed to pH 5.0 in freshwater for 30 days exhibited an average of 14% mortality in a seawater challenge, as well as a significant osmoregulatory stress measured by increases in plasma Na⁺ and Cl⁻ concentrations as well as osmolality compared to controls. Significantly lower critical swimming speed values (U(crit)) were also seen (22% reductions compared to controls). The data generated indicate that sockeye salmon are sensitive and do not acclimate to low pH under long-term exposure conditions, potentially decreasing the probability of survival in the marine environment.

The leakage occurs frequently and relatively centralized in the water-carriage system under the action of the high water head pressure since Tianhuangping Pumped-storage Station operated. The stability of the surrounding bedrock leakage under the long-term action of the high water head pressure receives much concern. This paper studies the water leakage in the branch construction tunnel in the water-carriage system of THP Station by the hydrogen and oxygen isotope analysis method combined with the inorganic hydrochemistry analysis method. The results shows that the value of δ D in the leakage water has obvious zonality and then is grouped in four types. What's more, the concentration of the δ 18O is relatively enriched, mainly produced from the isotopic fractionation caused by the interaction of the calcium hydroxide and soft water in the bulkhead concrete of the branch construction tunnel.

An annual study had been conducted on the physical and chemical factors, as well as water quality assessment, of 4 different types of reservoirs along the Yangtze River watershed in China during the period of 2006–2008. The reservoir water temperature range during the year was 5.5–31.0 °C, an average of 16.5 °C; There was obvious temporal and spatial variation in DO, DO was sufficient in all water levels. It was stable and was maintained at 6.5 mg / L or above; DIN horizontal distribution and seasonal change was evident, but there was no water layer distribution; PO 3 -P was extremely deficient, and P was the main limiting factor of nutrient salts; TN value in the winter was 3–5 times of that in the summer and the spring, except for the value of 0.392 mg/L in Jinsha River, the other three reservoirs were 0.700 mg/L or more, indicating that the water had been polluted by N in varying degrees; N/P was relatively large, the variation range was 7.6–142.6, with an average value of about 38.0; the variation range of ALK and TH was 1.0–2.6 mmol/L, which was classified as soft water. Thermocline appeared at about 10 m in all reservoirs, the difference between the upper and lower temperatures could reach 10 °C. In accordance with the relevant composite trophic state index (TSIc), combined with the reservoir nutrient type to draw the criteria for the classification, evaluation on the water quality of four reservoirs was conducted. The results were: Jinsha River was mesotrophic, Daoguan River was eutrophic, Xujia River and Taoyuan River were meso-eutrophic.

Fourth instars larvae of freshwater midge Chironomus javanus (Diptera, Chironomidae) were exposed for a 4-day period in laboratory conditions to a range of copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb), nickel (Ni), iron (Fe), aluminium (Al) and manganese (Mn) concentrations. Mortality was assessed and median lethal concentrations (LC50) were calculated. LC50 increased with the decrease in mean exposure times, for all metals. LC50s for 96 hours for Cu, Cd, Zn, Pb, Ni, Fe, Al and Mn were 0.17, 0.06, 5.57, 0.72, 5.32, 0.62, 1.43 and 5.27 mg/L, respectively. Metals bioconcentration in C. javanus increases with exposure to increasing concentrations and Cd was the most toxic to C. javanus, followed by Cu, Fe, Pb, Al, Mn, Zn and Ni (Cd > Cu > Fe > Pb > Al > Mn > Zn > Ni). Comparison of LC50 values for metals for this species with those for other freshwater midges reveals that C. javanus is equally or more sensitive to metals than most other tested dipteran.

The influence of dissolved organic carbon (DOC) on the toxicity of uranium (U) to three Australian tropical freshwater species, the Northern Trout Gudgeon (Mogurnda mogurnda), green hydra (Hydra viridissima) and unicellular green alga (Chlorella sp.) was assessed. Exposures were conducted in synthetic soft water without DOC and with DOC added in the form of standard Suwannee River Fulvic Acid (SRFA). Organisms were exposed to a range of U concentrations at a range of DOC concentrations (0-20 mg L(-1)). U toxicity was up to 20 times less in water containing 20 mg L(-1) DOC, relative to DOC-free test waters. U toxicity was also assessed using natural water from a tropical Australian billabong containing 10 mg L(-1) DOC. U toxicity was up to ten times less in the billabong water, relative to DOC--free test waters. SRFA was twice as effective at reducing U toxicity as the billabong water at equivalent DOC concentrations. Geochemical speciation modeling confirmed the decreased U toxicity that resulted from both DOC sources was primarily due to a decrease in the free uranyl ion (UO2(2+)) through complexation with DOC. A predictive model is presented for each of the organisms that can be used to predict U toxicity at a given U and DOC concentration.

The osmorespiratory compromise is a functional conflict between gas exchange and ion regulation that can occur at the gills of fish. Movement of both gases and ions depends upon diffusion, and in freshwater, any increase in surface area and/or reduction in epithelial thickness (lower diffusion distance) to promote O 2 uptake will also elevate rates of salt loss. Conversely, any reduction in surface area and/or increase in diffusion distance to limit ion loss could restrict O 2 uptake. Exercise, acclimation to soft water or freshwater, and gill remodeling are some of the treatments that elucidate the nature of the clash.

International audience; A filtration unit composed of two reverse osmosis membranes in series was evaluated for haemodialysis water production. For this purpose, hard and soft water were formulated based on European drinking water directives. The study showed that the double reverse osmosis process is efficient to produce haemodialysis water with the quality defined by the pharmacopeia requirements from synthetic soft water and hard water. In both cases, nitrate and sodium ions diffuse through the membrane limiting the water treatment. This phenomenon is correlated to the electrostatic interactions, the Donnan effect and the ion diffusivity, which govern the membrane selectivity.

Fathead minnows (Pimephales promelas) were exposed to 17 μg Cu∙L−1or 6 μg Cd∙L−1in synthetic soft water in the presence of competing ligands. Measured gill metal concentrations correlated with free metal ion concentrations, not with total metal. Langmuir isotherms were used to calculate conditional metal–gill equilibrium constants and the number of binding sites for each metal. Log KCu-gillwas estimated to be 7.4 and the number of Cu binding sites on a set of gills (70 mg, wet weight) was ~2 × 10−10mol (~30 nmol∙g wet weight−1). Log KCd-gillwas ~8.6, and the number of Cd binding sites on minnow gills was ~2 × 10−10mol (~2 nmol∙g wet weight−1). Stability constants for H+and Ca interactions at metal–gill binding sites and for metal interactions with dissolved organic carbon (DOC) were estimated using these metal–gill constants. All stability constants were entered into the MSNEQL+aquatic chemistry program, to predict metal accumulation on fish gills using metal, DOC, and Ca concentrations, and water pH. Calculated metal accumulation on gills correlated well with measured gill metal concentrations and with LC50values. Our approach of inserting biological data into an aquatic chemistry program is useful for modelling and predicting metal accumulation on gills and therefore toxicity to fish.

Atlantic salmon (Salmo salar L.) smolts were exposed to ammonia at 4 °C in an open flow system. The concentrations of un-ionized ammonia nitrogen (NH3-N) and total ammonia nitrogen (TAN) were increased abruptly twice during a period of 28 days. For concentrations in the range 1–15 µgl−1 un-ionized ammonia nitrogen (4.3–21.1 mgl−1 TAN), no effects were observed on the smolts. However, plasma glucose was not measured in this range. The observed results for higher concentrations may be divided into two categories of sublethal effects. (1) In smolts exposed to the concentration range 19–37 µgl−1 NH3-N (average 26 µgl−1 NH3-N; 34.9–50.5 mgl−1 TAN), the mean plasma glucose concentration was 1.3 times the mean of the control group. No other measured parameters were significantly altered. (2) For smolts exposed to 37–65 µgl−1 NH3-N (average 47 µgl−1 NH3-N; 57.7–84.5 mgl−1 TAN), the mean plasma glucose concentration was increased to 2.3 times, the mean plasma chloride level was reduced to 0.9 times, and mean haematocrit was increased to 1.1 times the control values. Histological examination of the gill tissue revealed extensive lamellar hypertrophy. Weight, length, condition factor and ventilation frequency were not significantly affected and no mortality took place during the exposure period (1–65 µgl−1 NH3-N; 4.3–84.5 mgl−1 TAN). Plasma glucose seemed to be the most sensitive parameter in detecting the sublethal stress response, and this investigation may thus demonstrate the importance of measuring plasma glucose in experiments concerning safe levels for ammonia.

Two populations of O. propinguus were studied from the hard water Ford River and soft water Baraga Creek in northern Michigan. The streams were physically and chemically similar, except for water hardness, alkalinity, conductivity and pH. Each population was sampled regularly by kick-seining into block nets. Mean abundance of young-of-the-year and year one size classes was higher in the hard water stream than in the soft water stream in 1989 (10.7 young-of-the-year/m2 vs. 1.2/m2, 9.2 year one individuals/m2 vs. 3.0/m2). Total annual net production of o. propinquus was higher in the hard water stream (5.0 g/m2 vs. 3.0 g/m2). Individual growth of both young-of-the-year and year one size classes was greater in the soft water stream. Thus, there was an inverse relationship between individual growth and crayfish density in the two streams. There was considerable year-to-year variation in mean abundance and growth (inferred from mean size) in the Ford River (10.1 year one individuals/m2 and 0.729 g dry...

1. 1. Responses of channel catfish ( Ictalurus punctatus ) swim-up fry to dietary calcium in soft ( 3 ) and hard (> 100 mg/1 as CaCO 3 ) water were determined by feeding purified egg-white diets containing 0, 0.5, 1.0, or 2.0% calcium from CaCO 3 for 8 weeks. 2. 2. Catfish fry fed the basal diet (0.03% Ca) in hard and soft water had lower whole-body ash and whole-body calcium concentrations but higher weight gain and survival than those fed calcium-supplemented diets. 3. 3. Fry in soft water generally had lower whole-body ash, whole-body calcium, and survival, as well as a higher incidence of spinal deformities than fry in hard water. 4. 4. Feeding higher levels of calcium to fry reared in soft water did not increase whole-body calcium levels or decrease spinal deformities to the levels observed for fry reared in hard water and fed supplemental calcium. 5. 5. These data indicate that calcium derived solely from dietary or environmental sources was not sufficient for optimum health of channel catfish fry.

Two strains of rainbow trout (Oncorhynchus mykiss) were exposed to soft water at pH 4.0 for 14 days, after ambient pH was reduced gradually. Several parameters, either indicators of acid stress, or reportedly involved in the adaptive response to low pH, were monitored. No mortality occurred during the exposure period; feeding behavior, haematocrit, and plasma protein levels were not affected. A transient depression of leucocrit was observed. A minor, but significant, hypochloremia and perturbations in plasma glucose levels occurred in acid-exposed fish from one strain only. There was no evidence of activation of the pituitary-interrenal axis in acid-exposed fish. Baseline plasma ACTH and Cortisol levels were indistinguishable from those of control fish, and there was no evidence of sensitization to additional stress in acid-exposed fish, in vitro baseline and ACTH-stimulated Cortisol secretion was not significantly different in the two groups. Ultrastructural evidence indicated an increased turnover rate of chloride cells and leucocyte infiltration in gills of acid-exposed fish. These results suggest that interrenal activation and catastrophic ion loss are not inevitable consequences of exposure of rainbow trout to pH 4.0 and that ultrastructural changes in the gills indicate locally regulated adaptive mechanisms.

A total of 26 soft-water, seepage lakes in the Northern Highlands (NH) of Wisconsin (N =16) and the Upper Peninsula (UP) of Michigan (N=10) were sampled four times between early May and mid October 1984 as part of the ‘PIRLA’ Project (Paleolimnological Investigations of Recent Lake Acidification). Because of low antecedent recharge of the local water-table, this ‘summer’ interval likely featured minimal groundwater inputs (

We evaluated stress due to net confinement among three genetically isolated strains of juvenile lake trout Salvelinus namaycush in relation to water hardness. Changes in plasma cortisol, glucose, sodium, and chloride were used as the stress indicators. In lake trout acclimated and then confined for 8 h in hard water, plasma glucose and cortisol increased significantly (by three- and sixfold, respectively), reaching a plateau by 4 h, while plasma Na+ and Cl– significantly decreased by about 7%. Fish transferred from hard water to soft water and then confined exhibited significantly greater changes in blood chemistry than did fish confined in hard water. This soft-water effect on the stress response disappeared if fish were first acclimated to soft water, but full soft-water acclimation may take at least 2 months. Comparisons of blood chemistry among three different strains of lake trout (Lake Manitou, Killala Lake, and Slate Island) revealed significant differences in their responses to confinemen...

At the Savannah River Site, liquid, low-level nuclear waste will be disposed by incorporating the waste into a solid, concrete waste form called saltstone. Saltstone monoliths will be buried in claycapped, subterranean vaults. Although the vault/cap burial system is designed to severely limit the access of vegetative roots to the saltstone, a study was begun In 1984 to determine the potential for root uptake of radionuclides. Thirty-two lysimeters were constructed and filled with soil. Saltstone samples, containing the liquid, low-level supernate from a waste disposal demonstration program, were buried in some of the lysimeters, at varying depths to investigate the relationship between source depth and plant uptake. Crops, grass, and trees were planted in the lysimiters and sampled periodically. Water samples also were collected from the lysimeter sumps and analyzed for radionuclide content. In the 5 yr following establishment of the lysimeters, only technetium-99 (Tc-99) and cesium-137 (Cs-137) could be detected at elevated concentrations In the vegetation. The Cs-137 concentration difference between the plants grown in control and saltstone lysimeters was barely detectable against background. The Tc-99 concentration was significantly higher in vegetation and sump water of lysimeters containing saltstone, when compared to the control lysimeters. The Tc-99 uptake bymore » vegetation and sump waters appears to be related to release of the Tc-99 from the saltstone into soft water. Similar patterns exist: initial period of very low concentrations,then a coincident buildup period and a period of relatively uniform concentration. Vegetative uptake factors were calculated for uptake of Tc-99 from soil water. The results were very similar for the vegetative parts of all the species grown, 111 to 376 (nBq/kg{sub vegetation})/(nBq/kg{sub water}). The uptake factor calculated for the seeds of crops was less by a factor of 100 than the uptake factor for vegetative parts.« less

Smolting Atlantic salmon, Salmo salar, were kept from 11 April to 24 May in soft water of pH 5 or in soft water of pH 5 and 50 μg aluminum (Al)∙L−1. Control fish were kept in soft water of pH 6.3–6.5. Water temperature was 8–14 °C. In mid-May, some of the control smolts were transferred to the test conditions for 8 d. Exposure to acid water resulted in osmoregulatory failure and high mortality rate. Al strongly enhanced toxicity. Sensitivity to low pH or low pH/Al exposure greatly increased when fish had developed to seawater tolerant smolts. In control and acid-exposed fish, gill carbonic anhydrase activity remained unchanged throughout the experiment whereas in Al-exposed fish, carbonic anhydrase activity decreased. Gill Na+K+-ATPase activity in control fish peaked in mid-May simulanteously with development of seawater tolerance. Fish from both acid-exposed groups had low seawater tolerance. Na+,K+-ATPase activity declined to 60% of start value in acid-exposed fish and to parr level in Al-exposed fish. Hypoosmoregulatory ability was linearly correlated with gill Na+K+-ATPase activity. Reduction in plasma Na+concentration in acid-exposed fish was linearly correlated with the reduction in gill Na+,K+-ATPase activity.

The acute toxicities of technical-grade bromoxynil octanoate (BO) and two commercial formulations, Buctril® and Bronate®, to < 24-h-old neonate Daphnia magna (Straus) were determined in soft, hard, and oligosaline water. In addition, effects of life stage, feeding, aging the herbicide, and exposure duration on BO toxicity to daphnids were investigated. Regardless of formulation, life stage, and water quality, BO was found to be extremely to highly toxic to daphnids in standard tests; 48-h EC50 values ranged from 41 to 161 mg/L. Bromoxynil octanoate was the most toxic to neonates in soft water and the least toxic in hard water. The acute toxicities of the three bromoxynil herbicides to a given age group of daphnids were similar within the same water type. Overall, neonates and 7-d-old adults were more sensitive than 14- or 15-d-old adults to each herbicide. Feeding daphnids during the toxicity test significantly decreased BO toxicity compared to not feeding them. Aging BO (as Buctril) in hard water decreased its toxicity, and the rate of deactivation was rapid, with an estimated half-life of biological activity of 13 h. Daphnids immobilized by exposures to toxic BO concentrations for ≤ 6 h recovered their mobility, whereas exposures of 18 and 24 h to BO produced toxic effects in daphnids similar to those exposed for 48 h. These results indicated that standard continuous exposure tests may not adequately predict the acute toxicity of BO to freshwater animals in the field.

The impacts of pH and dissolved organic carbon (DOC) on the acute toxicity of Cu to larval fathead minnow (Pimephales promelas) were determined using natural soft water from two Precambrian Shield lakes in south-central Ontario. By artificially manipulating the pH and DOC levels of the water, we demonstrated that both acidification and the removal of DOC increased the toxicity of Cu. The 96-h Cu LC50s were determined over a pH range from 5.4 to 7.3 and a DOC concentration range from 0.2 to 16 mg∙L−1. The LC50s ranged from a low of 2 μg∙L−1(pH 5.6, DOC 0.2 mg∙L−1) to a high of 182 μg∙L−1(pH 6.9, DOC 15.6 mg∙L−1). A multiple regression model (log1096-h Cu LC50 = −0.308 + 0.192 pH + 0.136 (pH∙log10DOC)) was used to describe the relationship between Cu toxicity, pH, and DOC. The model was significant (p

Brook trout Salvelinus fontinalis, mottled sculpins Cottus bairdi, and slimy sculpins Cottus cognatus occur in many Pennsylvania streams that have depressed pH and elevated aluminum concentrations during episodes of high stream discharge (acidic episodes). We performed 20-d in situ cage exposures with these species to determine their relative sensitivities to field conditions. We also exposed fish in the laboratory to synthetic soft water, without added Al, to elevate possible effects of Al on sodium flux rates and pH toxicity. Exposures were in five streams: Two with high pH (>5.60) and low Al concentrations (

Young-of-the-year largemouth bass were exposed to simulated overwintering conditions, 4 °C for 113 days, in soft ([CaCO3] 48 mg/L, [Ca] 13.4 mg/L) and very soft ([CaCO3] 4.6 mg/L, [Ca] 1.5 mg/L) water. In some treatments pH was reduced to 5.0 and 4.5, with no added Al; in others, a monomeric Al level of 30 μg/L was maintained. In the neutral pH treatments the bass had greatly thickened gill respiratory epithelium and large numbers of chloride cells (compared with bass kept at 20 °C in a prior experiment), and blood osmolalities declined and stabilized at about 260 mosmol/kg. In the acid treatments the bass had thickened respiratory lamellae and chloride cell numbers similar to those found in the neutral pH treatments. In very soft water, mean blood osmolalities declined to 242 and 219 mosmol/kg at pH 5.0 and 4.5, respectively, and did not stabilize. In the acid + Al treatments, respiratory lamellae were frequently obliterated by hyperplasia of the interlamellar epithelium, suggesting markedly compromised respiratory ability. In addition, chloride cell numbers were usually depressed, and those cells that were present were often vacuolated or covered by layers of pavement epithelium; blood osmolalities declined to the lethal and near-lethal level of about 200 mosmol/kg, and heavy mortalities occurred. After 84 days in cold soft water (pH 7.8), scale Ca content declined; this effect was more severe in very soft water (pH 7.0). Acidification did not cause further decline in scale Ca content in the very soft water. At pH 4.5 + Al, scale Ca levels were higher than at pH 4.5 without added Al and higher than at pH 7.0, suggesting that Al may interfere with normal utilization of scale Ca reserves. Substantial lipid reserves persisted throughout the experiment. Mortalities were correlated with pH-associated gill damage and electrolyte losses rather than with duration of exposure to low temperature per se. Modest levels of Al exacerbated gill damage and electrolyte losses. We suggest that overwintering, with only moderate elevation of acid and Al levels, may represent an important critical period for survival to young-of-the-year fish in northern climates, principally by adversely affecting electrolyte balance. The gills of juvenile largemouth bass undergo marked structural changes with prolonged exposure to cold water, possibly to retard electrolyte losses.

Adult brown trout were acclimated for 2–4 weeks to artificial soft water ([Ca2+] 25 μmol l−1) at neutral pH and at summer (15°C) temperature. During this period they swam against a current of approximately 0.25 ms −1. They then had their dorsal aorta cannulated and were exposed to neutral or sublethal pH (4.5) for 4 days in still water. After 4 days of exposure to sublethal pH, critical swimming speed (Ucrit) was 35% lower than that for fish at neutral pH. There were significant increases in arterial and in blood lactate concentrations at Ucrit compared with the values in resting fish at neutral pH and these led to significant reductions in plasma pH. There were no such changes in fish at sublethal pH. There were no significant changes in intracellular pH (pHi) of red blood cells at Ucrit, probably as a result of increases in the levels of plasma catecholamines. There were significant reductions in pHi of red and white muscle fibres at Ucrit. It is argued that these values were not as low in the white fibres as those seen in previous studies after fish have been chased to exhaustion and, therefore, that the fish in the present study were not completely exhausted, although they would no longer swim at a steady speed. As pHi of the red muscle was the same at Ucrit for fish at neutral and at sublethal pH, it is suggested that Ucrit (fatigue) coincides with a particular pHi of the red muscles and possible mechanisms are discussed.

Trace metals such as aluminum, when mobilized by acid deposition, may be important toxic agents in acidified waters. Beryllium is chemically similar to aluminum, and its solubility and aqueous speciation properties suggest that it may also be a problem in some acidic waters. Elevated beryllium levels have been found in some waters, but little is known of the potential toxic effects of beryllium in soft water at low pH. We exposed juvenile perch Perca fluviatilis and roach Rutilus rutilus to beryllium at two levels of pH. Beryllium concentrations of 10 μg/l or more caused increased mortality at pH 4.5 in perch, but only higher concentrations (>50 μg/l) were lethal at pH 5.5. In roach, beryllium concentrations ≥100 μg/l killed most fish within 96 h, regardless of pH. Beryllium also produced gill abnormalities similar to those caused by aluminum at concentrations as low as 10 μg/l. The abnormalities became more severe at higher beryllium levels, and included development of chloride cell apical crypts, increased mucus production, microridge loss, epithelial hyperplasia, and fusions of primary lamellae. The effects of beryllium and aluminum are similar, but beryllium causes gill damage at lower concentrations, suggesting that it may be an important, unrecognized contaminant in some acidic waters.

This study examined the effects of pH (5.0-8.5) on the toxicity of waterborne Cu to juvenile rainbow trout (Oncorhynchus mykiss) in soft water under flow-through conditions. Relationships between 96 h or 30 day Cu toxicity and 24 h lethal Cu accumulation on the gills (24 h LA(50-Acute) or 24 h LA(50-Chronic)) were examined in the context of predictions made using the biotic ligand model (BLM). Acute toxicity was relatively constant across pHs except for a 2- to 3-fold higher LC(50) at pH 5.0. In the chronic exposure, the fish had similar tolerance to Cu from pH 5.0 to 8.0, but were 3- to 4-fold more tolerant at pH 8.5. This pattern was not captured by the current BLM which predicts that acute and chronic LC(50) values should increase progressively from pH 5.0 to 8.5, with much greater values than those observed at the higher pH range. BLM-based water quality criteria would not be protective for trout at pH 8.0 or 8.5 in acute exposure to Cu in soft water. The measured 24 h LA(50-Acute) and LA(50-chronic) at pH 8.5 were higher, and 24 h LA(50-Chronic) at pH 5.0 was lower than those at the other pHs. This study indicates that gill Cu bioaccumulation does not explain toxicity at high or low pH, and the BLM needs revision to adequately predict Cu toxicity to trout in soft water.

Colonial aggregation of Microcystis plays a key role in bloom formation. Limited studies have been reported about effects of environmental factors on the aggregation of Microcystis. Calcium is an important chemical element in water system. In this study, we investigated the effects of a low- (0.015 g l−1) and a high-concentration of calcium (0.100 g l−1) on the aggregation and buoyancy of a colonial strain M. aeruginosa XW01. Results show that compared to the low concentration of calcium, the high-calcium condition results in bigger colonial size, higher level of buoyancy and increased production of extracellular polysaccharides (EPS) of M. aeruginosa XW01. Increased production of EPS induced by the high-calcium concentration should contribute to the colonial aggregation and buoyancy of M. aeruginosa XW01. These results suggest that an increase in calcium concentration may be beneficial for Microcystis blooms occurring in a soft water lake.

Minnows (Phoxinus phoxinus) were exposed in the laboratory to 3 nM Cd (Cd group), 2000 nM Zn (Zn group), or to both metals (CdZn group) in soft water for 142 d. A fourth group was kept with no metals added to the water (Low group). After 80 d, the Cd and Zn groups were statically exposed to 109Cd and 65Zn, respectively, for 24 h. The CdZn group was exposed to both tracers. Fish were sampled for 61 d after the tracer exposure. At the end of the experiment, an increased metallothionein level was detected in the kidney of fish exposed to the metal mixture (Low group: 0.14 nmol/g fish; CdZn group: 0.54 nmol/g fish). However, the fish did not acquire tolerance to the metals because mortality continued at a constant rate during the whole experiment. Metabolism of Cd and Zn was altered in fish exposed to the metal mixture compared with fish exposed to Cd or Zn alone. The main effect was a Zn-induced increase in Cd turnover rate in the fish. Nevertheless, the toxic action of metals was additive, since mortality at the end of the experiment was 24, 32, and 54% in the Zn, Cd, and CdZn groups, respectively.

SUMMARY 1. A survey of thirty-two rheocrene springs in central Pennsylvania revealed that, Like Gammarus in lakes and streams, Gammarus minus is absent from springs with pH

The minimum dietary zinc requirement of channel catfish swim-up fry was determined in soft ( 3 ) and hard (> 100 mg/l as CaCO 3 ) water. Purified egg-white diets supplemented with 0, 20, 40 or 80 mg Zn/kg were fed to swim-up fry for 6–8 weeks. Weight gain, whole-body ash, wholebody zinc and calcium, survival, mortality due to handling stress, and spinal deformities were determined. Channel catfish fry fed the basal diet in soft and hard water had decreased whole-body zinc levels and increased whole-body calcium levels. Fry in soft water generally had lower whole-body ash and calcium as well as a higher incidence of mortality and spinal deformities than fry in hard water. The minimum dietary zinc requirement of channel catfish fry grown in hard water was determined to be approximately 20 mg Zn/kg diet; whereas fry grown in soft water had a requirement between 20 and 40 mg Zn/kg diet. The greater zinc requirement of fry in soft water did not increase survival or decrease mortality from handling to the levels of fry reared in hard water. Results from this study indicate that environmental calcium interacts with dietary zinc and may influence growth, survival and tissue mineralization of channel catfish fry.

Cotton fabrics flame retarded with tetrakis (hydroxymethyl phosphonium chloride (THPC)-urea-ammonia polycondensate (Proban CC, Albright and Wilson Ltd., U.K.) have been subjected to up to 50 simulated hos pital wash cycles. Laundering variables include sodium perborate oxidant con centration, detergent type (liquid with no oxidant, powder with zeolite and sodium perborate and powder with polyphosphate and carbonate and per borate) and water hardness. The flame retardant system resisted all laundering systems in terms of the constancy of burning behaviour assessed by vertical strip (BS 5438) and limiting oxygen index (LOI) measurements. However, increased perborate con centration changed the thermogravimetric (TGA) response of laundered fabrics. Soft water washing promoted cotton fibre fibrillation independent of deter gent type; increased oxidant concentration promoted secondary wall damage. Hard water washing severely damaged fibre secondary walls and significant depositions of calcium ions often as phosphate occurred on fabric. Presence of the flame retardant was observed to have a stabilising fibrillar binding effect which was offset by a secondary wall crack promoting character.

The hypothesis that water $Ca^{++}$ plays a significant protective role in the regulation of ionic, acid-base, and nitrogen balance of fish in highly alkaline environments was tested in two experiments. In each experiment, rainbow trout were exposed to water of pH 10.1 in soft water ([CaCO₃], 4 mg · L⁻¹) and hard water ([CaCO₃], 320 mg· L⁻¹). The experiments consisted of a chronic experiment in which the fish were exposed to those conditions for 196 h, and an acute 12-h experiment in which the fish were subjected to four protocols, each lasting 3 h. Acid-base parameters, and concentrations of blood ions, ammonia, and urea nitrogen, were measured in each experiment. Mortality and blood cortisol concentrations were measured only in the chronic experiment, while ammonia flux rates and the effects of amiloride addition to the water on these parameters were determined only in the acute experiment. While all the fish chronically exposed to alkaline soft water died and exhibited stress, as evidenced by elevated ...

Adult rainbow trout, Oncorhynchus mykiss, were acutely exposed for 4 hours to low pH (4.4) and elevated Al-concentrations (300-mu-g l-1) in soft water (Ca2+ + Mg2+ = 25-mu-mol l-1). Comparison of branchial and renal ion fluxes (Na+, Cl-, Mg2+, C2+ and NH4+) gave evidence that pH and Al effects were primarily localized at the gill site. The negative whole body ion balance seemed to be caused by stimulatory effects on Na and Cl efflux especially under Al stress and to a lesser extent by inhibition of influx. Measurements of gill potentials indicated positive shifts, which were similar in response to increasing levels of H+ ions and Al. It is suggested that Al-induced changes of branchial potentials causes high diffusable loss of ions through interference with membrane-bound Ca2+ at the gill site.

Young-of-the-year largemouth bass (Micropterus salmoides) were exposed to pH levels from 8.0 to 4.5 in two water types, 1.5 and 13.4 mgCa/L. Exposures were conducted at 3.8 °C for 113 d, followed by 14 d of increasing temperature to 18 °C. Two treatments in the softer water, one each at pH 5.0 and 4.5, had Al added to attain 30 μg Al/L; all other treatments were at approximately 5 μg Al/L. The condition factor of fish in all treatment groups declined with exposure time at 3.8 °C. Fish in the 13.4 mg Ca/L water maintained osmotic homeostasis through pH 5.0. In the 1.5 mg Ca/L water, osmotic homeostasis was lost at pH 4.5 and at pH 5.0 when Al was added. Mortalities were most prevalent when exposed in the 1.5 mg Ca/L water with added Al. The probability of survival was directly correlated with blood osmolality; no correlation was found between survival probability and condition factor. A rise in blood osmolality occurred among fish from most exposure groups when the temperature was increased to 18 °C. When fish from these chronic treatments were challenged at pH 3.8, they had shorter survival times in the softer water and after longer preexposures.

Although generally rare in natural aquatic systems, cobalt concentrations can be elevated through ore and coal mining operations and discharges of certain textile dyes. The U.S. Environmental Protection Agency does not have an ambient water quality criterion for cobalt due to a lack of toxicological data. The present study determined whether freshwater acute and chronic cobalt toxicity were dependent on dilution water hardness. We specifically examined the relative toxicity of cobalt at high water hardness (≥ 200 mg/l as CaCO3) because cobalt often occurs in carbonate ores. Acute and chronic toxicity tests using both Ceriodaphnia dubia and Pimephales promelas were performed using four different synthetic waters: 50,200. 400, and 800 mg/l hardness as CaCO3. Diluent hardness appeared to have no effect on measured cobalt concentrations. Dissolved cobalt in water samples during testing was similar to the corresponding total recoverable cobalt in this study suggesting that most of the cobalt was in a soluble and presumably bioavailable form. LC50 values for P. promelas could not be calculated owing to their low sensitivity to high cobalt concentrations (≥ 5 mg/l) over a 48 h period. Regression analysis of P. promelas acute NOEC values and test water hardness indicated an R2 = 0.94 suggesting a direct relationship between water hardness and acute toxicity to cobalt for this species. C. dubia acute tests indicated water hardness effects after 48 h of exposure and non-linear dose responses in hard water (≥ 200 mg/l). Regression analysis of C. dubia 24 h LC50 values and test water hardness indicated an R2 = 0.91. For both cases, a simple power function gave the best regression fit. C. dubia appeared to be more sensitive than P. promelas at hardness ≥ 200 mg/l but the reverse was true in soft water ( ≤ 50 mg/l). The 7 d P. promelas chronic NOEC increased from 1232 μg/l cobalt (50 mg/l hardness) to ≥ 3833 μg/l (800 mg/l hardness). Effects were on fish survival and not growth. Regression analysis yielded an R2 = 0.97 based on the fish survival NOECs and the natural log of hardness. C. dubia chronic tests were inconclusive due to poor survival and reproduction in the synthetic waters. Available data suggest that within 50–200 mg/l water hardness, cobalt acute toxicily is inversely related to water hardness. Tentative cobalt acute criteria, based on power functions, are 288 μg/l and 873 μg/l for soft and hard water, respectively. Available chronic toxicity data suggest that daphnids are more sensitive to cobalt than other genera. Chronic endpoints for both P. promelus and D. magna were similar in soft and hard water (≤ 400 mg/l hardness) suggesting that chronic toxicity is not hardness-dependent over this range. However, chronic cndpoints at 800 mg/l hardness were 3.1 and ≥ 12 times higher than endpoints observed under soft water conditions for P. promelas and C. dubia respectively suggesting that very hard waters may significantly reduce chronic toxicity potential of cobalt.

1. Freshwater adapted mummichogs (Fundulus heteroclitus) were exposed to cadmium. In soft water (less than or equal to 5 mg/l CaCO3), the 4-day safe (TL100) and sublethal (TL50) tolerance limits (TLs) for cadmium were 0.14 microgram/l and 12.2 micrograms/l, respectively. 2. Survival declined with increasing cadmium concentration and the length of exposure. The toxicity of cadmium was reduced in water with high calcium concentration (200 mg/l CaCO3). Pre-exposure to calcium also prolonged the survival in cadmium-containing water. 3. The mummichog appears to be extremely well suited for monitoring environmental cadmium poisoning.

Adult brown trout were acclimated for 2–4 weeks to artificial, soft water (Ca2+ 25μmol l-1) at neutral pH and at summer (15°C) or winter (5°C) temperatures. During this period they swam against a current of approximately 0.25 ms-1. They were then exposed to neutral or sublethal pH for 4 days in still water. For fish with their dorsal aorta catheterized, sublethal pH was 4 at 5°C and 4.5 at 15°C. After 4 days of exposure to sublethal pH, resting oxygen uptake was 40 % higher than that at neutral pH for fish held at 15 °C and 38 % higher for fish held at 5°C. Critical swimming speeds (Ucrit), in contrast, were 35% and 31% lower, respectively. These two phenomena may be related in as much as the ‘metabolic cost’ of exposure to low pH may increase as swimming speed increases, thus reducing the scope for activity. Another important factor could be an impairment of oxygen delivery to the red muscle fibres. Although arterial O2 concentrations and heart rate are both similar for fish at Ucrit in neutral and acid water, there are signs of haemoconcentration in fish exposed to low pH, and the consequent increase in blood viscosity could disrupt the local circulation in the red fibres. Whatever its causes, an impairment of swimming activity resulting from exposure to acid water may have severe consequences for active fish such as salmonids. Exposure to sublethal pH caused significant reductions in plasma Na+ and Cl-concentrations at both temperatures, although these were more substantial at 5°C than at 15 °C. Swimming at Ucrit had no significant effect on plasma concentrations of Na+, K+ and Cl- except at sublethal pH at 5°C, when there were significant reductions in all three. Seasonal temperature had significant but small effects on resting and Ucrit, and these are discussed in terms of the possible effects of low temperature and continued swimming activity (training) on hypertrophy of skeletal and cardiac muscles and on the aerobic capacity of the ‘red’ muscle fibres.

Water pH in the gill micro-environment of adult fathead minnows (Pimephales promelas Rafinesque) was measured by means of opercular catheters and latex masks. Synthetic soft water of pH 5.7 was made more acidic, so that pH of the gill micro-environment stayed at approximately 5.4 to 5.9 over the inspired pH range 4.8 to 6.3. Copper would therefore be >99% Cu2+ at the gills. To measure Cu accumulation on gills, the target organ for Cu toxicity, adult fathead minnows were exposed for 2 to 3 h to 16 μg/L Cu in synthetic soft water (Ca2+ and Na+ approximately 50 μeq/L) at pH 4.8 and 6.3. Gill Cu concentrations were about 1.7 μg Cu/g wet tissue for the inspired pH 4.8 and 6.3 exposures. Added Ca2+ of 2,100 or 4,000 μeq/L reduced gill Cu accumulation during exposures at pH 4.8 but not at pH 6.3. EDTA eliminated Cu deposition at both pH 4.8 and pH 6.3 when equimolar with Cu, but reduced Cu deposition (by 50%) when half equimolar only in the pH 4.8 exposures. These results can be explained by Ca2+ and H+ competition with Cu for gill binding sites and by complexation of Cu by EDTA. Added CaCO3 did not reduce gill Cu, although both competition by Ca2+ and complexation by CO2−3 were expected. Water chemistry calculations suggested that because little CO2−3 is available at pH < 7, CO2−3 from CaCO3 is less likely to affect Cu deposition on fish gills than is Ca2+ from CaCO3.

Recruitment failure is considered to be a major factor contributing to the decline of fish populations in soft, acidic waters; direct mortality of embryo-larval fishes has been postulated as a major cause of the decline. Little is understood of the physiological consequences to embryo-larval fishes of prolonged exposure to soft, acidic waters; however, dysfunction of respiratory and ionoregulatory processes is suspected. In order to evaluate the effects of acid exposure on the respiratory and ionoregulatory systems of developing brook trout, Salvelinus fontinalis, differences in gill morphology and numbers of chloride cells were compared between groups cf developing embryo-larval fish continuously exposed to moderately hard well water (130.0 mg.l−1 as CaCO3, pH 7.94) or to reconstituted soft, acidic water (4.4 mg.l−1 as CaCO3, pH 5.25) designed to mimic acidic waters of northern Wisconsin acidified lakes. Exposures were maintained for up to 48 days (82 days after fertilization) during critical periods of growth and differentiation of branchial structures. The second right gill arch of each fish was examined for changes in the development of filaments and lamellae and for differences in numbers of chloride cells. Gills of fish that developed in soft, acidic water contained greater numbers of normal and degenerating chloride cells, exhibited hyperplasia of primary epithelium and multiple fusions of adjacent filaments and lamellar epithelium than the gills of control fish. Filament and lamellar lengths and numbers of lamellae per filament were significantly less (P

1. Atlantic salmon (Salmo salar) parr were exposed to (NH4)2SO4 solutions in static systems with aerated, soft water for 96 hr. The 96 hr-LC50 for un-ionized ammonia (expressed as mg/l NH3-N) ranged from 0.031 (2.1 degrees C) to 0.111 (17.1 degrees C) at pH 6.0 and from 0.030 (1.8 degrees C) to 0.146 (12.5 degrees C) at pH 6.4. 2. No mortality, was found in a KCl solution and a physiological salt solution with chloride concentrations approximately equivalent to the chloride concentration in a NH4Cl solution giving 45% mortality, and to the ammonia concentration in a (NH4)2SO4 solution giving 35% mortality, all solutions tested at pH 6.0 and 2 degrees C.

Short-term static bioassays were conducted in duplicate to determine the toxicity of the nitrate ion (NO3−) in soft water (hardness average value of 42.7 ppm CaCO3) to early and last instar larvae of Cheumatopsyche pettiti (Banks) and Hydropsyche occidentalis Banks (Trichoptera: Hydropsychidae), common insect species in macrobenthic communities of freshwater ecosystems in North America. Animals were exposed to five different concentrations of sodium nitrate (NaNO3) for 5 days. They were also exposed to a NaCl concentration of 1100 ppm as sodium and conductivity toxicity controls. No mortality was observed during NaCl tests, indicating that toxic effects generated by NaNO3 were fundamentally due to nitrate ions. In nitrate aquaria, net-spinning caddisfly larvae migrated from their retreat and capture nets and protruded their anal papillae before dying. The 72, 96 and 120 hour LC50 values were respectively 148.5, 97.3 and 65.5 ppm NO3N for the early instar of H. occidentalis, 183.5, 109.0 and 77.2 ppm NO3N for the last instar of H. occidentalis, 191.0, 113.5 and 106.5 ppm NO3N for the early instar of C. pettiti, and 210.0, 165.5 and 119.0 ppm NO3N for the last instar of C. pettiti. Larvae of H. occidentalis appear significantly (P

The effect of various environmental factors on the stability of aqueous solutions of amoxicillin-clavulanic acid combination in a veterinary water-soluble powder product was investigated. In the swine industry, the combination is administered via the drinking water, where both substances are quickly decomposed depending on several environmental factors. The degradation rate of the substances was determined in solutions of different water hardness levels (German hardness of 2, 6 and 10) and pH values (3.0, 7.0 and 10.0), and in troughs made of different materials (metal or plastic). Increasing the water hardness decreased the stability of both substances, amoxicillin being more stable at each hardness value than clavulanate. Amoxicillin trihydrate proved to be most stable at an acidic pH, while increasing the pH decreased its stability (P < 0.05). Maximum stability of potassium clavulanate was experienced at neutral pH, while its decomposition rate was significantly higher at acidic and alkaline pH values (P < 0.01). The stability of the amoxicillin-clavulanic acid combination depends mainly on the less stable clavulanate, although the effect of metallic ions significantly increased the decomposition rate of amoxicillin, rendering it less stable in metal troughs than clavulanate (P < 0.05). Therefore, the amoxicillin-clavulanic acid combination should be administered to the animals in soft water, at neutral pH and in plastic troughs.

To evaluate the population-level effects of heavy metals (copper, zinc, cadmium, hexavalent chromium, nickel) on fathead minnow, Pimephales promelas, we first estimated the concentration–effect relationships between the metal concentrations and individual traits (juvenile survivability, hatchability, fertility) by using toxicity data collected from the literature. A Leslie matrix model of fathead minnow was used to calculate population growth rates from these relationships. The population threshold concentrations (PTCs) leading to zero net growth of the fish population were as follows: Cu, 27.4; Cd, 33.2; Zn (soft water), 81.5; Zn (hard water), 85.8; Ni, 504.8; Cr, 3251.6 (μg L−1). By comparing the PTCs with no observed effect concentrations (NOECs), we found that some PTCs were equivalent to or even lower than the corresponding NOECs. This result suggests that current ecological risk assessments based on the NOECs can be inadequate for protecting aquatic populations and more efforts on the population-level studies are needed.

The current study evaluated acute and subchronic toxicity of arsenite (As(3+)) and zinc (Zn(2+)) to stage 25 tadpoles of Rhinella arenarum in both single and joint laboratory exposures. LC50 values obtained for As(3+) were elevated and remained within the range of 46 to 50 mg/L of As(3+) between 4 and 17 d of exposure. Growth of tadpoles was completely inhibited with 30 mg/L of As(3+), demonstrating the presence of ecologically relevant sublethal effects at concentrations lower than those resulting in lethality. With respect to Zn(2+), a 96-h LC50 value of 2.49 mg/L was calculated in soft water. Contrary to results obtained for As(3+), LC50 values of Zn(2+) gradually decreased with increasing exposure duration, from 2.49 mg/L at 96 h to 1.30 mg/L after 21 d. In joint exposures to both metals, the type of interaction observed between As(3+) and Zn(2+) was concentration dependent. Lethal effects of As(3+) were mitigated, unaffected, or potentiated by 0.01, 0.1, and 1-2 mg/L of Zn(2+), respectively. However, although 0.01 mg/L of Zn(2+) significantly reduced lethality of As(3+)-exposed tadpoles, the same concentration of Zn(2+) did not help to reverse the stunt growth of these animals. Further studies need to examine which are the lowest concentrations As(3+) required to reduce growth and whether Zn(2+) serves to antagonize growth effects in this range of concentrations.

Crustaceans are considered an important part of the soft water zooplankton community. Therefore they represent water organisms in the test set for the ecotoxicological characterization of wastes. Following ISO/CD guideline 20665, the chronic Ceriodaphnia dubia test was performed with three waste types: INC, SOI, and WOO. All the ten tests performed were classified as acceptable. Methodologically, almost no problems occurred. The min-max factors (2.08–2.54) between individual EC50 values and the CVs (31–33%) were low for waste eluates, showing that the chronic Ceriodaphnia dubia test is a robust method. These results are in agreement with the few data on substances known from the literature. The obtained data show that the test is able to discriminate different toxicity levels: INC = 4.8%, SOI > 90%, WOO = 0.08%. The sensitivity of the Ceriodaphnia chronic test is equivalent to the rotifer chronic test and slightly higher than the Algae test for the wood eluate. Therefore it is recommended for the toxicity assessment of waste.

The acute toxicity of nine inorganics associated with placer mining sediments to early life stages of Arctic grayling (Thymallus arcticus), coho salmon (Oncorhynchus kisutch), and rainbow trout (O. mykiss) was determined in soft water (hardness, 41 mg liter-1 CaCO3) at 12 degrees C. The relative toxicities of the inorganics varied by four orders of magnitude; from most toxic to least toxic, the rank order was cadmium, silver, mercury, nickel, gold, arsenite, selenite, selenate, and hexavalent chromium. In general, juvenile life stages of the three species tested were more sensitive to these inorganics than the alevin life stage. Among juveniles, no single species was consistently more sensitive to the inorganics than another; among alevins, Arctic grayling were generally more sensitive than coho salmon and rainbow trout. Based on the results of the present study, estimated no-effect concentrations of arsenic and mercury, but not cadmium, chromium, gold, nickel, selenium, or silver, are close to their concentrations reported in streams with active placer mines in Alaska. Thus, arsenic (as arsenite(III)) and mercury may pose a hazard to Arctic grayling and coho salmon in Alaskan streams with active placer mines.

Adult brook trout (Salvelinus fontinalis; 200–300 g) were preexposed for 10 wk to 75 μg Al3+∙L−1, pH = 5.2, in soft water (25 μequiv Ca2+∙L−1) and controls to the same conditions without Al3+. When challenged with a lethal dose of Al3+(333 μg∙L−1) at the same pH (5.2) and Ca2+(25 μequiv∙L−1), the control fish demonstrated a twofold increase in ventilation volume and ventilatory stroke volume within the first two hours, an increase in [Formula: see text], and a decrease in pHa and hemoglobin O2saturation. These effects were not seen in the group chronically preexposed to sublethal Al, indicating that some acclimation had occurred. Although the prechallenge [Formula: see text] and [Formula: see text] were the same in the two groups, the arterial pH, plasma [HCO3−], and hemoglobin O2saturation of the Al-preexposed fish were significantly below those of the control fish, suggesting that the acclimation was achieved at some cost. Possible mechanisms are discussed.

Yolk-sac fry, swim-up fry and 1–2 yr juveniles of brown trout, Sulmo trutta L., were exposed to episodes of aluminium and low pH, maximum aluminium concentration 12 μmol l−1 (323 μg l−1), minimum pH 4.5, total duration up to 54 h (yolk-sac fry) or up to 78 h (swim-up fry and juveniles), in an artificial soft water medium, [Ca] 20 μmol l−1 (0–8 mg l−1) (nominal baseline: pH 5.6, zero aluminium concentration). Yolk-sac fry mortality was nil or very low. A marked increase in susceptibility, with high mortalities, occurred when the yolk was fully absorbed. Mortality of juveniles exposed to two successive episodes was lower than would have been expected on the basis of comparisons with mortalities in single episodes, and mortality declined as the interval between the two episodes was increased. Disturbance of sodium, potassium or calcium balance or gill damage in surviving yolk-sac fry or juveniles was still evident 5 to 6 days after the end of a single episode.