The relative sensitivity of microtox®, daphnid,rainbow trout,and fathead minnow acute lethality tests

Relative sensitivity and correlations between the Microtox® test and three commonly used acute lethality bioassays (i.e., rainbow trout, fathead minnow, Daphnia) are reviewed and discussed. All relevant data available for comparison were separated and evaluated based on chemical groupings. Generally, Microtox was more sensitive than or as sensitive as the acute lethality tests for pure individual organics, but was less sensitive to most inorganics. Microtox was not as sensitive as acute lethality tests to effluents or leachates with a high component of insecticides, herbicides, inorganics, pharmaceuticals or textiles, or highly lipophilic contaminants. As the complexity and toxicity of industrial effluents increased, the correlations and sensitivity of Microtox increased, with a corresponding decrease in data variability. Additionally, limitations of the available data are that (1) comparisons of relative sensitivity varied with the compounds and organisms tested; (2) there was a lack of standardization in approach and a failure to provide adequate details on the origin of the cited toxicity data, which confused and obscured comparisons; and (3) published reviews commonly failed to identify fish species and test details for cited data.     

Effects of estrogens and antiestrogens on gene expression of fathead minnow (Pimephales promelas) early life stages

Endocrine disrupting chemicals (EDCs) are known to contaminate aquatic environments and alter the growth and reproduction of organisms. The objective of this study was to evaluate the sensitivity and utility of fathead minnow (Pimephales promelas) early life‐stages as a model to measure effects of estrogenic and antiestrogenic EDCs on physiological and gene expression endpoints relative to growth and reproduction. Embryos (<24‐h postfertilization, hpf) were exposed to a potent estrogen (17α‐ethinyl estradiol, EE₂, 2, 10, and 50 ng L^?1); a weak estrogen (mycotoxin zearalenone, ZEAR, same concentrations as above); an antiestrogen (ZM 189, 154; 40, 250, and 1000 ng L^?1); and to mixtures of EE₂ and ZM until swim‐up stage (～170 hpf). Exposure to all concentrations of ZEAR and to the lowest concentration of ZM resulted in increased body sizes, whereas high concentrations of EE₂ decreased body sizes. There was a significant increase in the frequency of abnormalities (mostly edema) in larvae exposed to all concentrations of EE₂, and high ZEAR, and EE₂ + ZM mixture groups. Expression of growth hormone was upregulated by most of the conditions tested. Exposure to 50 ng L^?1 ZEAR caused an induction of insulin‐like growth factor 1, whereas exposure to 40 ng L^?1 ZM caused a downregulation of this gene. Expression of steroidogenic acute regulatory protein gene was significantly upregulated after exposure to all concentrations of EE₂ and luteinizing hormone expression increased significantly in response to all treatments tested. As expected, EE₂ induced vitellogenin expression; however, ZEAR also induced expression of this gene to similar levels compared to EE₂. Overall, exposure to EE₂ + ZM mixture resulted in a different expression pattern compared to single exposures. The results of this study suggest that an early life stage 7‐day exposure is sufficient to recognize and evaluate effects of estrogenic compounds on gene expression in this fish model. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2009.     

Effects of maternal versus direct exposure to pulp and paper mill effluent on rainbow trout early life stages

The acute and chronic effects of secondary-treated effluent from a New Zealand pulp and paper mill were assessed using both long-term adult and early life stage (ELS) laboratory exposures of rainbow trout. The relative impact of maternal exposure versus ELS exposure was assessed by a comparison of directly exposed eggs and larvae with the eggs and larvae of exposed adult trout that were reared in reference water. Rainbow trout were exposed to a secondary-treated mixed thermomechanical/bleached kraft mill effluent at a concentration of 15% or to reference water from the egg through to 320-d-old juveniles. The 2 adult rainbow trout exposures were undertaken with nominal concentrations of 10% and 12% treated effluent, respectively. There was no marked effect of water hardening with 15% effluent on fertility or survival of eggs to 16 d. In a subsequent exposure (with hardening in reference water), no significant effects were found on mortality to hatch, time to hatch, length at hatch, mortality to swim-up, mortality to 320 d, or deformity rate at hatch. At experimental termination (320 d), direct-exposed juveniles had smaller livers and reduced condition factor, likely due to differences in food consumption. In 2 subsequent consecutive experiments, exposure of adult trout to 10% and 12% effluent for 2 mo, followed by incubation of the fertilized eggs in reference water, produced no impact on fertility, survival to hatch, survival to swim-up, or length and weight of fry at swim-up. Exposure of adult trout to 12% treated effluent for 8 mo prior to egg fertilization also did not result in differing rates of fertility, mortality to hatch or mortality to swim-up. However, the 8-mo maternal exposure did result in swim-up fry that were significantly shorter and weighed less than the reference swim-up fry. This difference was directly attributable to smaller eggs in the 8-mo-exposed female trout. These results demonstrate that this pulp and paper mill effluent is more likely to elicit indirect impacts on progeny size through chronic exposure of adults to effluent during gonadal recrudescence rather than through direct exposure of early life stages to effluent.     

Temperature-induced changes in pentachlorophenol chronic toxicity to early ufe stages of rainbow trout

Temperature was a controlling factor in pentachlorophenol (PCP) toxiciiy to rainbow trout (Salmo gairdnen). Eggs of frout exposed to PCP from fertilization to hatch showed elevated mortality and reduced weight at hatch. The effects on hatch weight were greatest in the cold regime (6°C) compared to (the warm (10°C). Continued PCP exposure after hatch resulted in significantly elevated mortality, reduced growth rates and reduced yolk sac resorption efficiency, and these effects were again greatest in the cold regime (6°C) compared to the warm (15°C). In contrast, during 4 wk of feeding after yolk sac resorption, PCP-induced mortality was unaffected by temperature but growth rates were reduced to the greatest extent in the warm regime (20°C) compared to the cold (12°C). The potential biomass of 1000 newly fertilized eggs at hatch, after yolk sac resorption, and after 4 wk of feeding was calculated from observed mortality and wet weights. The overall production of fish in the warm regime was reduced relative to controls at estimated threshold PCP concentrations of about 10 μg/l. In contrast, final biomass of fish in a cold regime was higher than control biomass at 10 μg/l and the estimated threshold of adverse effect was 20 μg/l. Although fish in a warm regime appeared to be affected at a lower concentration of PCP than those in the cold regime, the overall response to; the highest PCP concentration was similar. Trout exposed to PCP during the egg stage were far more sensitive to PCP than were those exposed only after hatch.     

Effects of copper on development of the fathead minnow,Pimephales promelas Rafinesque

Embryos of the fathead minnow, Pimephales promelas Rafinesque, were exposed to total copper concentrations (Cu_T) of 0.6, 61, 113, 204, 338 and 621 μg/l from 5 to 10 h post-fertilization through 2 days post-hatch. A decrease in hatching time was observed with increasing total copper concentration but there was no decrease in embryonic developmental rate. Therefore, embryos hatched at earlier stages of development. Significant (P ≤ 0.05) declines in percent survival and percent total hatch were observed at 621 μg/l Cu_T) but not at 338 μg/l Cu_T or lower concentrations. The percentage of embryos with abnormalities was greater at 338 and 621 μg/l Cu_T than at 204 μg/l Cu_T and lower concentrations.Individuals exposed to copper during early development were then exposed to the same test concentrations for 28 days post-hatch. Survivors at 113 through 338 μg/l Cu_T were at earlier stages of development than were control fish. The percentage of fish surviving decreased with increasing copper concentration over the range 61 through 204 μg/l Cu_T. The percentage of fish surviving at 204 μg/l Cu_T was not significantly different from that at 338 μg/l Cu_T, and there were no survivors at 621 μg/l Cu_T. Surviving larvae at all copper concentrations from 61 through 621 μg/l Cu_T showed decreased length, weight and coefficient of condition compared to controls. The percentage of larvae with abnormalities increased significantly with increasing copper concentration. The calculated 96-h LC₅₀ (larval stage) was 250 μg/l Cu_T and the 28-day LC₅₀ (larval stage) was approximately 123 μg/l Cu_T.     

Distribution and elimination of a polychlorinated biphenyl during early life stages of rainbow trout (Salmo gairdneri)

Distribution and elimination of 2,5,2′,5′-tetrachlorobi[¹⁴C]phenyl (4-CB) were studied during the egg, sac fry, and fry stages of rainbow trout development. Fertilized eggs were exposed to water-borne [¹⁴C]4-CB for 24 hr and transferred to an incubator containing flowing, 4-CB-free water. The whole egg and its component parts (yolk fluid and chorionic membrane) were analyzed separately for ¹⁴C immediately after exposure (T₀) and 1, 4, 7, 11, 14, and 21 days later. Whole sac fry and its component parts (yolk sac and larva) were analyzed on Days 26, 35, 42, and 49 and whole fry and its component parts (viscera and eviscerated body) on Days 56, 63, 77, 91, and 105. Immediately after exposure (T₀), 4-CB content of whole eggs was 0.22 ± 0.01 μg/egg (mean ± SE) and 4-CB concentration on a whole egg wet weight basis was 3.72 ± 0.08 ppm. The majority of 4-CB in the eggs was associated with the yolk fluid where it was apparently associated with water soluble lipoproteins and oil globules composed of triglycerides. During the sac fry stage the majority of 4-CB was associated with the yolk sac. However, as the yolk sac was gradually absorbed the 4-CB was transferred to the larva. The time during sac fry development when the greatest absolute amount of 4-CB was present in the larva was at the very end of the sac fry stage. This was also the time when the oil globules in the yolk sac were first consumed by the sac fry before they began feeding on their own. The highest concentration of 4-CB in the larva occurred at the start of the sac fry stage when the eggs hatched. Thereafter larva 4-CB concentration decreased due to larval growth. The most intriguing finding had to do with a change in the rate of whole body elimination of 4-CB during the transition period from the sac fry to fry stage of development. During the egg and first two-thirds of the sac fry stage, 4-CB elimination was slow ($\text{t}\text{1}\text{2}\text{= 231}\text{days}$), but during the last one-third of the sac fry stage and throughout the fry stage it was rapid ($\text{t}\text{1}\text{2}\text{= 15}\text{days}$). This increased rate of elimination resulted in a loss of nearly all of the 4-CB from the fry. Thus, whole body 4-CB concentration dropped precipitously in the fry and this was due primarily to enhanced 4-CB elimination but also dilution by growth. The mechanism for this rapid whole body elimination of 4-CB in rainbow trout fry is not known but may be related to the low fat content of the fry body.     

Effects of 2,3,7,8-tetrachlorodibenzo-dioxin (TCDD) on early life stages of rainbow trout (Salmo gairdneri, Richardson)

Rainbow trout eggs, yolk sac fry and juveniles were exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in different concentrations for 96 h. Exposure of eggs to the lowest concentration, used in this study, 0.1 ppt (10-13 glg), resulted in a significant growth retardation for 72 days. At higher concentrations significant numbers of the forthcoming fry developed generalized edemas and died. Histologically, degeneration and necrosis of liver parenchymal cells were observed. Remaining fry showed teratologic changes as foreshortened maxillas and opercular defects. Administration of TCDD to yolk sac fry had similar effects. Juvenile rainbow trout, exposed to 10 and 100 ppt TCCD for 96 h, showed growth retardation and developed slight edematous changes. At 100 ppt all fry had died within 27 days. Histologically, vacuolization of the liver parenchymal cells and intracellular inclusion bodies in liver, pancreas and stomach were observed.     

Effects of water hardness on the physiological responses to chronic waterborne silver exposure in early life stages of rainbow trout (Oncorhynchus mykiss)

Early life stages of rainbow trout were exposed to 0, 0.1 and 1 microg/L Ag (as AgNO(3)) in very soft water (2mg/L CaCO(3)), moderately hard water (150 mg/L CaCO(3)) and hard water (400mg/L CaCO(3)) of low dissolved organic carbon concentration (0.5mg C/L) from fertilization to swim-up (64 days) under flow-through conditions, and monitored for whole embryo/larval silver accumulation, Na(+) and Cl(-) concentrations, Na(+) uptake and Na(+)K(+)-ATPase activity. The objective of the study was to investigate potential protective effects of water hardness on the physiological responses to chronic silver exposure. In the absence of silver, there was little effect of hardness on the ionoregulatory parameters studied, though higher hardness did improve survival post-hatch. At all three water hardness levels, whole embryo/larval Na(+) uptake was low and relatively constant prior to 50% hatch, but dramatically increased following 50% hatch, whereas Na(+)K(+)-ATPase activity steadily increased over development. Whole embryo/larval Na(+) and Cl(-) concentrations were low and constant prior to 50% hatch, but following 50% hatch Na(+) concentration increased, while Cl(-) concentration decreased. Following 50% hatch, exposure to 0.1 and 1 microg/L Ag resulted in a decrease in whole embryo/larval Na(+) concentration, Cl(-) concentration, Na(+) uptake and Na(+)K(+)-ATPase activity, indicating that the mechanism of chronic silver toxicity involves an ionoregulatory disturbance, and is similar to the mechanism of acute silver toxicity. An increase in water hardness reduced or eliminated the effect of silver on these parameters while enhancing survival, suggesting that the nature of the protective effect of hardness involves effects on the ionoregulatory disturbance associated with silver exposure. An increase in water hardness did not fully protect against the accumulation of silver associated with silver exposure. These results suggest that it may be possible to model chronic silver toxicity using a biotic ligand type model, and that a physiologically based model may be more appropriate because Na(+)K(+)-ATPase activity or Na(+) uptake is an endpoint for prediction rather than whole embryo or larval silver accumulation.     

Acute toxicity of organic chemical mixtures to the fathead minnow

The acute joint toxicity of industrial organic chemicals to the fathead minnow was determined for binary and equitoxic multiple chemical mixtures. Results from binary tests were used to define isobole diagrams. The degree of joint toxic action was determined among 27 chemicals from seven different chemical classes. The slopes of the acute concentration response relationships were quite similar for all test chemicals. This suggests that the mode of acute toxic action for these chemicals is alike though it may not be identical. Intoxication signs of fish exposed to nearly all test chemicals were also similar and indicative of an anesthetic like effect. The results of isobole diagrams for binary mixtures, with 1-octanol as the reference chemical, demonstrated a near concentration additive acute joint action over a wide range of mixture ratios for each chemical from 7 different classes. Tests conducted with mixtures containing equitoxic levels of two to 21 chemicals also displayed a concentration additive acute joint action. All test chemicals can be modeled by a structure-toxicity relationship characteristic of a narcosis type of toxic action. These results are consistent with those of other investigators and are of particular importance when one realizes that numerous industrial chemicals are likely to cause lethality to aquatic organisms through similar toxic action.     

Window of sensitivity for the estrogenic effects of ethinylestradiol in early life-stages of fathead minnow,Pimephales promelas

Sexual differentiation in fish occurs after hatching during early life-stages and is believed to be a time when the gonad has a heightened sensitivity to disruption by chemicals that mimic hormones. In this study fathead minnows (Pimephales promelas) were exposed to an environmentally relevant concentration of ethinylestradiol (EE2) for short intervals in fish early life-stages and vitellogenic and gonadal responses were measured at 30 and 100 dph (sexual maturity), respectively. All EE2 exposure regimes induced vitellogenin (VTG) synthesis and disruption in duct development (a feminization) in males, with a window of enhanced sensitivity between 10 and 15 dph (where 60% of the males had feminized ducts). There was an altered pattern in sex cell development in males (inhibition of spermatogenesis) in the solvent controls (ethanol 0.1 ml/l) and all EE2 treatments when compared with the dilution water controls. Furthermore, fewer spermatozoa were observed in the testis of males exposed to EE2 from 15 to 20 dph and fertilized eggs (<24 h post-fertilization)-20 dph, compared with both the solvent and dilution water controls. These data show that short exposures of embryos/very early life-stage fathead minnows to an environmentally relevant concentration of EE2 lead to alterations in gonadal development that potentially have reproductive consequences and thus population level effects.     

Toxicity of the synthetic pyrethroids,permethrin and AC 222, 705 and their accumulation in early life stages of fathead minnows and snails

Early life stages of fathead minnows (Pimephales promelas) were exposed to permethrin and AC 222, 705 and snails (Helisoma trivolvis) were exposed to permethrin in continuous flow-through exposures for approximately 30 days. Saturated solutions of each pesticide were used to avoid the use of solvents.Survival of newly hatched larvae and early juveniles was found to be the most sensitive measure of effect on fathead minnows of both pesticides. AC 222, 705 was approximately 20 times more toxic to fathead minnows than permethrin by the end of the test period. Based on the chronic limits, as defined in these tests, the predicted chronic no-effect concentrations for fathead minnows were between 0.66 and 1.4 μ/l for permethrin and 0.03 and 0.07 μ/l for AC 222, 705. The no-effect concentration for permethrin and snails was ≥ 0.33 μg/l. The chronic values for these compounds were approximately one-sixteenth and one-fourth of the corresponding 96-h LC₅₀ values, respectively, for fathead minnows in Lake Superior water.The mean bioconcentration factors (BCFs) for permethrin were 2800 for fathead minnows and 800 for snails. The mean BCF for AC 222, 705 and fathead minnows was 4000. Residue concentrations for both pesticides increased with increased water concentrations.     

Copper bioaccumulation and hepatoprotein synthesis during acclimation to copper by juvenile rainbow trout

Rainbow trout were exposed for 3 wk to copper at 0.09, 0.18, 0.29, 0.40, or 0.59 of the mean control incipient lethal level (ILL) of copper. Whole body copper concentration increased with both exposure concentration and time. Mean residues stabilized in the range of 34 to 37 μg/g dry weight after 2 to 3 wk of exposure at 0.29 to 0.59 ILL.After 3 wk at 0.29 ILL of copper, most fish survived a subsequent exposure at 1.7 ILL, during which their elevated body concentration of copper did not change appreciably (35 to 33 μg/g). In contrast, control fish died rapidly, their body concentration rising from 3.8 to 7.4 μg/g).Sublethal copper exposure increased the protein content of a low-molecular-weight hepatoprotein fraction. There was also greater incorporation into that protein of ¹⁴C from intraperitoneally administered [¹⁴C]leucine. Fish exposed to cadmium showed a similar increase in hepatoprotein but not increased ¹⁴C incorporation. This suggests different, metal-specific proteins. Results are discussed with respect to a previously reported acclimation to copper by the fish, acclimation which significantly altered lethal tolerance of copper.     

The fathead minnow in aquatic toxicology: past, present and future

This paper reviews the roles of the fathead minnow (Pimephales promelas) as a small fish model in the field of aquatic toxicology. The species has been (and is) extensively used both for regulatory testing and research, especially in North America. For example, tests with the fathead minnow, ranging from 48-h lethality through partial and full life-cycle assays, are routinely used for regulatory programs aimed at assessing potential risks of new chemicals such as high-production volume materials and pesticides, as well as impacts of complex mixtures like effluents. The species also has been used for a wide variety of research applications focused on topics like the development of quantitative structure-activity relationship models, mixture toxicity, extrapolation of the effects of chemicals across species, and understanding the results of laboratory assays relative to impacts in the field. Attributes of the fathead minnow also make it an excellent model for addressing new challenges in aquatic toxicology, including identification of sensitive life-stages/endpoints for chemicals with differing modes/mechanisms of action, predicting population-level effects based on data collected from lower levels of biological organization, and exploring/understanding the emerging role of genomics in research and regulation.     

Histopathology of fathead minnow (Pimephales promelas) exposed to hydroxylated fullerenes

Hydroxylated fullerenes are reported to be very strong antioxidants, acting to quench reactive oxygen species, thus having strong potential for important and widespread applications in innovative therapies for a variety of disease processes. However, their potential for toxicological side effects is still largely controversial and unknown. Effects of hydroxylated fullerenes C₆₀(OH)₂₄ on the fathead minnow (Pimephales promelas) were investigated microscopically after a 72-hour (acute) exposure by intraperitoneal injection of 20 ppm of hydroxylated fullerenes per gram of body mass. Cumulative, semi-quantitative histopathologic evaluation of brain, liver, anterior kidney, posterior kidney, skin, coelom, gills and the vestibuloauditory system revealed significant differences between control and hydroxylated fullerene-treated fish. Fullerene-treated fish had much higher cumulative histopathology scores. Histopathologic changes included loss of cellularity in the interstitium of the kidney, a primary site of haematopoiesis in fish, and loss of intracytoplasmic glycogen in liver. In the coelom, variable numbers of leukocytes, including many macrophages and fewer heterophils and rodlet cells, were admixed with the nanomaterial. These findings raise concern about in vivo administration of hydroxylated fullerenes in experimental drugs and procedures in human medicine, and should be investigated in more detail.     

Sensitivity of early life stages of vendace,Coregonus albula,to acid pH in postmining lakes: An experimental approach

Since 1990, many highly acidic lakes with very hard water have formed in Lusatia, eastern Germany, following the decommissioning of most open‐cast lignite mines. Even after neutralization of the water, the lakes may reacidify due to the high acidification potential of soil and groundwater. Hence, investigation of critical pH‐levels for the respective fish species is required when planning to use the lakes for fisheries. Sensitivity of early life stages of vendace, Coregonus albula, to low pH was determined in reconstituted water with the hydrochemical characteristics of the postmining lakes. Eggs were transferred to test solutions with pH‐values ranging from 3.50 to 7.40 either 10 min after artificial insemination (series A) or 7 h later (series B) and incubated using a static‐renewal procedure. Water hardening of the eggs at exposure pH (series A) led to a severe reduction in egg diameter at pH≤5.00 and to an earlier and stronger increase in egg mortality, but by the time of hatching, differences between both series were small. Hatching percentages at pH≤5.00 were very low and the eleutheroembryos died shortly after hatching. In both series, hatching percentages at pH 5.50 did not differ from those at pH 7.40. Feeding activity of vendace exposed to pH 5.50 was, however, reduced and the fish did not survive. Hence, early life stages of vendace can be regarded as very sensitive to low pH and associated elevated concentrations of Al, and maintenance of neutral pH is essential when postmining lakes are stocked with vendace. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 214–224, 2000     

CYP1A induction and blue sac disease in early developmental stages of rainbow trout (Oncorhynchus Mykiss) exposed to retene

Early life stages of rainbow trout were exposed to different regimes of water-borne retene (7-isopropyl-1-methylphenanthrene) to determine if there is an ontogenic stage particularly sensitive to retene toxicity, and if cytochrome P-4501A (CYP1A) induction is a forerunner to blue sac disease (BSD), the syndrome of toxicity. CYP1A protein concentrations, measured by immunohistochemistry, were first detected during organogenesis, when organ and enzyme systems are first being developed, and steadily increased until swim-up. The prevalence of signs of BSD rose 1 wk following a marked increase in CYP1A activity after hatch, suggesting that CYP1A induction is related to BSD. The larval stage was the most sensitive to retene toxicity, based on CYP1A induction and a high prevalence of BSD. The most common signs of BSD were hemorrhaging, yolk-sac edema, and mortality, but hemorrhaging was the first and most frequently observed response. Tissue concentrations of retene were elevated just after fertilization, but decreased steadily as fish developed to the swim-up stage, most likely due to the establishment of more efficient metabolic and excretory systems in later stages of development.     

Effects of environmental exposure to diazepam on the reproductive behavior of fathead minnow,Pimephales promelas

Pharmaceutical drugs are continuously discharged into the aquatic environment primarily through wastewater discharge; therefore, their possible effects on wildlife is a reason of concern. Diazepam is a widely prescribed benzodiazepine drug used to treat insomnia and anxiety disorders, and it has been found in wastewater effluents worldwide. The present study tested the effects of diazepam on fecundity and the reproductive behavior of the fathead minnow, Pimephales promelas, a fish that exhibits male parental care. Sexually mature fathead minnows were housed at a ratio of one male and two females per tank and exposed to nominal (measured) concentrations of 0, 0.1 (0.14 ± 0.06), 1.0 (1.04 ± 0.15), 10 (13.4 ± 1.5) µg L^?1 for 21 days. Fish receiving the low diazepam treatment had significantly larger clutches than fish receiving the highest concentration but neither were different from controls. Diazepam exposure was not associated with a significant change in fertilization rate, hatchability or time to hatch, but a trend toward a higher number of eggs/day was observed in fish exposed to the low diazepam concentration relative to those exposed to the medium concentration. There were no significant differences in any of the behaviors analyzed when responses were averaged over time. The results showed that exposure to diazepam at concentrations as high as 13 µg L^?1 did not significantly impact the reproductive behavior of fathead minnow. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 561–568, 2016.     

The toxicity of acetylenic alcohols to the fathead minnow, Pimephales promelas: narcosis and proelectrophile activation

1. The 96-h LC50 values for 16 acetylenic alcohols in the fathead minnow (Pimephales promelas) were determined using continuous-flow diluters. The measured LC50 values for seven tertiary propargylic alcohols agreed closely with the QSAR predictions based upon data for other organic non-electrolytes acting by a narcosis mechanism. 2. Four primary and four secondary propargylic alcohols were 7 to 4600 times more toxic than the respective narcotic toxicity estimated by QSAR. Metabolic activation to electrophilic alpha,beta-unsaturated propargylic aldehydes or ketones is proposed to account for the increased toxicity. 3. 3-Butyn-1-ol and 4-pentyn-2-ol, primary and secondary homopropargylic alcohols, were 320 and 160, respectively, times more toxic than predicted. In this case an activation step involving biotransformation to an allenic electrophile intermediate was proposed.     

Subcellular interactions of dietary cadmium, copper and zinc in rainbow trout (Oncorhynchus mykiss)

Interactions of Cu, Cd and Zn were studied at the subcellular level in juvenile rainbow trout (Oncorhynchus mykiss) fed diets containing (μg/g) 500 Cu, 1000 Zn and 500 Cd singly and as a ternary mixture for 28 days. Livers were harvested and submitted to differential centrifugation to isolate components of metabolically active metal pool (MAP: heat-denaturable proteins (HDP), organelles, nuclei) and metabolically detoxified metal pool (MDP: heat stable proteins (HSP), NaOH-resistant granules). Results indicated that Cd accumulation was enhanced in all the subcellular compartments, albeit at different time points, in fish exposed to the metals mixture relative to those exposed to Cd alone, whereas Cu alone exposure increased Cd partitioning. Exposure to the metals mixture reduced (HDP) and enhanced (HSP, nuclei and granules) Cu accumulation while exposure to Zn alone enhanced Cu concentration in all the fractions analyzed without altering proportional distribution in MAP and MDP. Although subcellular Zn accumulation was less pronounced than that of either Cu or Cd, concentrations of Zn were enhanced in HDP, nuclei and granules from fish exposed to the metals mixture relative to those exposed to Zn alone. Cadmium alone exposure mobilized Zn and Cu from the nuclei and increased Zn accumulation in organelles and Cu in granules, while Cu alone exposure stimulated Zn accumulation in HSP, HDP and organelles. Interestingly, Cd alone exposure increased the partitioning of the three metals in MDP indicative of enhanced detoxification. Generally the accumulated metals were predominantly metabolically active: Cd, 67-83%; Cu, 68-79% and Zn, 60-76%. Taken together these results show both competitive and cooperative interactions dependent on the subcellular fraction, metal, exposure duration and relative metal exposure concentrations. Competitive interactions likely result from ionic mimicry with the metals displacing each other from common binding sites, whereas cooperative interactions suggest increased abundance of metal binding sites and/or existence of metal-specific non-interacting binding sites in some of the fractions. Moreover, the changes in subcellular distribution of the biometals Cu and Zn due to Cd exposure together with the shifts of the metals between MAP and MDP observed may have toxicological consequences.